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Last Updated :2024/09/29

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Master

Affiliation (Master)

  • Faculty of Engineering　Applied Chemistry　Functional Materials Chemistry

Affiliation (Master)

  • Faculty of Engineering　Applied Chemistry　Functional Materials Chemistry

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Profile and Settings

Affiliation

  • Hokkaido University, Faculty of EngineeringDivision of Materials Chemistry, Professor

Profile and Settings

  • Name (Japanese)

    Habazaki

  • Name (Kana)

    Hiroki

  • Name

    200901038068777831

Alternate Names

Affiliation

  • Hokkaido University, Faculty of EngineeringDivision of Materials Chemistry, Professor

Achievement

Research Interests

  • 水電解   撥液・滑液表面   Interfacial Electrochemistry   Anodizing   ナノポーラス材料   

Research Areas

  • Nanotechnology/Materials / Structural and functional materials
  • Nanotechnology/Materials / Material fabrication and microstructure control
  • Nanotechnology/Materials / Nanobioscience
  • Nanotechnology/Materials / Nanomaterials

Research Experience

  • 2010/04 - Today 北海道大学大学院工学研究院 教授
  • 2006/04 - 2010/03 Graduate School of Engineering, Hokkaido University Professor
  • 2000/04 - 2006/03 Graduate School of Engineering, Hokkaido University Associate Professor
  • 2000/10 - 2005/09 Corrosion and Protection Centre, UMIST Visiting Researcher
  • 1988/04 - 2000/03 Institute for Materials Research, Tohoku University Research Associate
  • 1993/11 - 1995/10 Corrosion and Protection Centre, UMIST Postdoctoral Researcher

Education

  • 1986/04 - 1988/03  Tohoku University  Graduate School of Science  Department of Chemistry
  • 1982/04 - 1986/03  Tohoku University  Faculty of Science  Department of Chemistry

Committee Memberships

  • 2023/01 -2024/12   International Society of Electrochemistry   Division Chair

Awards

  • 2020/03 電気化学会 フェロー
  • 2020/02 北海道大学 教育研究総長表彰
  • 2019/03 電気化学会 論文賞
     
    受賞者: 辻 悦司;松浦 志紀;青木 芳尚;幅崎 浩樹
  • 2013/03 電気化学会学術賞
     
    受賞者: 幅崎 浩樹
  • 2005/03 日本学術振興会 第1回日本学術振興会賞
     
    受賞者: 幅崎 浩樹
  • 1997/09 Institute of Corrosion T.P. Hoar Award
     
    受賞者: HABAZAKI Hiroki

Published Papers

  • Sho Kitano, Hiroya Motohashi, Mana Iwai, Koji Fushimi, Yoshitaka Aoki, Hiroki Habazaki
    Applied surface science 2024/10
  • Xiong Zetao, David Quintero, Sho Kitano, Tomoya Nagao, Mana Iwai, Yoshitaka Aoki, Koji Fushimi, Hiroki Habazaki
    Electrochimica Acta 491 0013-4686 2024/07/01 
    Anodizing is gaining popularity as a binder-free fabrication route for obtaining catalyst materials directly on the current collector without using noble metals, binders, or conductive carbon additives. Here, we fabricate promising highly active electrodes for alkaline water electrolysis by anodizing commercial FeNi and FeNiCo alloys (%wt. Fe range between 22 and 63) in an ethylene glycol-based fluoride electrolyte. Anodizing forms metal fluoride coatings, which are converted to OER active compounds (γ-NiOOH:Fe) during potential cycling in an alkaline aqueous solution (1 mol L−1 (M) KOH at 293 K) as a result of leaching of fluoride ions. The morphology, thickness, and number of active sites are influenced by the amount of Fe in the alloy, and the electrode with the highest electrochemical active surface area (Kovar alloy with a 54 %wt. Fe) shows the largest OER activity enhancement by anodizing. The performance evaluation in practical conditions (7 mol L−1 KOH at 343 K) demonstrated a highly active performance with an OER potential as low as 1.52 V at a current density of 600 mA cm−2 even for electrodes obtained in alloys with a low amount of Fe (78-Permalloy with a 22 %wt. Fe), demonstrating that anodizing is an effective way to develop highly active OER electrodes from commercially available alloys. On the other hand, anodizing is a good fluoridation route for transition metals with good results in the formation of F-enriched precursors that efficiently promote active phase formation during the catalytic process, offering the possibility of obtaining catalysts directly on the current collector in a one-step process, easily implemented in industrial applications.
  • Yuji Kunisada, Chiharu Kura, Norihito Sakaguchi, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    ACS Omega 9 (12) 13738 - 13745 2470-1343 2024/03/15 
    Nanocrystalline titanium nitride (TiN) has been determined to be a promising alternative to noble metal palladium (Pd) for fabricating base membranes for the energy-efficient production of pure hydrogen. However, the mechanism of transport of hydrogen through a TiN membrane remains unclear. In this study, we established an atomistic model of the transport of grain boundary hydride ions through such a membrane. High-resolution transmission electron microscopy and X-ray reflectivity confirmed that a nanocrystalline TiN1.0 membrane with a (100) preferred growth orientation retained about 4 Å-wide interfacial spaces along its grain boundaries. First-principles calculations based on the density functional theory showed that these grain boundaries allowed the diffusion of interfacial hydride ion defects with very small activation barriers (<12 kJ mol-1). This was substantiated by the experiment. In addition, the narrow boundary produced a sieving effect, resulting in a selective H permeation. Both the experimental and theoretical results confirmed that the granular microstructures with the 4 Å-wide interlayer enabled the transition metal nitride to exhibit pronounced hydrogen permeability.
  • Naoki Kamitani, Seong Woo Jeong, Hiroki Habazaki, Yoshitaka Aoki
    ACS Sustainable Chemistry and Engineering 12 (5) 2100 - 2109 2024/02/05 
    H2O-N2 coelectrolysis by protonic solid oxide cells (H+-SOCs) holds great promise as it enables the sustainable production of pure ammonia gas from air and water through renewable electricity. This investigation highlights the exceptional hydrogen ion diffusivity and limited hydrogen evolution reaction (HER) activity of VN0.9, establishing it as a valuable cathode material for H+-SOCs. The model cells were fabricated by sputter-depositing the dense VNx film cathode (x = 0.9 and 1.1) on BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411) bulk proton electrolytes. The hydrogen pumping measurements proved that the VN0.9 cathode allowed the bulk diffusion of the hydrogen ions while effectively retarding hydrogen evolution at its surfaces. Hence, coelectrolysis with the Ru-loaded VN0.9 cathode achieved an ammonia Faraday efficiency and production rate of 12% and 3.8 × 10-9 mol cm-2, respectively, which were 2 orders of magnitude higher than those of the coelectrolytic H+-SOCs using metal cathodes. Integration of electrochemical measurements and mass spectroscopy established that the desorption of ammonia products was the rate-controlling step of the ENRR on the Ru-loaded VN0.9 cathode. The Ru-loaded VN0.9 cathode enabled continuous ammonia synthesis at an average rate of 2.1 × 10-9 mol cm-2 over 50 h with periodic rest at open-circuit voltage for the catalyst reactivation by the release of chemisorbed NH3
  • Fujimura, A., Abe, M., Kawano, A., Iwai, M., Kitano, S., Habazaki, H., Fushimi, K.
    Corrosion Science 227 0010-938X 2024/02 
    The dissolved masses of Fe, Cr, Al, and Si in H2SO4 solution during the polarization of Cr-containing steels were quantified by online ICP-OES. The active dissolution current on 11Cr-2Al/-2Si was smaller than that on 11Cr due to the enrichment of Al/Si on the steel. The Cr dissolution from 11Cr2Al was suppressed in passive state, while that from 11Cr2Si was decreased in active-passive transition because accumulated Al or Si products have different physicochemical effects on the Cr-enrichment of the surface. Roles of Al/Si in corrosion process, especially passivation, were discussed based on quantitative analysis of dissolution products detected by ICP-OES.
  • Chunmei Tang, Ning Wang, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki, Siyu Ye
    Green Energy and Environment 2096-2797 2024 
    Protonic solid oxide electrolysis cells (P-SOECs) are a promising technology for water electrolysis to produce green hydrogen. However, there are still challenges related key materials and anode/electrolyte interface. P-SOECs with Zr-rich electrolyte, called Zr-rich side P-SOECs, possess high thermodynamically stability under high steam concentrations but the large reaction resistances and the current leakage, thus the inferior performances. In this study, an efficient functional interlayer Ba0.95La0.05Fe0.8Zn0.2O3−δ (BLFZ) in-between the anode and the electrolyte is developed. The electrochemical performances of P-SOECs are greatly enhanced because the BLFZ can greatly increase the interface contact, boost anode reaction kinetics, and increase proton injection into electrolyte. As a result, the P-SOEC yields high current density of 0.83 A cm−2 at 600 °C in 1.3 V among all the reported Zr-rich side cells. This work not only offers an efficient functional interlayer for P-SOECs but also holds the potential to achieve P-SOECs with high performances and long-term stability.
  • Quintero, D., Matsuya, H., Iwai, M., Kitano, S., Fushimi, K., Habazaki, H.
    ACS Applied Materials and Interfaces 16 (1) 1737 - 1748 1944-8252 2024 
    Aluminum solid polymer capacitors are promising devices for the increased demand for power electronics applications. Nonetheless, the low breakdown voltage of commercially available catalysts (∼100 V) limits their applications. In this study, a hydroxide-film-covered high-purity aluminum was anodized at 700 V in boric acid at 85 °C, and the effect of a second hot water immersion (posthydration treatment) after anodizing on the breakdown voltage was studied as a possible future treatment to enhance the withstand voltages of solid electrolytic capacitors. The dielectric breakdown voltage of the anodized aluminum with a PEDOT:PSS coating was ∼500 V, being ∼200 V less than the anodizing voltage; however, the dielectric breakdown voltage was increased above 700 V by introducing the posthydration treatment due to the formation of a nanovoid layer above the dielectric alumina film. Our research suggests that the highly dispersed nanovoids incorporated with PEDOT:PSS avoid the current concentration at some local regions, effectively increasing the dielectric breakdown voltage. The posthydration treatment increased the leakage current by introducing physical defects in the dielectric film. However, the leakage current was reduced by a voltage sweep below the breakdown voltage after the PEDOT:PSS coating or a second anodizing process before the coating, keeping the breakdown voltage above 600 V. A promising processing route to obtain aluminum solid capacitors with high withstand voltage (600 V) found in our research is, first, dipping in hot water; second, anodizing at 700 V; then a second hot water treatment; and a second anodizing at 400 V, which keeps the capacitance invariable with a breakdown voltage enhanced.
  • Hadi Sena, Sho Kitano, Hiroki Habazaki, Masayoshi Fuji
    Energy Advances 2 (9) 1495 - 1499 2023/08/08 
    Semiconductor photocatalytic water splitting is a promising method to address the worldwide energy issues. Fast carrier recombination and the limited visible-light absorption are two main challenges to be overcome, and designing p-n heterojunctions is an effective solution. In this study, two direct band gap semiconductors are selected to form a p-n heterojunction. The results show that liquid phase epitaxy of a thick film p-type CuGaO2 on an n-type GaN substrate is effective for the splitting of water into hydrogen and oxygen.
  • Toshiaki Kondo, Hisato Matsuya, Hiroki Habazaki
    Journal of the Electrochemical Society 170 (8) 0013-4651 2023/08/01 
    A STEM/EDS study of a porous Ga oxide film formed by an anodization process was conducted in this study to examine the crystalline structure of the film and the elemental distribution in the oxide film before and after heat treatment. The as-formed anodic film with a morphology resembling the well-known porous anodic Al oxide film was amorphous, crystallizing after heat treatment at 600 °C without changing the morphology and elemental distribution. The EDS elemental maps disclosed the duplex nature of the pore wall oxide; the phosphate anion was contaminated in the outer oxide layer next to the pores, and the inner layer consisted of relatively pure Ga oxide, practically free from phosphate. The similarity of morphology and elemental distributions between the porous anodic Al and Ga oxides suggests that the growth of both anodic oxide films proceeds under the same mechanism. In addition, crystallized porous Ga oxides are expected to be applied to fabricate various functional devices requiring geometrically controlled semiconductor nanohole arrays, such as devices for hydrogen formation.
  • Chunyu Zhu, Bo Zhao, Manami Takata, Yoshitaka Aoki, Hiroki Habazaki
    Journal of Applied Electrochemistry 53 (7) 1379 - 1388 0021-891X 2023/07 
    The preparation of porous carbon from biomass flour as high-performance electrocatalysts for oxygen reduction reaction (ORR) was reported in this paper. The fast and vigorous pyrolysis of flour was induced in the presence of magnesium nitrate, by which MgO nanoparticles were introduced as nano-template to create numerous nanopores and to increase the specific surface area (SSA). The pore structure, SSA and elemental dopant were influenced by the ratio of biomass to magnesium nitrate and calcination temperature. A highly hierarchical micro-meso-macroporous carbon, which was calcined at 1000 °C and had a high SSA of 1880 m2 g−1, exhibited the best ORR performance in terms of fast ORR kinetic, superior stability and excellent methanol tolerance. Graphical Abstract: [Figure not available: see fulltext.]
  • Hisato Matsuya, David Quintero, Sho Kitano, Hiroki Habazaki
    ECS Journal of Solid State Science and Technology 12 (7) 2162-8769 2023/07 
    Aluminum solid electrolytic capacitors using a conductive polymer as a cathode material has the advantages of low equivalent series resistance (ESR) and high thermal stability compared to aluminum electrolytic capacitors using liquid electrolytes. A disadvantage of aluminum solid electrolytic capacitors with a conductive polymer is the low breakdown voltages, limiting the operating voltage of the capacitors to ∼100 V or less. In this study, for a possible future increment of the withstand voltages of solid electrolytic capacitors, PEDOT:PSS-coated aluminum with an amorphous or crystalline alumina layer formed at 500 V has been characterized using SEM, STEM/EDS, and conductive AFM to understand the distribution of PEDOT:PSS conductive polymer and its influence on the electric properties. The crystalline alumina layer, developed beneath a porous hydrated alumina layer, contains many voids, which increase the leakage current compared to the void-less amorphous alumina layer. However, the crystalline alumina layer with PEDOT:PSS exhibits a higher breakdown voltage than the amorphous one. The limited incorporation of PEDOT:PSS into the inner part of the porous hydrated alumina layer may introduce a resistive surface layer, possibly contributing to the increased dielectric breakdown.
  • Laras Fadillah, Damian Kowalski, Sho Kitano, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    Electrochemistry Communications 149 1388-2481 2023/04 
    This study demonstrates the highly enhanced photocatalytic activity of Fe2O3 nanotubes by making a heterojunction with Fe2WO6 and doping of W6+ ions into the α-Fe2O3 phase for water splitting and decomposition of an organic pollutant. Both nanotubular and compact Fe2O3/Fe2WO6 films are formed by anodizing the magnetron-sputtered Fe-9 at% W alloy in fluoride-containing ethylene glycol electrolyte and subsequent annealing at 450 °C. Their photocatalytic activities are compared with W-free nanoporous Fe2O3 film formed on high-purity Fe. The nanotubular Fe2O3/Fe2WO6 film exhibits a markedly enhanced photoelectrochemical oxygen evolution reaction and photocatalytic degradation of methylene blue compared with the nanoporous W-free Fe2O3 film. Because of the larger surface area, the nanotubular Fe2O3/Fe2WO6 film reveals further increased activity than the compact Fe2O3/Fe2WO6 film. The STEM study discloses the dispersion of Fe2WO6 nanoparticles in the α-Fe2O3 phase after annealing at 450 °C, and XRD analysis shows the possible doping of W species into α-Fe2O3. The formation of the W-doped α-Fe2O3/Fe2WO6 heterojunction likely promotes the separation of photogenerated electron-hole pairs, enhancing photocatalytic activity. Hence, the nanotubular Fe2O3/Fe2WO6 film is a possible candidate for visible-light-driven photocatalysts.
  • Huijun Yang, Ruijie Zhu, Yang Yang, Ziyang Lu, Zhi Chang, Ping He, Chunyu Zhu, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki, Haoshen Zhou
    Energy and Environmental Science 1754-5692 2023 
    The re-evaluation of zinc (Zn)-based energy storage systems satisfies emerging demands in terms of safety and cost-effectiveness. However, the dendritic Zn morphology and resulting short circuits within the cell remain long-standing challenges. Moreover, diverse Zn dendrite propagation exacerbates the situation, particularly during high-capacity battery operation. The high-capacity Zn deposition/dissolution process involves numerous sites and interfaces, which leads to disordered Zn dendrite growth because of the inherent diffusion-limited aggregation mechanism. Here, we demonstrate a robust polymer separator that serves as both a physical barrier to stress-governed metal electrodeposition and an ionic charge carrier for fast Zn2+ diffusivity. These insights enable an ultra-high Zn reversibility (99.97%) for 2000 cycles at 20.0 mA cm−2 and 4.0 mA h cm−2, and a high-energy-density (115 W h kg−1 based on pouch cell) Zn-MnO2 full battery with an aggressive N/P capacity ratio (1.35). The abundant and environmentally friendly cell components make it a sustainable battery technology for global electrification.
  • Sho Kitano, Yuki Sato, Reiko Tagusari, Ruijie Zhu, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    RSC Advances 13 (16) 10681 - 10692 2023 
    Simple and durable: the multi-metal oxyhydroxide and spinal oxide composite catalyst containing Co, Fe and Ni are synthesized from hydroxide and layered double hydroxide composite precursors and shows excellent bifunctional ORR/OER activities.
  • Katsuya Akimoto, Ning Wang, Chunmei Tang, Kai Shuto, SeongWoo Jeong, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    ACS APPLIED ENERGY MATERIALS 5 (10) 12227 - 12238 2574-0962 2022/09 
    Efficient power generation with protonic solid oxide fuel cells (H-SOFCs) remains challenging because the mismatch between the primary ion carriers of the electrolyte and the cathode limits the effective cathode reaction area to the gas-electrolyte-cathode triple-phase boundary (TPB), resulting in large cathodic overpotentials at low operating temperatures. Herein, we report the role of functional layers between an electrolyte and a cathode in reducing the cathodic reaction resistance at the TPB. Thin-film fuel cells with BaZr0.1Ce0.7Y0.1Yb0.1O3-delta (BZCYYb1711) electrolytes were fabricated using a dense La0.5Sr0.5Co0O3-delta (LSC) nanofilm (approximately 100 nm) as a cathode functional layer (CFL) with the typical oxide ion/electron mixed conductor La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF), LSC, and the less-active Sb0.1Sn0.9O2 (ATO). The peak power densities of the cells increased by >100% when using a CFL, and cells having an LSC cathode and CFL achieved power densities of 500 mW cm(-2) at 500 degrees C. The distribution of relaxation times in the impedance spectra revealed the CFL's effect on the ohmic and polarization resistances. Crucially, cells without a CFL had large ohmic resistances because the proton-accessible electrode areas were confined to the gas-cathode-electrolyte TPB. However, the resistance decreased with the CFL because coupled partial proton conductivity and electrocatalytic activity of the LSC nanofilms increased the proton-accessible electrode area. The cells without a CFL showed a large polarization resistance because of the sluggish diffusion of O adatoms over the cathode resulting from the increased TPB length. This resistance decreased by >70% with an LSC CFL because the cells did not require long-range O diffusion because of the significantly extended proton-accessible reaction area near the gas-CFL-cathode TPB. Thus, using interfacial layers is an alternative way to design new cathode materials having low cathodic polarization for H-SOFCs.
  • Masahiro Nishimoto, Zetao Xiong, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHIMICA ACTA 427 0013-4686 2022/09 
    This study investigates the oxygen evolution reaction (OER) activity of the FeNiCo alloy anodized at several temperatures in a fluoride-containing ethylene glycol electrolyte. When the alloy is anodized at 10 V, the OER activity in KOH electrolyte is highly enhanced on the alloy anodized at 15 and 20 degrees C, at which non-uniform film growth proceeds. The fraction of the locally thick film regions increases with anodizing time, enhancing the OER activity. Only thin porous films are formed at >= 30 degrees C even though the anodizing current is high because of the promotion of film dissolution at high electrolyte temperatures. Because of the thickness limitation, the OER activity is relatively low when the anodic films are formed at >= 30 degrees C. A good correlation is found between the OER activity and the electric double-layer capacitance; thicker porous anodic films enhance the OER activity. The anodic film formed at each temperature consists of a rutile-type (FeNiCo)F-2 phase, but in KOH electrolyte, it is converted readily to an oxyhydroxide phase, which is OER active. A similar to 2 mu m-thick film obtained under the optimum anodizing condition reduces the overpotential of OER to 245 mV at 10 mA cm(-2) in 1.0 mol dm(-3) KOH electrolyte.
  • Tatsuyuki Takano, Hisato Matsuya, Damian Kowalski, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki
    Applied Surface Science 592 0169-4332 2022/08/01 
    Hydration treatment of aluminum in hot water is important for its corrosion protection, and also this treatment is a crucial pretreatment in forming dielectric crystalline alumina films on the aluminum anode in aluminum electrolytic capacitors. In this study, a two-layer hydrated film formed on high purity aluminum by hot water treatment was examined using a combination of glow discharge (GD) sputtering and Raman spectroscopy. In addition, the anion penetration behavior through the hydrated alumina layer during anodizing aluminum in several electrolytes was investigated. The results indicate that the outer layer, with a nanosheet-like morphology, consists of a crystalline pseudo-boehmite phase, whereas the relatively compact inner layer is amorphous or poorly crystalline. The inner amorphous layer plays a crucial role in the incorporation of the anions, which is found for the first time. When hydrated aluminum is anodized in phosphate, silicate, and tungstate electrolytes, the inner hydrated alumina layer impedes the penetration of these electrolyte anion species. In contrast, boron species readily penetrate the hydrated alumina layer into the barrier layer formed by anodization in boric acid. This anion-specific incorporation behavior is discussed in terms of ion-selective permeation in the amorphous hydrated alumina layer.
  • Hajime Toriumi, Genki Kobayashi, Takashi Saito, Takashi Kamiyama, Takaaki Sakai, Takahiro Nomura, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    CHEMISTRY OF MATERIALS 34 (16) 7389 - 7401 0897-4756 2022/08 
    Oxyhydrides have excellent potential as electrochemical and catalytic materials owing to the synergistic effects of the conductivity and redox activity of the hydride (H-) ion. However, harsh preparation conditions and their pyrolytic nature limit their applications. Herein, we discover highly durable oxyhydride perovskite BaZr0.5In(II)(0.5)O2.25H0.5 with enhanced H- ion-electron mixed conductivity. BaZr0.5In-(III)O-2.75, as the parent phase, was reductively hydrogenated to BaZr(0.5I)n(II)(0.5)O2.25H0.5 as via simple H-2 gas annealing at 800 degrees C under an ambient pressure with the incorporation of H- ions with simultaneous oxygen vacancy formation. Membrane devices comprising dense BaZr0.5In0.5O2.25H0.5 films on porous Ni-cermet supports were fabricated by conventional sintering and postreduction because low lattice contraction (-0.07%) following hydrogenation allowed for the bulk hydrogenation of BaZr0.5In0.5O2.75 sinters without structural collapse. The resulting devices exhibited higher hydrogen permeability than protonic ceramic ones at 500 degrees C because BaZr0.5In(II)(0.5)O2.25H0.5, allows H- ion hopping between the nearest-neighbor anion sites due to the significantly high oxygen deficiency (25% of O sites are vacant), giving rise to a H- ion conductivity of 10(-3) S cm(-1). Given their superior H- ion conductivity and ease of manufacturing, the synthesized materials have great potential for applications in mixed conducting electrodes and hydrogen-permeable membrane supports of ceramic electrochemical cells.
  • Chunmei Tang, Ning Wang, Ruijie Zhu, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    JOURNAL OF MATERIALS CHEMISTRY A 10 (29) 15719 - 15730 2050-7488 2022/07 
    Protonic solid oxide electrolysis cells (P-SOECs) are one of the most efficient devices for hydrogen production from renewable electricity, but the lack of suitable anodes has led to serious concerns in terms of high anodic overpotentials and low conversion efficiencies. Herein, we demonstrated that both the steam electrolysis performances and efficiency of P-SOECs based on a BaZr0.6Ce0.2Y0.1Yb0.1O3-delta electrolyte can be significantly improved by employing a Ba0.95La0.05Fe0.8Zn0.2O3-delta (BLFZ) H+/O2-/e(-) triple-conductor thin film at the anode/electrolyte interface as an anode functional layer (AFL). A broad survey of electrolysis performances was conducted for cells with various AFLs, including H+/O2-/e(-) triple conductors and O2-/e(-) double conductors. This investigation clarified that BLFZ can significantly decrease the ohmic and polarization resistances, and thus, greatly increase the electrolysis current. Because of the high proton conductivity and excellent electrochemical kinetics, the BLFZ AFL can allow the anodic reactions to occur over the surfaces of the BLFZ AFL without the long-range diffusion of oxygen species over the anode. Moreover, the BLFZ AFL can depress the hole injection in the electrolyte because the water partial pressure remained relatively high in comparison to the oxygen partial pressure at the AFL/electrolyte interface due to the excellent proton conductivity. Hence, the BLFZ cell offered a high electrolysis current of 570 mA cm(-2) at 1.3 V, and an increased efficiency of 75% from 46% for a cell without the BLFZ AFL at 500 degrees C. These results reveal that an effective AFL can boost the anodic reaction and optimize the efficiency of obtaining P-SOECs with excellent performances and outstanding ability for hydrogen production. Transition metal oxides combining high proton and low oxide ion conductivities could be promising AFLs for highly efficient P-SOECs.
  • Hiroyuki Okada, Etsushi Tsuji, Miho Hisada, Sho Kitano, Hiroki Habazaki, Satoshi Suganuma, Naonobu Katada
    SUSTAINABLE ENERGY & FUELS 6 (11) 2709 - 2717 2398-4902 2022/05 
    Towards the development of active and robust electrocatalysts for the oxygen evolution reaction (OER) to realize water splitting and CO2 electroreduction by renewable energies under practical conditions, brownmillerite-type composite oxide Ca2Fe2-xCoxO5 was synthesized by a sol-gel method and examined for the OER under neutral conditions. A pure brownmillerite-type Ca2Fe2-xCoxO5 phase, which was categorized as an oxygen-deficiency-ordered perovskite-type structure, was synthesized in a range of x = 0-1.25. Brownmillerite-type Ca2FeCoO5 showed higher activity and durability for the OER in a neutral solution than perovskite-type LaFe0.5Co0.5O3 and SrFe0.5Co0.5O3-delta. Furthermore, the durability of Ca2Fe2-xCoxO5 was drastically improved by increasing the Co content from x = 1 to 1.25. Ca2Fe0.75Co1.25O5 was remarkably durable for about 70 h during the OER in a neutral solution whereas Ca2FeCoO5 lost activity within 20 h, and perovskite-type oxides lost activity within a few hours. The detailed analysis of structures and compositions of local regions of Ca2Fe2-xCoxO5 and their changes by the reaction based on electron microscopy clarified the important role of the brownmillerite structure itself in catalytic activity under neutral conditions, while, under alkaline conditions, it has been known that the amorphous phase derived from brownmillerite mainly played the role of active species.
  • Yuki Sato, Naohito Yamada, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    JOURNAL OF MATERIALS CHEMISTRY A 10 (15) 8208 - 8217 2050-7488 2022/04 
    Carbon materials are used as electrocatalyst supports and conductive additives in various electrodes for electrochemical energy conversion and storage because of their high electrical conductivity and chemical stability. However, they suffer from electrochemical corrosion at high anodic potentials in aqueous electrolytes. This study demonstrates that highly graphitized platelet-type carbon nanofibers (pCNFs) are tolerant to electrochemical corrosion under oxygen evolution reaction (OER) conditions in a concentrated KOH electrolyte. An identical-location scanning electron microscopy study showed that the corrosion rate of the carbon edge plane of the pCNFs is very low compared with that of the carbon basal plane. Further scanning transmission electron microscopy/electron-energy loss spectroscopy studies indicate that the carbon edge plane of the pCNFs is covered with hydroxyl groups, whereas the oxygen-containing species are limited to the carbon basal plane. Thus, most surfaces of highly graphitized pCNFs, consisting of the carbon edge plane, are passivated with hydroxyl groups, resulting in the high resistance of pCNFs to electrochemical corrosion. These findings provide a novel material design for carbon with a high corrosion resistance in the OER.
  • Ruijie Zhu, Zetao Xiong, Huijun Yang, Tianhong Huang, Seongwoo Jeong, Damian Kowalski, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki, Chunyu Zhu
    ENERGY STORAGE MATERIALS 46 223 - 232 2405-8297 2022/04 
    Rechargeable aqueous zinc (Zn) batteries have attracted great interests because of its inherent safety and costeffectiveness. However, the uncontrollable Zn dendrite formation in aqueous electrolyte restricts its reversibility for long-life application. The bulge or passivation layer in pristine Zn surface serves as nuclei for large amount of Zn crystal aggregation and inhomogeneous Zn electrodeposition. Here, for the first time, we demonstrate a simple, effective, and non-corrosive electropolishing strategy to develop a smooth and clean Zn metal as compared with burdensome and unreliable mechanical polishing method in lab-scale research. After removing the primitive passivation layer, the fresh Zn anode can survive at a high current density of 40 mA cm(-2) over 6000 times. Moreover, the electropolished Zn gains more consistent and reliable electrochemical behaviors which contributes to study the mechanism of Zn electrodeposition and clarify the effectiveness of protective strategies in the follow research.
  • Hajime Toriumi, SeongWoo Jeong, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    ACS OMEGA 7 (11) 9944 - 9950 2470-1343 2022/03 
    Proton-conducting solid oxide electrolysis cells (H-SOEC) containing a 15-mu m-thick BaZr0.6Ce0.2Y0.2O3-delta (BZCY622) electrolyte thin film, porous cathode cermet support, and La0.6Sr0.4Co0.2Fe0.8O3-delta anodes were fabricated using a reactive cofiring process at approximately 1400 degrees C. Steam electrolysis was conducted by supplying wet air to the anode at a water partial pressure of 20 kPa. The performance was evaluated using electrochemical measurements and gas chromatography. At 600 degrees C, the cells generated an electrolysis current of 0.47 A cm(-2) at a 1.3 V bias while the Faradaic efficiency reached 56% using 400 mA cm(-2). The electrolysis performance was efficiently improved by introducing a 40-nm-thick La0.5Sr0.5CoO3-delta (LSC) nanolayer as an anode functional layer (AFL). The cells with LSC AFL produced an electrolysis current of 0.87 A cm(-2) at a 1.3 V bias at 600 degrees C, and the Faradaic efficiency reached 65% under 400 mA cm(-2). Impedance analysis showed that the introduction of the AFL decreased the ohmic resistances and improved interfacial proton transfer across the anode/electrolyte interface and polarization resistances related to the anode reaction. These results demonstrate opportunities for future research on AFL to improve the performance of H-SOECs with Zr-rich BaZrxCe1-x-yYyO3-delta electrolytes.
  • Yoshitaka Aoki, Shinichi Nishimura, SeongWoo Jeong, Sho Kitano, Hiroki Habazaki
    ACS APPLIED ENERGY MATERIALS 5 (2) 1385 - 1389 2574-0962 2022/02 
    This study is the first to report the development of hydrogen-permeable metal support electrolysis cells (HMECs) bearing a heterojunction of H+-conducting BaZrxCe0.8-xY0.2O3-delta (BZCY) electrolyte and H-permeable Pd. The HMECs could conduct galvanostatic steam electrolysis at 0.15 A cm(-2); the HMECs maintained a voltage of similar to 1.2 V and achieved a Faradaic efficiency of similar to 80% at 500 degrees C, which are higher than the values predicted for H+-conducting ceramic electrolysis cells with porous cathodes and anodes. The relatively high efficiency of HMECs could be attributed to a decrease in the hole carriers due to the defect thermodynamic equilibria near the BZCY/Pd heterointerface.
  • Ruijie Zhu, Huijun Yang, Wei Cui, Laras Fadillah, Tianhong Huang, Zetao Xiong, Chunmei Tang, Damian Kowalski, Sho Kitano, Chunyu Zhu, Daniel R. King, Takayuki Kurokawa, Yoshitaka Aoki, Hiroki Habazaki
    JOURNAL OF MATERIALS CHEMISTRY A 10 (6) 3122 - 3133 2050-7488 2022/02 
    Rechargeable aqueous zinc-ion batteries (RAZIBs) have some inherent advantages such as intrinsic safety, low-cost and theoretically high energy density, making them a current topic of interest. However, the phenomenon of zinc (Zn) dendrite growth at the anode results in the instability of RAZIBs and limits their real-world application. Herein, by employing a high strength hydrogel polymer electrolyte, the growth of dendritic Zn crystals is effectively eliminated through the mechanical suppression effect, resulting in a stable Zn anode that demonstrates dendrite-free plating/stripping with a long lifespan. Even under a high current density of 5 mA cm(-2), the Zn||Zn symmetric cell is shown to have a cyclic lifetime of longer than 1000 hours. Moreover, the stable cyclic performance of the Zn anode spawns a Zn||MnO2 battery with high capacity (4.8-1.9 mA h cm(-2)) and long lifetime (500 cycles at 9.2 mA cm(-2), 1C), which can meet the practical demands for portable devices. This work shows that high strength polymer gel electrolytes with internal energy dissipation mechanisms can overcome previous challenges that prevented practical utilization of RAZIBs. Together with the outstanding cyclic properties of the high capacity Zn||MnO2 batteries, this work provides a new pathway toward designing high energy density RAZIBs.
  • Zhu, R., Xiong, Z., Yang, H., Wang, N., Kitano, S., Zhu, C., Aoki, Y., Habazaki, H.
    Advanced Functional Materials 33 (8) 1616-3028 2022 
    Rechargeable aqueous zinc (Zn)-ion batteries (RAZIBs), which use non-flammable aqueous electrolytes and low-cost electrode materials, show great potential to boost the development of safe, cost-effective, and highly efficient energy storage systems. The adoption of lightweight and inexpensive aluminum (Al) as current collectors seems to be a good vision, but Al exhibits an easily-corroded nature and a high impedance in aqueous electrolytes, making it a challenge to realize the utilization of Al current collector in RAZIBs. In this study, through the direct current magnetron sputtering, niobium (Nb) coated Al (Al-Nb) foils are prepared, which shows superior corrosion-resistance in an aqueous solution, while maintaining a satisfying electronic conductivity. Moreover, the Al-Nb foils can be adopted to both anode and cathode current collectors while exhibiting high coulombic efficiency and good cycling stability even when they are tested under a condition that can meet the real-world application demands, e.g., the Zn||Al-Nb half-cell shows an average coulombic efficiency of 99.17% in 320 cycles under a current density of 25 mA cm−2 and a galvanizing capacity of 6.25 mAh cm−2. The superior performance of the modified Al current collectors may mark a significant step toward the development of high-energy-density aqueous batteries.
  • Shinichi Hata, Yuki Sakai, Nanami Tani, Sho Kitano, Hiroki Habazaki, Akari Hirakawa, Hinako Tanaka, Yusuke Inomata, Toru Murayama, Masatake Haruta, Yukou Du, Yukihide Shiraishi, Naoki Toshima
    ACS Applied Nano Materials 5 (11) 16231 - 16241 2022 
    Bimetallic or alloyed nanoparticles (NPs) are important materials that often exhibit chemical properties different from those of their monometallic counterparts. However, access to uniformly alloyed bimetallic particles, particularly in the Pd-Rh system, is difficult because of the thermodynamic immiscibility of the individual metals. Herein, we propose a method for accumulating Pd-Rh alloy particles on the surface of zeolite imidazolide framework-67 (ZIF-67), a chemically stable metal-organic framework, under mild conditions at 25 °C. The degradation of methyl orange was used to test the applicability of the resultant material as a heterogeneous catalyst. A turnover frequency of 38.5 h-1 was recorded for Pd0.12Rh0.88/ZIF-67, which is higher than that of catalysts with either Pd (17.2 h-1) or Rh (16.5 h-1). The acceleration of methyl orange decomposition was attributed to electron transfer from Pd to Rh in the alloy particles due to the differences in Pauling electronegativity and an increase in metallic Rh on the catalyst surface. No metal leakage or structural degradation of the ZIF-67 support was observed during the catalytic reaction. Pd0.12Rh0.88/ZIF-67 could actively degrade methyl orange, congo red, and methylene blue. The structure of the catalyst remained intact even when a mixed solution of all three dyes was circulated for 60 min in a fixed-bed system, and the catalyst conversion rate exceeded 99.7%. Our results collectively demonstrate the successful preparation of Pd-Rh-supported catalysts and their application to the continuous reduction of multicomponent dye mixtures. The metal NP-MOF composites prepared using the proposed approach are free from MOF pore damage and can maintain their specific surface area. Therefore, this strategy could give impetus to research on catalytic applications of NP-MOF composites.
  • 橋本功二, 熊谷直和, 泉屋宏一, 高野裕之, 四宮博之, 幅崎浩樹, 秋山英二
    触媒 64 (3) 140 - 147 0559-8958 2022 [Refereed][Invited]
  • SeongWoo Jeong, Ning Wang, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    ADVANCED ENERGY MATERIALS 11 (37) 1614-6832 2021/10 
    Among several types of low-temperature solid oxide fuel cells, hydrogen-permeable metal-supported fuel cells (HMFCs) are devices that can achieve outputs of approximately 1.0 W cm(-2) at 400 degrees C. This work clarifies the mechanism for promoting the cathode reaction on proton-conducting ceramics at such low temperatures. Combined numerical and electrochemical analyses demonstrate that blocking minor oxide ion conduction at metal/oxide heterojunctions promotes proton transfer at the cathode/electrolyte interfaces, thereby enhancing the turnover frequency of the cathode reaction at the triple-phase boundary. The electrolyte membrane in HMFCs is forced to gain extra protons to compensate for the charge of oxide ions that accumulate because of the blocking, resulting in an increment of the proton concentration gradients near the cathode/electrolyte interfaces so as to eject the excess amount of proton. The interfacial proton concentration gradient increases and thus the cathode polarization resistance of HMFCs decrease with the cell bias. An HMFC with a highly oxygen-deficient BaZr0.5Sc0.5O3-delta electrolyte accumulates a large amount of oxide ions, thereby developing large concentration gradients. Thus, it achieves a cathode reaction resistance of 0.54 omega cm(2) at 400 degrees C with conventional cathode materials, La0.6Sr0.4Co0.2Fe0.8O3-delta. These findings demonstrate that HMFCs can efficiently utilize overpotential.
  • Miku Saito, Chiharu Kura, Hajime Toriumi, Satoshi Hinokuma, Toshiaki Ina, Hiroki Habazaki, Yoshitaka Aoki
    ACS APPLIED ELECTRONIC MATERIALS 3 (9) 3980 - 3989 2021/09 
    The incorporation of mobile hydridic defects was demonstrated for low-crystalline zirconium nitride (Zr3N4-delta) films deposited by radio frequency reactive sputtering under a flow of nitrogen-rich reactive gases. Extended X-ray adsorption fine structure analysis confirmed that the local coordination environment around the Zr atoms was very close to that of the orthorhombic Eu3O4 phase. Pristine Zr3N4-delta films exhibited n-type semiconductor behavior due to the presence of nitrogen vacancy donors with a carrier concentration of 1.4 x 10(20) cm(-3) and an electron mobility of 2.2 x 10(-3) cm(2) V-1 s(-1) at room temperature. Electrochemical and spectroscopic measurements confirmed that Zr3N4-delta was readily hydrogenated upon exposure to H-2 gas at 300 degrees C to form hydridic defects via electron donation to hydrogen adatoms. Hence, the hydrogenated film exhibited H- ion/electron mixed conductor behavior in a H-2 atmosphere. These findings open the possibility for exploring new hydride ion conductors based on thermodynamically stable transition metal nitrides.
  • Kensuke Sakuraba, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ACS APPLIED MATERIALS & INTERFACES 13 (37) 45089 - 45096 1944-8244 2021/09 
    Slippery liquid-infused porous surfaces (SLIPSs) can be formed by impregnating lubricants in porous surfaces with low surface energy. In this study, SLIPSs have been obtained on practically important aluminum with a porous anodic alumina layer by impregnating lubricants containing organic additives. The additive-containing lubricants change the surface slippery even without prior organic coating of the porous alumina surface. The additive-containing SLIPSs reveal a low water sliding angle of <5 degrees and markedly improved corrosion resistance in an acetic acid solution containing chloride. The SLIPSs are formed by the in situ adsorption of the organic additives on the porous alumina surface. The scratched defects induce corrosion of the organic coating-type SLIPSs, whereas the additive-containing SLIPSs sustain high corrosion resistance even after introducing scratch defects. The adsorption of the organic additive in lubricants and refilling of the lubricant are responsible for the self-healing of the corrosion resistance. Thus, the additive-containing SLIPSs are promising selfhealing corrosion-resistant surfaces.
  • Nan Sheng, Jiahui Lu, Jingdong Hu, Ruijie Zhu, Laras Fadillah, Cheng Wang, Chunyu Zhu, Zhonghao Rao, Hiroki Habazaki
    CHEMICAL ENGINEERING JOURNAL 420 1385-8947 2021/09 
    Latent heat storage using metals as solid-liquid phase change materials (PCMs) have been concerned for medium-temperature thermal energy storage. However, due to the leakage and corrosion problems during phase transformation, the use of metallic PCMs are greatly limited. Encapsulation of PCM microparticles to form microencapsulated PCMs (MEPCMs) is an effective strategy, which is unfortunately technologically difficult for metallic PCMs. In this study, we develop metallic Sn MEPCMs coated by a stable SnO2 shell through a facile self-oxidation method. Sn@SnO2 core-shell MEPCMs are fabricated by two steps: firstly, Sn microspheres are pre-treated by vapor or water to form an oxide precursor shell on Sn microspheres; secondly, heat oxidation treatment under O-2 atmosphere is conducted to form a stable SnO2 shell. The Sn@SnO2 microcapsules exhibit a melting point of similar to 232 degrees C and latent heat of similar to 53 J/g. Importantly, the capsules present an excellent thermal cycling stability, in which after 100 cycles of melting-freezing the phase change properties and core-shell structure could be well retained. These results reinforce the promising application of microencapsulated Sn in medium-temperature thermal storage.
  • Shinichi Hata, Keita Iwamoto, Sho Kitano, Hiroki Habazaki, Akari Hirakawa, Nanami Tani, Yukou Du, Yukihide Shiraishi, Naoki Toshima
    COLLOID AND INTERFACE SCIENCE COMMUNICATIONS 43 2215-0382 2021/07 
    A room-temperature wet chemical method was developed for preparing a catalyst comprising Pd nanoparticles (NPs) supported on a zeolite imidazolide framework-8 (ZIF-8) surface (Pd/ZIF-8). The Pd/ZIF-8 catalyst exhibited a large surface area and high crystallinity, almost equal to those of pristine ZIF-8. The binding of the Pd NPs deposited on the ZIF-8 surface was shown to occur at the ZIF-8 particle surface rather than throughout the metal-organic framework (MOF) structure. The method was also suitable for complexing ZIF-8 with several other, nano-sized noble metals. The Pd/ZIF-8 heterogeneous catalyst was applied in the NaBH4-reduction of isomeric nitrophenols in both batch and fixed-bed systems. The catalyst was universally active against the isomeric nitrophenols, with a catalytic conversion of 99.7% after 1 h of cycling in the fixed-bed system. Thus, we have demonstrated the preparation of stable, supported catalysts and their application to the continuous reduction of multi-component nitrophenol mixtures.
  • Masahiro Nishimoto, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ACS SUSTAINABLE CHEMISTRY & ENGINEERING 9 (28) 9465 - 9473 2168-0485 2021/07 
    Developing highly active and durable electro-catalysts, consisting of earth-abundant elements, for oxygen evolution reaction (OER) is pivotal for large-scale water splitting for hydrogen production. Herein, we report that the commercially available FeNiCo alloy can be converted to a highly active electrocatalyst for OER by galvanostatic anodizing in a fluoride-containing ethylene glycol electrolyte. Anodizing of the alloy develops a porous film consisting of the (FeNiCo)F-2 phase, which is readily converted to a highly active porous oxyhydroxide during anodic polarization in a KOH electrolyte. The anodized alloy exhibits high activity and high durability for OER with an overpotential as low as 0.26 V at a current density of 10 mA cm(-2). The present study demonstrates that a simple and cost-effective anodizing process can be used to form a highly active OER electrode from a low-cost, practical, iron-based alloy. In addition, we found that fluorides containing Fe, Ni, and Co are excellent precursors for the formation of oxyhydroxides exhibiting high OER activity and durability.
  • Chunmei Tang, Katsuya Akimoto, Ning Wang, Laras Fadillah, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    JOURNAL OF MATERIALS CHEMISTRY A 9 (24) 14032 - 14042 2050-7488 2021/06 
    Protonic solid oxide steam electrolysis cells (P-SOECs) based on BaZrxCe0.8-xYb0.1Y0.1O3-delta proton conductors are promising to produce "green" hydrogen from renewable energy at intermediate temperatures. Herein, we demonstrate that the electrolysis performances of a cell with a high-Zr-content electrolyte, BaZr0.6Ce0.2Y0.1Yb0.1O3-delta (BZCYYb6211), can be significantly improved by using a La0.5Sr0.5CoO3-delta (LSC) thin film (similar to 90 nm) as an anode functional layer (AFL). Electrochemical measurements indicated that LSC-AFL significantly reduced the barrier height for the electrochemical proton incorporation reaction at the gas-electrolyte-electrode triple-phase boundary. Hence, both the ohmic and polarization resistances of the BZCYYb6211 cell decreased from 0.52 and 0.98 omega cm(2) to 0.26 and 0.57 omega cm(2), respectively, with the LSC-AFL at 600 degrees C. In addition, the BZCYYb6211 cell achieved a high electrolysis current of 1.22 A cm(-2) at 1.3 V with a Faraday efficiency of approximately 80%, which was equivalent to that (1.13 A cm(-2)) of the cell with a state-of-the-art electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3-delta (BZCYYb1711). BZCYYb6211 with LSC-AFL showed good durability at 500 degrees C under high steam conditions with an applied current of 1 A cm(-2) for 100 h. These results revealed that the introduction of an AFL is an effective method to obtain P-SOECs with excellent performances and durability.
  • Ruijie Zhu, Huijun Yang, Laras Fadillah, Zetao Xiong, Damian Kowalski, Chunyu Zhu, Sho Kitano, Yoshitaka Aoki, Hiroki Habazaki
    JOURNAL OF MATERIALS CHEMISTRY A 9 (22) 13332 - 13343 2050-7488 2021/06 
    On the way to achieve a practical lithium (Li) metal anode for next-generation batteries, the formation and accumulation of inactive "Dead Li" is an unavoidable issue. The accumulation of "Dead Li" leads to increased internal mass-transfer resistance which seriously deteriorates the performance of Li metal batteries during long-term cycling. In this study, by accommodating Li metal into a copper oxide coated carbon scroll host with a vertically aligned framework which possesses a unique low-tortuosity structure, the cycling stability of the Li anode can be significantly improved. It is demonstrated that the mass-transfer resistance and the concentration polarization near the Li metal surface can be greatly alleviated by using this low-tortuosity anode structure design. "Dead Li" that is formed on the electrode surface can automatically fall into the inner tunnel of the carbon host, endowing the anode with the capability of "Dead Li" self-cleaning. As a result, our new Li electrode can remain electrochemically active even after 1000 h in a symmetric cell measurement from 1 mA cm(-2) to 1 mA h for 500 cycles. The as-reported structure design of the Li anode in this work is compatible with most of the modification technologies that have been applied to conventional Li foil electrodes, providing this new Li anode with a great potential to be applied in subsequent Li anode studies.
  • Yoshitaka Aoki, Kentaro Takase, Hisao Kiuchi, Damian Kowalski, Yuki Sato, Hajime Toriumi, Sho Kitano, Hiroki Habazaki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 143 (17) 6505 - 6515 0002-7863 2021/05 
    The reaction pathway of the oxygen reduction reaction (ORR) is strongly affected by the electrolytic environment. Meanwhile, the ORR mechanism on transition-metal oxide catalysts has not been studied intensely in very concentrated alkaline solutions that are used in practical metal-air batteries. Herein, we report the in situ activation of ORR catalysis on manganese perovskite in a concentrated alkaline solution, mediated by the spontaneous formation of oxygen vacancy sites. Electrochemical analyses of the (100) epitaxial film electrodes reveal that the exchange current and electron number of the ORR on La0.7Sr0.3Mn0.9Ni0.1O3 significantly increase with the duration of the ORR when the KOH concentration is greater than 4 M. However, these values remain unchanged with time at less than 1 M KOH concentration. Operando synchrotron X-ray spectroscopy of the (100) epitaxial film confirmed that La0.7Sr0.3Mn0.9Ni0.1O3 involves the oxygen vacancy sites with the reduction of Mn atoms in concentrated KOH solution via the hydroxylation decomposition of perhydroxyl intermediates. Hence, the O-2 adsorption switched from an end-on to a bidentate mode because the cooperative active sites of the oxygen vacancy and neighboring Mn allow bidentate adsorption of the dissolved O-2. Due to the simultaneous interaction with the oxygen vacancy and Mn sites, the O-O bonds are activated and the potential barrier for the electron transfer to adsorbed O-2 is lowered, resulting in a shift in the reaction mechanism from that involving an indirect "2 + 2" transfer pathway to a direct 4-electron pathway.
  • Tae Hyeon Kim, Woojin Park, Seyoung Oh, So-Young Kim, Naohito Yamada, Hikaru Kobayashi, Hye Yeon Jang, Jae Hyeon Nam, Hiroki Habazaki, Byoung Hun Lee, Byungjin Cho
    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 218 (6) 1862-6300 2021/03 
    Although insertion of a thin insulating layer between metal electrodes and a semiconducting channel is an effective way to improve device performance, the exact reason for improvement in performance is not elucidated. Herein, the role of an Al2O3 interlayer sandwiched between Al metal electrodes and an amorphous indium-gallium-zinc-oxide semiconducting channel is systematically investigated. The Al2O3 interlayer results in not only a good transistor performance with increased on current but also improved gate bias stress stability. The improvement is primarily attributed to a doping effect and mitigation of interface defects. Energy-band diagrams, experimentally obtained from temperature-variable electrical characterization and electrostatic force microscopy, validate the channel doping effect, which increase the tunneling probability of the electron charge carriers via a reduction of the Schottky barrier width. A comprehensive study on the influence of various processing parameters, including Al2O3 thickness, post-annealing treatment conditions, and types of electrodes, on the transistor device is also performed. This approach guides the practical implementation of stable sol-gel oxide-based thin-film transistors and promotes integrated circuitry applications.
  • 幅崎浩樹
    表面技術 72 (11) 0915-1869 2021
  • Ning Wang, Hajime Toriumi, Yuki Sato, Chunmei Tang, Takashi Nakamura, Koji Amezawa, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    ACS APPLIED ENERGY MATERIALS 4 (1) 554 - 563 2574-0962 2021/01 
    Highly efficient mixed H+/e(-)/O2- triple conducting air electrodes are indispensable for improving the electrochemical performance of protonic ceramic fuel cells and electrolysis cells (PCFC/ECs) operating at intermediate temperatures. This study demonstrates that single perovskite-type La0.8Sr0.2Co1-xNixO3-delta families (LSCN, x = 0-0.3) are efficient H+/e(-)/O2- triple conductors due to a pronounced hydration ability at elevated temperatures with a related enthalpy of -107 kJ mol(-1). Thermogravimetry confirmed that the oxides were capable of a 0.01 mole fraction proton uptake at 600 degrees C and p(H2O) of 0.023 atm. Reversible protonic ceramic cells were fabricated using these oxides as an air electrode and exhibited promising performance with a peak power density of 0.88 W cm(-2) in fuel cell mode and an electrolysis current of 1.09 A cm(-2) at a thermal neutral voltage in electrolysis cell mode at 600 degrees C. Impedance analysis confirmed that the polarization resistance of the La0.8Sr0.2Co0.2Ni0.3O3-delta cell was 0.09 Omega cm(2) under an open circuit potential at 600 degrees C, which is much smaller than the polarization resistances reported for cells with a single or double perovskite-type triple conductor. The current results indicate that mixed H+/e(-)/O2- triple phase conducting LSCN oxides are promising air electrodes for protonic ceramic cells operating in the intermediate temperature region at approximately 600 degrees C.
  • Ryota Yamamoto, Damian Kowalski, Ruijie Zhu, Keisuke Wada, Yuki Sato, Sho Kitano, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    APPLIED SURFACE SCIENCE 537 0169-4332 2021/01 
    Copper is an important practical metal with a high thermal conductivity that is widely used as a heat exchanger material. However, a liquid film often forms on the Cu surface through water vapor condensation, causing a large resistance to heat transfer. To address this issue, a superhydrophobic Cu metal nanowire surface is developed herein via Cu anodizing in a KOH electrolyte to form Cu(OH)(2) nanowires, followed by hydrogen reduction at an elevated temperature and the application of a wet organic coating. The hydrogen treatment reduces the hydroxide to the metal while maintaining the nanowire morphology. The superhydrophobic Cu metal nanowire surface exhibits effective removal of water droplets formed through water vapor condensation. Furthermore, the metal nanowire surface exhibits highly improved heat transfer compared with the Cu(OH)(2) nanowire surface. Therefore, the combined process of anodizing and hydrogen reduction is a simple approach that forms an effective superhydrophobic Cu surface with high thermal conductivity.
  • Takayoshi Yano, Shin Ishikawa, Hiroki Habazaki
    MATERIALS TRANSACTIONS 62 (6) 836 - 845 1345-9678 2021 
    Highly functional and multifunctional material surfaces may be created through fabrication of unusual surface structures. We fabricated mushroom-like nanostructures on a stainless steel surface by simple processes: heat treatment under an atmosphere of low partial pressure of oxygen, followed by electrochemical etching. Island-like titanium oxide was formed on the Ti-containing stainless steel surface by selective oxidation during heat treatment. The titanium oxide became the cap part of the mushroom-like nanostructure and the stem part was fabricated by selective dissolution during electrochemical etching. Detailed analysis revealed that the cap part of the mushroom-like nanostructure was mainly composed of gamma-Ti3O5, and the stem part was composed of the stainless steel substrate. The contact resistance was significantly reduced by the fabrication of the mushroom-like nanostructures. The protrusions of electrically conductive gamma-Ti3O5 can contribute to the reduction of the contact resistance. The mushroom-like nanostructures improved the hydrophilicity of the surface without fluorine coating, but improved the hydrophobicity of the fluorine-coated surface. The contact between the stainless steel surface and the water droplet was in the Wenzel state.
  • Laras Fadillah, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHIMICA ACTA 364 0013-4686 2020/12 
    Anodizing of iron (100), (110) and (111) single crystals in mono-ethylene-glycol electrolyte containing 1.5 mol dm(-3) water and 0.1 mol dm(-3) ammonium fluoride leads to formation of anodic iron nanopores/nanotubes where the nanopores are essentially composed of oxide nanotubes separated by iron fluoride matrix. It was found that electrochemical thermodynamics for nanoporous/nanotubular film formation apparently depends on the index number of facet on which the anodic film is formed. The film formation on (100) facet is associated with extended gas evolution upon anodizing and consequently corresponds to a shift of current-time curve towards higher current density values comparing with those formed on higher index number facets. The nanotubes formed on (100) facet have a general chemical formula of Fe2O3 center dot FeF2, whereas those formed on higher index number are composed of Fe3O4 center dot FeF2. The anodic films formed on Fe (110) and Fe (111) are essentially amorphous whereas the one formed on (100) facet shows high degree of crystallinity. The results are discussed in view of anisotropic properties of iron. (C) 2020 Elsevier Ltd. All rights reserved.
  • Naohito Yamada, Sho Kitano, Yuya Yato, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ACS APPLIED ENERGY MATERIALS 3 (12) 12316 - 12326 2574-0962 2020/12 
    A simple anodizing technique has been employed to develop highly active electrocatalysts that can be applied to the oxygen evolution reaction (OER) in alkaline media. NiFe alloys were electrodeposited and anodized to form a porous electrocatalytic layer. This approach produces highly active electrodes without the need for noble metals, binders, or conductive carbon additives. The as-anodized electrode initially exhibits poor OER activity in 1.0 mol dm(-3) KOH; however, the effects of potential cycling improve the OER activity to an extent that an overpotential as low as 0.26 V at 10 mA cm(-2) is observed for the anodized Ni-11.8 at. % Fe electrode. Although significant in situ activation is achieved with anodized NiFe electrodes, this activation is less significant for as-deposited NiFe or anodized Ni electrodes. Furthermore, OER activity is observed to be composition-dependent, with the Ni-11.8 at. % Fe electrode exhibiting the greatest activity. A porous fluoride-rich, Fe-doped Ni oxyfluoride layer produced by anodizing is converted via potential cycling to an amorphous or poorly crystalline Fe-doped Ni(OH)(2) layer with a nanoflake-like morphology. The high activity is maintained even after the removal of most of the fluoride. Thus, the F-rich, Fe-doped Ni oxyfluoride is a promising precursor to develop a highly active OER electrode.
  • Ryoya Masuda, Damian Kowalski, Sho Kitano, Yoshitaka Aoki, Taisuke Nozawa, Hiroki Habazaki
    COATINGS 10 (11) 2020/11 
    In this study, zinc is anodized at different voltages in 0.1 mol center dot dm(-3) KOH electrolyte to form nanoporous anodic films. Dark-colored anodic films are formed at anodizing voltages <= 6 V, whereas colorless anodic films are developed at voltages >= 7 V. The anodic films formed at all voltages consist of crystalline ZnO, which was identified by X-ray diffraction and Raman spectroscopy. The Raman spectra of the dark-colored anodic films show the enhanced intensity of the LO phonon mode due to electric-field-induced Raman scattering, which may be associated with the presence of metallic Zn nanoparticles in the anodic films. Scanning electron micrographs and transmission electron micrographs of the cross-section of the dark-colored anodized zinc reveal the formation of two-layer porous anodic films with a highly rough metal/film interface. In contrast, nanoporous anodic films of uniform thickness with a relatively flat metal/film interface are formed for the colorless anodized zinc. The transmission electron microscopy (TEM)/energy dispersive X-ray spectroscopy (EDS) analysis suggested the presence of zinc nanoparticles in the dark-colored anodic films. The non-uniform anodizing and the formation of metal-nanoparticle-dispersed porous anodic films cause the formation of dark-colored anodic films on zinc.
  • M. Sepulveda, J. G. Castano, F. Echeverria, Y. Aoki, D. Kowalski, H. Habazaki
    ELECTROCHEMISTRY COMMUNICATIONS 120 1388-2481 2020/11 
    The effect of alloying sputter-deposited Ti with 2 at.% of Au on the growth of anodic nanotubes was studied in monoethylene glycol electrolyte containing 1.0 mol dm(-3) of water and 0.1 mol dm(-3) of ammonium fluoride. The classic shape of nanotubes modified with quasi-spherical clusters of Au48-198 was obtained on Ti-Au (2 at.%). The results were compared to the formation of a barrier-type anodic film which suggested that gold located at the alloy/anodic film interface is enriched as a consequence of the preferential oxidation of titanium during the prior anodizing period and transported to the cell boundary region of the nanotubular film in the form of quasispherical clusters of Au48-198. A consequence of the inclusion of Au48-198 in the structure of the nanotubes was a reduction in the rate of nanotubular film growth due to the generation of oxygen catalysed on the clusters. A further increase in gold content up to 8 at.% in the alloy resulted in the formation of sponge-like or nanoporous anodic layers, with the structure depending on electrolyte composition.
  • Tomohiro Inoue, Akira Koyama, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 217 (13) 1862-6300 2020/07 
    Slippery liquid-infused porous surfaces (SLIPS) have been receiving increased attention. Fluorinated compounds have been used to prepare SLIPS, but because of bioaccumulation and ecological impact of perfluoroalkyl building blocks, the fluorine-free SLIPS (F-free SLIPS) system is preferable for practical applications. Herein, SLIPS are prepared from a hierarchically porous aluminum substrate, tetradecylphosphonic acid monolayer coating, and silicone lubricant oil. The several properties of the SLIPS, including durability against lubricant loss, ice adhesion, and corrosion resistance, are compared with those with a fluoroalkyl monolayer coating and fluorinated lubricant oil. The findings demonstrate that the F-free SLIPS show higher durability against the removal of lubricant in air and also in water. Both fluorinated SLIPS (F-SLIPS) and F-free SLIPS samples exhibit extremely reduced ice adhesion compared with superhydrophobic surfaces obtained using the same hierarchically porous aluminum substrate with fluorinated or fluorine-free monolayer coating. The SLIPS samples have very high corrosion resistance in NaCl solution but not in alkaline solution. The solution-dependent corrosion resistance is discussed in terms of the stability of monolayer coating.
  • Yuki Sato, Yoshitaka Aoki, Kentaro Takase, Hisao Kiuchi, Damian Kowalski, Hiroki Habazaki
    ACS APPLIED ENERGY MATERIALS 3 (6) 5269 - 5276 2574-0962 2020/06 
    Brownmillerite-type Ca2FeCoO5 (CFCO) is a highly active electrocatalyst for the oxygen evolution reaction (OER). In this study, we identified the actual catalytically active phase of this oxide formed via the long-term OER and, moreover, demonstrated that the active phase can persist during the OER for 4 weeks without significant loss of electrocatalytic activity. The long-term durability tests were carried out on CFCO via continuous galvanostatic OER in 4 mol dm(-3) KOH aqueous solution for periods ranging from a few hours to 1 month, and the specimens submitted to the tests were characterized by means of electrochemical measurements and structural analysis using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Auger electron spectroscopy, and X-ray absorption fluorescence spectroscopy. CFCO was readily converted to amorphous cobalt oxyhydroxides with 10% Fe substituents through the OER process, and these compounds had a local rearrangement similar to that of the layered gamma-CoOOH-type structure. This transformation involved large morphological changes of the oxide particles because of the extensive dissolution of Ca and Fe, yielding skeletal grains made of oxyhydroxide nanosheet aggregates. The extended durability studies with total polarization charge density of the order of 10(5) C cm(-2) revealed that a (Co, Fe)OOH-like compound is the actual electrocatalytic phase.
  • Ning Wang, Satoshi Hinokuma, Toshiaki Ina, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    JOURNAL OF MATERIALS CHEMISTRY A 8 (21) 11043 - 11055 2050-7488 2020/06 
    It is challenging for materials chemists to develop efficient, cobalt-free cathode materials for solid oxide fuel cells mainly because of the resource scarcity. This study demonstrates that a cubic-type La0.7Sr0.3Mn0.7Ni0.3O3-delta (C-LSMN7373) perovskite is promising for intermediate-temperature protonic ceramic fuel cells (PCFCs) because of the sufficient H+/e(-)/O2- triple conductivity. The oxide can be hydrated by gaining 0.1 molar fraction of H2O under wet air at 415 degrees C, as confirmed by thermogravimetry analysis. An in situ extended X-ray absorption fine structure (EXAFS) analysis shows that the hydration reaction takes place via the association between H2O and oxygen vacancies, coupled with the redox of Mn and O atoms. Rhombohedral-type La0.7Sr0.3Mn1-xNixO3-delta cannot undergo hydration because the oxygen vacancy concentration required for water association is lower than the cubic phase concentration. The cathode performances of various PCFCs are examined by fabricating thin-film cells based on a Ba(Zr0.4Ce0.4Y0.2)O-3 electrolyte. The peak power density of the PCFCs with the cubic-type LSMN7373 cathode is 386 mW cm(-2) at 600 degrees C, which is much higher than the reported values for Zr-rich side electrolytes. Moreover, the cathodic polarization resistance is lower than that of a cell with the widely used La0.6Sr0.4Co0.2Fe0.8O3 cathode below 550 degrees C.
  • Damian Kowalski, Laras Fadillah, Yoshitaka Aoki, Hiroki Habazaki
    ECS Meeting Abstracts 2020/05/01
  • Yuki Sato, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ECS Meeting Abstracts {MA}2020-01 (51) 2805 - 2805 2020/05/01
  • Jaeun Kim, Tae Hyeon Kim, Seyoung Oh, Jae Hyeon Nam, Hye Yeon Jang, Yonghun Kim, Naohito Yamada, Hikaru Kobayashi, So-Young Kim, Byoung Hun Lee, Hiroki Habazaki, Woojin Park, Byungjin Cho
    ACS APPLIED ELECTRONIC MATERIALS 2 (5) 1478 - 1483 2637-6113 2020/05 
    Wide band gap oxide materials with additional infrared (IR) photosensing have rarely been reported because of the lack of the IR-associated sub band gap absorption. In this work, we report that the insertion of a thin aluminum oxide (Al2O3) layer between the Al electrode and indium gallium zinc oxide (IGZO) channel, deposited by atomic layer deposition, enables the material to absorb 850 nm IR light as well as light at visible wavelengths (400 and 530 nm). UV-visible absorption and photoluminescence measurements showed that the Al2O3/IGZO-stacked channel layers could induce additional IR absorption and, consequently, IR-excited charge carriers owing to sub-gap doping within the IGZO band gap. Notably, this approach provides the synergetic effect of enabling IR detection as well as improving the contact properties in the IGZO transistor. Furthermore, the clear dynamic photoswitching behavior was observed only for the Al2O3/IGZO transistor device, revealing a photocurrent 50 times higher than the device containing only IGZO. Thus, the simple approach of engineering the interface of wide band gap oxide materials made it possible to introduce unexpected dual-band gap photosensing characteristics, thereby extending the range of photonic applications of these materials.
  • Yuki Sato, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    APPLIED CATALYSIS A-GENERAL 597 0926-860X 2020/05 
    Highly durable air electrodes for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in highly alkaline media are necessary to catalyze reactions in metal-air secondary batteries. Carbon is able to provide electronic conductivity and co-catalyze reactions, however, is typically oxidized under high-potential conditions above 1.1 V vs RHE. Herein, we demonstrate highly durable platelet-type carbon nanofibers (pCNFs) for OER/ORR in alkaline media. The pCNFs have graphene layers arranged perpendicularly to the fiber axis of the nanofibers. Such a specific configuration of the graphene layers in combination with a high degree of graphitization was found to be highly efficient in providing long-term durability combined with a state-of-the-art brownmillerite-type Ca2FeCoO5 catalyst. The improved oxidation resistance of the pCNF carbon is associated with the high degree of graphitization and the extremely slow oxidation rate of carbon edge planes at the sidewalls of the nanofibers.
  • Ruijie Zhu, Chunyu Zhu, Nan Sheng, Zhonghao Rao, Yoshitaka Aoki, Hiroki Habazaki
    CHEMICAL ENGINEERING JOURNAL 388 1385-8947 2020/05 
    Hindered by dendrite growth, unceasing volume change and repeated regeneration of solid-state electrolyte interface, the practical application of lithium (Li) metal anode is still facing challenges from low Coulombic efficiency (CE), insufficient safety performance and poor cyclic stability. Current collector plays a key role in regulating Li deposition and suppressing dendrite growth. In this report, through a simple bio-template method, a textile-structured nickel (Ni) framework is fabricated as current collector for Li metal anode, whose unique micro-nano hierarchical structure is adequate for accommodating Li. A good performance after more than 200 cycles at 3 mA cm(-2) during repeated Li plating/stripping is remained in virtue of this unique structure design. By further introducing Ag2S nanoparticles uniformly to the current collector, a dendrite-free and high reversible Li metal anode is achieved, showing low over-potential (similar to 24 mV at 1 mA cm(-2)), high CE (similar to 98%) and excellent quick charging/discharging stability (up to 350 cycles at 10 mA cm(-2) in symmetric cell). Furthermore, this new strategy for constructing textile-structured metallic framework opens a foreground for various applications of porous metals.
  • Nan Sheng, Ruijie Zhu, Takahiro Nomura, Zhonghao Rao, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki, Tomohiro Akiyama
    SOLAR ENERGY MATERIALS AND SOLAR CELLS 206 0927-0248 2020/03 
    Organic phase change materials (PCM, such as paraffin) are broadly used in thermal energy storage systems, especially for the efficient utilization of solar energy and industrial waste heat, whereas their low shape-stability and poor heat transfer performance have hindered the practical applications. In this work, we aim at producing high-performance phase change composites (PCCs) with high, anisotropic thermal conductivity and good shape-stability. The PCCs are supported by a biomass-derived porous carbon scaffolds, which are constructed with graphene-wrapped and vertically aligned hollow carbon fibers. The PCC with a filler content of 8.5 wt% exhibits a high lateral thermal conductivity of 1.36 W m(-1) k(-1) and an even higher thermal conductivity of 2.68 W m(-1) K-1 along the axial fiber direction which is 10.7-fold higher than pure paraffin. The PCCs also show satisfactory shape stability, high latent heat, good thermal cycling and chemical stability. These results demonstrate the potential for fast thermal energy conversion and management using our novel carbon scaffold supported PCCs with tailored anisotropic thermal transfer properties.
  • Nan Sheng, Zhonghao Rao, Chunyu Zhu, Hiroki Habazaki
    SOLAR ENERGY MATERIALS AND SOLAR CELLS 205 0927-0248 2020/02 
    The development of thermal conductive and porous supporting scaffolds is believed to solve the problems of poor shape-stability and low thermal conductivity of solid-liquid transition-type phase change materials (PCMs), which are promisingly used for solar thermal energy storage and management. In this paper, textile-structured carbon scaffolds with flexible shape and high porosity are produced by the direct carbonization of cotton cloth. The carbon textile with versatilely changeable shape can be employed as good conductive and supporting scaffolds for PCMs, and paraffin PCM is evaluated. The composite PCMs exhibit good shape-stability and enhanced thermal transfer properties. The composites can present anisotropically improved thermal conductivity by aligning the carbon sheets in their main yarn direction. The thermal conductivity of the composite with a carbon weight ratio of 16.5 wt% is increased to 0.99 W K-1 m(-1) from the main yarn direction and 0.68 W K-1 m(-1) from the through sheet direction, which is greatly higher than the value of paraffin (0.25 W k(-1) m(-1)), and the composite show heat capacity of 170 J g(-1). With the facile production of flexible and shapeable carbon supporting scaffold, the high thermal storage capability, good shape-stability and high heat transfer property, the composite PCM has great potential applications in solar thermal energy storage.
  • SeongWoo Jeong, Tomoyuki Yamaguchi, Mamoru Okamoto, Chunyu Zhu, Hiroki Habazaki, Masaharu Nagayama, Yoshitaka Aoki
    ACS APPLIED ENERGY MATERIALS 3 (1) 1222 - 1234 2574-0962 2020/01 
    Protonic ceramic fuel cells (PCFCs) have limited application below 500 degrees C owing to their high ohmic and polarization resistances. Hence, efforts are ongoing to develop advanced fuel cells based on semiconductor device science as well as material interfacial engineering. Here, we demonstrate that hydrogen-permeable metal-supported fuel cells (HMFCs) exhibit improved energy conversion efficiency at relatively lower temperatures due to the retardation of secondary conduction (that of the oxide ions) at the oxide/metal heterointerface. The electrolyte membrane in HMFCs is forced to gain extra protons to compensate for the charge from the oxide ions accumulating via blocking, resulting in extremely high proton conductivity. Simultaneously, the heavily hydrated membrane pumps protons out of the cathode side during cell operation. This significantly promotes interfacial proton diffusion for cathode reactions. Hence, HMFCs can operate at high efficiency even at temperatures lower than the operational temperature of PCFCs and will help improve the power generation performance of protonic oxide fuel cells at temperatures lower than 500 degrees C.
  • Yuki Sato, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Naoko Fujiwara, Tsutomu Ioroi, Hiroki Habazaki
    ELECTROCHEMISTRY 88 (6) 566 - 573 1344-3542 2020 
    Development of highly active bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is required for air electrodes of zinc-air secondary batteries (ZAB). In this study, we synthesize spinel-type MnCo2O4 (MCO) nanoparticles on highly graphitized platelet-type carbon nanofibers (pCNF) via a solvothermal method. The pCNF is selected as carbon support in this study because of the excellent stability against anodic degradation under the OER condition. The MCO nanoparticles of 2-5 nm in diameter are uniformly dispersed on pCNF and the catalyst exhibits high activities for ORR due to strong interaction pCNF and MCO, in addition to the improvement of OER activities. The MCO/carbon hybrids show comparable electrocatalytic performances to state-of-the-art bifunctional electrodes for OER and ORR. (C) The Author(s) 2020. Published by ECSJ.
  • Nan Sheng, Zhonghao Rao, Chunyu Zhu, Hiroki Habazaki
    APPLIED THERMAL ENGINEERING 164 1359-4311 2020/01 
    Phase change materials (PCMs) have shown promising applications for thermal energy storage and management. With the purposes of solving the critical leakage problem and improving the thermal conductive property of paraffin PCM, composite PCMs as-supported by carbon fiber bundles were fabricated by a simple vacuum impregnation. The porous and honeycomb-shaped carbon fibers were prepared by the direct carbonization of biomass sisal fibers. As beneficial from the carbon supporting scaffolds, the composites illustrated great thermal conductivity increasement (1.73 W m(-1) K-1) over pure paraffin (0.25 W m(-1) K-1). The composite PCMs show satisfying latent heat (192.2 J g(-1) at a carbon ratio of 12.8%), good shape stability, favorable thermal reliability and cyclability. Moreover, due to the one-dimensionally arranged carbon fiber bundles, the composites also showed anisotropic thermal conductive property. All of those could reinforce the use of the low-cost sisal-derived carbon fibers as thermal conductive scaffolds to PCMs, which will promote their practical applications for advanced thermal energy storage in collecting solar energy and industrial waste heat.
  • Ruijie Zhu, Nan Sheng, Zhonghao Rao, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    JOURNAL OF MATERIALS CHEMISTRY A 7 (47) 27066 - 27073 2050-7488 2019/12 
    The utilization of a Li metal anode is necessary in the development of next generation high energy density Li batteries, which is still hindered by problems of dendrite growth, volume change and electrolyte depletion. To overcome these difficulties, the employment of 3D porous current collectors has been demonstrated to be an effective strategy. However, the widely used porous metallic current collectors, such as commercial Cu foam, are always too heavy to meet the demand for high energy density. In this work, we develop a low-weight, flexible, hierarchically porous and textile-structured Cu current collector via a smart cotton T-shirt template method. By employing a variant of Schweizer's reagent as the Cu source, the T-shirt moulded Cu framework can inherit the textile morphology. The hierarchically porous structure and high surface area can lower the local current density, and the unique 3D structure can confine the growth of Li crystals, all of which can endow the novel textile-structured Cu with superior performance as a current collector for Li metal anodes. Furthermore, this strategy provides a convenient route for designing template-structured frameworks, which is useful not only for the development of a current collector, but also for the preparation of numerous structure-oriented materials.
  • Yuki Sato, Hikaru Kobayashi, Damian Kowalski, Akira Koyama, Chunyu Zhu, Yoshitaka Aoki, Mikito Suto, Hiroki Habazaki
    ELECTROCHEMISTRY COMMUNICATIONS 108 1388-2481 2019/11 
    The formation of crystalline anatase films having important applications such as photocatalysis, solar cells, electrochromic applications, and bio-implants requires time-consuming multiple processes including heat treatments. In this paper, ultra-rapid formation of a crystalline anatase film on a tin substrate is realized by a cathodic deposition method, which is performed only for 3 s in an aqueous solution containing TiF62- at 60 degrees C without any heat treatment. The deposited nanocrystalline anatase film of similar to 90 nm thickness contains high concentration of tin species derived from the substrate metal and shows superhydrophilicity after UV light irradiation. The process utilized in this study provides a novel annealing-free approach for the rapid formation of a photoactive crystalline anatase film on heat-labile substrates.
  • Ning Wang, Satoshi Hinokuma, Toshiaki Ina, Hajime Toriumi, Misaki Katayama, Yasuhiro Inada, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    CHEMISTRY OF MATERIALS 31 (20) 8383 - 8393 0897-4756 2019/10 
    Mixed proton-electron conductors (MPECs) are indispensable for the efficient operation of proton conducting ceramic fuel cells and electrolyzer cells at intermediate temperatures (below 500 degrees C), but robust guidelines for their material design are still missing. Here, this study for the first time reports on the massive uptake of proton carriers in cubic perovskite type La0.7Sr0.3MnO3-delta at intermediate temperatures through the hydration reaction triggered by the coupled oxygen and manganese redox reaction. La0.7Sr0.3MnO3-delta undergoes decline of antibonding O 2p states hybridized with Mn 3d orbitals together with oxidation of Mn3+ to Mn4+ by hydration and thus retains bulk protons in the concentrations of 0.14 in wet air at around 420 degrees C, which is corresponding to the concentration of the well-known proton conductor BaZrxCe0.8-xY0.2O3-delta. The current results offer a general concept to design MPECs operating in air conditions, namely, that transition metal oxides possessing many oxygen vacancies and oxygen hole carriers could be promising candidates.
  • Cheong Kim, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHIMICA ACTA 314 173 - 187 0013-4686 2019/08 
    Biomass-derived porous carbons with very high specific surface area (SSA) and heteroatom-doping are important for obtaining high performance supercapacitor. In this study, we report a simple and straightforward strategy, which involves the efficient and exothermic pyrolysis of Mg/K/Mg center dot K-nitrate-urea-cellulose mixture with subsequent high temperature carbonization and washing treatment, to produce N-doped porous carbon with tunable pore structure. The vigorous exothermic pyrolysis of Mg/K/Mg center dot K-nitrate-urea-cellulose induces the formation of large macropores. The subsequent high temperature carbonization and washing treatments remove Mg,K compounds and facilitate the creation of numerous micro and mesopores. The pore size distribution of the obtained carbon is quite dependent on the Mg center dot K ratio in the precursors. In this manner, the three-dimensional hierarchical porous carbon with SSA larger than 2700 m(2) g(-1) is obtained. The obtained porous carbon as the electrodes for supercapacitor in two-electrode measurement shows high specific capacitance (279 Fg(-1) at 1 A g(-1) in a 6 M KOH electrolyte), excellent cycling stability (larger than 89% capacitance retention after 10,000 cycles at 2 Ag-1) and good rate capability (235 Fg(-1) at even 30 Ag-1). These results indicate that biomass cellulose-derived heteroatom-doped hierarchical porous carbon is a promising material for supercapacitor. (C) 2019 Elsevier Ltd. All rights reserved.
  • Damian Kowalski, Hisao Kiuchi, Teruki Motohashi, Yoshitaka Aoki, Hiroki Habazaki
    ACS APPLIED MATERIALS & INTERFACES 11 (32) 28823 - 28829 1944-8244 2019/08 
    Rechargeable zinc-air batteries are considered as one of the possible candidates to replace conventional lithium-ion batteries. One of the requirements for effective battery operation is an oxygen evolution reaction (OER) that needs to be generated in a highly alkaline electrolyte. The A(2)BB'O-5 brownmillerite-type Ca2FeCoO5 electrocatalyst having a 57 Pbcm symmetry exhibits very high electrocatalytic activity toward OER in 4 mol dm(-3) KOH. Our studies show that the electrocatalyst undergoes bulk amorphization upon OER and adequately activates catalytically active domains. The synchrotron radiation studies using the extended X-ray absorption fine structure (EXAFS) technique show that the central structural unit found in the polarized Ca2FeCoO5 is a cluster of edge-sharing CoO6 octahedra. The OER preferentially takes place on the edge-sharing CoO6 octahedra catalytic centers reconstructed in the brownmillerite-type electrocatalyst. The EXAFS second shell peaks at an interatomic distance of 2.8 angstrom are the fingerprints of the catalytically active domains.
  • M. Seo, H. Habazaki, M. Inaba, M. Yokomizo, T. Nakayama
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 23 (7) 2261 - 2275 1432-8488 2019/07 
    In situ X-ray absorption spectroscopy (XAS) was applied to investigate the Sn adlayer on platinized (pl-) Pt electrode in deaerated 0.2 M HClO4 solution containing 10(-3) M Sn2+ in relation to the effect of Sn addition on electrocatalysis of Pt. A periodical emersion method under potentiostatic polarization, using pl-Pt plate (roughness factor S-r = 770) as a working electrode was employed to detect sensitively the sub-monolayer coverage of Sn on Pt. The Sn K-edge absorption spectra in a scanning XAS mode were measured by monitoring the Sn K-alpha 1 fluorescence line. The Sn K-edge absorption near-edge structure (XANES) has indicated that the Sn species adsorbed on the pl-Pt electrode is partly oxygenated in the Sn-underpotential (UPD) region between - 0.05 and 0.25 V (RHE) which is overlapped with the UPD region of hydrogen. The extended X-ray absorption fine structure (EXAFS) analysis has supported a Sn overlayer model in which Sn atom occupies the hollow site of the nearest neighbor Pt atoms and is further bound with oxygen atoms in the Sn-UPD region. The coordination number of the Sn-Pt bond or Sn-Sn bond decreases with increasing potential, while the coordination number of the Sn-O bond increases reversely. In the potential region between 0.45 and 0.85 V (RHE), the EXAFS analysis has suggested that two-dimensional surface Sn oxide forms on the pl-Pt electrode, which is supported from the potential-pH equilibrium diagram of the Sn/H2O system.
  • Laras Fadillah, Kentaro Takase, Hikaru Kobayashi, Sylwia Turczyniak-Surdacka, Marcin Strawski, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHIMICA ACTA 309 274 - 282 0013-4686 2019/06 
    The effect of alloying of sputter-deposited Fe with 9 at.% tungsten on the growth of nanoporous anodic oxide was studied in ethylene glycol electrolyte containing 0.1 mol dm(-3) ammonium fluoride and 1.5 mol dm(-)(3) water. The classic nanoporous anodic film (Al2O3-like) was developed on pure Fe while the transition of nanopores to nanotubes (TiO2-like) was observed for anodizing of Fe-W alloy. The pores/ nanotubes having average diameter 50-110 nm and 30-60 nm on pure Fe and Fe-W alloy anodized at voltage 40-60 V, respectively. Both nanoporous/nanotubular anodic films grow in line with the field assisted flow model with a few fundamental details: i) transition of nanopores to nanotubes is observed upon anodizing of Fe-W alloy, ii) significant reduction of the cell size (nanotube diameter) is obtained on Fe-W alloy, iii) relatively thick layer is produced at Fe-W alloy/oxide interface. The primary reason of this transition to nanotubes as well as chemical changes is discussed in view of effective modification of the cell boundary region with tungsten species, probably WF6 compound, upon growth of anodic film under influence of high electric field strength. The possible reason of developing the space in between nanotubes is faster kinetics of WF6 reaction with water over the presence of low solubility FeFx species. Alloying of iron is one of the effective ways to modify the nanostructure of the anodic film on iron. (C) 2019 Elsevier Ltd. All rights reserved.
  • Hajime Toriumi, Taisei Kobayashi, Satoshi Hinokuma, Toshiaki Ina, Takashi Nakamura, Koji Amezawa, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    INORGANIC CHEMISTRY FRONTIERS 6 (6) 1587 - 1597 2052-1553 2019/06 
    Herein, high-valence-state Mn(v) oxide, barium manganate(v) (Ba-3(MnO4)(2)), is examined as an anode electrocatalyst of a H+-conducting solid oxide steam electrolysis cell (H-SOEC). Ba-3(MnO4)(2) comprises C-3v-symmetric MnO43- oxo-anions with three long Mn-O bonds and one short Mn-O bond at room temperature. Ba-3(MnO4)(2) caused a conductivity jump by one order of magnitude at approximately 600 degrees C owing to the antiferromagnetic/paramagnetic phase transition, accompanied by a shape change of the tetrahedral MnO43- anions from C-3v to T-d symmetry, as confirmed by the electrical conductivity measurements and the extended X-ray absorption fine structure at an elevated temperature. Hence, the Ba-3(MnO4)(2) base anode of the H-SOEC exhibited improved performance, with anode polarization resistances being lower than those of Sm0.5Sr0.5CoO3, a well-known H-SOEC anode material. Impedance analysis in terms of oxygen and water partial pressure revealed that the superior performance of the Ba-3(MnO4)(2) base anode can be attributed to the extended reaction area. Since abundant unoccupied 3d states of the high-valence-state Mn5+ cations are favorable for charge transfer interactions with water electron donors, thereby facilitating water adsorption, the oxygen evolution reaction could occur directly over the electrode surface, and thus the reaction sites were not limited to the gas-electrode-electrolyte triple phase boundary.
  • Nan Sheng, Takahiro Nomura, Chunyu Zhu, Hiroki Habazaki, Tomohiro Akiyama
    SOLAR ENERGY MATERIALS AND SOLAR CELLS 192 8 - 15 0927-0248 2019/04 
    The practical use of organic phase change materials (PCMs) for solar thermal energy storage is limited by the leakage problem and the low thermal conductivity. As a good supporting and thermal conductive framework for organic PCM with shape-stability, three-dimensional carbon sponges are produced by the direct carbonization of low-cost and sustainable biomass cotton. The carbon sponges are consisted of aerogels of the cotton-derived hollow carbon fibers, which have both interconnecting network and high porosity. The vacuum impregnated paraffin@carbon sponge composites not only present leakage-proof shape stability and enhanced thermal conductivity, but also show high thermal storage energy density (> 200 J g(-1), slightly lower than the pure paraffin) and good cyclability. The results indicate that the shape-stable PCMs as supported by cotton-derived carbon sponges are potentially to be widely used for thermal energy conversion and storage, especially for solar energy utilization.
  • Nan Sheng, Ruijie Zhu, Kaixin Dong, Takahiro Nomura, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki, Tomohiro Akiyama
    JOURNAL OF MATERIALS CHEMISTRY A 7 (9) 4934 - 4940 2050-7488 2019/03 
    The wide application of organic phase change materials for thermal energy storage and management is limited by their low thermal conductivity and poor shape stability. In this work, anisotropic thermally conductive and shape-stabilized phase change composites (PCCs) were successfully prepared with vertically aligned carbon fibers as supporting scaffolds. The aligned and hollow carbon fiber scaffolds with different densities were facilely fabricated by the direct carbonization of rolled cotton sheets with aligned and hollow cellulose fibers. PCCs were obtained by vacuum impregnation of paraffin wax. Because of the interconnected hollow carbon fiber frameworks with vertically aligned fibers and high porosity, PCCs present enhanced anisotropic thermal conductivity and good shape stability against leakage. The thermal conductivity in the axial direction along the fibers is higher than that in the lateral direction, since the aligned fiber scaffolds act as the thermal conduction pathway. The thermal conductivity of a PCC with a carbon ratio of 8.8 wt% is 0.77 W K-1 m(-1) (>3 times that of pure paraffin) in the axial direction, while the value in the lateral direction is 0.58 W K-1 m(-1). This work provides a novel strategy for designing anisotropic thermally conductive and shape-stabilized PCCs with potential applications in advanced thermal management and storage.
  • Cheong Kim, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH 58 (8) 3047 - 3059 0888-5885 2019/02 
    In this work, high-value-added N-doped hierarchical porous carbon (NHPC) for oxygen reduction reaction (ORR) electrocatalysis was prepared using biomass cellulose as the raw material. The pyrolysis of cellulose is accelerated by a redox combustion reaction of magnesium nitrate carbohydrates (urea and cellulose) as absorbed in cellulose fibers, which endows doping with nitrogen, exfoliates the cellulose to highly porous particles, and creates numerous pores simultaneously. After being further carbonized at high temperature and washed with acid, NHPCs were produced that have hierarchical porous structure and large specific surface area. These features are beneficial to the ORR. The influence of four preparation parameters, including species of magnesium salt, carbonization temperature, urea amount, and magnesium salt amount, on the porous characteristics and ORR performance is comprehensively investigated.
  • J. M. Torrescano-Alvarez, M. Curioni, H. Habazaki, T. Hashimoto, P. Skeldon, X. Zhou
    ELECTROCHIMICA ACTA 296 783 - 789 0013-4686 2019/02 
    The presence of alloying elements in aluminium alloys has a significant impact on the anodizing behaviour and results in the formation of porous anodic films with different chemical composition and morphology compared with those generated on pure aluminium. In this work, the effect of alloy element enrichment at the alloy/film interface and of cell diameter on the incorporation and distribution of alloying element species in porous anodic films is considered. It is proposed that above a critical cell diameter, D-crit, the critical alloy enrichment sufficient for oxidation of the alloying element and its incorporation into the film can be maintained across the alloy/film interface. Below D-crit, only a subcritical enrichment can be maintained and the alloying element is then incorporated into the film at the cell boundaries. D-crit depends on the concentration of the alloying element in solid solution and on the critical enrichment. The proposed role of D-crit is supported by alloying element distributions from literature data for model Al-Au and Al-W alloys and new results for anodic films on AA 2024-T3 alloy. (C) 2018 Elsevier Ltd. All rights reserved.
  • A. Zaffora, F. Di Quarto, H. Habazaki, I. Valov, M. Santamaria
    FARADAY DISCUSSIONS 213 165 - 181 1359-6640 2019/02 
    Redox-based resistive switching memories (ReRAMs) are the strongest candidates for next generation nonvolatile memories. These devices are commonly composed of metal/solid electrolyte/metal junctions, where the soLid electrolyte is usually an oxide Layer. A key aspect in the ReRAMs development is the soLid electrolyte engineering, since it is crucial to tailor the material properties for obtaining excellent switching properties (e.g. retention, endurance, etc.). Here we present an anodizing process as a non vacuum and Low temperature electrochemical technique for growing oxides with tailored structural and electronic properties. The effect of the anodizing conditions on the soLid state properties of the anodic oxides is studied in relation to the final ReRAM device performances demonstrating the great potentiality of this technique to produce high quality oxide thin films for resistive switching memories.
  • Y. Aoki, S. Jeong, M. Nagayama, C. Zhu, H. Habazaki
    ECS Transactions 91 (1) 917 - 920 1938-5862 2019 
    In general, protonic ceramic fuel cells (PCFCs) have structure of porous anode support composed of proton-conducting ceramic and metallic Ni. The porous anode type PCFCs have much lower power outputs than expected from the proton conductivity of electrolyte materials. Meanwhile, PCFCs with hydrogen-permeable dense metal anode, hydrogen-permeable metal-supported fuel cells (HMFCs), have reported outstanding power outputs even at 400oC with significantly lowered ohmic resistances despite the analogous electrolyte materials. Obscure is, however, what makes such different cell properties. In this study, we examined the electrochemical performances of both type of cells at around 500oC.
  • H. Toriumi, C. Zhu, H. Habazaki, Y. Aoki
    ECS Transactions 91 (1) 2669 - 2672 1938-5862 2019 
    BaCe0.8Y0.2O3-δ (BCY) has high proton conductivity but is less stable against CO2 and steam. The solid solution BaZrxCe1-x-yYyO3-δ (BZCY) tend to be more tolerant to CO2 and steam with increasing Zr contents. In this work, cathode-supported thin film cell was fabricated using BaZr0.6Ce0.2Y0.2O3-δ with higher Zr contents for the electrolyte of proton conducting solid oxide steam electrolysis cell (H+-SOEC). The cell composed of LSCF|BZCY622|Ni-BZCY622 yielded electrolysis currents of 330 and 200 mA cm-2 at 700 and 600ºC, respectively, at 1.5 V bias.
  • Atsushi Kasuga, Akira Koyama, Katsutoshi Nakayama, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ISIJ INTERNATIONAL 59 (2) 345 - 350 0915-1559 2019 
    Stainless steels is practically important corrosion-resistant metallic materials, and additional surface functionalities including self-cleaning, anti-fouling, anti-ice and snow sticking and fluid drag reduction by the introduction of superhydrophobic and superoleophobic surfaces are of recent interest. Here, we report the micro-/nano-hierarchical roughening of type 304 stainless steel surface by chemical and electrochemical etching and anodizing. Chemical etching in HCl + FeCl3 aqueous solution containing a surfactant introduces surface roughness of several tens micrometers scale and the electrochemical etching in HCl + HNO3 aqueous solution produces a number of etch pits of similar to 1 mu m in size. Then, a porous anodic layer of the pore size of similar to 20 nm is formed on the etched surface by anodizing in ethylene glycol electrolyte containing 0.1 mol dm(-3) NH4F and 0.1 mol dm(-3) H2O. After fluoroalkylsilane (FAS) coating of the hierarchically rough surface to reduce the surface energy, the surface becomes superhydrophobic and superoleophobic; the advanced contact angle for hexadecane (surface tension of 27.6 mN m(-1)) is similar to 160 degrees and the contact angle hysteresis is less than 10 degrees. Since the FAS-coated flat surface is oleophilic, so that such hierarchically rough surface is of significant importance to achieve the superoleophobicity even for low surface tension liquids.
  • Naohito Yamada, Damian Kowalski, Akira Koyama, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    RSC ADVANCES 9 (7) 3726 - 3733 2019/01 
    In this study, platelet-type carbon nanofibers prepared by the liquid phase carbonization of polymers in the pores of a porous anodic alumina template were used to prepare the Co3O4/carbon electrocatalysts. For comparison, Co3O4 nanoparticles were also deposited on multiwall carbon nanotubes (MWCNTs). Both the nitrogen-free platelet-type carbon nanofibers (pCNFs) and the nitrogen-containing analogue (N-pCNFs) exhibited better dispersion and higher amount of deposited Co3O4 nanoparticles compared to the MWCNTs. In addition, many individual Co3O4 nanoparticles were deposited separately on pCNF and N-pCNF, whereas aggregated deposition was commonplace on MWCNTs. The results indicated that the side wall of the pCNFs, which consisted of carbon edge planes, was the preferential nucleation site of Co3O4 nanoparticles rather than the basal planes of carbon that predominated the surface of the MWCNTs. The oxygen reduction reaction (ORR) activity of the Co3O4/pCNF composite in 0.1 mol dm(-3) KOH solution was better than that of Co3O4/MWCNTs. The N-pCNF further enhanced the ORR activity of the Co3O4/pCNFs even though the dispersion and supported amount of Co3O4 nanoparticles were negligibly affected by the presence of the nitrogen species. Synergistic interactions of the Co3O4 nanoparticles with N-doped CNFs contributed to the increased ORR activity.
  • Yoshitaka Aoki, Etsushi Tsuji, Teruki Motohashi, Damian Kowalski, Hiroki Habazaki
    JOURNAL OF PHYSICAL CHEMISTRY C 122 (39) 22301 - 22308 1932-7447 2018/10 
    Electrocatalytic activity for the four-electron-transfer oxygen reduction reaction (ORR) was examined with perovskite-type La0.7Sr0.3Mn1-xNixO3-delta (x = 0-0.5) compounds in concentrated KOH. Electrochemical measurements by means of a rotating ring-disk electrode technique revealed that 10% substitution of Mn by Ni atoms significantly improved ORR activity whereas further Ni substitution significantly decreased the catalytic performance. Moreover, La0.7Sr0.3Mn0.9Ni0.1O3-delta could achieve the ideal reaction electron number (similar to 4) without the aid of carbon additives, whereas compounds with x > 0.1 achieved a number less than 4 in the absence of carbon cocatalysts, attributed to lowered reaction rates related to two-electron reduction from oxygen to peroxide. Combined with the results of X-ray photoelectron spectroscopy, the pronounced catalytic activity of La0.7Sr0.3Mn0.9Ni0.1O3-delta could be correlated with the population of Mn3+ states with (e(g))(1) configuration.
  • Katsutoshi Nakayama, Akira Koyama, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ADVANCED MATERIALS INTERFACES 5 (19) 2196-7350 2018/10 
    This paper reports rapid self-healing on superoleophobic hierarchically porous aluminum surfaces within 1 h even at room temperature. This self-healing surface is prepared by infiltration of a liquid fluoroalkylsilane (FAS) coating into the substrate pores. The FAS-infiltrated dual-pore superoleophobic surface becomes superoleophilic after oxygen plasma treatment due to the damage done to the organic coating. However, the superoleophobicity is completely recovered by exposure to normal atmosphere at room temperature, and this rapid self-healing is repeatable. The FAS liquid appears to coat the nanopore walls, rather than filling the nanopores. The high wettability of FAS on surfaces induces the rapid recoating of the plasma-damaged surface, contributing to the self-healing of the superoleophobicity.
  • Chunyu Zhu, Manami Takata, Yoshitaka Aoki, Hiroki Habazaki
    CHEMICAL ENGINEERING JOURNAL 350 278 - 289 1385-8947 2018/10 
    Porous carbon has attracted great interest because of its distinctive structure and superior properties for designing electrochemical energy storage devices. In this work, we report a novel and facile method to fabricate nitrogen-doped porous carbon (NPC) with designed hierarchical multi-porous structure. The NPC is prepared using a facile and scalable MgO template method as-mediated by a magnesium nitrate-glycine solution combustion synthesis (SCS), in which the preparation conditions of calcination temperature and glycine-nitrate ratio are carefully studied. The NPC shows a high specific surface area up to 1958 m(2) g(-1) and contains hierarchical multi-pores of interconnected macro-, meso-and micro-pores. When applied as ORR electrocatalyst, the NPC-n2-1000 sample shows the highest activity, good durability and high tolerance against methanol, which is among the best reported carbon-base catalysts. The NPC samples also shows great potential as the active electrode material for supercapacitors. NPC-n2-900 sample exhibits a high specific capacitance of 232 F g(-1) at 1 A g(-1) in 6 M KOH electrolyte, a superior rate capability (205 F g(-1) at 10 A g(-1)) and a good cycling performance. The present work demonstrates that the combination of glycine-nitrate SCS and template introduction in one-step can turn the carbohydrate fuel to advanced porous carbon with prospective applications in high-performance energy storage devices.
  • A. Nemcova, Y. Li, I. Kubena, I. Vickridge, J. -J. Ganem, A. Yerokhin, H. Habazaki, P. Skeldon
    ELECTROCHIMICA ACTA 280 300 - 307 0013-4686 2018/08 
    Binary Mg-Ag alloys are of interest as antibacterial biodegradable materials. In the present work, the behaviour of silver during galvanostatic anodizing of a sputtering-deposited Mg-0.6 at.% Ag alloy in a fluoride/glycerol electrolyte containing 5 or 60 vol.% water was investigated. Similar alloy compositions have been shown to have potential as biomaterials in in-vitro tests. The resultant barrier-type anodic films were examined using scanning and transmission electron microscopies, glow discharge optical emission spectroscopy and Rutherford backscattering spectroscopy. The films were shown to be nano-crystalline and to contain oxide and fluoride species, with O:F atomic ratios dependent on the amount of water in the electrolyte. Silver species were incorporated into the films, accompanied by loss of silver species to the electrolyte. Notably, silver was enriched in a <6 nm thick alloy layer, to concentration of at least 12 at.%. (C) 2018 Elsevier Ltd. All rights reserved.
  • Jin-Hui Cao, Yuki Sato, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Yingliang Cheng, Hiroki Habazaki
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 22 (7) 2073 - 2081 1432-8488 2018/07 
    The growth of a uniform barrier-type anodic film on aluminum is usually terminated by electric breakdown, which is controlled by the resistance of electrolyte or anion concentration. In this study, highly resistive porous layers have been introduced by anodizing aluminum in sulfuric acid electrolyte followed by boiling water treatment to examine their influence on the electric breakdown potential. The pores of the porous alumina film are sealed by forming hydrated alumina (pseudo-boehmite) after the boiling water treatment. The breakdown potential increases to over 1500 V for the pore-sealed aluminum specimens on anodizing in sodium tungstate electrolyte. The electrochemical impedance spectroscopy measurements revealed an increased resistance of the porous layer after the pore-sealing treatment. GDOES depth profile analysis disclosed that the sealed porous layer impedes the incorporation of tungsten species into the barrier layer. The introduction of a highly resistive layer that also suppresses the anion incorporation on aluminum is effective in increasing the breakdown potential of anodic films.
  • Jinhui Cao, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ACS SUSTAINABLE CHEMISTRY & ENGINEERING 6 (6) 7292 - 7303 2168-0485 2018/06 
    The development of green and clean synthetic techniques to produce carbon materials for energy storage and conversion applications has motivated researchers to use sustainable biomass. In this study, hierarchical porous carbon (HPC) with very high specific surface area and controlled porosity is synthesized by a novel and facile method, which employs an exothermic pyrolysis process of starch magnesium nitrate raw materials with subsequent high temperature thermal treatment and acid washing. The biomass starch acts as both a reductant and carbon source, while magnesium nitrate is an oxidant and provides MgO template as pore creator. The vigorous exothermic pyrolysis of starch magnesium nitrate mixture introduces MgO@C precursor with a highly 3D porous network containing meso- and macropores. After MgO template is removed, plenty of micro- and mesopores are further created. Experimental parameters including calcination temperature, starch nitrate ratio, and magnesium salt species are comprehensively evaluated. The HPC shows a very large specific surface area up to about 2300 m(2) g(-1) and a hierarchical porous architecture composed of interconnected micro-, meso- and macropores. As an electrode material for supercapacitors, the HPC exhibits high specific capacitance (229 F g(-1) at 1 A g(-1) in a 6 M KOH electrolyte), good rate capability (211 F g(-1) at even 10 A g(-1)) and outstanding cycling stability (94% capacitance retention after 10 000 cycles at 2 A g(-1)). The superior electrochemical performance of the HPC stems from both high surface area and the hierarchical multiporous structure, which provides an accessible pathway for electrolyte transport. These results demonstrate a very effective and low-cost method for scalable preparation of HPC using green biomass carbon source for supercapacitors, which also has potential applications such as adsorbent for water/gas treatment.
  • Andrea Zaffora, Roberto Macaluso, Hiroki Habazaki, Ilia Valov, Monica Santamaria
    ELECTROCHIMICA ACTA 274 103 - 111 0013-4686 2018/06 
    Redox-based resistive switching memories (ReRAM) based on metal oxides are considered as the next generation non-volatile memories and building units for neuromorphic computing. Using different deposition techniques results however in different structural and electric properties, modulating the device performance. In this study HfO2 and Nb2O5 were prepared electrochemically by anodizing sputtering-deposited Hf and Nb in borate buffer solution. Photoelectrochemical measurements were used to study the solid state properties of the anodic oxides, such as band gap and flat band potential. In the case of anodic HfO2, detected photocurrent is ascribed to optical transitions between localized (generated by the presence of oxygen vacancies into the oxide) and extended states. Impedance measurements disclosed the formation of n-type Nb2O5 and insulating HfO2. Pt top electrode was deposited onto the metal/anodic oxide junctions to fabricate ReRAM cells. Whereas switching behaviour of Nb/anodic Nb2O5/Pt cells was not reliable, good endurance and retention performances were proved in the case of Hf/anodic HfO2/Pt cells, showing that electrochemical growth of the oxides can be a reliable way to fabricate solid electrolytes for resistive switching memories. (C) 2018 Elsevier Ltd. All rights reserved.
  • R. Elaish, M. Curioni, K. Gowers, A. Kasuga, H. Habazaki, T. Hashimoto, P. Skeldon
    SURFACE & COATINGS TECHNOLOGY 342 233 - 243 0257-8972 2018/05 
    The study examined the influence of fluorozirconic acid additions to the electrolyte on the growth rate and composition of porous anodic films formed on AA 2024-T3 alloy in sulphuric acid and tartaric-sulphuric acid electrolytes. A range of anodizing voltages, electrolyte temperatures, fluorozirconic acid concentrations and anodizing times was employed. High purity aluminium was employed as a reference material. Fluorozirconic acid increased the film growth rate, with a reducing influence as the temperature increased from 0 to 37 degrees C. The growth rate was enhanced by increased additions of fluorozirconic acid to the electrolyte, although chemical dissolution of the film was also accelerated. The films contained fluoride and sulphate ions from the electrolyte, with the fluoride concentrations decreasing with increasing temperature whereas the sulphate concentration was relatively unaffected.
  • Andrea Zaffora, Francesco Di Quarto, Chiharu Kura, Yuki Sato, Yoshitaka Aoki, Hiroki Habazaki, Monica Santamaria
    ADVANCED ELECTRONIC MATERIALS 4 (5) 2199-160X 2018/05 
    Metal oxides with high dielectric constant are extensively studied in the frame of substituting SiO2 as gate dielectric in nanoelectronic devices. Here, high-k mixed HfO2/Nb2O5 oxides are prepared by a facile electrochemical route starting from sputtering-deposited Hf-Nb alloys with several compositions. Transmission electron microscopy, grazing incidence X-ray diffraction, and glow discharge optical emission spectroscopy are employed to study the oxide structures, disclosing a crystalline-amorphous transition of the electrochemically prepared oxides by increasing the Nb content. Photo-electrochemical measurements allow the observation of optical transitions ascribed to localized states inside oxide bandgap induced by the presence of oxygen vacancies for Hf-rich oxides. Impedance measurements, coupled with withstand voltage and leakage current estimates, provide a comprehensive view of the real dielectric properties of the oxides. The highest epsilon is estimated for the anodic oxide grown on Hf-39 at% Nb (i.e., 45) but thin film grown on Hf-57 at% Nb alloy shows the best dielectric properties, revealing high dielectric constant, high withstand voltage, and low leakage current. Promising equivalent oxide thickness (down to 0.38 nm) is estimated for the oxide thin layers. The electrochemical oxidation represents a valuable and reliable way to prepare high-k thin oxide films with tailored and controlled dielectric properties.
  • Etsushi Tsuji, Teruki Motohashi, Hiroyuki Noda, Yoshitaka Aoki, Hiroki Habazaki
    JOURNAL OF PHYSICAL CHEMISTRY C 122 (13) 7081 - 7087 1932-7447 2018/04 
    The oxygen reduction reaction (ORR) catalytic activity was systematically studied on the BaLnMn(2)O(5) series (Ln = Y, Gd, Nd, and La) with a layered double-perovskite-type structure in an alkaline aqueous solution. The onset ORR. potential and the number of electrons involved in ORR were found to be strongly Ln-dependent: both values were significantly higher for larger Ln = La and Nd than for smaller Ln = Gd and Y, despite similarities in their chemical compositions and crystal structures. The enhanced ORR activity of the Ln = La and Nd compounds is likely attributed to their stronger affinity to oxygen species, consistent with the greater oxygen storage capability of these compounds, as revealed by the water dissolution reaction at elevated temperatures.
  • Khurram Shahzad, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ChemElectroChem 5 (4) 566 - 566 2018/02/16
  • Chiharu Kura, Sho Fujimoto, Yuji Kunisada, Damian Kowalski, Etsushi Tsuji, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    JOURNAL OF MATERIALS CHEMISTRY A 6 (6) 2730 - 2741 2050-7488 2018/02 
    Hydrogen permeability based on mixed hydride ion electron conduction was demonstrated for hafnium nitride HfNx (film thickness of 100-500 nm, x = 0.8 and 1.0) nanocrystalline membranes. Nanocrystalline films with a (100) orientation and crystallite sizes of a few tens of nanometers were prepared on porous alumina supports by radio frequency (RF) reactive sputtering. Combined spectroscopic, permeability, and microbalance analysis suggests that the nanocrystalline matrices were readily hydrogenated by the formation of Hf-H terminal groups on the internal grain surfaces at ambient temperature and thus efficient hydrogen permeation took place due to an enhanced diffusion of hydridic defects through the grain boundaries; this was further aided by the Hf-H bond exchange process. Hence, membranes with an average crystallite size of 11 nm yielded a hydrogen flux of 6 x 10(-7) mol cm(-2) s(-1) at 25 degrees C at an applied hydrogen partial pressure of 50 kPa; this value is higher than those exhibited by the current state-of-the-art Pd membranes. These findings establish a new concept for Pd alternatives based on the pronounced hydric conductivity of transition metal nitride nanomaterials.
  • Khurram Shahzad, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    CHEMELECTROCHEM 5 (4) 610 - 618 2196-0216 2018/02 
    Anodizing involves a high-voltage electrochemical conversion process that forms barrier-type oxide layers or self-organized nanoporous/nanotubular structures. So far, Al2O3-like nanopores and TiO2-like nanotubes could be successfully synthesized on many metals and alloys. The proposed models of anodic oxide nanotubes growth, however, sacrifice from lack of evidence of the transition from nanopores to nanotubes. The present study demonstrates a missing piece of this anodizing puzzle, which is responsible for the formation of nanotubes in fluoride-containing organic electrolytes. For this purpose, we choose an anodic oxide formed on iron, as a model case, because both nanotubes and nanopores can be formed and slow kinetics of transition between those two forms allows us to observe, ex situ, a fluoride-rich-layer upon nanopores/nanotubes transition. The compositional fingerprints of this transition shed a light on the general mechanism of nanotubes growth in fluoride-containing electrolytes.
  • Hiroyuki Ogata, Hiroki Habazaki
    Zairyo to Kankyo/ Corrosion Engineering 67 (1) 41 - 49 1881-9664 2018 
    Recently, the authors reported the improved corrosion resistance of the electro-galvanized steel coated with epoxy resin organic layers by the simultaneous additions of flaky Al and particulate Ni powders for the use in fuel tanks. In order to understand the roles of Ni and Al powders in the coatings on the corrosion behavior of the coated electro-galvanized steel, the electro-galvanized steel was coated with epoxy resin layers containing either Ni or Al powders, and their corrosion behavior was examined by the corrosion immersion tests in aqueous solution containing formic acid, acetic acid and NaCl, potentiodynamic polarization measurements, electrochemical impedance spectroscopy（EIS）, and oxygen gas and water vapor permeation measurements. Both Ni and Al powders in the organic coatings accelerated the corrosion. The potentiodynamic polarization curves disclosed the increased anodic and cathodic currents and the EIS study showed the reduced coating resistance by the addition of Ni or Al powders. Findings in this study suggested that the improved corrosion resistance of the coatings containing both Al and Ni powders were not simply explained by the corrosion behavior of the coated steel containing only Ni or Al powders and a possible synergistic effect of Ni and Al powders in improving the corrosion resistance is discussed.
  • Yoshitaka Aoki, Tomoyuki Yamaguchi, Shohei Kobayashi, Damian Kowalski, Chunyu Zhu, Hiroki Habazaki
    GLOBAL CHALLENGES 2 (1) 2018/01 
    A direct ammonia-type intermediate temperature fuel cell is examined by means of a hydrogen membrane fuel cell (HMFC) comprising 1-mu m-thick BaZr0.1Ce0.7Y0.2O3-delta (BZCY) thin-film electrolyte and Pd solid anode. It generates the maximum power density of 0.58 W cm(-2) at 600 degrees C with ammonia fuels, and this value is found to be three times larger than the champion data of the recently reported direct ammonia-type proton-conducting ceramic fuel cells (PCFCs). AC impedance spectroscopy is performed to determine the interfacial polarization resistances, disclosing that the anodic overpotentials of HMFCs are at least one order of magnitude smaller than those of anode-supported PCFC under relatively high DC outputs. The anode reactions are driven by the oxidation of monoatomic hydrogen dissolving at the BZCY/Pd solid-solid interface, mediated via proton transfer from Pd to BZCY. The electrochemical analysis reveals that the BZCY/Pd junction forms Ohmic contact without growth of wide depletion layer and thus facilitates the proton transfer reactions because the interfacial region beneath Pd electrode can accommodate amounts of protonic defects as well as the bulk of BZCY due to the small depletion of holes under hole-proton thermodynamic equilibrium.
  • Seongwoo Jeong, Taisei Kobayashi, Kosuke Kuroda, Hyuna Kwon, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    RSC ADVANCES 8 (46) 26309 - 26317 2018 
    This paper reports a survey of power generation characteristics of anode-supported thin film fuel cells with Zr-rich BaZrxCe0.8-xY0.2O3-delta (x = 0.4, 0.6, 0.7, and 0.8) proton-conducting electrolytes, which were fabricated by single step co-firing with Zn(NO3)(2) additives at a relatively low temperature (1400 degrees C). The grain sizes significantly increased to several mu m for x = 0.4 and 0.6, whereas the grain sizes remained in the sub-mu m ranges for x = 0.7 and 0.8, which resulted in large gaps of the fuel cell performances at x over and below 0.6. The cells for x = 0.4 and 0.6 exhibited efficient power generation, yielding peak powers of 279 and 336 mW cm(-2) at 600 degrees C, respectively, which were higher than those of the corresponding cells previously reported. However, the performances abruptly deteriorated with the increasing x to more than 0.7 because the electrolyte films were highly resistive due to the coarse-grained microstructures. Impedance spectroscopy for the dense sintered BaZrxCe0.8-xY0.2O3-delta discs confirmed that the total proton conductivity of BaZr0.6Ce0.2Y0.2O3-delta was higher than that of BaZr0.4Ce0.4Y0.2O3-delta at temperatures above 500 degrees C despite relatively small grain sizes. In addition, BaZr0.6Ce0.2Y0.2O3-delta cells could gain a stable current throughout a continuous run for a few days under CO2-containing fuel supply, which was due to high fraction of thermodynamically stable BaZrO3 matrices. It was demonstrated that BaZr0.6Ce0.2Y0.2O3-delta is a promising electrolyte for proton-conducting ceramic fuel cells with excellent proton conductivity and CO2 tolerance at intermediate temperatures.
  • Taisei Kobayashi, Kosuke Kuroda, SeongWoo Jeong, Hyuna Kwon, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 165 (5) F342 - F349 0013-4651 2018 
    Anodic reaction pathways in proton-conducting solid oxide electrolyzer cells (H+ -SOECs) were investigated using electrochemical impedance spectroscopy with a cell structure of Sm0.5Sr0.5CoO3 (anode) vertical bar BaZr0.4Ce0.4Y0.2O3-delta vertical bar Pt (cathode). Densely sintered BaZr0.4Ce0.4Y0.2O3-delta ceramics (>97% relative density) were fabricated by a reactive sintering process with a 2 mol% Zn(NO3)(2) additive and were applied as the electrolyte. The impedance spectra were measured while the oxygen (p(O2)) and water partial pressures (p(H2O)) in the anode side were systematically varied, which revealed that the SOECs have two polarization resistances at the anode side, one proportional to p(O2)(-1/4) and p(H2O)(0) and another insensitive to p(O2) and p(H2O). A comparison between the experimental results and elementary step modeling revealed that the actual anode reactions could be described by the reverse mode H+-SOFC cathode reactions, and, thus, the elementary steps dominating the anodic polarization resistance were assigned. (C) 2018 The Electrochemical Society.
  • V. A. Safonov, H. Habazaki, P. Glatzel, L. A. Fishgoit, O. A. Drozhzhin, S. Lafuerza, O. V. Safonova
    APPLIED SURFACE SCIENCE 427 566 - 572 0169-4332 2018/01 
    C Cr-C coatings containing different amount of carbon ranging from similar to 5 to 50 at.% were prepared by the direct current (DC) magnetron sputtering on a polished substrate of polycrystalline silicon. The thickness of the samples was about 400 nm. We characterized the composition and the structure of the as-received coatings and those annealed at 500 degrees C by X-ray diffraction (XRD), Energy dispersion X-ray spectroscopy (EDX) and valence-to-core X-ray emission spectroscopy (vtc-XES) methods As follows from XRD measurements, the samples with the carbon content above 35 at.% do not demonstrate any sign of the long-range order and annealing at 500 degrees C does not change their crystallinity. The vtc-XES curves of the as-prepared and annealed samples can be fitted as a superposition of corresponding spectra of chromium metal and chromium carbide (Cr3C2) phases. After the annealing, the content of carbides in the samples (and, correspondingly, the content of covalently bonded carbon) somewhat increases. This suggests that the as-received coatings contain a certain amount of carbon that is not covalently bonded to chromium (most likely, elemental carbon) and their annealing at 500 degrees C transforms this carbon into the additional (of the order of 2-5 at.%) amount of chromium carbide compounds. It deserves mentioning that for Cr-C coatings prepared by the electrochemical deposition from Cr(III) electrolytes containing organic compounds we have not observed changes in the vtc-X-ray emission spectra after similar annealing. This suggests that electrochemical deposition method in contrast to magnetron sputtering technique even at low temperatures favors the formation of only covalently bonded carbon. (C) 2017 Elsevier B.V. All rights reserved.
  • Etsushi Tsuji, Shiki Matsuura, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHEMISTRY 86 (4) 184 - 189 1344-3542 2018 
    This paper reports unusual diffusion-controlled growth of TiO2 mesoporous anodic films on titanium in hot phosphate/glycerol electrolytes. The formation behavior was investigated by cyclic voltammetry (CV) between 0 and 5V vs. Pt at 433 K. The current density became almost constant above 1.5V vs. Pt during the positive potential sweep, and was maintained even during the negative potential sweep. This is contrast to a drastic decrease in current density in changing the direction of potential sweep from the positive to negative in fluoride-containing ethylene glycol electrolyte. The constant current density between 1.5 and 5V vs. Pt increased with an increase in the basicity of the hot phosphate electrolyte, suggesting that the rate-determining step of the film formation in the hot phosphate electrolyte was diffusion process of oxygen sources in the electrolyte, not the ion migration in the thin barrier layer under the high electric field. When CV measurements were conducted to higher potentials up to 20V vs. Pt, anatase was developed above 7V vs. Pt, leading to generate oxygen gas. The film morphology was also potential-dependent and the diffusion current was also influenced by the film morphology as well as oxygen gas generation. (c) The Electrochemical Society of Japan, All rights reserved.
  • Katsutoshi Nakayama, Takuya Hiraga, Chunyu Zhu, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    APPLIED SURFACE SCIENCE 423 968 - 976 0169-4332 2017/11 
    Herein we report simple electrochemical processes to fabricate a self-healing superhydrophobic CeO2 coating on Type 304 stainless steel. The CeO2 surface anodically deposited on flat stainless steel surface is hydrophilic, although high temperature-sintered and sputter-deposited CeO2 surface was reported to be hydrophobic. The anodically deposited hydrophilic CeO2 surface is transformed to hydrophobic during air exposure. Specific accumulation of contaminant hydrocarbon on the CeO2 surface is responsible for the transformation to hydrophobic state. The deposition of CeO2 on hierarchically rough stainless steel surface produces superhydrophobic CeO2 surface, which also shows self-healing ability; the surface changes to superhydrophilic after oxygen plasma treatment but superhydrophobic state is recovered repeatedly by air exposure. This work provides a facile method for preparing a self-healing superhydrophobic surface using practical electrochemical processes. (C) 2017 Elsevier B.V. All rights reserved.
  • Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION 34 (11) 0934-0866 2017/11 
    Electrochemical oxygen reduction reaction (ORR), using nonprecious metal catalysts, has attracted great attention due to the importance in renewable energy technologies, such as fuel cells and metal-air batteries. A simple and scalable synthetic route is demonstrated for the preparation of a novel 3D hybrid nanocatalyst consisting of Co9S8 nanoparticles which are incorporated in N, S-doped carbon (N, S-C) with rational structure design. In particular, the hybrid catalyst is prepared by direct pyrolysis and calcination of a gel mixture of Mg, Co nitrate-thiourea-glycine under Ar atmosphere, with subsequent HCl washing. The properties of obtained hybrid catalyst are quite dependent on calcination temperature and added glycine amount. Under a molar ratio of Co5-Mg15-tu10-gl45 and a calcination temperature of 900 degrees C, Co9S8 nanoparticles are embedded in a well-developed carbon matrix which shows a porous 3D few-layer graphene-like N, S-C with open and hierarchical micro-meso-macro pore structure. Because of the synergistic effect between Co9S8 nanoparticles and well-developed carbon support, the composite exhibits high ORR activity close to that of commercial Pt/C catalyst. More importantly, the composite displays superior long-term stability and good tolerance against methanol. The strategy developed here provides a novel and efficient approach to prepare a cost-effective and highly active ORR electrocatalyst.
  • H. Habazaki, K. Kobayashi, E. Tsuji, C. Zhu, Y. Aoki, S. Nagata
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 21 (10) 2807 - 2816 1432-8488 2017/10 
    Heat treatment of Zr-24 at% Ti alloy with barrier-type dielectric anodic oxide films was conducted at 473 K in air to examine the thermal stability of the dielectric oxide films for possible electrolytic capacitor application. The anodic oxide film was formed by anodizing of the alloy at 50 V for 30 min in 0.1 mol dm(-3) ammonium pentaborate electrolyte. The anodic oxide film of 125 nm thickness was crystalline, containing both monoclinic and tetragonal ZrO2 phase. It was found that marked thickening of the oxide film with generation of cracks occurred during heat treatment at 473 K. Thus, the dielectric loss was largely increased along with the capacitance increase. In contrast, the anodic oxide film formed on the oxygen-incorporated alloy remained uniform, and no significant increase in dielectric loss was observed even after the heat treatment. The capacitance of the anodic film became as high as 4.8 mF m(-2), which was nearly twice that on Ta. The high capacitance was associated with the preferential formation of tetragonal ZrO2 phase in the anodic oxide film on the oxygen-incorporated alloy. Findings indicated that the oxygen-incorporated Zr-Ti alloy is a promising novel material for capacitor application.
  • Cheng-Gong Han, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki, Tomohiro Akiyama
    GREEN ENERGY & ENVIRONMENT 2 (4) 377 - 386 2096-2797 2017/10 
    We herein report a facile one-pot synthesis of MnO/N-doped carbon (N-C) composites via a sustainable cotton-template glycine-nitrate combustion synthesis to yield superior anode materials for Li+ ion batteries. MnO nanoparticles with several nanometers were well-embedded in a porous N-doped carbon matrix. It displays the unique characteristics, including the shortened Lition transport path, increased contact areas with the electrolyte solution, inhibited volume changes and agglomeration of nanoparticles, as well as good conductivity and structural stability during the cycling process, thereby benefiting the superior cycling performance and rate capability. This favorable electrochemical performance of obtained MnO/N-C composites via a one-pot biomass-templated glycine/nitrate combustion synthesis renders the suitability as anode materials for Li-ion batteries. (C) 2017, Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.
  • Chiharu Kura, Yuji Kunisada, Etsushi Tsuji, Chunyu Zhu, Hiroki Habazaki, Shinji Nagata, Michael P. Mueller, Roger A. De Souza, Yoshitaka Aoki
    NATURE ENERGY 2 (10) 2058-7546 2017/10 
    The production of pure hydrogen for use in energy applications and related industries often relies on the permeation of hydrogen through palladium-based membranes. However, the scarcity of Pd reserves necessitates the development of affordable alternatives with high hydrogen permeability. Here we report room-temperature hydrogen permeability of titanium nitrides (widely used as tough and inert coating materials) enabled by mixed hydride ion-electron conductivity. Combined spectroscopic, permeability and microgravimetric measurements reveal that nanocrystalline TiNx membranes feature enhanced grain-boundary diffusion of hydride anions associated with interfacial Ti cations on nanograins. Since the corresponding activation energies are very low (<10kJmol(-1)), these membranes yield a considerably higher room-temperature hydrogen flux than Pd membranes of equivalent thickness. Overall, the current study establishes general guidelines for developing hydride ion transport membranes based on a simple transition metal nitride for hydrogen purification, membrane reactors and other applications.
  • Chunyu Zhu, Cheong Kim, Yoshitaka Aoki, Hiroki Habazaki
    ADVANCED MATERIALS INTERFACES 4 (19) 2196-7350 2017/10 
    Hierarchical porous carbon has attracted great interest because of its distinctive structure and superior properties for designing electrochemical energy storage and conversion devices. In this work, a novel method to fabricate nitrogen-doped hierarchical porous carbon (NHPC) is reported, which is incorporated with Co nanoparticles and carbon nanotubes (CNTs). The NHPC is prepared using a facile and scalable MgO-Co template method. Metal nitrate-glycine solution combustion synthesis, followed by a high temperature calcination, is used to prepare MgO-Co/N-doped carbon precursor. CNTs are formed by the in situ Co-catalytic growth during heat treatment; at the same time, localized graphitic layers are also formed around the Co nanoparticles. After acid washing, NHPC with hierarchical multipores and ultrafine Co nanoparticles is obtained. When applied as oxygen reduction reaction (ORR) catalyst, the NHPC displays high catalytic activity not only in terms of onset potential and current density, but also superior durability and tolerance to methanol crossover in alkaline electrolyte. The remarkable ORR activity is originated from the cooperative effects of high specific surface area, hierarchical pore structure, ultrasmall Co nanocrystals, localized graphitic layers, CNTs, and N-doping.
  • Yoshitaka Aoki, Kosuke Kuroda, Satoshi Hinokuma, Chiharu Kura, Chunyu Zhu, Etsushi Tsuji, Aiko Nakao, Makoto Wakeshima, Yukio Hinatsu, Hiroki Habazaki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 139 (32) 11197 - 11206 0002-7863 2017/08 
    The oxygen storage capability and related defect structure of tetrahedral orthochromite(V) compound YCr1-xPxO4 (x = 0, 0.3, 0.5, and 0.7) were investigated by employing thermal gravimetry and in situ X-ray spectroscopy for reversible oxygen store/release driven by healing-cooling cycles in the temperature range from 50 to 600 degrees C. YCr1-xPxO4 started releasing oxygen as heated from 50 degrees C under ambient atmosphere, with reduction of Cr-V to Cr-IV, while the reduced YCr1-xPxO4-delta phase was significantly reoxidized via absorbing oxygen by cooling to 50 degrees C under ambient atmosphere, recovering the original stoichiometric phase. Operando X-ray adsorption spectroscopy and first-principles calculations demonstrate that nonstoichiometric YCr1-xPxO4-delta phases were stabilized by forming linking polyhedral (Cr2O76-)-O-IV via corner sharing between oxygen-deficient (CrO32-)-O-IV and adjacent (CrO44-)-O-IV. YCr1-xPxO4 was found to have an extremely low reduction enthalpy of about 20 kJ mol(-1) probably due to the relatively high reduction potential of high-valence-state Cr(V)/Cr(IV) redox pairs, thereby resulting in reversible oxygen storage in such a low-temperature region.
  • R. Elaish, M. Curioni, K. Gowers, A. Kasuga, H. Habazaki, T. Hashimoto, P. Skeldon
    ELECTROCHIMICA ACTA 245 854 - 862 0013-4686 2017/08 
    Fluoride ions are commonly present in solutions used in pre-treatments and conversion treatments of aluminium alloys. Because of the intrinsically reactive nature of aluminium metal, alumina layers are either already present on an aluminium surface or form within a matter of seconds on pre-etched aluminium. Hence fluoride ion transport through an alumina layer is an integral part of conversion coating formation. In order to understand the behaviour of fluoride ions in alumina films, the present study investigated the behaviour of fluoride ions during the growth of barrier-type anodic films formed on aluminium at 5 mA cm(-2) in 0.1 M ammonium pentaborate solution. The films were examined by analytical transmission electron microscopy, scanning electron microscopy and glow discharge optical emission spectroscopy in order to determine their composition and morphology. Fluoride ions were incorporated into the films by adding sodium fluoride to the electrolyte. Additions of up to 3.5 x 10(-3) M sodium fluoride had a negligible influence on the film growth, which occurred at a high efficiency. In contrast, additions of 3.5 x 10(-2) M sodium fluoride reduced the efficiency to about 60%. Dissolution studies demonstrated that fluoride ions had promoted the field-assisted ejection of Al3+ ions from the film surface. Using sequential anodizing, the fluoride ions were shown to migrate inwards in the film at a rate about twice that of O-2(-) ions. Thus, a thin fluoride-rich layer of the film was formed next to the aluminium/film interface. Increasing the sodium fluoride content to 3.5 x 10(-1) M led to a porous film formed at a low voltage. (C) 2017 The Authors. Published by Elsevier Ltd.
  • Etsushi Tsuji, Teruki Motohashi, Hiroyuki Noda, Damian Kowalski, Yoshitaka Aoki, Hajime Tanida, Junji Niikura, Yukinori Koyama, Masahiro Mori, Hajime Arai, Tsutomu Ioroi, Naoko Fujiwara, Yoshiharu Uchimoto, Zempachi Ogumi, Hiroki Habazaki
    CHEMSUSCHEM 10 (14) 2864 - 2868 1864-5631 2017/07 
    Here, we report remarkable oxygen evolution reaction (OER) catalytic activity of brownmillerite (BM)-type Ca2FeCoO5. The OER activity of this oxide is comparable to or beyond those of the state-of-the-art perovskite (PV)-catalyst Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and a precious-metal catalyst RuO2, emphasizing the importance of the characteristic BM structure with multiple coordination environments of transition metal (TM) species. Also, Ca2FeCoO5 is clearly advantageous in terms of expense/laboriousness of the material synthesis. These facts make this oxide a promising OER catalyst used in many energy conversion technologies such as metal-air secondary batteries and hydrogen production from electrochemical/photocatalytic water splitting.
  • Cheng-Gong Han, Chunyu Zhu, Nan Sheng, Yoshitaka Aoki, Hiroki Habazaki, Tomohiro Akiyama
    ELECTROCHIMICA ACTA 235 88 - 97 0013-4686 2017/05 
    Iron oxide has been considered as one of the most promising anode materials due to its high theoretical capacity, low cost and environmental friendliness. However, few simple and effective method is explored for preparing iron oxides with high electrochemical performance via alleviating the volume change and agglomeration of active particles. In this work, FeOx/carbon/graphene composites are fabricated by a facile solution combustion synthesis within several minutes in one step. Characterization demonstrates that FeOx nanoparticles are well-dispersed in the graphene matrix. The presence of graphene effectively alleviates the agglomeration of FeOx nanoparticles, and accommodates the volume changes during the cycling process, thereby resulting in the excellent electrochemical performance. FeOx/carbon/graphene (31.4 wt.% graphene) delivers a higher discharge capacity of 824 mAh g (1) after 100 cycles at 0.4 A g (1), in comparison to the value of 301 mAh g (1) for the composite without graphene. This easily prepared FeOx/carbon/graphene composite with excellent electrochemical performance can be considered as one promising anode material used for lithium-ion batteries. (C) 2017 Elsevier Ltd. All rights reserved.
  • Y. Aoki, T. Yamaguchi, S. Kobayashi, C. Zhu, H. Habazaki
    SOLID OXIDE FUEL CELLS 15 (SOFC-XV) 78 (1) 1511 - 1515 1938-5862 2017 
    Hydrogen membrane fuel cells, HMFC, were fabricated by RF sputtering deposition of BaZr0.1Ce0.7Y0.2O3-delta thin films on Pd solid anode. The HMFC can give OCV of 1.0 V and peak power density of 0.8 W cm(-2) at 600 degrees C by using H-2 fuels. The direct NH3 fueled HMFC reveals OCV of 0.92 V and peak power density of 0.58 W cm(-2) at 600 degrees C. These performances are superior to the best data of direct ammonia PCFC.
  • Yoshitaka Aoki, Tomoyuki Yamaguchi, Shohei Kobayashi, Chunyu Zhu, Hiroki Habazaki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 164 (6) F577 - F581 0013-4651 2017 
    Fuel cell performances at intermediate temperature 600 degrees C were examined for the hydrogen membrane fuel cell (HMFC) designed by rf sputter deposition of a BaCe0.8Y0.2O3-delta thin film electrolyte (1 mu m thickness) on a Pd1-xAgx (x = 0, 0.2 and 0.4) solid anode. The maximum power density reached to 1.2 W cm(-2) at 600 degrees C with the Pd0.8Ag0.2 anodes, and this value was much higher than the champion data of the recent anode-supported proton-conducting ceramic fuel cells (PCFCs). By electrochemical impedance analysis, it was demonstrated that the hydrogen permeability was crucial to the anode polarization losses of the HMFC because the charge transfer resistances and concentration overpotentials at BaCe0.8Y0.2O3-delta/Pd oxide-metal interfaces are simultaneously improved with the alloys having higher hydrogen permeability. (C) 2017 The Electrochemical Society. All rights reserved.
  • R. Elaish, M. Curioni, K. Gowers, A. Kasuga, H. Habazaki, T. Hashimoto, P. Skeldon
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 164 (13) C831 - C839 0013-4651 2017 
    The effects of additions of fluorozirconic acid to sulfuric acid on the anodizing behavior of aluminum have been investigated under a constant voltage at temperatures of 0 and 20 degrees C. The fluoroacid increased the rate of film growth, with a dependence on the fluoroacid concentration, the electrolyte temperature and the anodizing time. Compositional analyses showed that fluorine species were present in the films. However, zirconium species were absent. The fluoroacid generally enhanced film dissolution, although this effect was less important at low fluoroacid concentration, low electrolyte temperature and short anodizing times. Sodium fluoride additions influenced the anodizing behavior similarly to the fluoroacid. (c) The Author(s) 2017. Published by ECS. All rights reserved.
  • Hiroyuki Ogata, Hiroki Habazaki
    ISIJ INTERNATIONAL 57 (12) 2207 - 2213 0915-1559 2017 
    Pb- and Cr(VI)-free galvanized steel sheets for fuel tanks are coated with epoxy-resin films (thickness: approx. 3 mu m) containing particulate Ni powder and flaky Al powder to provide a combination of weld ability and degraded gasoline resistance (sour gasoline resistance). The corrosion behavior of galvanized steel specimens coated with epoxy resin containing different amounts of the two types of metal powders was investigated in a solution containing acetic acid, formic acid and NaCI at pH 3.2 and 40 degrees C to elucidate the mechanism of corrosion protection by the coatings. The oxygen gas permeability and water vapor permeability of the coatings were also examined. The results indicated that the addition of particulate Ni powder promoted galvanic corrosion between the Ni and the Zn coating. Voids generated around the embedded Ni powder particles also appeared to accelerate the penetration of the corrosive solution through the coating. On the other hand, the addition of the flaky Al powder improved corrosion resistance. This improved corrosion resistance is associated with the suppression of direct contact between the Ni powder and the Zn coating and also with increased barrier properties, which could be confirmed from oxygen gas and water vapor permeation measurements.
  • D. Quintero, M. A. Gomez, J. G. Castano, E. Tsuji, Y. Aoki, F. Echeverria, H. Habazaki
    SURFACE & COATINGS TECHNOLOGY 310 180 - 189 0257-8972 2017/01 
    Spark anodizing of Ti6A14V alloy has been performed in alkaline electrolytes containing aluminate to form wear resistant coatings. Coatings obtained under potentiostatic conditions exhibit a better wear resistance, with a wear rate approx. 10 times lower than galvanostatic coatings, due to the formation of coatings with low porosity since potentiostatic mode controls the size of the micro-discharges. The coatings consist mainly of gamma-Al2O3, whilst Al2TiO5 is present in minor proportions. For some coatings, the formation of Al6KO5,5 is observed due to the incorporation of potassium into the coating. EDS analysis shows that aluminum is the main constituent of the coatings, being mainly incorporated from the anodizing solution and homogeneously distributed into the coating. A decrease in pore density between 15 and 30% and roughness reduction of 10 to 60% was obtained with KOH and Na2WO4 additions, improving the coating wear resistance in pin-on-disc wear tests, especially by Na2WO4 addition. (C) 2016 Elsevier B.V. All rights reserved.
  • R. Tomizawa, C. Zhu, E. Tsuji, Y. Aoki, H. Habazaki
    OXIDE FILMS: A SYMPOSIUM IN HONOR OF MASAHIRO SEO 75 (27) 67 - 75 1938-5862 2017 
    In this study, a nanoporous anodic film was successfully formed on Fe-41 mass% Ni alloy at a constant voltage of 40 V in ethylene glycol electrolyte containing 0.1 mol dm-(3) NH4F and 0.5 mol dm(-3) H2O. The resultant anodic film contained fluoride species and was rather soluble even in de-ionized water. The heat treatment in an argon atmosphere at and above 673 K converted a poorly crystalline anodic film to a crystalline film with a (FeNi)(3)O-4 spinel phase with the nanoporous morphology remaining unchanged. The activity of the heattreated specimens for oxygen evolution reaction (OER) was examined and the results were compared with the anodized iron specimens after heat treatment. The Fe-Ni alloy specimen heattreated at optimized temperature showed the improved activity in comparison with the corresponding iron specimen. Anodizing is promising to form a highly porous electrode directly on metal substrate.
  • Andrea Zaffora, Francesco Di Franco, Francesco Di Quarto, Roberto Macaluso, Mauro Mosca, Hiroki Habazaki, Monica Santamaria
    ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY 6 (4) N25 - N31 2162-8769 2017 
    Hafnium oxide and Nb doped HfO2 were grown by anodizing sputtering-deposited Hf and Hf-4at.% Nb. Photoelectrochemical characterization was carried out in order to estimate solid state properties such as band gap, flat band potential and electrons internal photoemission threshold energy as a function of thickness and composition of anodic oxides. Optical transitions at energy lower than the band gap value of the investigated anodic films were evidenced, and they are attributed to optical transitions involving localized states inside the band gap. Such states were located at 3.6 eV and 3.9 eV below the conduction band edge for the Nb free and Nb containing hafnium oxide, respectively. Impedance measurements were performed in a wide range of electrode potentials under anodic and cathodic polarization with respect to the flat band potential, confirming the formation of insulating oxides with high dielectric constant. The latter increases from 20 to 41 due to incorporation of Nb into the oxide. (C) 2017 The Electrochemical Society. All rights reserved.
  • H. Takano, Y. Kirihata, K. Izumiya, N. Kumagai, H. Habazaki, K. Hashimoto
    APPLIED SURFACE SCIENCE 388 653 - 663 0169-4332 2016/12 
    The catalytic methanation of CO2 was carried out on Ni catalysts supported on Y-doped ZrO2 with various Y3+ concentrations and Ni/(Zr + Y) molar ratio = 1. The catalysts were characterized by X-ray diffraction, scanning transmission electron microscopy, specific surface area, temperature-programmed desorption of CO2, and temperature-programmed reaction. In addition, operando diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFT) was used to identify the adsorbed reaction intermediate. Catalysts supported on Y-doped ZrO2 show higher catalytic activity than the catalyst on Y-free ZrO2 with a monoclinic ZrO2 phase. The catalytic activity is also dependent upon the Y3+ concentration, and the highest activity was obtained for the catalyst with a Y/(Zr + Y) molar ratio of 0.333, which consists mainly of fcc Ni and cubic ZrO2 phase. Y3+ doping into ZrO2 introduces oxygen vacancies, which play an important role in enhancing the catalytic activity. The operando DRIFT study reveals that a CO adsorption intermediate is absent, and bidentate carbonate is an important intermediate for CH4 formation. (C) 2015 Elsevier B.V. All rights reserved.
  • A. Nemcova, O. Galal, P. Skeldon, I. Kubena, M. Smid, E. Briand, I. Vickridge, J-J. Ganem, H. Habazaki
    ELECTROCHIMICA ACTA 219 28 - 37 0013-4686 2016/11 
    The effect of anodizing AZ31 magnesium alloy in a fluoride/glycerol electrolyte containing from 1 to 40 vol.% water on the compositions of the anodic film and the underlying alloy has been investigated. A range of constant current densities and water contents of the electrolyte were employed. Scanning and transmission electron microscopy, with energy-dispersive X-ray spectroscopy, X-ray diffraction and ion beam analyses were used to analyse the anodized alloy. Barrier films, containing fluoride and oxide species, were formed above the matrix, at high current efficiency; a porous film was formed above Al-Mn intermetallic particles. The current density and the water content of the electrolyte affected the O:F atomic ratio and the ionic transport in the films. Significant enrichments of zinc and aluminium were generated in a thin layer of the matrix immediately beneath the film under all conditions of anodizing, with the enrichment of zinc reaching 6.2 x 10(15) at cm(-2) in the enriched alloy layer. The cause of the enrichments and the consequences to film growth are discussed. (C) 2016 The Authors. Published by Elsevier Ltd.
  • Masahiro Seo, Hiroki Habazaki, Takenori Nakayama
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 20 (11) 3133 - 3142 1432-8488 2016/11 
    The potentio-dynamic polarization curves of pure Fe, Fe-30 Ni, and Fe-70 Ni alloys in acidic perchlorate solutions (pH 1.9) without and with 10(-3) M Pb2+ were measured to investigate the effect of Pb-underpotential deposition (Pb-UPD) on anodic dissolution and passivation in relation to Pb-induced stress corrosion cracking (Pb-SCC) of Ni base alloys. The addition of 10(-3) M Pb2+ shifts the open circuit potentials of pure Fe and Fe-Ni alloys toward noble direction to inhibit the anodic dissolution and promote the passivation, which results from Pb-UPD on substrate metals. The electro-desorption of Pb proceeds with anodic potential sweep and the anodic dissolution is enhanced when the surface coverage of Pb is reduced to a critical level. Tafel slopes (b (+) = 8.5 similar to 15 mV decade(-1)) of anodic dissolution for pure Fe and Fe-Ni alloys in the presence of Pb2+ are significantly low as compared with those (b (+) = 34 similar to 40 mV decade(-1)) in the absence of Pb2+, which reflects on the rapid enhancement in surface reactivity as a result of electro-desorption of Pb. It is found that the potential region in which anodic dissolution is inhibited by Pb-UPD is located within the potential window of Pb-UPD estimated from the differences in work-function between substrate metals and Pb.
  • Cheong Kim, Hiroki Habazaki, Soo Gil Park
    JOURNAL OF ELECTROCHEMICAL SCIENCE AND TECHNOLOGY 7 (3) 214 - 217 2093-8551 2016/09 
    In this study, we studied the enhancement of the energy densities of electrochemical capacitors by improving the working voltage range of the electrolyte. To prevent the decomposition of the electrolyte, stable SEI layers were formed by reductive degradation of additive materials such as fluoro-ethylene carbonate (FEC) and vinyl ethylene carbonate (VEC) before degradation of the base electrolyte. As a result, the solution resistance (R-s) of EC:DMC + SL 20 % + VEC 1 % electrolytes observed 1.47 Omega and the charge transfer resistance (R-ct) was 2.64 Omega at the open circuit voltage. Additionally, a cycle retention of 94 % was observed for EC:DMC + SL 20 % + VEC 1 % after 500 cycles at 3.5 V.
  • Yoshitaka Aoki, Shohei Kobayashi, Tomoyuki Yamaguchi, Etsushi Tsuji, Hiroki Habazaki, Keiji Yashiro, Tetsuya Kawada, Toshiaki Ohtsuka
    JOURNAL OF PHYSICAL CHEMISTRY C 120 (29) 15976 - 15985 1932-7447 2016/07 
    A hydrogen membrane fuel cell (HMFC) consisting of a Pd solid anode, 1 mu m thick BaCe0.8Y0.2O3-delta thin-film electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 cathode was examined. A single-phase BaCe0.8Y0.2O3-delta thin film was successfully deposited by radio frequency cosputtering with BaCe0.8Y0.2O3 and Ce0.9Y0.1O2 double targets, as checked by X-ray diffraction, transmission electron microscopy, and wavelength dispersive X-ray analysis. The maximum power density reached 1.05 W cm-(2) at 600 degrees C, and this value was higher than the champion data of the recently reported proton-conducting ceramic fuel cells (PCFCs). Electrochemical impedance analysis was performed to characterize the anode and cathode polarization behavior. The impedance responses of HMFC were explicable with an equivalent circuit built by a series connection of cathode charge-transfer elements and anode mass-transfer elements. The contribution of the mass transfer in Pd bulk was found to be relatively small in comparison to cathode polarization and ohmic loss in normal fuel cell atmosphere. Moreover, the cathodic charge-transfer resistance of HMFC was found to be 25 times smaller than those of the recent PCFC systems. The current results demonstrated that the HMFC retained relatively large gas-proton-electron triple-boundary zones near the interface between the BaCe0.8Y0.2O3-delta electrolyte and porous La0.6Sr0.4Co0.2Fe0.8O3-delta cathode.
  • Katsutoshi Nakayama, Etsushi Tsuji, Yoshitaka Aoki, Soo-Gil Park, Hiroki Habazaki
    JOURNAL OF PHYSICAL CHEMISTRY C 120 (29) 15684 - 15690 1932-7447 2016/07 
    This paper reports the formation of hierarchically structured aluminum mesh by a combination of simple chemical etching and anodizing. The former introduced micrometer-sized etch pits, and the latter produced nanopores of the order of 10 nm on the mesh with 150 mu m mesh openings. Coating the mesh with a monolayer of fluoroalkyl phosphate made the surface superoleophobic to practically any liquid, including hexane with a surface tension as low as 18.4 mN m(-1). The hierarchical triple similar to 100 mu m/similar to 1 mu m/similar to 10 nm pore surface morphology improved the superoleophobicity compared to the dual similar to 100 mu m/similar to 10 nm and similar to 1 mu m/similar to 10 nm pore structures. When the aluminum mesh was coated with a fluorine-free alkylphosphate monolayer, the surface was superhydrophobic, but superoleophilic. The noncoated aluminum mesh was superhydrophilic and superoleophilic with a liquid contact angle close to 0 degrees. Using the aluminum mesh with an alkylphosphate coating, a water/oil mixture was successfully separated by allowing only the oil to pass through the mesh. In addition, the mixture was separated using noncoated mesh wetted with water, since oil was not able to pass through the mesh in this case.
  • H. Habazaki, T. Kimura, Y. Aoki, E. Tsuji, T. Yano, K. Shimizu, A. W. Hassel
    ELECTROCHIMICA ACTA 201 311 - 319 0013-4686 2016/05 
    Highly corrosion-resistant, similar to 65-nm-thick, layer-by-layer aluminosilicate coatings have been prepared by multiple spin casting on Type 430 stainless steel. These coatings have been characterized by field emission scanning electron microscopy, transmission electron microscopy, conductive atomic force microscopy, and micro-electrochemical measurements using a microcapillary cell. The coatings annealed at 400 degrees C are non-uniform and contain fine iron oxide nodules, which are formed in high densities on the {111} grain surface of the steel. The iron oxide nodules arise from the outward diffusion of the oxidized iron from the substrate through the coating. The coatings annealed at 400 degrees C are more insulating compared with those before annealing; however, the nodule sites are less insulating owing to the development of more conductive iron oxide channels in the coatings. A microcapillary cell study reveals that the coated specimens prepared from diluted precursor solutions by a layer-by-layer process exhibit higher pitting potential in 3.5 wt% NaCl solution compared with those prepared through a single-layer process. Moreover, the coated specimen obtained from the layer-by-layer process exhibits similarly high pitting potential even at the flaw sites in the coating; in contrast, the pitting potential in the flaw-containing regions of the coated specimen obtained from a single-layer process shifts towards the less noble direction. The layer-by-layer coating is also effective in suppressing the corrosion of the scratched region of the coated specimens, owing possibly to the excellent adhesion between the coating and the substrate. (C) 2015 Elsevier Ltd. All rights reserved.
  • Andrea Zaffora, Monica Santamari, Francesco Di Franco, Hiroki Habazaki, Francesco Di Quarto
    ELECTROCHIMICA ACTA 201 333 - 339 0013-4686 2016/05 
    Anodic films of different thickness (similar to 30 nm and 70 nm) were grown by anodizing sputtering-deposited Ta-19at% Al to different formation voltages. N incorporation into the anodic films was inducing by performing the anodizing process in ammonium containing solutions. Layered anodic films were prepared by a double formation procedure with a first anodizing step in ammonium biborate solution and second anodizing step in borate buffer solution, or vice versa. Glow Discharge Optical Emission Spectroscopy was employed to show the distribution of N across the oxide. Photoelectrochemical measurements evidenced a red shift of the light absorption threshold due to N incorporation. A model was proposed and tested to model the dependence of quantum yield on photon energy and, thus, to estimate the band gap of the layers for both anodized Ta and Ta-19at% Al. (C) 2015 Elsevier Ltd. All rights reserved.
  • A. Nemcova, I. Kubena, M. Smid, H. Habazaki, P. Skeldon, G. E. Thompson
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 20 (4) 1155 - 1165 1432-8488 2016/04 
    Anodizing of a Mg-Zn-RE alloy was carried out at constant current densities from 0.1 to 10 mA cm(2) in a fluoride/glycerol/water electrolyte. Rutherford backscattering spectroscopy, nuclear reaction analysis and analytical transmission electron microscopy revealed harrier-type films composed of oxide and fluoride species. The films were formed by outward migration of cations and inward migration of anions. The transport number of cations in the film above the matrix was in the range 0.5 to 0.6, and 0.1 in the film above the grain boundary Mg-Zn-RE phase. From the oxidation behaviour of the Zn-Zr phases, it is suggested that anions and cations migrate through short-circuit paths in the film.
  • Yoshitaka Aoki, Kosuke Kuroda, Etsushi Tsuji, Hiroki Habazaki
    SOLID STATE IONICS 285 175 - 179 0167-2738 2016/02 
    Redox transformation of (NdCrO4)-O-V involved by insertion/desertion of protons was examined by XRD, XPS, in situ FT-IR and fuel cell tests. It was found that NdCrO4 caused bulk reduction with H-2 gas at around 400 degrees C, changing to amorphous Nd(III)-Cr(III) hydroxide phase. This hydroxide phase, however, could recover to the original zircon type oxide phase by air oxidation at the same temperature region. Proton-conducting ceramic fuel cells having NdCrO4 film as an interlayer between cathode and electrolyte was fabricated and the cell was confirmed to exhibit remarkable power generation giving rise to OCV of more than 1.0 Vat 500 degrees C. It was speculated that the interlayer facilitates proton transfer from electrolyte to cathode because redox cycling of NdCrO4 and the corresponding hydroxide was driven by the high proton chemical potential at the interface with electrolyte and plenty of oxygen in cathode gases. (C) 2015 Elsevier B.V. All rights reserved.
  • Yoshiki Konno, Ahmed A. Farag, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 163 (7) C386 - C393 0013-4651 2016 
    The growth behavior of nanoporous anodic films on carbon steel containing 0.213 mass% carbon has been examined. The films were grown by anodizing in an ethylene glycol (EG) electrolyte containing 0.1 mol dm(-3) NH4F and 0.5 mol dm(-3) H2O. The steel contains carbide precipitates with sizes in the range 50-800 nm. The anodic film formed on the carbide phase grew more slowly and was more chemically soluble during anodizing, resulting in submicrometer pits on the anodic film. The nanoporous morphology of the anodic films formed on an alpha-Fe matrix resembled those formed on iron. Heat treatment of the anodized specimens caused transformation of the chemically soluble fluoride-containing amorphous or poorly crystalline anodic films to crystalline oxide films containing alpha-Fe2O3 and Fe3O4. Polypyrrole (PPy) was electropolymerized on the transformed surfaces to form a corrosion-protective composite coating. The resultant specimens coated with the composite coating showed improved durability compared to passivated steel with a PPy coating. (C) The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.
  • Chiharu Kura, Yoshitaka Aoki, Etsushi Tsuji, Hiroki Habazaki, Manfred Martin
    RSC ADVANCES 6 (11) 8964 - 8970 2046-2069 2016 
    Resistive switching gallium oxide base thin films with tailored oxygen deficiency were fabricated by rf cosputtering of Ga2O3 and Cr. XPS and STEM-EDX analyses were used to determine that the resultant film was made of a homogeneous oxide glass layer with mixed valance states of Ga(III)-Ga(I). The amount of Ga(I) and the corresponding oxygen deficiency was precisely controlled because the following redox reaction subsequently progresses within the deposited films: 3Ga(III) + 2Cr(0) -> 3Ga(I) + 2Cr(III). The on/off resistance ratio was largely varied by changing the Ga(I) fraction in relation to the oxide ion conductivity, and Ga0.82Cr0.18O1.2 thin film was found to exhibit an optimal switching performance. The film resistance state was tunable by 100's of ms pulse biasing and was incrementally changed by increasing the applied pulse numbers. The strongly time-dependent switching events and area dependent current level of Cr-GaOx films were distinct from the abrupt switching behavior of the filamentary mechanism TiOx thin film devices. It was demonstrated that rf cosputtering of the metal oxides and the corresponding oxygen scavenging metals was a powerful technique to design the bulk state resistive switching devices based on nonstoichiometric metal oxide thin films.
  • Masato Onishi, Hisayoshi Matsushima, Mikito Ueda, Hiroki Habazaki, Kota Washio, Akira Kato
    MOLTEN SALTS AND IONIC LIQUIDS 20 75 (15) 297 - 304 1938-5862 2016 
    To investigate the relationship between adhesion strength of Al electroplated film and Al concentration in Mg alloy substrates and the grain size of the Mg alloy, Al electroplating was carried out with AZ31, AZ61, AZ91, and of AZ31 with different grain sizes in an ionic liquid of a mixture of aluminum chloride and 1-ethyle-3-methyl-imidazolium chloride at 283 K. Dense Al electrodeposits were formed on all the substrates. The adhesion strength increased with increases in the Al content of the Mg alloys. Increasing the average grain size also resulted in increases in the adhesive strength.
  • Khurram Shahzad, Chunyu Zhu, Etsushi Tsuji, Yoshitaka Aoki, Shinji Nagata, Hiroki Habazaki
    MATERIALS TRANSACTIONS 57 (9) 1552 - 1559 1345-9678 2016 
    In this study, we report the formation of barrier-type anodic films on magnetron-sputtered magnesium films at a constant current density of 10 A m(-2) in ethylene glycol (EG)-H2O electrolytes containing 0.1 mol dm(-3) ammonium fluoride and 0.1 mol dm-3 dipotassium hydrogen phosphate. The growth efficiency is close to 100% up to 10 vol% H2O, but decreases to 52% in the EG-free aqueous electrolyte. Even at such a low efficiency in the aqueous electrolyte a uniform barrier-type anodic film with flat and parallel metal/film and film/electrolyte interfaces is developed over 100 V. This is contrast to the non-uniform film growth and low breakdown voltage in the phosphate-free aqueous electrolyte containing ammonium fluoride. The anodic films appear to be amorphous regardless of H2O concentration in the phosphate-containing electrolytes, and consist of phosphate-incorporated oxyfluoride. The phosphate incorporation is suppressed by an increase in H2O concentration. In addition, the anodic films consist of two layers with an inner layer containing less amount of phosphate. The outer layer is probably formed at the film/electrolyte interface by the migration of Mg2+ ions outwards, while the inner layer is formed at the metal/film interface. The film formation at the former interface even in the aqueous electrolyte at low efficiency is likely to contribute to the formation of barrier films, not porous anodic films.
  • A. Zaffora, M. Santamaria, F. Di Franco, H. Habazaki, F. Di Quarto
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 18 (1) 351 - 360 1463-9076 2016/01 
    Anodic films were grown to 20 V on sputtering-deposited Al-Ta alloys in ammonium biborate and borate buffer solutions. According to glow discharge optical emission spectroscopy, anodizing in ammonium containing solution leads to the formation of N containing anodic layers. Impedance measurements did not evidence significant differences between the dielectric properties of the anodic films as a function of the anodizing electrolyte. Photoelectrochemical investigation allowed evidencing that N incorporation induces a red-shift in the light absorption threshold of the films due to the formation of allowed localized states inside their mobility gap. The estimated Fowler threshold for the internal photoemission processes of electrons resulted to be independent of the anodizing electrolyte confirming that N incorporation does not appreciably affect the density of states distribution close to the conduction band mobility edge. The transport of photogenerated carriers has been rationalized according to the Pai-Enck model of geminate recombination.
  • Hiroki Habazaki, Su-Il Pyun
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 19 (12) 3425 - 3426 1432-8488 2015/12
  • Po-Chieh Li, Chi-Chang Hu, Hiroyuki Noda, Hiroki Habazaki
    JOURNAL OF POWER SOURCES 298 102 - 113 0378-7753 2015/12 
    Manganese oxides (MnOx) in alpha-, beta-, delta-MnO2 phases, Mn3O4, Mn2O3, and MnOOH are synthesized for systematically comparing their electrocatalytic activity of the oxygen reduction reaction (ORR) in the Zn -air battery application. The optimal MnOx/XC-72 mass ratio for the ORR is equal to 1 and the oxide crystalline structure effect on the ORR is compared. The order of composites with respect to decreasing the ORR activity is: alpha-MnO2/XC-72 > gamma-MnO2/XC-72 > beta-MnO2/XC-72 > delta-MnO2/XC-72 > Mn2O3/XC-72 > Mn3O4/XC-72 > MnOOH/XC-72. The textural properties of MnOx are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N-2 adsorption/desorption isotherms with Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Electrochemical studies include linear sweep voltammetry (LSV), rotating ring-disk electrode (RRDE) voltammetry, and the full-cell discharge test. The discharge peak power density of Zn-air batteries varies from 61.5 mW cm(-2) (alpha-MnO2/XC-72) to 47.1 mW cm(-2) (Mn3O4/XC-72). The maximum peak power density is 102 mW cm(-2) for the Zn-air battery with an air cathode containing alpha-MnO2/XC-72 under an oxygen atmosphere when the carbon paper is 10AA. The specific capacity of all full-cell tests is higher than 750 mAh g(-1) at all discharge current densities. (C) 2015 Elsevier B.V. All rights reserved.
  • D. Quintero, O. Galvis, J. A. Calderon, M. A. Gomez, J. G. Castano, F. Echeverria, H. Habazaki
    SURFACE & COATINGS TECHNOLOGY 283 210 - 222 0257-8972 2015/12 
    Spark anodizing on Ti6Al4V has been performed in three alkaline solutions using different electrical parameters in order to study the coating formation. The surface features show a dependence on the shape and distribution of the electric microdischarges. In addition, the surface features and the chemical composition of the coatings are dependent on the anodizing solution employed. The tribological properties of the coatings formed are correlated with the morphology and the internal structure of the coatings. The variation of the internal structure of the coatings was evidenced by EIS analysis. Results indicate that it is possible to control the physical properties of the anodic film by an adequate selection of the process parameters. A porous structure is obtained using a solution mainly composed of hypophosphite, which exhibits a good tribological performance. Low porosity and compact structure can be obtained in the anodic film by using an anodizing solution composed of hypophosphite and metasilicate; furthermore, these coatings exhibit a good corrosion protection. Highly porous structure is achieved by using an anodizing solution composed of hypophosphite and sulfate. The best wear resistances were observed in coatings formed at potentiostatic mode, as demonstrated by the results of ball-on-disc wear tests. (C) 2015 Elsevier B.V. All rights reserved.
  • Hiroki Habazaki, Fumitaka Kataoka, Khurram Shahzad, Etsushi Tsuji, Yoshitaka Aoki, Shinji Nagata, Peter Skeldon, George E. Thompson
    ELECTROCHIMICA ACTA 179 402 - 410 0013-4686 2015/10 
    This study demonstrates the formation of uniform barrier-type anodic films on magnetron-sputtered magnesium films at high current efficiency in ethylene glycol electrolytes containing 0.1 mol dm (3) NH4F and various concentrations (0.1-28 mol dm (3)) of H2O. The anodic films containing a crystalline MgF2 phase develop both at the metal/film and film/electrolyte interfaces due to simultaneous migrations of anions inwards and cations outwards, respectively. When a Mg - 1.2 at% Au/Mg bilayer film is anodized, initial prior oxidation of magnesium proceeds with gold atoms accumulating in a thin layer beneath the anodic film. The accumulated gold atoms are incorporated into the anodic film as a band when the alloy layer is completely anodized. Fluoride-containing gold species are formed by the incorporation and the gold species migrate outwards at a rate of 0.4 times the rate of Mg2+ ions. The addition of phosphate in the electrolyte results in the formation of an amorphous anodic film, and the phosphate incorporated into the anodic film is distributed throughout the film thickness. The transport number of cations is also influenced by the phosphate incorporation. (C) 2015 Elsevier Ltd. All rights reserved.
  • Andrea Zaffora, Francesco Di Franco, Monica Santamaria, Hiroki Habazaki, Francesco Di Quarto
    ELECTROCHIMICA ACTA 180 666 - 678 0013-4686 2015/10 
    Al-Ta mixed oxides were grown by anodizing sputter-deposited Al-Ta alloys of different composition. Photocurrent spectra revealed a band gap, E-g, slightly independent on Ta content and very close to that of anodic Ta2O3 (similar to 4.3 eV) with the exception of the anodic film on Al-10at% Ta, which resulted to be not photoactive under strong anodic polarization. The photoelectrochemical characterization allowed to estimate also the oxides flat band potential and to get the necessary information to sketch the energetic of the metal/oxide/electrolyte interfaces. Impedance measurements allowed to confirm the formation of insulating material and to estimate the dielectric constant of the oxides, which resulted to be monotonically increasing with increasing Ta content (from 9 for pure Al2O3 to 30 for pure Ta2O5). (C) 2015 Elsevier Ltd. All rights reserved.
  • H. Takano, H. Shinomiya, K. Izumiya, N. Kumagai, H. Habazaki, K. Hashimoto
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 40 (26) 8347 - 8355 0360-3199 2015/07 
    This paper reports highly active CO2 methanation catalysts of Ni supported on tetragonal ZrO2 for supply of renewable energy in the form of CH4 via electrolytic H-2 generation. The Ni/tetragonal ZrO2 catalysts with the nominal cationic compositions of 50 at.% Ni-(Zr + Ca) (Ca/(Zr + Ca) molar ratios of 0.125-0.333), were prepared by calcination of a ZrO2 sol mixed with nickel and calcium nitrates at 650 and 800 degrees C and subsequent H-2 reduction of NiO. All the catalysts prepared exhibited almost 100% CH4 selectivity, and the activity increased with the calcium content up to a Ca/(Zr + Ca) molar ratio between 0.167 and 0.200, above which the activity tended to decrease. At the optimized calcium content, a tetragonal ZrO2 phase with cation vacancies introduced by Ca2+ and Ni2+ doping was predominant, in addition to fcc Ni. A monoclinic ZrO2 phase was also present below the optimized calcium content, while a Ca-rich amorphous or CaZrO3 phase was formed with tetragonal ZrO2 above the optimized calcium content. The high catalytic activity of the catalyst with the optimized composition could be correlated with the presence of tetragonal ZrO2 with oxygen vacancies. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
  • Etsushi Tsuji, Takenori Yamasaki, Yoshitaka Aoki, Soo-Gil Park, Ken-ichi Shimizu, Hiroki Habazaki
    CARBON 87 1 - 9 0008-6223 2015/06 
    We report the preparation and characterization of highly durable platinum catalysts supported on platelet-structure carbon nanofibers (Pt/p-CNFs) for the oxygen reduction reaction. The p-CNFs were prepared by liquid phase carbonization of polyvinyl chloride using a porous anodic alumina template at 600 degrees C; their degree of graphitization was increased by the subsequent heat treatment at higher temperatures of up to 1400 degrees C. The platinum nanoparticles with similar to 3 nm diameter were deposited more uniformly on the p-CNFs compared with those on the commercial Ketjen black (KB). The catalytic activity and durability of the Pt/p-CNFs for the oxygen reduction reaction (ORR) in H2SO4 solution were improved by increasing the heat-treatment temperature of p-CNFs. The durability of the Pt/p-CNFs was much higher than that of Pt/KB; in particular, a loss of less than 10% was observed in the ORR activity of Pt/p-CNF heat-treated at 1400 degrees C after potential cycling from 0.5 to 1.5 V vs. RHE for 200 cycles in an argon-saturated H2SO4 aqueous solution. (C) 2015 Elsevier Ltd. All rights reserved.
  • Angus Cook, Gerald Frankel, Alison Davenport, Trevor Hughes, Simon Gibbon, David Williams, Hendrik Bluhm, Vincent Maurice, Stephen Lyth, Philippe Marcus, David Shoesmith, Clara Wren, Julian Wharton, Gregory Hunt, Stuart Lyon, Tom Majchrowski, Rob Lindsay, Geraint Williams, Beatriz Rico Oller, Mira Todorova, Sonja Nixon, Su-Ting Cheng, John Scully, Ann Wilson, Frank Renner, Ying-Hsuan Chen, Christopher Taylor, Hiroki Habazaki, Angelos Michaelides, Suzanne Morsch, Peter Visser, Line Kyhl, Anton Kokalj
    FARADAY DISCUSSIONS 180 543 - 576 1359-6640 2015
  • Gerald Frankel, Janine Mauzeroll, Geoffrey Thornton, Hendrik Bluhm, Jonathan Morrison, Vincent Maurice, Trevor Rayment, David Williams, Angus Cook, Gaurav Joshi, Alison Davenport, Simon Gibbon, Denis Kramer, Matthew Acres, Markus Tautschnig, Hiroki Habazaki, Philippe Marcus, David Shoesmith, Clara Wren, Tom Majchrowski, Rob Lindsay, Mary Wood, Mira Todorova, John Scully, Frank Renner, Anton Kokalj, Christopher Taylor, Sannakaisa Virtanen, Julian Wharton
    FARADAY DISCUSSIONS 180 205 - 232 1359-6640 2015
  • Yoshiki Konno, Etsushi Tsuji, Yoshitaka Aoki, Toshiaki Ohtsuka, Hiroki Habazaki
    FARADAY DISCUSSIONS 180 479 - 493 1359-6640 2015 
    Conducting polymers (CPs), including polypyrrole, have attracted attention for their potential in the protection of metals against corrosion; however, CP coatings have the limitation of poor adhesion to metal substrates. In this study, a composite coating, comprising a self-organized porous anodic oxide layer and a polypyrrole layer, has been developed on iron. Because of electropolymerization in the pores of the anodic oxide layer, the composite coating showed improved adhesion to the substrate along with prolonged corrosion protection in a NaCl aqueous corrosive environment. The anodic oxide layers are formed in a fluoride-containing organic electrolyte and contain a large amount of fluoride species. The removal of these fluoride species from the oxide layer and the metal/oxide interface region is crucial for improving the corrosion protection.
  • M. S. Palagonia, A. Nemcova, I. Kubena, M. Smid, S. Gao, H. Liu, X. L. Zhong, S. J. Haigh, M. Santamaria, F. Di Quarto, H. Habazaki, P. Skeldon, G. E. Thompson
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 162 (9) C487 - C494 0013-4651 2015 
    Anodizing of sputtering-deposited magnesium and Mg-0.75at.%Cu and Mg-1.23at.%W alloys has been carried out in a fluoride/glycerol electrolyte. The aims of the study were to investigate the enrichment of alloying elements in the alloy immediately beneath the anodic film and the migration of alloying element species in the film. The specimens were examined by electron microscopy and ion beam analysis. An enrichment of copper is revealed in the Mg-Cu alloy that increases with the anodizing time up to similar to 6 x10(15) Cu atoms cm(-2). Copper species are then incorporated into the anodic film and migrate outwards. In contrast, no enrichment of tungsten occurs in the Mg-W alloy, and tungsten species are immobile in the film. (C) The Author(s) 2015. Published by ECS.
  • Khurram Shahzad, Etsushi Tsuji, Yoshitaka Aoki, Shinji Nagata, Hiroki Habazaki
    ELECTROCHIMICA ACTA 151 363 - 369 0013-4686 2015/01 
    Magnetron-sputtered iron films were potentiodynamically anodized at two different sweep rates to 50 V in an ethylene glycol electrolyte containing ammonium fluoride and water. At a high sweep rate of 1.0 V s(-1), a barrier-type anodic film was formed even though the current efficiency was as low as similar to 50%. In contrast, a nanoporous anodic film developed at a low sweep rate of 0.05 V s(-1), and the film-formation efficiency reduced to 37%. The main part of the anodic films consists of iron (III) hydroxyfluoride with a thin inner layer composed of FeF3. The inner fluoride layer is formed owing to the faster inward migration of fluoride ions compared to that of the oxygen species. During immersion or re-anodizing of the iron specimen with an approximately 100-nm-thick, barrier-type anodic film at and below 15 V, thinning of the anodic film proceeded uniformly and film dissolution was enhanced by applying an electric field. The impact of the electric field on film formation and dissolution is discussed. (C) 2014 Elsevier Ltd. All rights reserved.
  • Rosa M. Vazquez, Alexander Mozalev, Raul Calavia, Francesc Gispert-Guirado, Xavier Vilanova, Hiroki Habazaki, Eduard Llobet
    SENSORS AND ACTUATORS B-CHEMICAL 204 588 - 595 2014/12 
    The sensing properties of nanostructured Zr-W mixed oxide film have been investigated. The film was prepared via anodizing a sputter-deposited Zr-W alloy layer through nanopores in an anodic alumina layer superimposed on the alloy. The morphology, structure and chemical composition of the film were examined by SEM and XRD. The film consists of an array of self-ordered nanocolumns protruding from a continuous thin oxide layer. The initially amorphous film material crystallizes to monoclinic WO3 and orthorhombic ZrO2 due to a high temperature annealing in air. A sensor employing the ZrO2-WO3 oxide film as active layer was fabricated and used for detecting various concentrations (1-1000 ppm) of H-2, CO, C2H5OH and NO2 at temperatures up to 300 degrees C. In hydrogen detection experiments, the sensor was very fast, with a response time of 19 s, and highly sensitive to hydrogen, with a response value of up to 50, while showing incomparably weaker and slower responses to carbon monoxide, ethanol and nitrogen dioxide. The features of the films revealed to date are of importance for improving the chemical, structural and exploitation stability of nanostructured tungsten-oxide-based films and their selectivity in hydrogen gas detection. (C) 2014 Elsevier B.V. All rights reserved.
  • Ryo Nonaka, Yoshitaka Aoki, Etsushi Tsuji, Shinji Nagata, Hiroki Habazaki
    ELECTROCHEMISTRY 82 (10) 859 - 864 1344-3542 2014/10 
    An electrochemical analysis was conducted with respect to a hydrogen membrane fuel cell (HMFC) comprising proton-conducting, amorphous zirconium phosphate, a-ZrP2.5O8.9H1.3, thin film electrolyte supported on a dense Pd anode. The HMFC gave rise to an OCV of 1.0 V, but the maximum power density was limited and was about 1 mW cm(-2) at 400 degrees C. The impedance spectroscopy revealed that the interfacial polarizations were decreased by two orders of magnitude when the cell configuration was changed from the fuel cell setup to the hydrogen concentration cell with an anode symmetric configuration. These results indicated that the polarization losses at the solid-solid anode interface are not a main contribution to the voltage loss of the HMFC. The large cathode polarization might be attributed to the lessened conductivity of amorphous zirconium phosphate electrolyte thin film formed on a precious metal electrode. (C) The Electrochemical Society of Japan, All rights reserved.
  • Hiroki Habazaki, Fumitaka Kataoka, Etsushi Tsuji, Yoshitaka Aoki, Shinji Nagata, Peter Skeldon, George E. Thompson
    ELECTROCHEMISTRY COMMUNICATIONS 46 30 - 32 1388-2481 2014/09 
    The present study reports, for the first time, the highly efficient formation of barrier-type anodic films, with flat and parallel metal/film and film/electrolyte interfaces, on magnesium in ethylene glycol electrolytes containing ammonium fluoride and water. The anodizing voltage increases linearly with time during galvanostatic anodizing at 10Am(-2) up to 350 V.The anodic film formed to 200V is 247 nm thick, containing a crystalline MgF2 phase. Analysis by Rutherford backscattering spectroscopy discloses the film composition of MgF1.8O0.1 and Pilling-Bedworth ratio (PBR) of 1.67. The PBR value greater than unity and the formation of chemically stable fluoride-based films may contribute to the film growth at high current efficiency. (C) 2014 Elsevier B.V. All rights reserved.
  • Tatsuya Kikuchi, Masumi Yoshida, Shiki Matsuura, Shungo Natsui, Etsuji Tsuji, Hiroki Habazaki, Ryosuke O. Suzuki
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 75 (9) 1041 - 1048 0022-3697 2014/09 
    Micro-, submicron-, and nano-scale titanium dioxide particles were reduced by reduction with a metallic calcium reductant in calcium chloride molten salt at 1173 K, and the reduction mechanism of the oxides by the calcium reductant was explored. These oxide particles, metallic calcium as a reducing agent, and calcium chloride as a molten salt were placed in a titanium crucible and heated under an argon atmosphere. Titanium dioxide was reduced to metallic titanium through a calcium titanate and lower titanium oxide, and the materials were sintered together to form a micro-porous titanium structure in molten salt at high temperature. The reduction rate of titanium dioxide was observed to increase with decreasing particle size; accordingly, the residual oxygen content in the reduced titanium decreases. The obtained micro-porous titanium appeared dark gray in color because of its low surface reflection. Microporous metallic titanium with a low oxygen content (0.42 wt%) and a large surface area (1.794 m(2) g(-1)) can be successfully obtained by reduction under optimal conditions. (C) 2014 Elsevier Ltd. All rights reserved.
  • Seong-Ki Ahn, Jeong-Jin Yang, Hong-Il Kim, Hiroki Habazaki, Soo-Gil Park
    CHEMISTRY LETTERS 43 (6) 898 - 900 0366-7022 2014/06 
    We have investigated the effects of heat treatment on the electrochemical properties of carbon nanofibers (CNFs) for use as an anode material in lithium ion capacitors. The CNFs were fabricated by liquid-phase carbonization on a porous alumina template that was anodized in oxalic acid at 40 V for 30 mm and subjected to a pore-widening process in phosphoric acid at room temperature. The CNFs were heated at temperatures of 600, 1000, and 1400 degrees C to facilitate rearrangement of the carbon structure.
  • E. Tsuji, Y. Taguchi, Y. Aoki, T. Hashimoto, P. Skeldon, G. E. Thompson, H. Habazaki
    APPLIED SURFACE SCIENCE 301 500 - 507 0169-4332 2014/05 
    We report the size-selective photocatalytic decomposition of organic molecules using crystalline anodic TiO2 nanochannel films as the photocatalyst. The porous TiO2 films were formed by anodizing titanium at 20 V in glycerol electrolyte containing various amounts of K3PO4, K2HPO4, and KH2PO4 at 433K. Regardless of the electrolyte composition, the as-formed TiO2 films had a crystalline anatase structure. The basicity of the electrolyte markedly influenced the morphology of the TiO2 nanochannel films; more regular nanochannels developed with increasing basicity of the electrolyte. Because the diameter of the nanochannels in the films formed in a basic electrolyte was as small as similar to 10 nm, the anodic TiO2 nanochannel films with a thickness of 5 mu m revealed a selective photocatalytic decomposition of methylene blue (MB) in a mixture of MB and direct red 80 (DR) kept under UV irradiation. The importance of the diameter of the nanochannels and their uniformity for size-selective decomposition of organic molecules were investigated. (C) 2014 Elsevier B.V. All rights reserved.
  • Hiroki Habazaki, Rokuro Nishimura, Kenji Okitsu, Hiroyuki Inoue, Ikuo Kiriyama, Fumitaka Kataoka, Masatoshi Sakairi, Hideaki Takahashi
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 18 (2) 369 - 376 1432-8488 2014/02 
    The pitting corrosion behavior of high-purity aluminum covered with barrier-type anodic films, which are formed in neutral borate and phosphate electrolytes, has been examined in 0.5 mol dm(-3) NaCl solution at an applied potential of -0.6 V versus Ag/AgCl, which is slightly nobler than the pitting potential of -0.64 V in the same solution. The pitting current density, i (p), increased with time after an incubation time, t (i). The double logarithmic plot of i (p) and polarization time, t, reveal two straight lines, which are separated at the time, tau. The slope becomes larger after tau for the specimens anodized in the phosphate electrolyte, while it becomes smaller for those in the borate electrolyte. Both the t (i) and tau increase with the thickness of the anodic films, and at the similar film thickness, they are much larger for the anodic films formed in the phosphate electrolyte than for those in the borate electrolyte. The corrosion process can be divided into three stages: the incubation period up to t (i), the pit nucleation period before tau, and the pit growth period after tau. We have discussed the different pitting corrosion behavior of the aluminum specimens covered with the anodic films formed in the borate and phosphate electrolytes in terms of ion selectivity of the anodic films.
  • Tatsuya Kikuchi, Masumi Yoshida, Yoshiaki Taguchi, Hiroki Habazaki, Ryosuke O. Suzuki
    JOURNAL OF ALLOYS AND COMPOUNDS 586 148 - 154 0925-8388 2014/02 
    A metallic titanium and zirconium micro-porous alloy for electrolytic capacitor applications was produced by electroless reduction with a calcium reductant in calcium chloride molten salt at 1173 K. Mixed TiO2-70 at%ZrO2 oxides, metallic calcium, and calcium chloride were placed in a titanium crucible and heated under argon atmosphere to reduce the oxides with the calcium reductant. A metallic Ti-Zr alloy was obtained by electroless reduction in the presence of excess calcium reductant and showed a microporous morphology due to the sintering of each of the reduced particles during the reduction. The residual oxygen content and surface area of the reduced Ti-Zr alloy decreased over time during the electroless reduction. The element distributions were slightly different at the positions of the alloy and were in the composition range of Ti-69.3 at% to 74.3 at% Zr. A micro-porous Ti-Zr alloy with low oxygen content (0.20 wt%) and large surface area (0.55 m(2) g (1)) was successfully fabricated by electroless reduction under optimal conditions. The reduction mechanisms of the mixed and pure oxides by the calcium reductant are also discussed. (C) 2013 Elsevier B. V. All rights reserved.
  • Soo-Gil Park, Jeong-Jin Yang, Jin-Woo Rho, Hong-Il Kim, Hiroki Habazaki
    JOURNAL OF THE KOREAN ELECTROCHEMICAL SOCIETY 17 (1) 13 - 17 1229-1935 2014/02 
    The TiO2 nanotube/Ti electrode are used as an anode in thin-film lithium microbatteries is known to have high oxidation-reduction potential of 1.8 V (vs. Li/Li +). It can prevent from dendrite growth of lithium during charging. The TiO2 nanotube/Ti electrode was prepared by anodizing at constant voltages for thin-film lithium microbatteries. The capacities of TiO2 nanotube/Ti anode prepared by anodizing at 10 V, 20 V and 30 V were observed to be 23.9 mu Ah cm(-2), 43.1 mu Ah cm-2 and 74.0 mu Ah cm(-2). We identified it was found that the capacity of TiO2 nanotube/Ti increases with increasing anodizing voltage and the anatase structure of TiO2 nanotube/Ti compared with amorphous structure has batter cycle performance than amorphous TiO2 nanotube/Ti.
  • Yoshitaka Aoki, Kazumasa Kikutani, Etsushi Tsuji, Hiroki Habazaki
    ECS ELECTROCHEMISTRY LETTERS 3 (10) F61 - F64 2162-8726 2014 
    This is the first report to investigate on the electrical conductivity of unusual high valence state pentavalent chromium oxides in terms of defect thermodynamics. Calcium chromium(V) apatite was prepared as a single phase, and the electrical conductivity was examined as a function of oxygen partial pressure p(O2). The conductivity was increased at higher p(O2) in wet atmosphere but it was not dependent on p(O2) in dry atmosphere. The water concentration cell gives stable electromotive force. The features disclosed that the chromium(V) apatite reveals proton electron mixed conductivity under wet oxidative condition. (C) 2014 The Electrochemical Society. All rights reserved.
  • Hiroki Habazaki, Taiki Kimura, Yoshitaka Aoki, Etsushi Tsuji, Takayoshi Yano
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 161 (1) C57 - C61 0013-4651 2014 
    In this study, aluminosilicate sol-gel coatings were deposited on Type 430 stainless steel by multiple spin casting cycles. Amorphous aluminosilicate coatings, 65 nm thick, were prepared from precursor solutions with 50, 100, and 500 mmol dm(-3) total concentrations of aluminum and silicon species (molar ratio of Al/Si = 1/4) by 10, 5, and 1 spin casting cycles, respectively. Although the obtained coatings had a similar composition with a molar ratio of Al/Si = 25/75, the coatings with increased density were formed by reducing the concentration of precursor solution. The pitting potentials of the coated stainless steels, measured by potentiodynamic polarization in 3.5% NaCl solution, increased remarkably (to 1.1 V vs Ag/AgCl) with a decrease in the concentration of precursor solution. Cyclic corrosion tests, consisting of 30 cycles of spraying of 5% NaCl solution at 35 degrees C for 2 h, drying at 60 degrees C for 4 h, and wetting at 50 degrees C and >95% relative humidity for 2 h, revealed highly improved corrosion resistance. Layer-by-layer sal-gel deposition using diluted precursor solutions is an effective way to obtain highly protective coatings. (C) 2013 The Electrochemical Society.
  • Alexander Mozalev, Masatoshi Sakairi, Hideaki Takahashi, Hiroki Habazaki, Jaromir Hubalek
    THIN SOLID FILMS 550 486 - 494 0040-6090 2014/01 
    Three types of thin solid films with the nanoscale inner structures were synthesized by sputtering-deposition and anodizing of Al layer, Al-1.5 at.% Si alloy layer, and Al/Ta bilayer on Si wafers. All the anodic films comprised 1 mu m thick nanoporous alumina layer as the key component. The essential differences were due to the silicon impurities (AlSi alloy) and the array of nanosized tantalum oxide protrusions in the alumina barrier layer (Al/Ta bilayer). The films were examined by scanning and transmission electron microscopy and electrochemical impedance spectroscopy. Integral capacitors utilizing the anodic films as dielectrics combine the small-value capacitance (6.5 nF cm(-2)) with the excellent properties of high withstand field strength (1.7-2.7 MV cm(-1)), low leakage current ((3-20) x 10(-12) A mm(-2) at 1.0 MV cm(-1)), and low loss tangent (tg delta = (4-6) x 10(-3)). The revealed dispersion of dielectric constant, although within 10%, and the presence of loss peaks on the temperature and frequency dependencies of tgd denote the influence of ion-relaxation mechanism on dielectrics' polarizability, with the characteristic times ranging from 10 to 145 mu s depending on the dielectric type. By selecting appropriate technological and electrolytic conditions, the functionality of the capacitors can be optimized to meet the needs of a specific range, from 1 kHz to about 300 MHz operating frequencies. (C) 2012 Elsevier B. V. All rights reserved.
  • Alexander Mozalev, Rosa M. Vazquez, Carla Bittencourt, Damien Cossement, Francesc Gispert-Guirado, Eduard Llobet, Hiroki Habazaki
    JOURNAL OF MATERIALS CHEMISTRY C 2 (24) 4847 - 4860 2050-7526 2014 
    Nanostructured niobium oxide (NO) semiconductors are gaining increasing attention as electronic, optical, and electro-optic materials. However, the preparation of stable NO nanofilms with reproducible morphology and behavior remains a challenge. Here we show a rapid, well-controlled, and efficient way to synthesize NO films with self-organized columnlike nanostructured morphologies and advanced functional properties. The films are developed via the growth of a nanoporous anodic alumina layer, followed by the pore-directed anodization of the Nb underlayer. The columns may grow 30-150 nm wide, up to 900 nm long, with an aspect ratio of up to 20, being anchored to a thin continuous oxide layer that separates the columns from the substrate. The as-anodized films have a graded chemical composition changing from amorphous Nb2O5 mixed with Al2O3, Si-, and P-containing species in the surface region to NbO2 in the lower film layer. The post-anodization treatments result in the controlled formation of Nb2O5, NbO2, and NbO crystal phases, accompanied by transformation from nearly perfect dielectric to n-type semiconductor behavior of the films. The approach allows for the smooth film growth without early dielectric breakdown, stress-generated defects, or destructive dissolution at the respective interfaces, which is a unique situation in the oxide films on niobium. The functional properties of the NO films, revealed to date, allow for potential applications as nanocomposite capacitor dielectrics and active layers for semiconductor gas microsensors with the sensitivity to ethanol and the response to hydrogen being among best ever reported.
  • Katsutoshi Nakayama, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    RSC ADVANCES 4 (58) 30927 - 30933 2046-2069 2014 
    This study demonstrates the fabrication of hierarchical surfaces with super-repellency even for low-surface-tension liquids, including octane (surface tension of 21.7 mN m(-1)). Dual-pore surfaces were prepared by a combination of practical wet processes on an aluminium substrate: chemical etching, anodizing, and organic monolayer coating. The size of the larger pores formed by the chemical etching of aluminium is controlled by the concentration of HCl in the CuCl2/HCl etching solution. The etched aluminium is then anodized to introduce nanopores, followed by a pore-widening treatment that controls the nanopore size and porosity. The repellency for low-surface-tension liquids is enhanced by increasing the size of the larger pores as well as the porosity of the walls of the larger pores in this dual-pore morphology. Under optimized morphology with a fluoroalkyl-phosphate monolayer coating, an advancing contact angle close to 160 degrees, a contact angle hysteresis of less than 5 degrees and a sliding angle of 10 degrees is achieved even for octane.
  • M. Seo, H. Habazaki, M. Inaba, M. Yokomizo, T. Wakabayashi, T. Nakayama
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 161 (4) H195 - H202 0013-4651 2014 
    In situ X-ray absorption spectroscopy (XAS) was applied to investigate the Sn underpotential deposition (UPD) on Ni surface from 0.2 M HClO4 solution containing 10(-3) M Sn2+ with relation to the inhibition effect of Sn on aqueous corrosion of Ni. The periodical emersion method under potentiostatic polarization, using the surface-roughened Ni plate (surface roughness S-r = 78.3) as a working electrode was employed to detect sensitively the sub-monolayer coverage of Sn on Ni. The Sn K-edge absorption spectra in a scanning XAS mode were measured by monitoring the Sn K-alpha 1 fluorescence line. The Sn K-edge absorption near-edge structure (XANES) in the Sn-UPD potential region has revealed that the Sn-UPD layer on Ni is oxygenated. The extended X-ray absorption fine structure (EXAFS) analysis was performed with a two shell fit of the nearest neighbor Sn-Ni and Sn-O interactions, assuming that the uppermost Ni surface exposed to the solution is mainly oriented to the (111) plane. The results have indicated that Sn atoms are substituted like a surface alloy at face-center-cubic sites in the first Ni layer and further bonded with oxygen atoms. The strong inhibition effect of Sn on aqueous corrosion of Ni is ascribed to the bond between Sn and O atoms in. addition to the bond between Sn and Ni atoms. (C)2014 The Electrochemical Society.
  • Masahiro Seo, Atsushi Hyono, Hiroki Habazaki, Takenori Nakayama
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 161 (12) C550 - C556 0013-4651 2014 
    The effect of Sn2+ on the anodic dissolution of nickel was investigated in deaerated 0.2 M HClO4 solution containing Sn2+ at room temperature. It has been found that the addition of 10(-3) M Sn2+ inhibits completely the anodic dissolution of Ni. In contrast, tin itself is not passivated in 0.2 M HClO4 irrespective of the addition of 10(-3) M Sn2+. Besides, the anodic dissolution of Ni is not inhibited by the surface coating with Sn (IV) colloid which mainly consistis of hydrous or amorphous nano-crystalline SnO2. X-ray photoelectron spectroscopy (XPS) analysis used to supplement our recent X-ray absorption spectroscopy (XAS) results has indicated that the inhibition effect of Sn2+ on anodic dissolution of Ni is associated with the underpotential deposition (UPD) of Sn on Ni. The metallic bond between Sn and Ni in the Sn-UPD layer on Ni is a prerequisite to the formation of Sn residue adhered to the Ni substrate at the more noble potential that brings the inhibition effect on anodic dissolution of Ni. Moreover, the difference between inhibition effects of Sn2+ and Pb2+ on anodic dissolution of Ni was discussed on the basis of the difference between Sn- and Pb-UPD on Ni. (c) 2014 The Electrochemical Society. All rights reserved.
  • A. Baron-Wiechec, M. G. Burke, T. Hashimoto, H. Liu, P. Skeldon, G. E. Thompson, H. Habazaki, J. - J. Ganem, I. C. Vickridge
    ELECTROCHIMICA ACTA 113 302 - 312 0013-4686 2013/12 
    Arsenic species are utilized as tracers in a study of pore initiation in anodic films that were formed at constant potentials on aluminium in phosphoric acid. The films were grown first in sodium arsenate solution and then in phosphoric acid, and examined using ion beam analysis and scanning and transmission electron microscopies. The analysis of the arsenic content of specimens indicates that the growth mechanisms of incipient and major pores involve mainly field-assisted dissolution and field-assisted flow of the alumina, respectively. The transition between incipient and major pore formation is suggested to be initiated by preferential growth of certain incipient pores, leading to a locally increased current density at the pore bases. The major pores subsequently develop by the flow oxide away from the pore bases, which is evident from the behaviour of the arsenic tracer. The results suggest that the flow is associated with the non-uniform distribution of ionic current and a relatively low volume of formed film material compared with the volume of oxidized aluminium. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
  • M. Santamaria, S. Terracina, Y. Konno, H. Habazaki, F. Di Quarto
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 17 (12) 3005 - 3014 1432-8488 2013/12 
    Iron oxide films with a nanoporous structure were grown by anodizing sputter-deposited Fe in a fluoride containing ethylene glycol solution and annealed under air exposure at different temperatures. X-ray diffraction and Raman spectroscopy allowed to identify the presence of hematite and/or magnetite after thermal treatment for films annealed at T a parts per thousand yenaEuro parts per thousand 400 A degrees C under air exposure. According to GDOES compositional depth profiles, the thermal treatment sensitively reduced the amount of fluoride species incorporated into the film during the anodizing process. A band gap value of similar to 2.0 eV was estimated for all the investigated layers, while a flat band potential dependent on both the growth conditions as well as on the annealing temperature was estimated.
  • F. Di Quarto, F. Di Franco, C. Monarca, M. Santamaria, H. Habazaki
    ELECTROCHIMICA ACTA 110 517 - 525 0013-4686 2013/11 
    The solid state properties of anodic films grown galvanostatically on sputtering-deposited Ti-6at.%Si alloys were studied as a function of the formation voltage (5-40 V). From the photocurrent spectra a band gap of similar to 3.4 eV was estimated for all the investigated thicknesses, which is almost coincident with the value measured for amorphous TiO2. The photocharacteristics allowed to estimate the flat band potential of the films, which resulted to be more anodic for thicker layers and allowed to evidence a change from n-type semiconducting material to insulator by increasing the formation voltage. A dielectric constant of similar to 31 was estimated by differential capacitance measurements. The dependence of photocurrent on electrode potential was studied in the frame of Onsager-Braun theory, which allows to evidence the influence of the initial recombination on the photocurrent yield for amorphous material. (C) 2013 Elsevier Ltd. All rights reserved.
  • Masatoshi Ishizuka, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHEMISTRY 81 (10) 840 - 844 1344-3542 2013/10 
    Barrier-type anodic films are formed on magnetron sputtered Ta-W alloy films to various formation potentials in 0.1 mol dm(-3) ammonium pentaborate electrolyte. The anodic films consist of two layers, comprising an outer thin Ta2O5 layer free from tungsten species and an inner layer containing both tantalum and tungsten species. Slower migration of W6+ ions with respect to Ta5+ ions results in the formation of the two-layered films. Because of the absence. of more soluble tungsten species in the outer layer, the anodic films grow at high current efficiency. The reciprocal of capacitance of the anodic films changes linearly with formation voltage, as a consequence of linear thickening of the anodic films with the formation potential. The capacitance is enhanced by the addition of tungsten, particularly at low formation potential. The shift of the potential, at which the anodic film growth commences, to the noble direction, contributes to the enhanced capacitance at the low formation voltages. (C) The Electrochemical Society of Japan, All rights reserved.
  • H. Sato, T. Fujii, E. Tsuji, Y. Aoki, K. Shimizu, P. Skeldon, G. E. Thompson, H. Habazaki
    SURFACE AND INTERFACE ANALYSIS 45 (10) 1441 - 1445 0142-2421 2013/10 
    Self-assembled alkyl phosphate layers have been formed on a flat, anodized aluminum substrate in dilute ethanol solution containing 2wt% n-tetradecylphosphonic acid (TDP) and examined by low-voltage scanning electron microscopy as well as atomic force microscopy and X-ray photoelectron spectroscopy. Locally, multi-layered alkyl phosphate films have been formed on aluminum, being clearly observed by a low-voltage scanning electron microscope operated at less than 1kV. Atomic force microscopy observations disclosed that bilayers of tetradecylphosphonic acid are stacked on the substrate to form multilayers. The present study revealed that the uniform self-organized monolayer is not always formed readily on an oxidized aluminum surface. Copyright (c) 2013 John Wiley & Sons, Ltd.
  • Y. Aoki, R. Nonaka, H. Habazaki
    SOLID OXIDE FUEL CELLS 13 (SOFC-XIII) 57 (1) 911 - 916 1938-5862 2013 
    Novel thin film fuel cell based on the 100 nm-thick electrolyte of amorphous ZrP2.5Ox, working at 400 degrees C, was demonstrated. The hydrogen permeable membrane fuel cell (HMFC) using a Pd foil as a nonporous solid anode was fabricated. Ni interlayer of several hundreds nm thickness was introduced between the Pd anode and the ZrP2.5Ox electrolyte in order to suppress the deterioration of the electrolyte nanofilm by the deformation of the Pd anode during hydrogen absorption. In the ZrP2.5Ox electrolyte the transport number of proton was unity at 400 degrees C as determined by an EMF measurement. The modification of the Ni anode surface by an ultrathin Pt or Pd layer effectively decreased the anode/electrolyte interfacial polarization. Consequently, the HMFC revealed the OCV of 1.0 V and the maximum power density of 3.6 mW cm(-2) at 400 degrees C.
  • H. Habazaki, T. Fujii, E. Tsuji, Y. Aoki
    PITS AND PORES 5: A SYMPOSIUM IN HONOR OF DAVID LOCKWOOD 50 (37) 217 - 224 1938-5862 2013 
    In this study, hierarchical dual pore surfaces have been developed by two-step anodizing of aluminum. The first anodizing has been carried out at 390 V in 2 wt% citric acid, and then, the resultant anodic film has been dissolved to disclose the scalloped aluminum substrate with a cell size of similar to 900 nm. Subsequently, the second anodizing has been carried out at 25 V in 0.3 mol dm(-3) sulfuric acid electrolyte to generate smaller nanopores. The size of nanopores has been further controlled by pore-widening treatment in 5 wt% phosphoric acid at 303 K. After coating with a fluoroalkyl phosphate monolayer to reduce the surface energy, the dual pillar surfaces with enlarged nanopores show super-repellency even for rapeseed oil as well as for water.
  • K. Hashimoto, N. Kumagai, K. Izumiya, H. Takano, P. R. Zabinski, A. A. El-Moneim, M. Yamasaki, Z. Kato, E. Akiyama, H. Habazaki
    ARCHIVES OF METALLURGY AND MATERIALS 58 (1) 231 - 239 1733-3490 2013 
    Extrapolation of world energy consumption from 1990 to 2010 indicates the complete exhaustion of world reserves of oil, natural gas, uranium and coal by 2040, 2043, 2046 and 2053, respectively. For the survival of all people in the whole world, intermittent and fluctuating electricity generated from renewable energy should be supplied in the form of usable fuel to all people in the whole world. We have been working on research and development of global carbon dioxide recycling for the use of renewable energy in the form of methane via electrolytic hydrogen generation using carbon dioxide as the feedstock. We created energy-saving cathodes for hydrogen production, anodes for oxygen evolution without chlorine formation in seawater electrolysis, and catalysts for methanation of carbon dioxide and built pilot plants of industrial scale. Recent advances in materials are described. Industrial applications are in progress.
  • M. Ishizuka, E. Tsuji, Y. Aoki, A. Hyono, T. Ohtsuka, N. Sakaguchi, S. Nagata, H. Habazaki
    ELECTROCHEMICAL CAPACITORS 50 (43) 245 - 254 1938-5862 2013 
    The sputter-deposited Zr-Si-Y film was anodized to form a high capacitance composite anodic film, comprising a tetragonal ZrO2 nanocrystalline phase and a silicon-enriched amorphous phase. It was found that the nanocomposite anodic film, as well as the yttrium-free ZrO2-SiO2 anodic film, showed markedly increased capacitance compared with the anodic film ZrO2 film on zirconium. The incorporation of yttrium species to the anodic ZrO2-SiO2 film did not change the thickness and permittivity of the anodic oxide film, although a thicker anodic film was formed on zirconium by the incorporation of yttrium, which may introduce oxygen vacancies in the crystalline ZrO2. The findings suggest that in the composite ZrO2-SiO2 anodic films the film thickness is mainly controlled by the silicon-enriched amorphous phase.
  • Y. Konno, S. Yang, E. Tuji, Y. Aoki, P. Skeldon, G. E. Thompson, H. Habazaki
    PITS AND PORES 5: A SYMPOSIUM IN HONOR OF DAVID LOCKWOOD 50 (37) 183 - 190 1938-5862 2013 
    The growth behavior of nanoporous anodic films on carbon steel containing 0.213 mass% carbon has been examined during anodizing in ethylene glycol containing 0.1 mol dm(-3) NH4F and 0.5 mol dm(-3) H2O. The nanopores in the anodic films are generated preferentially along with steps and at "kink-like" sites of the steel surface generated by rf-GD sputtering. The steel contains carbide precipitates with a size of 50-800 nm. The anodic oxide formed on the carbide phase is more chemically soluble during anodizing, producing pits in the anodic films.
  • Etsushi Tsuji, Naoto Hirata, Yoshitaka Aoki, Hiroki Habazaki
    MATERIALS LETTERS 91 39 - 41 0167-577X 2013/01 
    In this study, mesoporous TiO2 films were formed on ITO conductive glasses by anodizing of titanium thin films without post-annealing. The titanium thin films, similar to 200 nm thick, sputter-deposited on to the ITO substrates were anodized at 20 V in a phosphate/glycerol electrolyte at 433 K. A completely. transparent TiO2 specimen was obtained by anodizing for 60 s. The as-anodized mesoporous,TiO2 films consisted of anatase, even without post-annealing. The transparent mesoporous TiO2 films anodized for a suitable time showed much better photoelectrochemical performance than the post-annealed TiO2 nanotubular film. (C) 2012 Elsevier B.V. All rights reserved.
  • Ke Ye, Yoshitaka Aoki, Etsushi Tsuji, Shinji Nagata, Hiroki Habazaki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 160 (9) F1096 - F1102 0013-4651 2013 
    Novel proton-conducting ZrO2-WO3-SiO2 nanofilms of various compositions and thicknesses (similar to 50 to similar to 300 nm) have been prepared by anodizing of magnetron-sputtered Zr-W-Si alloys in 0.1 mol dm(-3) phosphoric acid electrolyte at 20 degrees C. All the anodic oxide nanofilms examined reveal efficient proton conductivity after post-annealing at 250 degrees C. Further increase in the post-annealing temperature results in the conductivity degradation for the anodic oxide nanofilms on the alloy containing only 5 at% silicon, while the high conductivity is maintained even after post-annealing at 300 degrees C for those containing 15 at% or more silicon. The proton conductivity is dependent upon tungsten content; the conductivity of 5 x 10(-6) S cm(-1) for the similar to 100 nm-thick films on the Zr31W55Si14 at 100 degrees C is approximately 10 times that on the Zr48W37Si15. The anodic oxide nanofilms consist of two layers, comprising a thin outer ZrO2 layer and an inner ZrO2-WO3-SiO2 layer. Both layers show thickness-dependent conductivity and the proton conductivity of the two-layer anodic films is enhanced one order of magnitude by reducing the film thickness from similar to 300 nm to similar to 100 mu. Different mechanisms are proposed for the thickness dependence of the conductivity of the outer and inner layers. (C) 2013 The Electrochemical Society. All rights reserved.
  • Ke Ye, Yoshitaka Aoki, Etsushi Tsuji, Shinji Nagata, Hiroki Habazaki
    SOLID STATE IONIC DEVICES 9 - ION CONDUCTING THIN FILMS AND MULTILAYERS 50 (27) 193 - 201 1938-5862 2013 
    The proton conductivity of the anodic ZrO2-WO3-SiO2 nanofilms prepared by anodizing of sputter-deposited Zr37W47Si16 alloy at several formation voltages for 1.8 ks in 0.1 mol dm(-3) phosphoric acid electrolyte at 20 degrees C has been examined below 250 degrees C in various environments. The proton conductivity activated by thermal treatment at 250 degrees C is not influenced by the presence of O-2 and H2O in the atmosphere. However, the conductivity is enhanced by one order of magnitude in H-2-containing atmosphere. The H-2-induced conductivity enhancement is reversible; the enhanced conductivity is returned to an original value by exposing again in an O-2-containing atmosphere.
  • Y. Konno, E. Tsuji, P. Skeldon, G. E. Thompson, H. Habazaki
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 16 (12) 3887 - 3896 1432-8488 2012/12 
    The growth behaviour of nanoporous anodic films on iron during galvanostatic anodizing in ethylene glycol electrolytes containing NH4F and H2O is examined at various current densities, H2O concentrations in electrolytes and temperatures. The film morphology is mainly controlled by the formation voltage, regardless of anodizing conditions. Relatively regular cylindrical pores are formed at formation voltages less than 50 V, while rather disordered pores are formed above 100 V. The decrease in the H2O concentration suppresses chemical dissolution of anodic films in addition to the increased growth efficiency, resulting in the formation of anodic films with a steady thickness of similar to 7 mu m. The cell size of the anodic films depends upon the H2O concentration as well as the formation voltage, but not upon the current density. Findings in this study will be useful for controlled growth of the anodic films on iron.
  • Takashi Fujii, Hina Sato, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    JOURNAL OF PHYSICAL CHEMISTRY C 116 (44) 23308 - 23314 1932-7447 2012/11 
    This work reports the importance of nanopore morphology in designing super liquid-repellent submicropillar/nanopore hierarchical surfaces. The hierarchical surfaces were fabricated using a combined process of oblique angle sputter deposition of aluminum with subsequent anodizing, and the surfaces were coated with a fluorinated alkyl phosphate layer to reduce the surface energy. The size of the nanopores, the interpore distance, and the porosity of the anodic films on the submicrometer pillars were controlled by varying the anodizing and pore-widening conditions. The present study demonstrates that super liquid repellency can be achieved on intrinsically oleophilic surfaces by introducing hierarchical submicropillar/nanopore morphology even for oils with surface energies as low as similar to 25 mN m(-1). The porosity in the submicrometer pillars was a key factor in influencing the contact angle hysteresis; higher porosity is needed to reduce the contact angle hysteresis.
  • Alexander Mozalev, Hiroki Habazaki, Jaromir Hubalek
    ELECTROCHIMICA ACTA 82 90 - 97 0013-4686 2012/11 
    Al/Nb (aluminium-on-niobium) and Al/Ta (aluminium-on-tantalum) metal layers sputter-deposited onto Si wafers were anodized respectively in 0.06 and 0.1 mol dm(-3) citric acid electrolytes under a high voltage of 480 and 400V in order to consecutively grow porous alumina layers with the longest interpore distances, this followed by growth of self-organized arrays of micro-sized goblets-like niobium oxide structures and eryngii-mushrooms-like tantalum oxide structures protruding through the alumina barrier layer. The shape and size of the metal oxide microstructures were additionally tailored by post-anodizing treatment combining partial open-circuit dissolution of the alumina pores with reanodizing the underlying metal through the as grown and expanded pores. The structured metal oxide surfaces derived after selectively dissolving away the anodic alumina layers were coated with fluoroalkyl phosphate (FAP) and tested for their non-wetting properties by measuring static contact angles for water droplets. Both the FAP-coated goblet and eryngii-mushroom surfaces showed superhydrophobic behaviour with the contact angles of 158 and 156 respectively. The effect is due to the creation of composite solid-liquid-air interfaces that allow for dramatically decreased liquid-to-solid contact area and adhesion, in accord with the Cassie-Baxter model. (c) 2012 Elsevier Ltd. All rights reserved.
  • H. Habazaki, S. Tsunekawa, E. Tsuji, T. Nakayama
    APPLIED SURFACE SCIENCE 259 711 - 718 0169-4332 2012/10 
    Plasma electrolytic oxidation of single beta-phase Ti-15 mass% V-3 mass% Al-3 mass% Cr-3 mass% Sn (hereafter denoted as Ti-15-3) alloy has been conducted in alkaline aluminate electrolyte at different electrolyte temperatures between 278 and 313 K. The results obtained disclose the highly improved wear resistance of the coatings formed at the lowest temperature of 278 K. The coating formed at this temperature has lower porosity and contains higher concentration of alpha-Al2O3 phase in addition to the Al2TiO5 major phase. In contrast, non-uniform coatings are formed at higher temperatures and their porosity is relatively high. Thus, the highest wear resistance of the Ti-15-3 is obtained when the coating is formed at 278 K. Such influence of the electrolyte temperature on the coating morphology and composition is discussed by direct imaging based on direct video imaging data during the coating process. (C) 2012 Elsevier B. V. All rights reserved.
  • Yoshiaki Taguchi, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    APPLIED SURFACE SCIENCE 258 (24) 9810 - 9815 0169-4332 2012/10 
    In this study, anatase crystalline TiO2 mesoporous film was formed by anodizing of titanium specimens without annealing procedures. The specimens were anodized at 3 and 20 V in 0.6 mol dm(-3) K2HPO4 and 0.2 mol dm(-3) K3PO4/glycerol electrolyte at 433 K. The obtained films had mesoporous structures with pore diameters as small as similar to 10 nm. The mesoporous film formed at 20 V without annealing (MP-20V) was a mixture of amorphous phase and nanograined anatase, which clearly showed strong < 0 0 1 > preferred orientation, whereas that at 3 V was completely amorphous. Even without annealing, the MP-20V showed high photocatalytic activities for decomposition of water and methylene blue. In contrast, the anodic TiO2 nanotube film formed in NH4F/ethylene glycol electrolyte revealed photocatalytic activities only after annealing at 723 K, because of the amorphous nature of the as-anodized nanotube film. The MP-20V film also showed superhydrophilicity with UV light irradiation. (C) 2012 Elsevier B. V. All rights reserved.
  • K. Kure, Y. Konno, E. Tsuji, P. Skeldon, G. E. Thompson, H. Habazaki
    ELECTROCHEMISTRY COMMUNICATIONS 21 1 - 4 1388-2481 2012/07 
    The formation of self-organized nanoporous anodic films on Type 304 stainless steel in fluoride-containing ethylene glycol electrolyte is reported. A key factor in the formation of the nanoporous anodic films is the water concentration in the electrolyte, which must be 0.3 mol dm(-3) or less for the present conditions of film formation, although nanoporous anodic films have been formed on iron at higher water concentrations. The films contain relatively high concentrations of iron, chromium, nickel, oxygen and fluorine species distributed throughout the film thicknesses. The fluoride species can be removed by post-annealing in air, which improves the chemical stability of the films without damaging the nanoporous morphology of the remaining oxide. (C) 2012 Elsevier B.V. All rights reserved.
  • Ke Ye, Yoshitaka Aoki, Etsushi Tsuji, Shinji Nagata, Hiroki Habazaki
    JOURNAL OF POWER SOURCES 205 194 - 200 0378-7753 2012/05 
    Amorphous ZrO2-WO3-SiO2 nanofilms are simply prepared by anodizing of sputter-deposited Zr37W47Si16 alloy at several formation voltages for 1.8 ks in 0.1 mol dm(-3) phosphoric acid electrolyte at 20 degrees C. Efficient proton conductivity was observed after thermal treatment at 250 degrees C with the conductivity enhanced by reducing the film thickness. The conductivity is enhanced more than one order of magnitude by reducing the thickness from 300 to 140 nm. The anodic oxide films consist of two layers, comprising a thin outer ZrO2 layer free from silicon and tungsten species and an inner main layer containing all zirconium, silicon and tungsten species. The thickness-dependent conductivity of the anodic ZrO2-WO3-SiO2 films is associated with the conductivity of the outer ZrO2 layer, which increases exponentially with reducing the film thickness. The area-specific resistivity of 0.14 Omega cm(2), which is below the minimum requirement (0.2 Omega cm(2)) for a practical electrolyte membrane in commercial fuel cells, is achieved at a temperature at 225 degrees C for 100 nm-thick anodic ZrO2-WO3-SiO2 films. (C) 2012 Elsevier B.V. All rights reserved.
  • S. Komiyama, E. Tsuji, Y. Aoki, H. Habazaki, M. Santamaria, F. Di Quarto, P. Skeldon, G. E. Thompson
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 16 (4) 1595 - 1604 1432-8488 2012/04 
    The growth behavior of amorphous anodic films on Ta-Nb solid solution alloys has been investigated over a wide composition range at a constant current density of 50 A m(-2) in 0.1 mol dm(-3) ammonium pentaborate electrolyte. The anodic films consist of two layers, comprising a thin outer Nb2O5 layer and an inner layer consisting of units of Ta2O5 and Nb2O5. The outer Nb2O5 layer is formed as a consequence of the faster outward migration of Nb5+ ions, compared with Ta5+ ions, during film growth under the high electric field. Their relative migration rates are independent of the alloy composition. The formation ratio, density, and capacitance of the films show a linear relation to the alloy composition. The susceptibility of the anodic films to field crystallization during anodizing at constant voltage increases with increasing niobium content of the alloy.
  • Masahiro Seo, Koji Fushimi, Yoshitaka Aoki, Hiroki Habazaki, Masayuki Inaba, Mitsutoshi Yokomizo, Takazumi Hayakawa, Takenori Nakayama
    JOURNAL OF ELECTROANALYTICAL CHEMISTRY 671 7 - 15 1572-6657 2012/04 
    In situ X-ray absorption spectroscopy (XAS) using a synchrotron radiation was applied to identify the Pb species adsorbed on Ni surface in acidic perchlorate solution containing 10(-4) M Pb2+ with relation to the Pb-induced stress corrosion cracking (Pb-SCC) of Ni-base alloys used as tubing materials of steam generators in nuclear power plants. The periodical emersion method under potentiostatic polarization, using the Ni plate with large specific surface area (surface roughness, S-r = 78.3) as a working electrode, was developed to detect sensitively the sub-monolayer coverage of Pb on Ni. The Pb L-III absorption spectra in a scanning XAS mode were measured by monitoring the Pb L alpha fluorescence line. The Pb L-III absorption near-edge structure (XANES) at the potential more positive than -0.245 V (SHE) corresponding to the equilibrium potential of Pb-electrodeposition in 10(-4) M Pb2+ solution has revealed that the Pb species adsorbed on the Ni surface are metallic, providing the clear evidence of underpotential deposition (UPD) of Pb on the Ni surface. Moreover, the extended X-ray absorption fine structure (EXAFS) analysis was performed with a two-shell fit involving Pb-Ni and Pb-Pb interactions assuming that the Ni (1 1 1) plane is mainly exposed to the solution. The EXAFS results were convincingly explained in terms of the Pb-UPD model which represents the coexistence of the surface alloy phase and the adlayer with the same p(2 x 2) structure in the narrow potential range of -0.185 V (SHE) to -0.245 V (SHE). (C) 2012 Elsevier B.V. All rights reserved.
  • Santosh Prasad Sah, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    CORROSION SCIENCE 55 90 - 96 0010-938X 2012/02 
    Sequential anodic and cathodic pulse voltages were applied on anodised Al micro-electrodes in alkaline silicate electrolyte to explore the role of cathodic pulse in AC or bipolar plasma electrolytic oxidation (PEO) process. SEM observation was carried out to observe the sites of anodic and cathodic breakdown and their morphologies. The prior anodic breakdown accelerated the cathodic breakdown at -50 V, and the acceleration was associated with the preferential cathodic breakdown at the anodic breakdown sites. However, the succeeding anodic breakdown during applying anodic pulse of 420 V for 2 ms was highly suppressed at the cathodic breakdown sites. This would randomise the anodic breakdown sites. Such role may contribute to the formation of rather uniform coatings on aluminium in this electrolyte without large discharge channels when larger cathodic current is applied with respect to the anodic current in AC PEO. (C) 2011 Elsevier Ltd. All rights reserved.
  • Yoshitaka Aoki, Akihisa Harada, Aiko Nakao, Toyoki Kunitake, Hiroki Habazaki
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 14 (8) 2735 - 2742 1463-9076 2012 
    The finite size effect of proton conductivity of amorphous aluminosilicate thin films, a-AlnSi1-nOx (n = 0.07, 0.1, 0.2, 0.3 and 0.45), prepared by a sol-gel process was investigated by experimental and numerical techniques. High-resolution TEM clarified that a-AlnSi1-nOx films had the heterogeneous nanoscale microstructures comprised of the ion-conducting, condensed glass microdomain and the poor-conductive, uncondensed glass microdomain. s of the films with n <= 0.1 exponentially increased upon decreasing thickness in the sub-100 nm range because the volume fraction of conductive domains was less than the percolation threshold and cluster size scaling of the conductive domain was operative. The numerical simulation suggested that conductance of the condensed domain was higher than that of the uncondensed domain by 2 orders of magnitude. Volume fractions of the condensed domain increased with increasing Al/Si molar ratio and were over the percolation threshold (24.5%) with n >= 0.2. However, conductance of the condensed domain decreased with increasing Al/Si ratio with n >= 0.2 because the aluminosilicate glass framework made of 4-fold-connected MO4 tetrahedra was deformed by forming the octahedral AlO6 moieties, as checked by Al K-edge XAS. It was found that the optimal Al/Si composition in terms of the conductance of the condensed domain is not in coincidence with that in terms of the average conductivity of the films.
  • A. Baron-Wiechec, O. Ekundayo, S. J. Garcia-Vergara, H. Habazaki, H. Liu, P. Skeldon, G. E. Thompson
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 159 (7) C312 - C317 0013-4651 2012 
    Film morphologies and ionic migration are investigated for anodic oxides formed galvanostatically on electropolished aluminum in selenate electrolyte. Anionic selenium species that migrate at similar to 0.2 to 0.3 times the rate of O2- ions were present in barrier films. Further, porous films could be generated by the use of sputtering-deposited aluminum substrates, although the film thickness is limited to similar to 70 nm. Re-anodizing in pentaborate electrolyte at high efficiency revealed also a cationic selenium species that migrates at similar to 0.6 to 0.7 times the rate of Al3+ ions, suggesting that the migration of selenium is affected by the morphology and growth mechanism of the film. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.044207jes] All rights reserved.
  • F. Di Franco, G. Zampardi, M. Santamaria, F. Di Quarto, H. Habazaki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 159 (1) C33 - C39 0013-4651 2012 
    Tantalum oxide, niobium oxide and Ta-Nb containing mixed oxides were grown by anodizing sputter-deposited Ta, Nb and Ta-Nb alloys of different compositions. A photoelectrochemical investigation was performed in order to estimate the band gap and the flat band potential of the oxides as a function of their composition. The band gap of the investigated Ta-Nb containing mixed oxides changed monotonically between those estimated for Ta(2)O(5) (4.1 eV) and Nb(2)O(5) (3.4 eV) and in agreement with a proposed correlation between the Band gap of an oxide and the difference of electronegativity of the oxide constituents. From the differential capacitance curves recorded in a wide range of electrode potential and for several frequencies of the alternative signal, the dielectric constant of the investigated oxides were estimated. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.031201jes]
  • F. Di Franco, M. Santamaria, F. Di Quarto, E. Tsuji, H. Habazaki
    ELECTROCHIMICA ACTA 59 382 - 386 0013-4686 2012/01 
    Anodic oxides were grown on sputter-deposited Ta in different aqueous solutions. A photoelectrochemical investigation was performed in order to estimate the band gap of the films as a function of the anodizing bath composition and formation voltage, i.e. thickness. Photoelectrochemical results provided evidence of sub-band gap photocurrent for films formed in a bath containing ammonium ions at pH 9. Elemental depth profiles obtained by glow discharge optical emission spectroscopy revealed the presence of nitrogen species in the outer part of the anodic films, which is bonded to Ta according to XPS analysis. A mechanism of nitrogen incorporation is proposed in order to account for the pH dependence of film composition. (C) 2011 Elsevier Ltd. All rights reserved.
  • Alexander Mozalev, Rosa Maria Vazquez, Raul Calavia, Carla Bittencourt, Francesc Gispert-Guirado, Eduard Llobet, Jaromir Hubalek, Hiroki Habazaki
    NANOCON 2012, 4TH INTERNATIONAL CONFERENCE 33 - 38 2012 
    Niobium oxide is now starting to replace tantalum oxide as a dielectric material in specific capacitors, being also applied to optic-electronic screens and solar-energy conversion cells since the oxide shows electrochromic and photoelectrochemical properties. In this work, we have synthesized nanosized niobium and niobium-aluminium mixed-oxide films with unique self-organized morphology and assessed their applicability to chemical sensors and capacitor dielectrics.Experimental samples were Al/Nb layers sputtered-deposited onto Si wafers and anodized at voltages 25 to 52 V, this followed by reanodizingto a more anodic voltage, which caused the growth of a porous alumina film, followed by pore-assisted oxidation of the niobium underlayer. The samples were annealed at 600-800 degrees C to examine crystallization and phase transition effects.The films were found to consist of discrete metal-oxide nano-columns, penetrating the alumina pores, in addition to a lower solid portion that forms under the pores. The films are mainly composed ofmixed Nb2O5-Al2O3 (columns) and niobium suboxides (solid portion). The as anodized films show perfect dielectric behavior, while the annealing promotes formation of Nb(2)O(5)nano-crystallites with transformation to n-type semiconductor behavior. A test sensor employing the alumina-free nanocolumnarfilm exhibits gas sensing properties, responding, for example, to low concentrations of ethanol (5-20 ppm) at temperatures 150 to 200 degrees C.Potential applications of the films are as capacitor dielectrics, gas sensing layers, films with anisotropic conductivity, nanostructured supports for catalysts and many more.
  • F. Muratore, A. Baron-Wiechec, T. Hashimoto, A. Gholinia, H. Habazaki, P. Skeldon, G. E. Thompson
    ELECTROCHEMICAL AND SOLID STATE LETTERS 15 (5) C8 - C11 1099-0062 2012 
    A study of the distribution of species in a porous anodic film formed on a sputtered Zr-22 atom%W alloy in a fluoride/glycerol electrolyte is presented. The film consists of nanotubes within a fluoride-enriched matrix and forms with loss of similar to 24% of the oxidized zirconium to the electrolyte. In contrast, loss of tungsten species is negligible, these species being retained in the nanotubes and separated from the pores by a tungsten-free region of the film material. The results suggest that the nanotubes are generated by the flow of material away from the nanotube base into the tube walls. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.005206esl] All rights reserved.
  • F. Zhou, A. Baron-Wiechec, S. J. Garcia-Vergara, M. Curioni, H. Habazaki, P. Skeldon, G. E. Thompson
    ELECTROCHIMICA ACTA 59 186 - 195 0013-4686 2012/01 
    The formation of porous anodic alumina in 0.4 M oxalic acid is investigated over a range of current density and electrolyte temperature using sputtering-deposited substrates containing tungsten tracer layers. The findings reveal volume expansion factors and efficiencies of film growth that increase with the increase of the current density and decrease of the temperature. Pore generation by the flow of the anodic alumina in the barrier layer toward the pore walls is proposed to dominate at relatively high current densities (above 2 mA cm(-2)), with tungsten tracer species being retained within films. Conversely, losses of tungsten species occur at lower current densities, possibly due to increased field-assisted ejection of Al3+ ions and/or field-assisted dissolution of the anodic alumina. (C) 2011 Elsevier Ltd. All rights reserved.
  • Hiroki Habazaki, Maria Janik Czachor, Pawel Kulesza
    APPLIED SURFACE SCIENCE 257 (19) 8139 - 8140 0169-4332 2011/07
  • F. Di Franco, G. Zampardi, M. Santamaria, F. Di Quarto, H. Habazaki
    PHYSICS AND TECHNOLOGY OF HIGH-K MATERIALS 9 41 (3) 293 - 310 1938-5862 2011 
    Tantalum oxide, niobium oxide and Ta-Nb containing mixed oxides were grown by anodizing sputter-deposited TaxNb(1-x) alloys with 0 <= x <= 1. A photoelectrochemical investigation was performed in order to estimate the band gap values of the oxides as a function of their composition as well as to estimate their flat band potential. Differential capacitance, C, curves were recorded for all the investigated oxides in a wide range of electrode potential and for several frequencies of the alternative signal. The dependence of C on the applied potential and a. c. frequency was interpreted on the basis of amorphous semiconductor Schottky barrier, and allowed to estimate the dielectric constant of the investigated oxides.
  • F. La Mantia, H. Habazaki, M. Santamaria, F. Di Quarto
    RUSSIAN JOURNAL OF ELECTROCHEMISTRY 46 (11) 1306 - 1322 1023-1935 2010/11 
    The widespread use of the Mott-Schottky plots to characterize the energetics of passive film/electrolyte junction is critically reviewed in order to point out the limitation of such approach in describing the electronic properties of passive film as well in deriving the correct location of the characteristic energy levels of the junction. The frequency dependency of M-S plots frequently observed in the experimental data gathered in a sufficiently large range of frequency is extensively discussed for a relatively thick (160 nm) thermally aged amorphous niobia (alpha-Nb2O5) film immersed in electrolytic solution. The relatively simple equivalent electrical circuit describing an ideally blocking behaviour of the junction allows a direct comparison of the experimental data analysis based on the use of Mott-Schottky or amorphous semiconductor Schottky barrier interpretative models. Moreover the theoretical simulations of the M-S plots based on the theory of crystalline semiconductor suggest an electronic structure of the investigated passive film containing a distribution of localized electronic states deep lying in energy in agreement with the model of amorphous semiconductor Schottky barrier.
  • Hiroki Habazaki
    CORROSION SCIENCE 51 (7) 1481 - 1481 0010-938X 2009/07
  • Y. Oikawa, K. Fushimi, Y. Aoki, H. Habazaki
    ECS Transactions 16 (3) 345 - 351 1938-5862 2008 [Refereed][Not invited]
     
    Porous anodic films have been developed on niobium at constant formation voltages between 5 and 50 V in glycerol electrolyte containing 0.8 mol dm -3 dibasic potassium phosphate at 433 K. Except at the formation voltage of 5 V, at which the current density is approximately constant during anodizing, the current shows the minimum and then maximum. After the current maximum, the current density decreases gradually, which follows the Cottrell equation. Thus, diffusion of some species in the pores should control the growth rate of the anodic films. The porous films developed are practically Nb 2O5 with a small amount of carbon contamination. Incorporation of phosphorus species, which often occurs in aqueous electrolytes, is negligible at all the formation voltages in the present electrolyte. Based on the results obtained, the growth process of the porous anodic films on niobium in this hot organic electrolyte is discussed. © The Electrochemical Society.
  • MA Arenas, L Iglesias-Rubianes, Y Liu, P Skeldon, GE Thompson, H Habazaki, K Shimizu, P Bailey, TCQ Noakes
    CORROSION SCIENCE 47 (9) 2321 - 2331 0010-938X 2005/09 
    The enrichments of zinc developed in binary, solid solution Al-0.3at.%Zn, Al-0.4at.%Zn and Al-1at.%Zn alloys by electropolishing and alkaline etching are examined using Rutherford backscattering spectroscopy and medium energy ion scattering with additional interest in how such enrichments affect the corrosion potentials of the alloys. During alkaline etching in 0.1 M sodium hydroxide solution, significant enrichments of zinc arise in the alloy, similar to that achieved by an anodizing treatment. However, enrichment is unusually low following electropolishing in perchloric acid solution. Contrary to the effect of enriched copper in Al-Cu alloys, zinc enrichment has minor influence on the corrosion potentials of etched alloys in ammonium pentaborate solution, which remain roughly within +/-100 mV of those of non-enriched alloys. (C) 2004 Elsevier Ltd. All rights reserved.
  • H Habazaki, T Ogasawara, H Konno, K Shimizu, K Asami, K Saito, S Nagata, P Skeldon, GE Thompson
    ELECTROCHIMICA ACTA 50 (27) 5334 - 5339 0013-4686 2005/09 
    The present study is directed at understanding of the influence of oxygen in the metal on anodic film growth on niobium, using sputter-deposited niobium containing from about 0-52 at.% oxygen, with anodizing carried out at high efficiency in phosphoric acid electrolyte. The findings reveal amorphous anodic niobia films, with no significant effect of oxygen on the field strength, transport numbers, mobility of impurity species and capacitance. However, since niobium is partially oxidized due to presence of oxygen in the substrate, less charge is required to form the films, hence reducing the time to reach a particular film thickness and anodizing voltage. Further, the relative thickness of film material formed at the metal/film interface is increased by the incorporation of oxygen species into the films from the substrate, with an associated altered depth of incorporation of phosphorus species into the films. (C) 2005 Elsevier Ltd. All rights reserved.
  • H Habazaki, K Shimizu, S Nagata, K Asami, K Takayama, Y Oda, P Skeldon, GE Thompson
    THIN SOLID FILMS 479 (1-2) 144 - 151 0040-6090 2005/05 
    Crystalline anodic oxide films have been formed on sputter-deposited zirconium and Zr-Ti alloys in 0.1 mol dm(-3) ammonium pentaborate electrolyte, with their structure, composition, dielectric properties and growth behaviour examined using X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and electrochemical impedance spectroscopy. The films formed on zirconium consist of a high-temperature stable ZrO2 phase (cubic or tetragonal) as well as monoclinic ZrO2, with the latter predominant with increasing formation voltage. The incorporation of titanium species into the films stabilizes the high-temperature phase up to high voltages. Associated with the change in the crystalline structure with the incorporation of titanium species, the permittivities of the oxides increase, in agreement with the higher permittivity of bulk cubic and tetragonal ZrO2 containing stabilizing cations compared with that of bulk monoclinic ZrO2. The transport number of cations during crystalline oxide growth is about 0.05, irrespective of titanium incorporation. (c) 2004 Elsevier B.V. All rights reserved.
  • H Konno, T Kinomura, H Habazaki, M Aramata
    SURFACE & COATINGS TECHNOLOGY 194 (1) 24 - 30 0257-8972 2005/04 
    Two types of silicone compounds and a trace amount of Pt catalyst were impregnated into exfoliated graphite (EG) by sorption and cured under different conditions. By this process, graphite sheets composing EG were coated with very thin (<< 1 gm) silicone layer. Thus, obtained precursors were converted to oxidation resistant graphite flakes by the beat-treatment at a temperature in a range of 1000- 1300 degrees C for 1 h in inert atmosphere. The coatings were intact and they were mixtures of Si-C-O glass-like composites and amorphous silica, which were confirmed by SEM, XRD and MAS-NMR. As formed graphite flakes showed instantaneous mass losses of 5-13% by oxidation at 1000 degrees C for 1 h in pure O-2, but after that the mass change was very small. By removing free carbons on the surface beforehand, the mass loss became less than 1% for all products. The mass loss of the sample molded into a disk-shape was about 1% after the first cycle (1 h) of repetitive oxidation at 1000 degrees C in air but from the second cycle an appreciable mass loss was not observed up to 20 h. The present method is promising for the production of oxidation resistant graphite flakes. (c) 2004 Elsevier B.V. All rights reserved.
  • Y Liu, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    CORROSION SCIENCE 47 (2) 341 - 354 0010-938X 2005/02 
    The study compares the formation of chromate/fluoride conversion coatings, composed mainly of amorphous hydrated chromia, on model, solid-solution, binary Al-Cu alloys, of a range of compositions, and on 2014-T6 aluminium alloy. The model alloys, produced by magnetron sputtering, reveal the importance of copper in limiting the thickness of the coatings by promoting loss of coating material. This occurs at an earlier time in the treatment with increasing copper content of the alloy. The coating loss follows closely upon the achievement of the required level of copper enrichment for incorporation of copper into the coating, with a thin alumina film beneath the hydrated chromia sustaining the enrichment process. The coating on the 2014-T6 alloy is of non-uniform thickness, with much thinner coating developing at copper-rich second phases, consistent with the results of model alloys. (C) 2004 Elsevier Ltd. All rights reserved.
  • K Asami, H Habazaki, A Inoue, K Hashimoto
    NEW FRONTIERS OF PROCESSING AND ENGINEERING IN ADVANCED MATERIALS 502 225 - 230 0255-5476 2005 
    Recent development of corrosion resistant bulk glassy alloys such as Zr-, Fe-, Ni- and Cu-base alloys were presented. It was clarified that the enrichment of cations in the passive film, which is responsible to corrosion resistance, depends on both alloy composition and environment. TEM observation also made it clear that alloys lose their advantageous properties such as corrosion resistance when they are devoid of or lose amorphous structure even in part due to low glass forming ability or heating. These findings were essentially similar to those of conventional amorphous alloys.
  • H Habazaki, M Uozumi, H Konno, K Shimizu, S Nagata, K Takayama, Y Oda, P Skeldon, GE Thompson
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 152 (8) B263 - B270 0013-4651 2005 
    The influence of tungsten on an amorphous-to-crystalline transition, leading to formation of anatase, and dielectric properties is examined for anodic oxides on Ti-W alloys. The structural change, which occurs at voltages of similar to 10 V on high- purity titanium, and provides sites for generation of high- pressure gas oxygen bubbles, is suppressed to progressively increased voltages by increasing tungsten content of the film. Phosphorus species, derived from the electrolyte, also hinder the change. The tungsten species are located in the inner similar to 80% of the film thickness as result of the faster migration of Ti4+ ions relative to that of W6+ ions in the growing oxide. Although the reported permittivity of anodic tungsten oxide is higher than that of amorphous anodic titania, the permittivity of the films on alloys decreases gradually with increasing tungsten content. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1940750] All rights reserved.
  • Y Liu, AM Arenas, SG Garcia-Vergara, P Skeldon, GE Thompson, K Shimizu, H Habazaki
    CORROSION SCIENCE 47 (1) 145 - 150 0010-938X 2005/01 
    Conversion coatings have been formed in two stages on sputtering-deposited aluminium using a chromate/fluoride bath. The first stage, common to all specimens, was conversion treatment for 1 min to produce a coating of thickness of about 70 nm, with associated thinning of the aluminium substrate. Further treatment was then carried out for 13 min, either immediately or with intervening ageing in humid air, water or laboratory air. Notably, ageing in laboratory air for 1 h was sufficient to prevent significant growth of new coating material upon re-immersion in the coating bath. In contrast, ageing in humid air or water allowed additional thickening of the coating, although with a reduced growth rate. The behaviour appears to be related to loss of free or weakly bound water from the coatings in laboratory air, with the composition and structure of the coating being modified such that transport of reactant and product species of the coating process is impeded. (C) 2004 Elsevier Ltd. All rights reserved.
  • Q Lu, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    THIN SOLID FILMS 471 (1-2) 118 - 122 0040-6090 2005/01 
    The unusual occurrence of anodic films of unlimited thickness has been recently reported for anodizing of tantalum in certain dehydrated, high-temperature electrolytes with organic solvents. The precise nature of these films is still uncertain. In the present work, non-thickness-limited (NTL) anodic films were formed at 0.1 mA cm(-2) on aluminium and tantalum in glycerol/phosphate electrolyte at 453 K and then examined by Rutherford backscattering spectroscopy (RBS). The results disclosed films composed of alumina and tantala, free of phosphorus 3 species at the resolution of the measurements. Most notably, the densities of the NTL alumina and tantala were about 2.4 and 3.6 g cm(-3), respectively. These values are less than those of compact anodic films of the type usually grown at high efficiency in aqueous electrolytes by respective factors of about 1.3 and 2.2. This difference in density is attributed primarily to the morphology and structure of NTL film materials, which incorporate significant porosity. (C) 2004 Elsevier B.V. All rights reserved.
  • Q Lu, T Hashimoto, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    ELECTROCHEMICAL AND SOLID STATE LETTERS 8 (5) B17 - B20 1099-0062 2005 
    High-resolution transmission electron microscopy and electron energy loss spectroscopy/energy-dispersive X-ray analysis were employed to reveal the development of nanoporous, amorphous anodic oxide films on niobium. The oxide was formed at 10 A m(-2) in a dehydrated phosphate/glycerol electrolyte at 453 K. The relatively nonuniform pore network comprised pores about 5 nm wide, which connect the film surface to an similar to 5 nm thick barrier layer at the film base. The film is presumed to grow at the metal/oxide interface by inward migration of O2- ions through the barrier layer, while field-assisted dissolution proceeds at the pore bases. (C) 2005 The Electrochemical Society.
  • F Monfort, A Berkani, E Matykina, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 152 (6) C382 - C387 0013-4651 2005 
    Sequential anodizing is employed to investigate the mechanism of coating growth on aluminum under sparking in a phosphate electrolyte. Thus, coatings are formed in a silicate electrolyte and then in the phosphate electrolyte, with the location of phosphorus in the final coating being identified by electron probe microanalysis. The presence of silicon primarily in the outer region of the coating and of phosphorus primarily in the inner region of the coating indicates short-circuit transport of phosphorus species through the coating, with new coating material being formed in the vicinity of the metal/coating interface. The transport path is presumed to be associated with pores, cracks, and channels in the coating produced by dielectric breakdown events. (c) 2005 The Electrochemical Society. All rights reserved.
  • Q Lu, P Skeldon, GE Thompson, D Masheder, H Habazaki, K Shimizu
    CORROSION SCIENCE 46 (11) 2817 - 2824 0010-938X 2004/11 
    The transport numbers of metal and oxygen species have been determined in amorphous anodic tantala films, using transmission electron microscopy to locate ion-implanted xenon marker layers within the films. The films were formed on sputtering-deposited tantalum at constant current density, in the range 0.01-10 mA cm(-2), in 0.06 wt% H3PO4 solution at either 20 or 85 degreesC. The films grow by migration of metal and oxygen species through the film thickness, with formation of new film material at the film/electrolyte and metal/film interfaces respectively. The cation transport number, t(+), increases due to either increase in current density or decrease in temperature: for current densities in the selected range, t(+) increases from 0.18 to 0.32 at 20 degreesC and from 0.14 to 0.29 at 85 degreesC. Low concentrations of phosphorus species, incorporated into an outer layer of the film, migrate inward during film growth. The migration rates are slower than those of oxygen species, by a factor in the range 0.2-0.3. (C) 2004 Elsevier Ltd. All rights reserved.
  • M Abulsain, A Berkani, FA Bonilla, Y Liu, MA Arenas, R Skeleton, GE Thompson, P Bailey, TCQ Noakes, K Shimizu, H Habazaki
    ELECTROCHIMICA ACTA 49 (26) 4803 - 4803 0013-4686 2004/10
  • Y Aoki, H Habazaki, H Konno
    CHEMISTRY LETTERS 33 (8) 992 - 993 0366-7022 2004/08 
    The novel sensing property of neodymium (III) chromate(V), NdCrO4, to methanol has been demonstrated. The electrical response of this compound did not rely on the surface potential change by the interaction with methanol gas, but was instead due to the redox interconversion of zircon-type (NdCrO4)-O-V to KDP-type (NdH2CrO4)-O-III. The NdCrO4 film prepared on alumina substrates with 2.5-mum thickness could respond to methanol of ppm order concentration with an apparent increase in electrical resistance.
  • H Habazaki, H Konno, K Shimizu, S Nagata, P Skeldon, GE Thompson
    CORROSION SCIENCE 46 (8) 2041 - 2053 0010-938X 2004/08 
    Enrichment of nickel at the alloy/film interface and incorporation of nickel species into the anodic film have been examined for a sputtering-deposited Al-1.2at.%Ni alloy in order to assist understanding of oxygen generation in barrier anodic alumina films. Anodizing of the alloy proceeds in two stages similarly to other dilute aluminium alloys, for example Al-Cr and Al-Cu alloys, where the Gibbs free energies per equivalent for formation of alloying element oxide exceeds the value for alumina. In the first stage, a nickel-free alumina film is formed, with nickel enriching in an alloy layer, 2 nm thick, immediately beneath the anodic oxide film. In the second stage, nickel atoms are oxidized together with aluminium, with oxygen generation forming gas bubbles within the anodic oxide film. This stage commences after accumulation of about 5.4 x 10(15) nickel atoms cm(-2) in the enriched alloy layer. Oxygen generation also occurs when a thin layer of the alloy, containing about 2.0 x 10(19) nickel atoms m(-2), on electropolished aluminium, is completely anodized, contrasting with thin Al-Cr and Al-Cu alloy layers on electropolished aluminium, for which oxygen generation is essentially absent. A mechanism of oxygen generation, based on electron impurity levels of amorphous alumina and local oxide compositions, is discussed in order to explain the observations. (C) 2004 Elsevier Ltd. All rights reserved.
  • M Abulsain, A Berkani, FA Bonilla, Y Liu, MA Arenas, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, K Shimizu, H Habazaki
    ELECTROCHIMICA ACTA 49 (6) 899 - 904 0013-4686 2004/03 
    Metastable, solid-solution Mg-0.8 at.% Cu and Mg-1.4 at.% Zn alloys have been anodized up to 250 V at 10 mA cm(-2) in an alkaline phosphate electrolyte at 293 K in order to investigate the enriching of alloying elements beneath the anodic films. Rutherford backscattering spectroscopy (RBS) revealed enrichments to about 4.1 X 10(15) Cu atoms cm(-2) and 5.2 x 10(15) Zn atoms cm(-2), which correlate with the higher standard Gibbs free energies per equivalent for formation of copper and zinc oxides relative to that for formation of MgO. The enriched layers were of thickness about 1.5-4.0 nm by medium energy ion scattering (MEIS). The anodic films, composed mainly of magnesium hydroxide, contained copper and zinc species throughout their thicknesses; the Cu:Mg and Zn:Mg atomic ratios were about 18 and 25% of those of the alloys, respectively. Phosphorus species were present in most of the film regions, with a P:Mg atomic ratio of about 0.16. The magnesium ions in the film account for about 30% of the charge passed during anodizing. (C) 2003 Elsevier Ltd. All rights reserved.
  • Y Liu, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    CORROSION SCIENCE 46 (2) 297 - 312 0010-938X 2004/02 
    The growth kinetics of chromate/fluoride conversion coatings are examined for 99.99% aluminium, and Al-2.3at.%Cu, Al-1.9at.%Au and Al-20at.%Au alloys. The thickening of coatings and thinning of substrates, the latter deposited by magnetron sputtering, are determined by transmission electron microscopy. The results reveal consumption of substrates during the coating process, to the maximum immersion time of 24 min. Initial relatively rapid thinning in the period to 6 min is followed by slower, approximately constant thinning at about 9.3, 6.2, 6.0 and 5.4 nm min(-1) for the 99.99%Al, Al-2.3at.%Cu, Al-1.9at.%Au and Al-20at.%Au alloys respectively. The ratio of the number of chromium atoms in the conversion coating, determined by Rutherford backscattering spectroscopy, to the number of oxidized substrate atoms is about 3, indicating a low efficiency of coating growth. Alloying decreases the coating thickness, as well as metal consumption. Alloying elements initially enrich beneath the coating, in alloy layers of a few nanometres thickness. Later, copper may be oxidized, and then enter the coating, whereas gold is occluded as nanoparticles. The gold nanoparticles act as markers to indicate formation of coating material at the metal/coating interface. Sudden loss of coating on the alloys, after about 6-9 min, occurs soon after entry of alloying element species into the coating. The loss may be related to the presence of nanoparticles of gold and copper near the alloy/coating interface, the latter possibly forming by reduction of copper species, that disrupt the bonding of the coating either directly though their presence or through their action as local cathodes. (C) 2003 Elsevier Ltd. All rights reserved.
  • S Garcia-Vergara, F Colin, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 151 (1) B16 - B21 0013-4651 2004/01 
    Using Al-Cu alloys, containing between 0.1 and 26 atom % Cu, deposited by magnetron sputtering and etching in sodium hydroxide solution, enrichments of copper have been developed selectively in the alloys. Rutherford backscattering spectroscopy and medium energy ion scattering quantified the enrichments and their locations just beneath the alumina-based oxides remaining from the etching. In some cases, the enrichment was sufficient for oxidation of copper to take place; in other cases, it was not, so that only aluminum was oxidized, with copper being confined to the alloy, enriching in an alloy layer about 2 nm thick. The potentials of the etched alloys in 0.1 M ammonium pentaborate solution at 293 K increased as the copper content of the enriched alloy layer increased. The enrichment of copper in the alloy beneath an alumina-based film free of copper species, i.e., without requirement for oxidation of copper and incorporation of copper species into the oxide, was sufficient to generate increases in potential of similar magnitude to those found for specimens in which oxidation of copper had taken place. The potential increased by similar to410 mV with an increase in the level of enrichment to similar to6.5x10(15) Cu atoms cm(-2). (C) 2003 The Electrochemical Society.
  • H Konno, S Sato, H Habazaki, M Inagaki
    CARBON 42 (12-13) 2756 - 2759 0008-6223 2004
  • K Shimizu, R Payling, H Habazaki, P Skeldon, GE Thompson
    JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 19 (5) 692 - 695 0267-9477 2004 
    The first example of depth profiling analysis, by rf-GDOES, of a layer of sub-nanometre thickness is presented. The example selected is that of a monolayer of thiourea adsorbed on a mirror-polished copper substrate. The adsorbed layer is disclosed clearly in the depth profile as narrow peaks, above the copper substrate, of carbon, hydrogen, nitrogen and sulfur. Further, the positions of peaks are separated and located in the order that is expected from the orientation of the thiourea molecules adsorbed on the copper substrate, namely the nitrogen peak was observed prior to the sulfur peak.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, H Habazaki, K Shimizu
    CORROSION SCIENCE 45 (12) 2915 - 2923 0010-938X 2003/12 
    The effect of oxidation rate on enrichment of tungsten in metastable, solid-solution Al-W alloys during anodizing has been investigated by Rutherford backscattering spectroscopy and medium energy ion scattering. The oxidation rate has negligible influence upon enrichment for current densities in the range 0.01-100 mA cm(-2), with levels between 1.3 x 10(15) and 1.5 x 10(15) W atoms cm(-2) for an Al-0.7at.%W alloy. Further, enrichment factors, expressing the ratio of the enrichment of tungsten in the alloy, in units of 10(15) atoms cm(-2), to the bulk composition of the alloy, in units of at.%, for alloys of compositions in the range 0.1-30 at.%W, decrease progressively in the approximate range 2.5-0.2. (C) 2003 Elsevier Ltd. All rights reserved.
  • S Mato, G Alcala, GE Thompson, P Skeldon, K Shimizu, H Habazaki, T Quance, MJ Graham, D Masheder
    CORROSION SCIENCE 45 (12) 2881 - 2892 0010-938X 2003/12 
    The behaviour of iron during anodizing of sputter-deposited Ta/Fe alloys in ammonium pentaborate electrolyte has been examined by transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. Anodic films on Ta/1.5 at.% Fe, Ta/3 at.% Fe and Ta/7 at.% Fe alloys are amorphous and featureless and develop at high current efficiency with respective formation ratios of 1.67, 1.60 and 1.55 nm V-1. Anodic oxidation of the alloys proceeds without significant enrichment of iron in the alloy in the vicinity of the alloy/film interface and without oxygen generation during film growth, unlike the behaviour of Al/Fe alloys containing similar concentrations of iron. The higher migration rate of iron species relative to that of tantalum ions leads to the formation of an outer iron-rich layer at the film surface. (C) 2003 Elsevier Ltd. All rights reserved.
  • TH Teh, A Berkani, S Mato, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    CORROSION SCIENCE 45 (12) 2757 - 2768 0010-938X 2003/12 
    The initial stages of oxide growth on titanium are examined in a recently developed commercial alkaline pyrophosphate/aluminate electrolyte of interest for plasma electrolytic oxidation of light metal alloys. Constant current anodizing was employed, with resultant films examined by scanning and transmission electron microscopies and Rutherford backscattering spectroscopy. The initial film is relatively uniform and composed of TiO2, with low concentrations of aluminium and phosphorus species incorporated from the electrolyte. With increase in voltage the film breaks down locally, and regions of original and modified film develop simultaneously, with the latter occupying more of the surface as the voltage rises. Porous regions due to dielectric breakdown also become increasingly evident. At similar to240 V, sparking commences, and the surface reveals extensive, relatively uniform porosity, with the coating now containing much enhanced concentrations of aluminium and phosphorus species compared with the coating at lower voltages. The films develop at low efficiency due to generation of oxygen. The oxygen is produced within the original film material and at sites of dielectric breakdown. The former type of film develops a two-layered morphology, with an outer layer of amorphous TiO2 and an inner layer with numerous fine and course cavities. The cavities are due to the generation of oxygen that may be associated with the formation of anatase in the inner layer. (C) 2003 Elsevier Ltd. All rights reserved.
  • H Habazaki, T Matsuo, H Konno, K Shimizu, S Nagata, K Matsumoto, K Takayama, Y Oda, P Skeldon, GE Thompson
    ELECTROCHIMICA ACTA 48 (23) 3519 - 3526 0013-4686 2003/10 
    The influence of incorporation of silicon species on the electric properties of anodic niobia, formed in 0.1 mol dm(-3) ammonium pentaborate electrolyte, has been examined using sputter-deposited Nb-Si alloys containing 5 and 17 at.% silicon. The potential dependence of the capacitance of anodic niobia, originating from its n-type semiconducting properties, becomes less significant by incorporation of silicon species. In addition, the leakage current decreases with increasing silicon content in the alloy. The thermal stability of the anodic niobia is also enhanced by silicon species; the capacitance and leakage current, which increase significantly for niobium, are little influenced by annealing up to 523 K. The silicon species are incorporated in the inner 72% of the film thickness, as a consequence of immobility of the species in growing anodic niobia. The immobility of silicon species is associated with a strong Si4+ -O bond, which may also contribute to the reduction of leakage current. (C) 2003 Elsevier Ltd. All rights reserved.
  • H Habazaki, M Uozumi, H Konno, K Shimizu, P Skeldon, GE Thompson
    CORROSION SCIENCE 45 (9) 2063 - 2073 0010-938X 2003/09 
    Crystallization of amorphous anodic films grown at constant current density on sputtering-deposited titanium, and Ti-Si and Ti-Al alloys, in ammonium pentaborate electrolyte, has been examined directly by transmission electron microscopy. In the case of titanium, anatase develops at relatively low voltage in the inner film region, formed by inward migration of oxygen species. In contrast, the outer film region, formed at the film/electrolyte interface, is composed of amorphous oxide only. Oxide crystals are particularly found near the plane, separating the two regions, which is located at a depth of 35-38% of the film thickness. Oxide zones, of size similar to I nm, with a relatively ordered structure, developed at the metal/film interface, are considered to lead to transformation of the inner region structure. The incorporation into the film of either aluminium or silicon species suppresses the formation of crystalline oxide to much increased voltages. However, eventually nanocrystals form at similar to40% of the film thickness, probably originating from pre-cursor nuclei in the air-formed on the as-deposited alloy. (C) 2003 Elsevier Science Ltd. All rights reserved.
  • H Habazaki, M Uozumi, H Konno, K Shimizu, S Nagata, K Asami, K Matsumoto, K Takayama, Y Oda, P Skeldon, GE Thompson
    ELECTROCHIMICA ACTA 48 (20-22) 3257 - 3266 0013-4686 2003/09 
    Sputter-deposited Ti-Zr alloys of various compositions have been anodized at a constant current density in 0.1 mol dm(-3) ammonium pentaborate electrolyte at 298 K. The resultant anodic films have been characterized using transmission electron microscopy (TEM), glow discharge optical emission spectroscopy (GD-OES), Rutherford backscattering spectroscopy and capacitance measurements to elucidate the influence of alloy composition oil their structure, growth behavior and dielectric properties. The Ti-10.5 at.% Zr alloy reveals oxygen formation within the film above similar to 40 V, associated with crystallization of the anodic oxide to anatase. In contrast, amorphous anodic films, with a thin outer layer consisting of zirconium-free TiO2, grow up to about 250 V on Ti-23.0 at.% Zr and Ti-42.0 at.% Zr alloys at high current efficiency. Further increase in zirconium content to 62.5 at.% results in the formation of a film containing nanocrystals of monoclinic ZrO2 phase in an amorphous matrix. The crystalline oxide is formed predominantly in the inner region of the film that is developed by anion migration inward. An anodic Film composed of monoclinic ZrO2 throughout the film thickness is formed on the zirconium. The influences of structure and composition of the anodic films on their growth behavior and dielectric properties are discussed and compared with findings for Al-Ta alloys, which form amorphous oxides over the entire composition range. (C) 2003 Elsevier Science Ltd. All rights reserved.
  • S Mato, G Alcala, P Skeldon, GE Thompson, D Masheder, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 150 (9) B439 - B444 0013-4651 2003/09 
    Evidence is presented of compositional self-ordering in the amorphous anodic film that develops during anodizing of a Mg/40 atom % Ta alloy in sodium hydroxide electrolyte. This is manifested in an outer layer of film material, representing about 60% of the film thickness, that in cross section consists of bands, alternatively magnesium-rich and tantalum-rich, orientated normal to the film surface. Each band is typically about 10-20 nm wide. The remainder of the film is uniform in composition, comprising units of MgO and Ta2O5 in an amorphous network, similar to that of the tantalum-rich bands. The development of the bands is a consequence of the faster migration of Mg2+ ions relative to that of Ta5+ ions in the tantalum-rich oxide and the relatively high ionic resistance of the magnesium-rich material. Thus, ionic current flows preferentially through the tantalum-rich oxide, with compositional reorganization suggested to take place at the tips of the fingers close to the surface of the film. (C) 2003 The Electrochemical Society.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson
    SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY 58 (9) 1573 - 1583 0584-8547 2003/09 
    The capabilities of RF-GD-OES for depth profiling analysis are illustrated based on the recent results from the authors' laboratories. Through the analysis of a hard disk, a thin anodic alumina layer with a delta function marker layer, and a 5-nm thick air-formed oxide film on sputter deposited stainless steel, it is demonstrated that RF-GD-OES has enormous potential for depth profiling analysis of ultra-thin layers, less than 10-nm thick, as well as films of several tens of microns thickness. The remarkable features of RF-GD-OES arise from the nature of RF-GD sputtering where samples, conducting or non-conducting, are sputtered stably with Ar+ ions of very low energy (< 50 eV) and a current flux of the order of similar to100 mA cm(-2). (C) 2003 Elsevier Science B.V. All rights reserved.
  • G Alcala, S Mato, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, H Habazaki, K Shimizu
    CORROSION SCIENCE 45 (8) 1803 - 1813 0010-938X 2003/08 
    The ionic transport numbers, relative migration rates of cation species and formation ratios are reported for barrier anodic films formed on metastable, solid solution Al-Ta alloys, with compositions extending from the aluminium-rich to the tantalum-rich ends of the system. The data were obtained by marker experiments, using ion implanted xenon, transmission electron microscopy, Rutherford backscattering spectroscopy and medium energy ion scattering. The films are amorphous and form by migration of metal and oxygen species. The ionic transport numbers and the formation ratios depend approximately linearly upon the composition of the alloy, between the values for anodic alumina and anodic tantala. The migration rate of Al3+ ions exceeds that of Ta5+ ions, but reduces in relative magnitude as the tantalum content of film increases. The faster migration of Al3+ ions is consistent with the higher energy of the Ta5+-O bond compared with that of the Al3+-O bond. Due to the difference in mobilities of the cation species, the films comprise an outer layer of alumina and an inner layer containing units of both alumina and tantala. The two-layered films can develop fingers of inner layer oxide that penetrate the outer alumina layer due to the higher ionic resistivity of the alumina. Such channelling of current can lead to mixing of inner layer oxide and alumina and thereby hinder formation of an alumina layer, particularly in films on the more tantalum-rich alloys. (C) 2003 Elsevier Science Ltd. All rights reserved.
  • G Alcala, S Mato, P Skeldon, GE Thompson, AB Mann, H Habazaki, K Shimizu
    SURFACE & COATINGS TECHNOLOGY 173 (2-3) 293 - 298 0257-8972 2003/08 
    This work uses nanoindentation to determine the mechanical properties of barrier-type anodic alumina films formed on aluminium in ammonium pentaborate electrolyte. Using indents to a depth of similar to45 nm and a maximum load of 0.5 mN, with films of thicknesses 480 and 600 nm, values of similar to140 and similar to 8.5 GPa were indicated for the elastic modulus and the hardness, respectively. Lower values were obtained for deeper indents, at higher loads, and for specimens with thinner films. The reduction of hardness was consistent with the commonly applied rule that the indent depth should not exceed 10% of the film thickness in order to avoid influences of the substrate. Although substrate properties can affect modulus measurement to shallower depths, the similarity of results for the two thickest films suggests a reasonable estimate of the film property. (C) 2003 Elsevier Science B.V. All rights reserved.
  • S Mato, G Alcala, P Skeldon, GE Thompson, T Quance, MJ Graham, H Habazaki, K Shimizu, D Masheder
    PHILOSOPHICAL MAGAZINE 83 (23) 2733 - 2746 1478-6443 2003/08 
    Comparison is made of the influences of copper in the development of amorphous anodic films on Ta-Cu alloys, containing up to 57at.%Cu, in ammonium pentaborate electrolyte at 293 K. The various films are based on tantala. with low concentrations of copper, relative to those of the alloys, since copper species migrate through the films more rapidly than Ta5+ ions and are lost to the electrolyte on reaching the film Surface. Of particular interest, film growth on Ta-1.5at.% Cu alloy at 1, 0.1 and 0.01 mA cm(-2) proceeds with generation of oxygen, which is contained in nanoscale bubbles within the oxide. Bubbles are more numerous as the current density decreases. In the case of Ta-12 at.% Cu and Ta-57 at.% Cu alloys, the films are flawed extensively by more numerous oxygen bubbles, which are present mainly in the outer parts of the anodic films, oxygen production and film damage due to the bursting of bubbles limit the anodizing voltage to relatively low values. It is suggested that copper species modify the electron levels, and possibly structure, of the tantala-based films, thereby facilitating oxygen generation within the bulk film by oxidation of O2- ions of the oxide.
  • K Azumi, T Yugiri, T Kurihara, M Seo, H Habazaki, S Fujimoto
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 150 (7) C461 - C464 0013-4651 2003/07 
    Direct plating of electroless Ni-P layers on Al-Ni alloy films formed on glass substrates was performed using magnetron-sputtered deposition and ion beam-assisted deposition methods. Dissolution of Al from the alloy films occurred in the initial stage of the plating process and resulted in enrichment of Ni on the surface. Since Ni acts as a catalyst for the Ni-P deposition reaction, Ni-P deposition occurs on the alloy surface without zincate pretreatment. In the case of an Al-10Ni alloy film, however, Ni clusters dropped from the Al-Ni alloy surface, and Ni-P particles grew in the plating bath, causing dissipation of chemicals in the bath. Such particles also readhered to the surface, resulting in a nonuniform plating layer. A lower concentration of Ni in an alloy such as an Al-3Ni or Al-1Ni alloy resulted in a rather smooth plating surface. In the case of a neutral plating bath containing a low concentration of P, cone structures were formed in the plating layer. Such structures seem to form at the nucleation sites of Ni deposition in the initial stage of the plating process. (C) 2003 The Electrochemical Society.
  • H Habazaki, T Matsuo, H Konno, K Shimizu, K Matsumoto, K Takayama, Y Oda, P Skeldon, GE Thompson
    SURFACE AND INTERFACE ANALYSIS 35 (7) 618 - 622 0142-2421 2003/07 
    Sputter-deposited niobium layers containing nitrogen form anodic films with resultant capacitance and leakage current density little influenced by annealing up to 523 K. The nitrogen species incorporated into the anodic oxide films at the alloy/film interface are distributed in the inner 70-75% of the film thickness, with fine bubbles containing high-pressure N2O gas being evident. Glow discharge optical emission spectroscopy (GDOES) analysis reveals their continued presence after annealing at 523 K. The insignificant changes in GDOES depth profiles also suggest that the formation of low-valent oxide at the metal/film interface as a result of annealing is not responsible for the behaviour. For thermal treatments above 400 K, capacitances and leakage currents increase significantly for niobium, with nitrogen additions diminishing the effects. Such behaviour is suggested to arise from suppression of mechanical damage to films through the presence of highly pressurized gas in the inner part of the films. Copyright (C) 2003 John Wiley Sons, Ltd.
  • Y Liu, F Colin, P Skeldon, GE Thompson, Zhou, X, H Habazaki, K Shimizu
    CORROSION SCIENCE 45 (7) 1539 - 1544 0010-938X 2003/07 
    Surface treatments, including chemical polishing, alkaline etching, acid pickling, and electropolishing, of aluminium and copper-containing aluminium alloys lead to enrichment of solid solution copper in the metal just beneath the residual oxide films of the treatment processes. The paper presents the enrichment factor for copper as a function of the copper content of the bulk matrix material. The factor is defined as the ratio of the copper enrichment, measured in units of 10(15) atoms cm(-2), to the copper content of the matrix in at.%. Although absolute levels of enrichment increase with increase in copper content of the alloy, the enrichment factor increases in the opposite sense. (C) 2003 Elsevier Science Ltd. All rights reserved.
  • H Habazaki, M Uozumi, H Konno, S Nagata, K Shimizu
    SURFACE & COATINGS TECHNOLOGY 169 151 - 154 0257-8972 2003/06 
    Barrier-type amorphous anodic films with uniform thickness grow at high current efficiency on sputter-deposited Ti-Mo alloys containing 11.5-37.0 at.% molybdenum to high voltages of more than 100 V in 0.1 mol dm(-3) ammonium pentaborate electrolyte, in contrast to an amorphous-to-crystalline transition of anodic film on titanium and subsequent oxygen formation at relatively low voltages of less than 20 V. During anodizing of the alloys at a constant voltage of 80 V, the currents decrease to the order of 10(-2) A m(-2) within 3 h, whereas the current for titanium decreases only to the order of 1 A m(-2), due to the presence of flaws in the film. associated with oxygen evolution. The capacitance of the anodic films formed on the Ti-11.5 at.% Mo alloy is almost comparable to that formed on tantalum at the same voltage. The increase in molybdenum content in the alloy results in a slight decrease in the capacitance of the films. From these results, the structure of anodic films on titanium can be modified by incorporation of molybdenum species from the substrate so that uniform amorphous anodic films with a relatively high capacitance and a low defect density have been obtained. (C) 2003 Elsevier Science B.V. All rights reserved.
  • T Takenaka, H Habazaki, H Konno
    SURFACE & COATINGS TECHNOLOGY 169 155 - 159 0257-8972 2003/06 
    Galvanostatic anodizing of aluminum in oxalic acid electrolytes containing sulfate and [TiO(C2O4)(2)](2-) complex anions results in the formation of black porous anodic film. The initial voltage-time response in the present electrolytes is similar to that in usual acid electrolytes: after showing a maximum voltage, anodizing voltage becomes almost constant, i.e. 40-50 V. Then, the anodizing voltage increases almost linearly with time, and black coloring of the films takes place. The films become darker with an increase in anodizing voltage. In contrast, the black films are not formed in the oxalic acid-titanium complex anion mixed solutions without sulfate anions, although the similar voltage increase has been observed in the sulfate-free electrolyte. From morphological examinations. it has been found that the presence of sulfate ions in the electrolytes reduces the cell size of the porous films formed before the voltage increase. After the voltage increase, the cell structure in the inner part of the film becomes rather irregular and cell size becomes larger. In addition, the metal/film interface is extremely rough, and particles of metallic aluminum are incorporated in the anodic films near the metal/film interface. Glow discharge optical emission spectroscopy analysis has revealed that a small amount of titanium species is present in the inner part of the film. From these results, the mechanism of the black coloring of the anodic films has been discussed. (C) 2003 Elsevier Science B.V. All rights reserved.
  • S Mato, G Alcala, P Skeldon, GE Thompson, AB Mann, D Masheder, H Habazaki, K Shimizu
    SURFACE AND INTERFACE ANALYSIS 35 (5) 477 - 482 0142-2421 2003/05 
    Anodic oxidation at high efficiency of sputtering-deposited Ta-Ti alloys containing 0.6-40 at.% Ti is shown to result in amorphous films comprising a relatively thin outer layer of TiO2-based material and an inner layer consisting of units of TiO2 and Ta2O5. The two layers develop due to the faster migration of Ti4+ ions in the inner layer relative to that of Ta5+ ions. The formation ratios for the various films are in the approximate range 1.6-1.9 nm V-1. The dielectric constants of the films are similar to28, which is a similar value to that of anodic tantala. Nanoindentation revealed that the elastic modulus and hardness of the films are essentially independent of film composition, with average values of 134 and 5.3 GPa, respectively. Copyright (C) 2003 John Wiley Sons, Ltd.
  • H Habazaki, T Matsuo, H Konno, K Shimizu, S Nagata, K Takayama, Y Oda, P Skeldon, GE Thompson
    THIN SOLID FILMS 429 (1-2) 159 - 166 0040-6090 2003/04 
    Sputter-deposited niobium, and Nb90N10, Nb83N17 and Nb60N40 alloys, have been anodized at 50 A m(-2) in 0.1 mol dm(-3) ammonium pentaborate electrolyte at 293 K and resultant amorphous anodic films have been characterized by transmission electron microscopy, glow discharge optical emission spectroscopy, Rutherford backscattering spectrometry and Fourier-transform, infra-red spectroscopy Except for the Nb60N40 alloy, which shows a breakdown at approximately 60 V, the deposited layers reveal a linear voltage increase to more than 150 V, with the rate decreasing with the niobium content. Additionally, anodic films, with flat and parallel metal/film and film/electrolyte interfaces, are formed on the specimens with the formation ratio decreasing with increasing nitrogen content in the deposited films. Nitrogen is incorporated into the inner similar to70-75% of the film thickness as N2O molecules, forming fine bubbles, with typical sizes up to 10 nm, in a Nb2O5-based matrix material. The remaining 25-30% of the film comprises a layer of Nb2O5 with the outer regions containing boron species derived from the electrolyte. Release of high pressure N2O gas is associated with the relatively low breakdown voltage for the Nb60N40 alloy of highest nitrogen content. The two-layered nature of the anodic films arises from the film growth mechanism that involves outward migration of niobium species and inward migration of oxygen species; in contrast nitrogen species are immobile due either to the relatively high energy of the N-O bond or to their presence in bubbles. (C) 2003 Elsevier Science B.V. All rights reserved.
  • Y Liu, EA Sultan, EV Koroleva, P Skeldon, GE Thompson, Zhou, X, K Shimizu, H Habazaki
    CORROSION SCIENCE 45 (4) 789 - 797 0010-938X 2003/04 
    Anodizing of solid-solution Al-lat.%Cu alloy in ammonium pentaborate electrolyte is shown to develop two distinct types of amorphous film. On alloy grains of {100} orientation, the alumina film is of uniform thickness and relatively featureless. For other grains, the film is of non-uniform thickness and contains oxygen bubbles. In both cases, copper species are distributed throughout the film. Copper is enriched in the alloy to similar to5.8 x 10(15) Cu atoms cm(-2) for bubble-free grains, with similar or slightly lower levels for other grains. Evidently, copper enrichment alone does not lead to generation of oxygen. Other factors suggested to be involved, each dependent upon grain orientation, are the structure of the enriched alloy layer, the cyclic nature of the oxidation of copper, and the generation of modulated film compositions. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Potentiodynamic polarization studies of aluminium alloys with enriching alloying elements
    S. Garcia-Vergara, M. A. Arenas, P. Skeldon, G. E. Thompson, K. Shimizu, H. Habazaki
    Journal of corrosion science and engineering 6 1466-8858 2003 
    The present work uses potentiodynamic polarization in naturally aerated 0.1 M ammonium pentaborate electrolyte to explore the effects of enrichment of alloying elements on corrosion potentials of aluminium alloys. The selected alloys were Al-1.1 at.%Au and Al-0.95at.%Cu alloys deposited by magnetron sputtering, with enriching of the alloying element being achieved by controlled anodic etching in sodium hydroxide solution. Such etching results in large positive shifts, of several hundred millivolts, in the corrosion potential in ammonium pentaborate electrolyte, while the alloying element remains in the enriching alloy layer, of thickness about 2 nm, just beneath the surface oxide film. The results provide evidence of effects of enrichment on the anodic reaction, i.e. oxidation of aluminium, and on the cathodic reaction, i.e. reduction of oxygen. The former may arise due to the relatively high concentrations of alloying elements in the enriched alloy layer, while that later may relate to increased electron tunnelling through the oxide film. However, there may also be effects of flaws, which cannot be eliminated in the present experiments, although there was no direct evidence of their role.
  • S Garcia-Vergara, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, H Habazaki, K Shimizu
    APPLIED SURFACE SCIENCE 205 (1-4) 121 - 127 0169-4332 2003/01 
    Using medium energy ion scattering, combined with Rutherford backscattering spectroscopy, transmission electron microscopy and atomic force microscopy, the development of the copper-enriched alloy layer during anodizing of a sputtering-deposited Al-0.4 at.% Cu alloy has been examined. The enriched layer is located just beneath the amorphous alumina film that is produced on the anodized alloy. Importantly for understanding the mechanism of formation of the enriched layer, the layer is revealed to be of thickness similar to2.1 nm from the start of the anodizing, when enrichment of copper is very low, with no significant increase in the thickness of the layer as the copper enriches to similar to3 x 10(15) Cu atoms cm(-2), the maximum measured in the present experiments. The findings are consistent with a model of the layer in which the copper is present mainly in copper-rich clusters. (C) 2002 Elsevier Science B.V. All rights reserved.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, U Kreissig, D Grambole, H Habazaki, K Shimizu
    THIN SOLID FILMS 424 (2) 201 - 207 0040-6090 2003/01 
    The present study examines the behaviour of hydrogen impurity in an Al-6.5 at.% W alloy during anodizing, using elastic recoil detection and nuclear reaction analyses. Increased concentrations of hydrogen are found near the alloy/anodic film interface, amounting to similar to 2 X 10(15) H atoms cm(-2) for the particular alloy, containing 0.1-0.3 at.% hydrogen in the bulk regions, and conditions of anodizing. The enrichment arises from hydrogen in the alloy (i) diffusing to the interface, which acts as a trap, or (ii) accumulating at the interface, due to the growth of the anodic film, or a combination of both processes. Diffusion is consistent with the known mobility of hydrogen in aluminium near ambient temperature. Further, accumulation, and subsequent oxidation, of hydrogen are expected based on the general behaviour of alloying elements in anodized aluminium. The anodic films contained similar to0.1-0.3 at.% hydrogen, originating from either the electrolyte or the alloy. (C) 2002 Elsevier Science B.V. All rights reserved.
  • GE Thompson, P Skeldon, Zhou, X, K Shimizu, H Habazaki, CFE Smith
    AIRCRAFT ENGINEERING AND AEROSPACE TECHNOLOGY 75 (4) 372 - 379 0002-2667 2003 
    This paper reviews the role of alloying elements in aluminium and alloy fabrication on performance during surface treatment and surface finishing. Such elements may be present in solid solution as fine segregates, strengthening phase and equilibrium phases. For surface treatment and finishes, which generally proceed in the presence of alumina film, knowledge of the processes proceeding at the alloy/film and film/electrolyte interfaces, and those within anodic alumina films, gives rise to the possibility of controlling features of nanoscale dimensions, for improved performance, arises. Its influence on nanotextures at treated surfaces and compositionally and morphologically modified films is explained briefly.
  • Z Ashitaka, P Skeldon, GE Thompson, K Shimizu, H Habazaki
    CORROSION SCIENCE 44 (12) 2725 - 2735 0010-938X 2002/12 
    The behaviour of gallium is examined after heat and surface treatments of aluminium foils containing either 120 or 1300 ppm gallium, with low enrichments of gallium at the surfaces arising from foil manufacture. Vacuum heat treatment at 823 K for 20 ks caused negligible additional enrichment, probably associated with the high solubility of gallium in aluminium. Subsequent alkaline etching in 0.25 M sodium hydroxide for 60 s at 348 K increased significantly enrichments, to about 3.2 x 10(14) and 3.6 x 10(15) Ga atoms cm(-2) for the foils containing 120 and 1300 ppm gallium respectively. The enrichments were probably located in both the metal and the overlying etching products. In contrast, electropolishing in perchloric acid/ ethanol eliminated pre-existing enrichments, probably due to activation of the foil, with no enrichment developing during the electropolishing procedure. Barrier-type anodic films formed on the alkaline-etched foils contained gallium species, with increased concentrations at the film surface. Gallium enriched the metal region immediately beneath the anodic film during anodizing and led eventually to detachment of the growing film from the etched foil, followed by growth of a second film beneath the detached film. The combined amounts of gallium in the anodic film and enriched metal layer were similar to the levels at the surface regions of the etched foils. The anodic films formed on the electropolished foils, with no preexisting enrichment, were free of gallium species and remained attached to the foils, since insufficient gallium could enrich in the metal beneath the anodic film during the relatively short period of anodizing. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • P Bailey, TCQ Noakes, Y Liu, MR Alexander, EV Koroleva, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 197 (3-4) 265 - 270 0168-583X 2002/12 
    Following previous observations of detachment of amorphous, anodic alumina films from aluminium by 100 keV H+ ions, further experiments have been carried out using H+, D+, He-3(+) and He-4(+) ions, at energies in the range of 0.5-270 keV, to irradiate anodized aluminium with oxides of thickness from 30 to 500 nm. Surface damage was investigated by field-emission-gun scanning electron microscopy and transmission electron microscopy. Detachment of the oxide, which takes place close to, or at, the metal/oxide interface, occurred only following irradiation by H+ and D+ ions, with the ions being stopped in the metal rather than the oxide. The threshold fluence for initiation of detachment is approximately 3 x 10(15) ions cm(-2). No detachment was detected following irradiations by He-3(+) and He-4(+) ions with fluences up to 5 x 10(16) ions cm(-2) and ranges similar to those of H+ and D+ ions, although vacancy production is much greater for helium ions. These findings indicate that detachment is associated with accumulation of hydrogen species in the vicinity of the metal/oxide interface, rather than condensation of vacancies. Such behaviour is consistent with the expected mobility of hydrogen, but not of helium, in aluminium near room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Q Lu, P Skeldon, GE Thompson, MJ Graham, D Masheder, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 149 (12) B531 - B533 0013-4651 2002/12 
    Non-thickness-limited (NTL) growth of anodic films on tantalum is a remarkable recently reported phenomenon whereby anodic films can be formed on tantalum to high thickness due to a change in the film growth mechanism from the usual high-field type of process. The present work employs transmission electron microscopy to reveal the structure, composition, and morphology of an NTL-type film formed by anodizing tantalum at 1 A m(-2) in 10 wt % dibasic potassium phosphate/glycerol electrolyte at 453 K. A relatively compact, amorphous layer of NTL-type film material, composed of essentially tantala, was formed above an inner layer of usual high-field-type tantala under the selected conditions of anodizing and drying of the electrolyte. The field for growth of NTL-type film material is less than or equal to10 MV m(-1), compared with similar to400 MV m(-1) for high-field growth. Thus, the thickness of the inner layer is approximately equal to the product of the formation ratio for usual anodic tantala and the final anodizing voltage. (C) 2002 The Electrochemical Society.
  • Q Lu, G Alcala, P Skeldon, GE Thompson, MJ Graham, D Masheder, K Shimizu, H Habazaki
    ELECTROCHIMICA ACTA 48 (1) 37 - 42 0013-4686 2002/11 
    The present study demonstrates that the phenomenon of non-thickness limited (NTL) growth of anodic films in a phosphate/ glycerol electrolyte at 453 K on tantalum and aluminium is due to the formation of porous films. For both tantala and alumina films, the resultant morphology comprises cells of material orientated approximately normal to the metal/film interface, with each cell containing a central pore of typical diameter in the range 3-15 nm and a barrier layer of film material at the base of the pore. The total porosity is about 5%. The hardness of NTL tantala films, determined by nanoindentation, was 5.1 GPa, reasonably similar to that of conventional anodic tantala. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • FA Bonilla, A Berkani, P Skeldon, GE Thompson, H Habazaki, K Shimizu, C John, K Stevens
    CORROSION SCIENCE 44 (9) 1941 - 1948 0010-938X 2002/09 
    The possibility of enrichment of alloying elements in magnesium alloys as a consequence of growth of an anodic film has been investigated for sputtering-deposited Mg-0.4 at.% W and Mg-1.0 at.% W alloys. The alloys were anodized at 10 mA cm(-2) to various voltages, up to 150 V, in 3 M ammonium hydroxide/0.05 M ammonium phosphate electrolyte at 293 K. The alloys revealed enrichments of tungsten to at least 1.7 x 10(15) and 2.9 x 10(15) W atoms cm(-2) for the Mg-0.4 at.% W and Mg-1.0 at.% W alloys respectively. The enrichment behaviour appears to be similar to that in dilute aluminium alloys, which occurs for alloying elements with oxides having Gibbs free energies per equivalent for formation exceeding that for formation of alumina. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • H Habazaki, M Uozumi, H Konno, K Shimizu, S Nagata, K Asami, P Skeldon, GE Thompson
    ELECTROCHIMICA ACTA 47 (24) 3837 - 3845 0013-4686 2002/09 
    Ti-Mo, bcc, solid-solution alloys, containing 11.5-37.0 at.% molybdenum, have been anodised galvanostatically in 0.1 mol dm(-3) ammonium pentaborate and 1.0 mol dm(-3) phosphoric acid electrolytes, with resultant anodic films characterised by scanning electron microscopy, transmission electron microscopy, Rutherford backscattering spectroscopy and glow discharge optical emission spectroscopy. Uniform amorphous films are formed at high current efficiency to > 100 V, with formation ratios of 2.3 and 2.2 nm V in the respective electrolytes, contrasting with the amorphous-to-crystalline transition of anodic titania on titanium that occurs at similar to 20-50 V. Apart from minor incorporation of electrolyte species, the films comprise an outer layer of TiO2 and an inner oxide layer containing Ti4+ and Mo6+ ions. The films grow by migration of both cations and anions, with Ti4+ ions migrating faster than Mo6+ ions that is related to the energies of Ti4+ -O and Mo6+ -O bonds. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • T Matsui, H Habazaki, A Kawashima, K Asami, N Kumagai, K Hashimoto
    JOURNAL OF APPLIED ELECTROCHEMISTRY 32 (9) 993 - 1000 0021-891X 2002/09 
    Ternary manganese molybdenum tungsten oxides were anodically deposited on to IrO2-coated titanium substrates at current densities of 60-600 A m(-2) in 0.4 M MnSO4 solutions containing 0.003 M Na2MoO4 and 0.003 M Na2WO4 at pH 0-1.5 and at 30-90degreesC. The effect of anodic deposition conditions on the activity, selectivity and durability of the anodes for oxygen evolution in 0.5 M NaCl solution was investigated. Most of the oxide anodes prepared initially gave an oxygen evolution efficiency of almost 100%. When the anodic deposition was performed at temperatures lower than 90degreesC gradual oxidative dissolution occurred during the electrolysis in the NaCl solution, due to formation of poorly crystalline oxides. In contrast, the oxide deposited at 90 degreesC revealed no obvious dissolution during electrolysis for more than 1500 h. The oxygen evolution efficiency, however, decreased gradually with time of electrolysis because of partial detachment of the deposited oxide. The anodic deposition in electrolytes at lower pH and at higher current density resulted in the formation of oxides with better adhesion to the substrate, resulting in improved anode durability. The durability was further improved by repeated anodic deposition with the oxide surface washed during intervals.
  • E Zhuravlyova, L Iglesias-Rubianes, A Pakes, P Skeldon, GE Thompson, Zhou, X, T Quance, MJ Graham, H Habazaki, K Shimizu
    CORROSION SCIENCE 44 (9) 2153 - 2159 0010-938X 2002/09 
    Using residual gas analysis, with scraping of oxide films, it is demonstrated that oxygen gas can be generated within anodic films on Al-Cu alloys and InP. The oxygen is produced by oxidation of O2- ions of the film material, and is present in numerous bubbles in the bulk film. The generation of oxygen is suggested to be related to the electron energy levels of the film material, which in the case of alumina films are modified by the incorporation of copper species and, from previous work, other non-valve, transition metal species. Oxygen is also present in low amounts in alumina films nominally free of the latter species; the oxygen may be located either in the bulk oxide or at flaws. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • G Alcala, P Skeldon, GE Thompson, AB Mann, H Habazaki, K Shimizu
    NANOTECHNOLOGY 13 (4) 451 - 455 0957-4484 2002/08 
    The hardness and Young's modulus of barrier-type, amorphous anodic oxides have been determined by nanoindentation. The procedure used shallow indents, of 55 nm depth, with alumina, tantala and alumina/tantala 'mixed oxide' films of about 500 nm thickness. The results revealed respective hardnesses of approximately 7.0, 5.3 and 6.5 GPa, and respective Young's moduli of approximately 122, 140 and 130 GPa. Thus, the hardness and Young's modulus followed opposite trends, with alumina having the highest hardness and lowest modulus, and the 'mixed oxide' having intermediate properties. The hardness and Young's modulus of amorphous alumina are factors of about 3.1-3.7 times lower than those of crystalline aluminas.
  • CE Caicedo-Martinez, EV Koroleva, GE Thompson, P Skeldon, K Shimizu, H Habazaki, G Hoellrigl
    SURFACE AND INTERFACE ANALYSIS 34 (1) 405 - 408 0142-2421 2002/08 
    Chemical polishing and electropolishing of aluminium result in fine cellular textures of nanometre dimensions, which play a role in the electrochemical behaviour of aluminium and its response to further treatment processes such as conversion coating and anodizing. Concerning the latter, the surface texture is highlighted by porous anodic film growth for protection of the substrate. The influence of residual impurities and low additions of alloying elements on the development of the textures is investigated here for superpure aluminium (99.99%) and an Al-0.4wt.%Mn alloy, respectively. Complementary analytical approaches, including atomic force microscopy and transmission electron microscopy, disclose scalloped cellular textures comprising adjacent peaks and troughs, with a dependence on the grain orientation of the aluminium substrate. In addition to texture development, enrichment of copper impurity in the alloy occurs adjacent to the alloy/oxide film interface, as revealed by in-depth elemental profiles generated by r.f. glow discharge optical emission spectroscopy. The absence of similar enrichments of iron and silicon in the alloy suggests that these elements are distributed mainly as fine segregates in the aluminium, unlike copper, which is in solid solution. At low alloying levels, manganese reveals limited enrichment and is also probably present mainly as segregates. The origin of the textures and their dependence on grain orientation are thus considered to be related to the presence and location of relatively high-melting-point elemental impurities in the alloy and their local electrochemical responses relative to the adjacent alloy surface. Copyright (C) 2002 John Wiley Sons, Ltd.
  • Q Lu, S Mato, P Skeldon, GE Thompson, D Masheder, H Habazaki, K Shimizu
    ELECTROCHIMICA ACTA 47 (17) 2761 - 2767 0013-4686 2002/07 
    The effects of current density and temperature on the anodic films formed on tantalum in dilute H3PO4 (0.06%wt) solution have been studied by transmission electron microscopy, using ultramicrotomed sections, and Rutherford backscattering spectroscopy. Two-layered films have been identified, comprising an inner relatively pure Ta2O5 layer, adjacent to the metal/film interface, and an outer layer containing incorporated pO(4)(3-) anions. The total amount and depth of incorporated phosphorus species increase with 4 increasing current density and decreasing temperature, in correspondence with the enhancement of the electric field. The formation conditions for the films include those relevant to the commercial anodising of tantalum for capacitors for which the extent of phosphorus incorporation is shown to be comparatively low. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • H Habazaki, K Shimizu, S Nagata, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 44 (5) 1047 - 1055 0010-938X 2002/05 
    Incorporation of silicon species from an alloy substrate into anodic titania is shown to stabilise the structure of the film, facilitating investigation of the ionic transport processes in amorphous titania grown at high efficiency. Thus, an amorphous anodic film developed on a sputtering-deposited Ti-6 at.%Si alloy formed to 100 V in phosphoric acid electrolyte in contrast to a partially crystalline film developed on relatively pure titanium at <20 V. Silicon species, which are immobile and act as marker species in the growing film, are present in the inner 58% of the film thickness. Evidently, the film material forms simultaneously at the film/electrolyte and alloy/film interfaces by co-operative transport of cations and anions, as is usual in amorphous anodic oxides. The phosphate anions incorporated from the electrolyte migrate inward at 0.34 times the rate of O2- ions and hence are present in the outer 62% of the film thickness. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • CE Caicedo-Martinez, E Koroleva, P Skeldon, GE Thompson, G Hoellrigl, P Bailey, TCQ Noakes, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 149 (4) B139 - B145 0013-4651 2002/04 
    The behavior of impurity and minor elements during electropolishing, chemical polishing, and anodizing treatments is examined for 99.99% Al and Al-0.2 atom % Mn alloy containing iron, copper, and silicon impurities in the parts per million range. Copper is enriched strongly, to at least 2-4 x 10(14) copper atoms cm(-2), during the two polishing treatments. Assuming that the copper is located in a metal layer of thickness 1 nm, just beneath the surface film, the enrichment corresponds to an average concentration of about 5 atom % copper. In contrast, iron and silicon impurities were not enriched significantly by the various treatments. Manganese was enriched in the Al-0.2 atom % Mn alloy to about 7 x 10(14) atoms cm(-2). Manganese appeared to interact with copper impurity in the alloy to reduce the level of copper enrichment. The factors determining the degree of enrichment include the Gibbs free energies per equivalent for formation of the various impurity and alloying element oxides, interactions between coenriching elements, and the location of the particular atoms in the metal, especially the proportions of the atoms in solid solution, in fine particulates, and segregated at cellular and grain boundaries. (C) 2002 The Electrochemical Society.
  • L Iglesias-Rubianes, P Skeldon, TE Thompson, H Habazaki, K Shimizu
    CORROSION SCIENCE 44 (4) 751 - 760 0010-938X 2002/04 
    Previous experiments involving stepped changes in current during anodizing of aluminium alloys have disclosed subtle transient and long-term influences of current density on film growth. The present work employs a current reduction of a factor of 10(4), much larger than that in earlier work, to investigate the phenomena further. The findings from transmission electron microscopy of film sections disclose that the step in current leads to generation of fine light bands of film material, each about 6 nm thick, at the alloy/film and film/electrolyte interfaces. Further, the film material formed at the alloy/film interface following the step in current is generally of lighter appearance than that formed previously. The lighter film material probably contains relatively less tungsten species, and/or is of reduced density, compared with adjacent material. The greater reduction in current, compared with that of previous studies, appears to accentuate the alterations in composition and/or density of film material. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Y Liu, M Alexander, E Koroleva, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, K Shimizu, H Habazaki
    SURFACE AND INTERFACE ANALYSIS 33 (4) 318 - 321 0142-2421 2002/04 
    Irradiation of aluminium covered by anodic oxide films 3-14 nm thick using 100 keV H+ ions is shown to result in detachment of the oxide film. A dose of 6.6 x 10(16) H+ ions cm(-2) on a 6.5 rim thick film causes the removal of large pieces of oxide with dimensions at least 15 pm. Atomic force microscopy analysis shows that the location of the failure is within similar to1 nm of the metal/oxide interface. The large aspect ratio (width to thickness) of the detached pieces is thus similar to2000:1 and indicates that there is a disruption of the oxide bonding over large areas. The bombardment also results in the formation of blisters with diameters lap to several hundred nanometres in the oxide, accompanied by shallow depressions, similar to5 nm deep in the underlying metal. The detachment is suggested to be associated with either condensation of vacancies generated in the metal by the H+ ions or accumulation of hydrogen atoms deposited in the metal by the ion beam in the region of the metal/oxide interface. Although the beam energy and dose were expected to cause some disruption in the implanted material, the complete detachment of large areas of oxide was not anticipated. In fact, this appears to be the first time such gross detachment of an anodic film by H+ ion irradiation has been reported. Copyright (C) 2002 John Wiley Sons, Ltd.
  • H Habazaki, K Shimizu, S Nagata, P Skeldon, GE Thompson, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 149 (3) B70 - B74 0013-4651 2002/03 
    The mobilities of various electrolyte-derived species in amorphous anodic titania have been determined, with stabilization of the oxide structure by incorporation of silicon species from a sputter-deposited Ti-6 atom % Si alloy. From comparison of the distributions of silicon marker species and electrolyte-derived species in films formed at high current efficiency, boron, chromium, molybdenum, and tungsten species migrate outward more slowly than do Ti4+ ions. Their migration rates, relative to that of Ti4+ ions, correlate well with the energies of the respective metal-oxygen bonds. Further, chromium species incorporated into the film from chromate electrolyte are mainly present in the trivalent state, indicating reduction of Cr6+ ions to Cr3+ ions in the growing anodic oxide. This reduction of chromium species can be explained by considering the influences of Cr3+ and Cr6+ ions on the band structure of titania. (C) 2002 The Electrochemical Society.
  • H Habazaki, H Mitsui, K Ito, K Asami, K Hashimoto, S Mrowec
    CORROSION SCIENCE 44 (2) 285 - 301 0010-938X 2002/02 
    Our recent results of the sulfidation and oxidation behavior of sputter-deposited Al- and Cr-refractory metal alloys at high temperatures are reviewed, and the roles of the aluminum and chromium in sulfidation and oxidation of these alloys are discussed in this paper. Niobium, molybdenum and tantalum are highly resistant to sulfide corrosion. Their sulfidation resistance is further enhanced by alloying with aluminum. Although Cr-refractory metal alloys also reveal high sulfidation resistance, their sulfidation rates do not become lower than those of the corresponding refractory metals. The sulfide scales formed on the Al-refractory metal and Cr-refractory metal alloys consist of two layers., comprising an outer Al2S3 or Cr2S3 layer and an inner refractory metal disulfide layer. The inner layer has a columnar structure, and the growth direction of the refractory metal disulfides is perpendicular to 001 direction. Intercalation of Al3+ ions into NbS2 and a decrease in the sulfur activity at the outer layer/inner layer interface by the presence of the Al2S3 layer are probably responsible for the improvement of the sulfidation resistance by the addition of aluminum. The oxidation resistance of niobium and tantalum is improved more effectively by the addition of chromium rather than aluminum. Although preferential oxidation of chromium does not occur, an outer protective Cr2O3 layer in the oxide scales is formed on Cr-rich Cr-Nb and Cr-Ta alloys due to outward diffusion of Cr3+ ions. In contrast, continuous alumina layer cannot be formed on the Al-Nb and Al-Ta alloys, and the alloys reveal a pest phenomenon at 1073 K, and at higher temperatures rapid oxidation occurs. Concerning the oxidation of molybdenum, the addition of aluminum, which has higher activity for oxidation than chromium, is more effective in improving the oxidation resistance of molybdenum than chromium addition, since preferential oxidation of aluminum suppresses the formation of volatile molybdenum oxide. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • K Hashimoto, M Yamasaki, S Meguro, T Sasaki, H Katagiri, K Izumiya, N Kumagai, H Habazaki, E Akiyama, K Asami
    CORROSION SCIENCE 44 (2) 371 - 386 0010-938X 2002/02 
    CO2 emissions, which induce global warming, increase with the development of economic activity. It is impossible to decrease the CO2 emissions by suppression of the economic activity. Global CO2 recycling can solve this problem. The global CO2 recycling consists of three district: The electricity is generated by solar cells on deserts. At desert coasts, the electricity is used for H-2 production by seawater electrolysis and H-2 is used for CH4 production by the reaction with CO2 CH4 which is the main component of liquefied natural gas is liquefied and transported to energy consuming districts where CO2 is recovered, liquefied and transported to the desert coasts. A CO2 recycling plant for substantiation of our idea has been built on the roof of the Institute for Materials Research in 1996. Key materials necessary for the global CO2 recycling are the anode and cathode for seawater electrolysis and the catalyst for CO2 conversion. All or them have been tailored by us. They have very high activity and selectivity for necessary reactions in addition to excellent durability. A pilot plant consisting of minimum units in an industrial scale is going to be built in three years. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 149 (2) B23 - B26 0013-4651 2002/02 
    The growth of an anodic oxide film on a specimen consisting of a layer of aluminum deposited upon a layer of tungsten was examined by transmission electron microscopy. The findings reveal initial growth of anodic alumina, followed by penetration of the alumina by fingers of tungsten oxide once the metal/film interface reaches the tungsten layer. The fingers are approximately cylindrical or lanceolate, with width in the range 1-15 nm and aspect ratios up to about 40. The current flows preferentially to regions of tungsten oxide rather than the alumina due to the lower electric field for growth of the former oxide. The penetration of the alumina is assisted by the relatively high Pilling-Bedworth ratio for W/WO3 and the inherent plasticity in amorphous anodic oxides. The tungsten oxide of the fingers appears to be of higher density than that formed at the metal/film interface after the aluminum has been fully oxidized, which may be due to the penetration of the alumina layer by a displacement process. (C) 2001 The Electrochemical Society.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    ELECTROCHIMICA ACTA 47 (8) 1225 - 1228 0013-4686 2002/02 
    The generation of oxygen gas within an amorphous anodic alumina film is reported. The film was formed by anodizing aluminum, which was first electropolished and then chemically polished in CrO3-H3PO4 solution, in sodium tungstate electrolyte. The procedure results in incorporation of mobile Cr3+ species, from the chemical polishing film, and mobile W6+ species, from the electrolyte, into the amorphous structure. The tungsten species are present in the outer 27% of the film thickness, while Cr6+ species occupy a thin layer within the tungsten-containing region. Above the Cr3+ containing layer, a band develops that contains oxygen bubbles of a few nanometres size. The oxygen is generated by oxidation of O2- ions of the alumina. A mechanism of oxygen generation within the alumina is proposed based on the electronic band structure of the oxide, modified by the Cr3+ and W6+ species. and on the ionic transport processes during oxide growth. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • FA Bonilla, A Berkani, Y Liu, P Skeldon, GE Thompson, H Habazaki, K Shimizu, C John, K Stevens
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 149 (1) B4 - B13 0013-4651 2002/01 
    The development of anodic films at a constant current density of 10 mA cm(-2) has been studied for Mg-W alloys, containing 0.4 and 1.0 atom % W, in 3 M ammonium hydroxide/0.05 M ammonium phosphate electrolyte at 293 K. The structure, morphology, and composition of the films were determined by X-ray diffraction, scanning electron microscopy, atomic force microscopy, glow discharge optical emission spectroscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis. During anodizing to about 50 V, a relatively smooth film develops. Cross-sectional atomic force microscopy suggests the film may be finely porous. With an increase in voltage, the film transforms gradually to a coarse, porous morphology due to dielectric breakdown. The transformation coincides with a reduction in slope of the voltage-time response. Significant regions of both types of film morphology coexist during anodizing to 150 V. With further anodizing, a porous film, developed in the presence of sparking above about 270 V, eventually covers all of the macroscopic surface. Magnesium, phosphorus, oxygen, hydrogen, and nitrogen species are present throughout the film thickness at the resolution of the measurements. However, the films are initially free of tungsten species due to enrichment of tungsten in the alloy. The O: Mg atomic ratio is in the range 1.7 to 2.1, reducing with an increase in voltage for films formed up to 220 V, consistent with films composed primarily of hydroxide or oxyhydroxide. The P:O atomic ratio increases with an increase in voltage, starting at about 0.03 for voltages below 50 V and reaching 0.29 at 330 V. The films form at a reduced efficiency, typically about 40-50%. (C) 2001 The Electrochemical Society.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, K Shimizu, H Habazaki
    CORROSION SCIENCE 43 (12) 2217 - 2227 0010-938X 2001/12 
    The influences of current density in development of amorphous, barrier anodic films on a metastable, solid solution, Al-6.5at.%W alloy is examined, with focus on enrichments in the alloy, oxidation processes at the alloy/film interface and migration of species in the film. The films were formed at current densities between 0.01-100 mA cm(-2) in sodium tungstate electrolyte and examined by transmission electron microscopy and Rutherford backscattering spectroscopy. Enrichments of tungsten in the alloy develop at each of the selected current densities, with enrichments in the range 2-4 x 10(15) W atoms cm(-2). incorporation of tungsten species into the films at the alloy/film interface proceeds non-uniformly, with cycles of local enrichment of the alloy, oxidation of the enriched tungsten and subsequent depletion of the alloy. The tungsten species migrate more slowly than Al3+ ions, leading to layering of the film composition. The cyclic incorporation of tungsten species into the film and the migration of tungsten species within the film are similar for the selected current densities, at the resolution of the experiments. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • Y Liu, P Skeldon, GE Thompson, Zhou, X, H Habazaki, K Shimizu
    CORROSION SCIENCE 43 (12) 2349 - 2357 0010-938X 2001/12 
    Previous work of the authors has revealed detachment of anodic films during anodizing of elect to polished, solid-solution Al-3 at.%Mg alloy at constant current density, with the possibility of the electropolishing pre-treatment having a significant influence on the loss of the film material. Here, anodic films were formed on a similar alloy, with pre-treatment by electropolishing, alkaline etching or mechanical polishing. The results disclose the detachment of the anodic film for all pre-treatments, thus demonstrating that prior electro polishing is not essential for initiation of detachment. However, the occurrence of detachment was sensitive to the current density, with lower current densities promoting detachment at earlier stages of growth of the anodic film for a particular pre-treatment. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson
    SURFACE AND INTERFACE ANALYSIS 31 (12) 1085 - 1086 0142-2421 2001/12 
    The reproducibility in radiofrequency glow discharge optical emission spectroscopy (r.f.-GDOES) depth profiling has been examined using a 360 nm thick anodic alumina film with a chromium-containing delta-function layer. The time required to sputter through the film was constant, to within 1%, whereas the signal intensities of film species agreed to within 3%. This level of reproducibility together with high depth resolution makes the technique ideal for on-site quality control of various surface-enhanced industrial products, embracing electronics and protective surface treatments. Copyright (C) 2001 John Wiley & Sons, Ltd.
  • H Habazaki, H Ukai, K Izumiya, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 318 (1-2) 77 - 86 0921-5093 2001/11 
    Amorphous Ni-Cr-Nb-16P-4B bulk alloys highly corrosion-resistant in a 6 M HCl solution have been obtained by copper mould casting. The as-cast Ni-Cr-Nb-16P-4B alloys (Cr, Nb = 5 or 10 at.%) of 1 mm diameter are composed of an amorphous single phase. and they are spontaneously passive in the 6 M HCl solution at 303 K. Their polarization curves are almost the same as those of the corresponding rapidly quenched amorphous alloy ribbons. A larger Ni-10Cr-5Nb-16P-4B bulk specimen of about 20 x 20 x 2 mm in size has been also prepared by consolidation of gas-atomized amorphous alloy powders by sheath rolling at 708 K, at which the alloy is in the super-cooled liquid state. Although X-ray diffraction pattern of the specimen revealed a halo, typical of amorphous structure, its corrosion resistance in the 6 M HCl is not as high as that of the as-cast one. After immersion of the sheath-rolled specimen in the 6 M HCl solution, spherical pit-like attacks have been observed on the surface, suggesting the presence of nanocrystalline precipitates locally. Thus, for the Ni-Cr-Nb-P-B alloys the formation of single amorphous phase appears to be necessary to have high corrosion resistance in aggressive environments. (C) 2001 Elsevier Science B.V. All rights reserved.
  • H Konno, R Matsuura, M Yamasaki, H Habazaki
    SYNTHETIC METALS 125 (2) 167 - 170 0379-6779 2001/11 
    Carbon spheres containing fine particles of Co metal were prepared by carbonization of the chelate resin complexed with Co (II) ions in pure argon. Diffraction peaks of cubic cobalt were found in XRD patterns from 600 degreesC but the particle size observed by TEM was 10-50 nm in diameter even at 1000 degreesC. Cobalt promoted the decomposition of polyamine functional groups in the resin and the transformation of amorphous carbon to turbostratic structure. The spheres prepared at 700-1000 degreesC had a specific surface area of 170-250 m(2) g(-1) (C) 2001 Elsevier Science B.V. All rights reserved.
  • A Pakes, F Echeverria, P Skeldon, GE Thompson, JW Fraser, JP McCaffrey, S Moisa, MJ Graham, H Habazaki, K Shimizu
    CORROSION SCIENCE 43 (11) 2173 - 2184 0010-938X 2001/11 
    The morphologies of barrier-type anodic films grown on InP have been investigated using atomic force microscopy. scanning electron microscopy and transmission electron microscopy in order to gain further understanding of the non-linear voltage-time behaviour and the development of blisters in the films. The films. which are two layered, with an outer layer of In2O3 and an inner phosphorus-rich layer, containing also indium species, were formed at 50 A m-(2) in aqueous 0.1 M sodium tungstate electrolyte at 298 K. During the early stages of anodizing, i.e. within the initial region of linear voltage-time response, a relatively compact and uniform film forms, with a comparatively featureless surface. However, as the voltage increases, cavities develop within the film., and in places the anodic film material detaches partially from the substrate. The film surface then discloses fine-textured roughness and coarse protuberances associated with cavity formation and detachment respectively. Such transformation of the film morphology correlates with a decrease in slope of the voltage-time response, which commences at a formation voltage of approximately 17 V, with a film thickness of about 25 nm. The behaviour is explained by generation of oxygen within the anodic film material, which forms high pressure bubbles of gas. Such gas formation is related to the presence of an In2O3 outer layer of the film and the presence of units of In2O3 in the inner layer of the film, which facilitate oxidation of O2- ions of the film material. (C) 2001 Elsevier Science Ltd, All rights reserved.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, RK Marcus
    SURFACE AND INTERFACE ANALYSIS 31 (9) 869 - + 0142-2421 2001/09 
    Factors controlling the depth resolution in radio frequency glow discharge optical emission spectroscopy (rf-GDOES) depth profiling analysis of thin films have been investigated using anodic alumina films of varying thicknesses with delta function marker layers of similar to2 nm width located at various depths from the oxide surface. In rf-GDOES depth profiling analysis, where a relatively large area of similar to4 mm in diameter is analysed, it was found that the depth resolution is determined mainly by the large-scale variation of sputtering rate across the crater. Despite the relatively large area analysed, the uniformity of sputtering rate across the crater was constant to within 1% under the optimum Ar pressure except for near-edge regions of similar to0.4 min width, where the sputtering rate was similar to6% higher than in the central crater region. Owing to this relatively minor non-uniformity of sputtering rate, the depth resolution degrades approximately linearly with depth. A depth resolution of similar to1.3 nm was realized to depths of similar to 25 mn, where the degradation of depth resolution due to the non-uniformity in sputtering rate is insignificant. The depth resolution is close to the ultimate depth resolution in sputter depth profiling, claimed to be 0.7-1.0 run, and arises from the minimal atomic mixing associated with film sputtering with Ar(+)ions of very low energy, similar to 50 eV, in rf-GDOES analysis. Copyright (C) 2001 John Wiley & Sons, Ltd.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    ELECTROCHIMICA ACTA 46 (28) 4379 - 4382 0013-4686 2001/08 
    The migration rate of oxalate ions, (COO-)(2) in anodic alumina has been determined by analysis of a barrier film, containing an immobile boron marker and thin oxalate-doped layer, by SIMS depth profiling. From the relative distributions of the boron marker and the carbon species in the depth-profiled film, it is shown that oxalate ions migrate inward at a rate of about 0.57 relative to that of oxygen ions. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 43 (7) 1393 - 1402 0010-938X 2001/07 
    Interfacial enrichment of iron atoms and iron ions has been observed at the alloy/film and film/electrolyte interfaces respectively during anodizing of sputtering-deposited, non-equilibrium Al-7.5 at.% Fe alloys. The formation of the anodic oxide involves initial oxidation of aluminium and enrichment of iron in a layer of alloy, about 2 nm thick, immediately beneath the oxide film. When the level of enrichment reaches about 3.8 x 10(19) Fe atoms m(-2), corresponding to an average composition of the enriched alloy layer of approximately Al-25 at.% Fe, both aluminium and iron species are incorporated into the film in the presence of the enriched layer. The incorporated iron species, namely Fe3+ ions, migrate outward in the growing anodic film, about 2.0 times faster than Al3+ ions. Consequently, the iron species eventually reach the film/electrolyte interface forming a thin, amorphous layer probably composed of Fe2O3. Oxygen is generated at, or near, the alloy/film interface subsequent to incorporation of iron species into the film. The general anodizing behaviour is similar to that reported previously for an Al-4 at.% Fe alloy, although in that case significant oxygen generation and void formation, which limits thickening of uniform films, is postponed to higher voltages, while the outer, iron-rich layer is composed mainly of crystalline FeOOH. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • P Bailey, P Skeldon, TCQ Noakes, GE Thompson, M Sakairi, H Habazaki, K Shimizu
    SURFACE AND INTERFACE ANALYSIS 31 (6) 480 - 483 0142-2421 2001/06 
    The topmost 20 nm of an electropolished Al-1 at.% Cu alloy has been investigated at sub-nanometre resolution using medium-energy ion scattering. Differences in the composition and depth of the enriched Cu layer are observed. Most significantly, the enriched layer contains regions of differing structure and/or lattice orientation with Cu atoms located in distinct ordered regions, consist ent with the presence of Cu-rich clusters, Surface-segregated Si and Cu are observed and CI and Cu are found in the oxide. Copyright (C) 2001 John Wiley & Sons, Ltd.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES 81 (6) 1579 - 1595 0141-8610 2001/06 
    Stepped-current experiments are applied to the study of barrier film formation on an Al-6.5 at.% W alloy prepared by magnetron sputtering. These reveal transient changes in the composition and/or the density in local regions of the anodic film immediately following changes in the current density between 0.1 and 10 mA cm-(2). Specifically,following an increase and a decrease in the current, bands of film material approximately 6 nm thick are generated at, or near, the alloy-film interface, which are, firstly, respectively enriched and depleted in tungsten species and/or, secondly, of enhanced and reduced density respectively. There is also evidence that similar bands are generated simultaneously at, or near, the film-electrolyte interface. Further, either the density or the composition of film material formed at the alloy-film interface, or a combination of these factors, depends upon the current, with material retaining to some extent its original property as the film develops at the new current. Possible reasons for the occurrence of these features are considered.
  • K Asami, BP Zhang, M Mehmood, H Habazaki, K Hashimoto
    SCRIPTA MATERIALIA 44 (8-9) 1655 - 1658 1359-6462 2001/05
  • H Habazaki, T Sato, A Kawashima, K Asami, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 304 696 - 700 0921-5093 2001/05 
    Cylindrical amorphous Ni-15Cr-10Mo-16P-4B and Ni-(10 and 15)Cr-5Ta-16P-4B alloys of 1 and 2 mm in diameter have been obtained by a copper mould casting method. These amorphous alloys are spontaneously passive in 6 M HCl at 303 K, and the corrosion resistance of the bulk alloys of 1 nm diameter in 6M HCl at 303 Ii; is as high as that of the rapidly quenched alloy ribbons with. the same composition. However potentiodynamic polarization reveals that the corrosion rate of the Ni-10Cr-5Ta-16P-4B alloy of 2 nun diameter is about three times higher than that of the alloy of 1 mm diameter though both sizes of the specimens are identified to be amorphous from;X-ray diffraction patterns. The further detailed structural analysis using high resolution transmission electron microscopy indicates the presence of fee nickel precipitates, 2-3 nm size, in the amorphous matrix only for the specimen of 2 mm diameter. The Ni-15Cr-10Mo-16P-4B alloy of 2 mm diameter contains larger precipitates, about 20 nm rite, of fee nickel, showing about two orders of magnitude higher anodic current density than the amorphous single phase alloy of 1 nun diameter Thus, the precipitation of a nanocrystalline nickel phase, which actively dissolves in 6M HCl, is detrimental to the corrosion resistance of the amorphous Ni-Cr-(Mo or Ta)-P-B alloys, although the smaller size of the precipitates is less detrimental. (C) 2001 Elsevier Science B.V. All rights reserved.
  • H Habazaki, T Matsui, A Kawashima, K Asami, N Kumagai, K Hashimoto
    SCRIPTA MATERIALIA 44 (8-9) 1659 - 1662 1359-6462 2001/05
  • K Hashimoto, H Habazaki, M Yamasaki, S Meguro, T Sasaki, H Katagiri, T Matsui, K Fujimura, K Izumiya, N Kumagai, E Akiyama
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 304 88 - 96 0921-5093 2001/05 
    CO2 emission increase inducing global Warming occurs mostly with the growth of the economic activity. Global CO recycling can prevent global warming and supply abundant renewable energy. Global CO2 recycling consists of three district. The electricity is generated by solar cells on deserts. At coasts close to the deserts, the electricity is used for hydrogen production by seawater electrolysis and hydrogen is used for methane production by the reaction with CO2. Methane (CH4) is liquefied and transported to energy consuming districts where after CH4 is used as a fuel CO2 is recovered, liquefied anti transported to the coasts close to the deserts, Ii;ey materials necessary for the global CO2 recycling are the anode and cathode for seawater electrolysis and the catalyst for CO2 conversion All uf them have been tailored by us. amorphous and nanocrystalline nickel alloys are active cathodes for hydrogen production in seawater electrolysis. Anodically deposited nanocrystalline Mn-Mo and Mn-W oxides are the unique substance which can evolve oxygen with 100% efficiency without evolving chlorine in seawater electrolysis. Amorphous Ni-Zr alloys ale excellent precursors of catalysts for conversion of CO2 into CH4 by the reaction with hydrogen at 1 atm. A prototype CO2 recycling plant to supply clean energy preventing global warming has been built on the roof of our Institute (IMR) in 1996 using these key materials and has been operating successfully, (C) 2001 Elsevier Science B.V. All lights reserved.
  • A Kawashima, H Habazaki, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 304 753 - 757 0921-5093 2001/05 
    Bulk amorphous Wi-Nb-Ta-P alloys were successfully prepared by copper mold casting method. The addition of tantalum is effective in decreasing the corrosion rate. The corrosion rates of the alloys containing certain amounts of tantalum are more than four orders of magnitude lower than that of nickel metal and are almost equivalent to that of tantalum even in aggressive 12M HCl open to air at 30 degreesC, They are spontaneously passive and are characterized by immune to pitting by anodic polarization. The corrosion behavior of the bulk amorphous alloys is almost the same as corresponding melt-spun amorphous alloy ribbons. (C) 2001 Elsevier Science B.V. All rights reserved.
  • S Mato, GE Thompson, P Skeldon, K Shimizu, H Habazaki, D Masheder
    CORROSION SCIENCE 43 (5) 993 - 1002 0010-938X 2001/05 
    In order to elucidate the factors controlling enrichment of alloying elements during anodic oxidation of alloys, and anodic oxidation behaviour of alloys generally, the influence of anodic film growth on a Ta-1.5 at.% Cu alloy has been examined by transmission electron microscopy, Rutherford backscattering spectroscopy and glow discharge optical emission spectroscopy. Contrasting with the behaviour of Al-Cu alloys, film growth proceeds without significant enrichment of copper in the tantalum alloy substrate, although a thermodynamic driving force for enrichment exists. Factors controlling the development of enriched alloy lavers are considered, including influences of distributions of alloying element in the substrate, film structure and ionic transport in the anodic film. Comparisons of alloy systems suggest kinetic factors may be important, in particular the influence of film formation at the alloy/oxide interface on concentrations of vacancies and diffusion rates in the alloy layer immediately beneath the growing oxide film. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • F Echeverria, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    JOURNAL OF MATERIALS SCIENCE 36 (5) 1253 - 1259 0022-2461 2001/03 
    The composition and morphology of the double-layered anodic film formed at 5 mA cm(-2) on InP in aqueous sodium tungstate electrolyte is examined by transmission electron microscopy (TEM), atomic force microscopy (AFM), Rutherford backscattering spectroscopy and nuclear reaction analysis. The outer layer is composed mainly of In2O3 of relatively low atomic density, about 50% that of crystalline In2O3. The low density is probably due partly to the presence of numerous cavities in the layer, revealed by TEM and AFM. The inner layer is enriched in phosphorus relative to the composition of the substrate, with a P : In atomic ratio of about 2.17. From the measured ratio of phosphorus to indium, the composition of the inner layer can be expressed as either In2O3.2.17P(2)O(5) or In(PO3)(2.17). The average nm V-1 ratio is 1.99 +/- 0.07. However, there are wide variations of the local film thickness, associated with roughness at the substrate/film and film/electrolyte interfaces and local variability in the ionic current density due to cavities in the film. The film forms with a small loss of indium species to the electrolyte. The outer layer represents about 32% of the total thickness of a film formed at 100% efficiency. (C) 2001 Kluwer Academic Publishers.
  • E Akiyama, K Asami, H Habazaki, A Kawashima, K Hashimoto
    CORROSION AND CORROSION PROTECTION 2001 (22) 1 - 8 2001 
    Alloying additions of Ni to amorphous Al-Ti alloy and Mo to Al-Cr alloys and simultaneous addition of Ti and Cr to Al have been performed to improve the corrosion resistance of amorphous Al-Ti and Al-Cr alloy, which are not passivated in 1 M HCl. Mg addition to Al-Ti alloys was also performed expecting enrichment of Ti in the surface film caused by rapid dissolution of alloying constituents unnecessary for passivation. The amorphous Al-Ti-Ni, Al-Cr-Ti and Al-Cr-Mo alloys were passivated spontaneously even in 1 M HCl solution and showed higher pitting potentials than those of Al-Ti and AI-Cr binary alloys. The addition of relatively small amount of Mg to Al-Ti alloys increased the pitting potential of Al-Ti alloys. X-ray photoelectron spectroscopy (XPS) measurement allowed to correlate the protective ability of the passive films to the stability of Cr or Ti enriched surface layer of the passive films.
  • Z Ashitaka, GE Thompson, P Skeldon, H Habazaki, K Shimizu
    JOURNAL OF MATERIALS SCIENCE 36 (9) 2237 - 2243 0022-2461 2001 
    The production of high specification, aluminium-based, electrolytic capacitors requires optimization of material composition and heat and surface treatments in order to maximize the area available for formation of the dielectric, anodic film. Commercial foils contain low additions of copper and lead in order to achieve this goal. The present study examines the effects of heat and surface treatments on aluminium foil containing either 50 or 1000 ppm bismuth, as a replacement for lead, by a combination of Rutherford backscattering spectroscopy and scanning electron microscopy. Heat treatment at 823 K results in segregation of bismuth to the surface regions of the foils, with enrichments in the range 4-8 x 10(14) Bi atoms cm(-2), localized mainly just beneath the thermal oxide, for the selected treatment conditions. The enrichment reduces following alkaline etching, to the range 1-4 x 10(14) Bi atoms cm(-)2. This level of enrichment is maintained during subsequent anodizing, with the enrichment partitioned between the metal and the outermost layers of the anodic films. The enrichment of the metal is about 4 x 10(13) Bi atoms cm(-)2. Electropolishing in perchloric acid solution eliminates the enrichment developed during the heat treatment, probably due to activation during the polishing process. The enrichment remains very low or negligible during subsequent anodizing. The general behaviours of bismuth and lead are similar in aluminium foils subject to the selected heat and surface treatments. However, additional studies are needed of tunnel etching to determine the feasibility of substitution of lead by bismuth in commercial foils. (C) 2001 Kluwer Academic Publishers.
  • H Habazaki, Y Naruse, H Konno, H Ukai, K Izumiya, K Hashimoto
    CORROSION AND CORROSION PROTECTION 2001 (22) 130 - 137 2001 
    Bulk amorphous Ni-Cr-Nb-16P-4B alloys with extremely high corrosion resistance in hydrochloric acid solutions have been prepared successfully by copper mold casting. The cylindrical amorphous alloys thus prepared are spontaneously passive in 1, 6 and even 12 mol dm(-3) HCl solutions at 303 K, although precipitation of a nanocrystalline fcc Ni phase in the amorphous matrix reduces their high corrosion resistance slightly. Since the maximum diameter of the amorphizable cylindrical specimens by this casting technique is 2 mm, a larger amorphous Ni-10Cr-5Nb-16P-4B alloy plate of 2 mm thickness has been prepared by sheath rolling of He gas-atomized amorphous alloy powders at 708 K, at which the alloy is in the supercooled liquid state. The alloy plate reveals high corrosion resistance in 6 mol dm(-3) HCl solution, which is as high as that of the corresponding rapidly quenched alloy ribbon.
  • K Hashimoto, H Katagiri, H Habazaki, M Yamasaki, A Kawashima, K Izumiya, H Ukai, K Asami, S Meguro
    ELECTROCHEMICAL AND CHEMICAL REACTIVITY OF AMORPHOUS AND NANOCRYSTALLINE MATERIALS 377 1 - 8 0255-5476 2001 
    The addition of chromium, tantalum and molybdenum was the best combination of small additions in enhancing the corrosion resistance of amorphous Ni-16P-4B alloys in concentrated hydrochloric acid, Preparation of rod-shaped amorphous alloys with small contents of these three corrosion-resistant elements were attempted by copper-mold casting. Ni-5Cr-5Ta-3Mo-16P-4B alloy of I mm diameter is identified as a single amorphous phase alloy and spontaneously passive in 6 and 12 M HCl, similarly to melt-spun amorphous counterpart, although high resolution TEM observation reveals the presence of nanocrystal line precipitates of about 2 mn in diameter. Ni-5Cr-5Ta-5Mo-16P-4B alloy is also amorphous by X-ray diffraction but contains nanocrystallites of about 5 nm in diameter, the anodic current in 6 M HCl being more than one order of magnitude higher than that of the melt-spun amorphous counterpart. All other copper-mold cast Ni-Cr-Ta-Mo-16P-4B alloys are composed of crystalline precipitates in the amorphous matrix. Sheath-rolling consolidation of gas-atomized amorphous alloy powders to form the amorphous alloy sheet of about 2 mm was attempted for the Ni-10Cr-5Nb-16B-4B alloy which has a particularly wide temperature interval of the supercooled liquid of 64K. The sheath-rolled alloy specimen are identified as an amorphous single phase by X-ray diffraction and high resolution transmission microscopy. However, because of inclusions of very minor crystalline powders in the major amorphous alloy powders before consolidation, crystalline powder inclusions in the consolidated amorphous matrix was preferentially dissolved by an immersion test in 6 M HCl. In a waste incinerator, the sheath-rolled Ni-10Cr-5Nb-16P-4B alloy showed no detectable weight loss at 393 and 433K for 20 days, maintaining metallic luster.
  • K Hashimoto, H Katagiri, H Habazaki, M Yamasaki, S Meguro, A Kawashima, K Asami
    CORROSION AND CORROSION PROTECTION 2001 (22) 18 - 25 2001 
    Copper-mold casting was applied to prepare amorphous alloy rods of 1mm diameter. Ni-19Ta-10Mo-11Nb-5P, Ni-22Ta-5Mo-13Nb-5P and Ni-2.5Cr-22Ta-2.5Mo-13N6-5P alloys were identified as amorphous alloys by X-ray diffraction and are spontaneously passive in 6 and 12 M HCl at 303 K. Among them, the Ni-2.5Cr-22Ta-2.5Mo-13Nb--5P alloy showed no corrosion weight loss by immersion in 12 M HCl for 168 h. Corrosion-resistant elements were significantly concentrated in air-formed films on these alloys. No film composition change occurs for the Ni-2.5Cr-22Ta-2.5Mo-13Nb-5P alloy by immersion in 12 M HCl. It has been reconfirmed that the addition of three corrosion-resistant elements, chromium, tantalum and molybdenum is the most effective combination in enhancing the corrosion resistance in concentrated hydrochloric acids.
  • H Katagiri, S Meguro, M Yamasaki, H Habazaki, T Sato, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 43 (1) 171 - 182 0010-938X 2001/01 
    The best combination of small additions of corrosion-resistant elements in enhancing the corrosion resistance in 6 M HCl open to air at 303 K is examined for amorphous Ni-16P-4B alloys by adding chromium, tantalum and molybdenum The highest corrosion resistance is obtained by the additions of all three corrosion-resistant elements. The Ni-5Cr-5Ta-5Mo-16P-4B alloy is immune to corrosion. The most protective passive film for med on the Ni-5Cr-5Ta-(3-5)Mo-16P-4B alloys consists of outer double oxyhydroxide of Ta5+ and Cr3+ and inner Mo4+ oxide. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • H Katagiri, S Meguro, M Yamasaki, H Habazaki, T Sato, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 43 (1) 183 - 191 0010-938X 2001/01 
    Preparation of cylindrical amorphous alloys with low contents of three corrosion-resistant elements, chromium, tantalum and molybdenum, were attempted by copper-mold casting. Ni-5Cr-5Ta-3Mo-16P-4B alloy of I mm diameter is identified as a single amorphous phase alloy and spontaneously passive in 6 and 12 M I-ICI, similar to the melt-spun amorphous counterpart, although high resolution TEM observation reveals the presence of nanocrystalline precipitates of about 2 nm diameter. Ni-5Cr-5Ta-5Mo-16P-4B alloy is also amorphous as shown by X-ray diffraction studies but contains nanocrystallites of about 5 nm diameter, the anodic current in 6 M HCl being more than one order of magnitude higher than that of the melt-spun amorphous counterpart. All other copper-mold cast Ni-16P-4B alloys with chromium, tantalum and molybdenum are composed of crystalline precipitates in the amorphous matrix. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • S Mato, P Skeldon, GE Thompson, D Masheder, GI Sproule, MJ Graham, H Habazaki, K Shimizu
    SURFACE AND INTERFACE ANALYSIS 29 (12) 895 - 902 0142-2421 2000/12 
    The anodic oxidation behaviour of two compositions of Nb-Cu alloy is examined with particular reference to the oxidation of copper at the alloy/film interface and the generation of oxygen within the anodic film. Anodizing of an Nb-3 at. % Cu alloy results in a uniform, niobia-based anodic film, with copper species, which migrate faster than Nb5+ ions, distributed throughout the film. The oxidation of copper proceeds without significant enrichment of copper in the alloy. Further, the film is free of bubbles of oxygen, which is not generated in significant amounts during film growth to relatively high voltages. In contrast, copious amounts of oxygen are generated during anodizing of an Nb-30 at,% Cu alloy, with the consequential development of a highly flawed anodic film of non-uniform thickness. The oxygen is present mainly in numerous bubbles located within the niobia-based film material. Bursting of the bubbles, with release of trapped oxygen, leads to a highly damaged film. The continuous generation of oxygen consumes much of the current and limits the anodizing voltage to a low value. The large-scale generation of oxygen for the more concentrated alloy is suggested to be associated with the distribution of copper in the alloy, with copper having a tendency to form copper-rich clusters, which are enhanced in size by an initial brief period of uniform film growth. Oxygen is then generated, probably following oxidation of such clusters. Copyright (C) 2000 John Wiley & Sons, Ltd.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson
    SURFACE AND INTERFACE ANALYSIS 29 (12) 887 - 890 0142-2421 2000/12 
    Through the analysis of a commercial hard disk, it is demonstrated that glow discharge optical emission spectroscopy (GDOES) is a powerful technique for depth profiling analysis of surfaces coated with multilayers of widely differing thicknesses, ranging from a few tens of nanometres to several tens of microns. This arises from its high depth resolution, resulting from highly uniform sputtering, and its wide thickness range, resulting from its high sputtering rate. The depth profile obtained agreed precisely with the layered structure of the disk revealed directly by cross-sectional transmission electron microscopy, Copyright (C) 2000 John Wiley & Sons, Ltd.
  • M Yamasaki, H Habazaki, K Asami, K Hashimoto
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 147 (12) 4502 - 4506 0013-4651 2000/12 
    In order to control the: oxidation products of amorphous Ni-Zr and Ni-Zr-rare earth clement alloys, which have an important role in the catalytic activity of amorphous alloy-derived catalysts, their oxidation behavior was examined as a function of nickel and samarium contents. Faster oxidation occurs for the nickel-rich Ni-Zr binary alloys compared with the zirconium-rich alloys. The addition of samarium further accelerates the oxidation. due to thr formation of a poorly protective oxide scale. The: oxides formed from amorphous Ni-Zr and Ni-Zr-Sm alloys are nanograined zirconia as well as NiO. The zirconia consists of metastable tetragonal and monoclinic phases. The relative amount of the tetragonal phase increases with an increase in the alloy nickel content. The suppression of grain growth of zirconia by the fine dispersion of NiO results in the formation of the metastable tetragonal phase. The addition of samarium to the Ni-Zr alloys further promotes the formation of the tetragonal phase as a result of the stabilization of the tetragonal phase by doping of samarium ions. (C) 2000 The Electrochemical Society. S0013-4651(00)04-067-2. All rights reserved.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    SURFACE AND INTERFACE ANALYSIS 29 (11) 743 - 746 0142-2421 2000/11 
    An air-formed film, similar to2 nm thick, on sputter-deposited Type 304 stainless steel has been analysed by glow discharge optical emission spectroscopy (GDOES) depth profiling. The distributions of iron, chromium, nickel and hydrogen in the film and alloy substrate have been revealed, with excellent depth resolution. The film consists of two distinct layers: an outer iron oxide layer and an inner oxide layer highly enriched with chromium oxide. Further, a thin nickel-enriched layer is evident in the alloy immediately beneath the oxide film. The implications of these findings for the structure and mechanism of growth of the film are discussed. Copyright (C) 2000 John Whey & Sons, Ltd.
  • AE Herrera-Erazo, H Habazaki, K Shimizu, P Skeldon, GE Thompson
    CORROSION SCIENCE 42 (10) 1823 - 1830 0010-938X 2000/10 
    Anodizing of an Al-10at.%Nd sputtering deposited alloy is examined by a combination of transmission electron microscopy, Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy, in order to determine the role of neodymium during film growth. An amorphous oxide him forms, containing units of Al2O3 and Nd2O3, on a mainly amorphous alloy. The film grows by migration of O2- ions inward and Al3+ and Nd3+ ions outward. Nd3+ ions migrate faster than Al3+ ions, by a factor of approximately 2.0, and form a thin layer of Nd2O3, which is readily hydrated, at the surface of the film. The efficiency of film growth is close to 100% under the selected conditions of anodizing. The anodic oxidation of the alloy proceeds without the development of a neodymium-rich alloy layer, which is consistent with the lower Gibbs free energy per equivalent for formation of Nd2O3 relative to Al2O3. The field strength for film growth is reduced as compared with that for anodic alumina, due to the presence of units of Nd2O3. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • F Echeverria, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    THIN SOLID FILMS 371 (1-2) 303 - 309 0040-6090 2000/08 
    The growth of amorphous anodic oxides on InAs in aqueous sodium tungstate electrolyte at 5 mA cm(-2) has been examined using transmission electron microscopy, atomic force microscopy and Rutherford backscattering spectroscopy. Films formed at similar to 100% efficiency are two-layered, with an outer layer composed of In2O3 above an inner layer composed of units of In2O3 and As2O3. The composition of the inner layer is approximately In2O3 . 1.45As(2)O(3). The outer layer, which comprises approximately 23% of the film thickness, results from faster outward migration of In3+ ions relative to that of As3+ ions. The In2O3 layer has a low ionic density compared with the inner layer material, which may be associated with cavities observed by microscopy. The outer layer is absent from films if the efficiency is less than similar to 85%. The nm V-1 ratios for growth of single-layered and double-layered films are approximately 1.9 and 1.8, respectively. Tungsten species are present in the outer regions of the film. (C) 2000 Elsevier Science S.A. All rights reserved.
  • S Meguro, T Sasaki, H Katagiri, H Habazaki, A Kawashima, T Sakaki, K Asami, K Hashimoto
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 147 (8) 3003 - 3009 0013-4651 2000/08 
    Tailoring of active nickel alloy cathodes fur hydrogen evolution in a hot concentrated hydroxide solution was attempted by electrodeposition. Electrodeposited iron is naturally more active for hydrogen evolution than nickel, but Ni-Fe alloys show further high activity for hydrogen evolution, although the rate-determining step being assumed as proton discharge is not changed. The carbon addition to iron or nickel remarkably enhances the activity for hydrogen evolution and changes the mechanism of hydrogen evolution. Ternary Ni-Fe-C alloys show the highest activity for hydrogen evolution, and the Tafel slope of hydrogen evolution is about 33 mV/dec, suggesting the rate-determining step of desorption of adsorbed hydrogen by recombination. XPS analysis reveals that the charge transfer occurs From nickel to iron in alloys and the carbon addition particularly enhances the charge transfer. Accelerated proton discharge due to enhanced charge transfer from nickel to iron seems responsible for the high activity of the Ni-Fe-C alloys for hydrogen evolution. (C) 2000 The Electrochemical Society. S0013-4651(00)01-083-1. All rights reserved.
  • K Tzoganakou, P Skeldon, GE Thompson, Zhou, X, U Kreissig, E Wieser, H Habazaki, K Shimizu
    CORROSION SCIENCE 42 (6) 1083 - 1091 0010-938X 2000/06 
    The mobility of lithium species in the barrier anodic film formed on an Al-3 at% Li alloy in ammonium pentaborate electrolyte has been determined from measurements of film composition by glow discharge optical emission spectroscopy and elastic recoil detection analysis. The results reveal the presence of lithium species throughout the thickness of the anodic film, with a reduced amount of lithium in the film compared with that in the alloy. The level of reduction in lithium content indicates that lithium species migrate outward about eight times faster than Al3+ ions. The lithium species are lost to the electrolyte on reaching the film/electrolyte interface, leading to a slight loss in the efficiency of film growth. In contrast, aluminium species are retained within the film, as revealed by the distribution of boron in the outer similar to 40% of the film thickness. Determination of hydrogen profiles indicates insignificant amounts of hydrogen in the film. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • H Habazaki, K Takahiro, S Yamaguchi, K Shimizu, P Skeldon, GE Thompson, GC Wood
    PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES 80 (5) 1027 - 1042 0141-8610 2000/05 
    Barrier-type anodic oxide films, with relatively uniform distributions of Al3+ and Zr4+ ions, have been formed on sputter-deposited, non-equilibrium Zr-Al alloys, containing 5, 15 and 43 at.% Al, in 0.01 M ammonium pentaborate electrolyte at 393 K. The films formed on the last two alloys are primarily amorphous, with transport numbers of cations of about 0.18 and 0.25 respectively, i.e., increasing with increase in aluminium content. Thus, as for other amorphous anodic oxides, both cation and anion transport contribute significantly to film growth. However, nanocrystals, suggested to be based on cubic ZrO2, are formed near the alloy-film interface in the amorphous oxide matrix, in association with bubbles due to generation of oxygen gas in the vicinity of the alloy-film interface. Increase in the zirconium content to 95 at.% leads to the formation of a relatively uniform, crystalline anodic film with a monoclinic ZrO2 structure; film growth now proceeds predominantly due to migration of anions, similar to films formed on high purity zirconium.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 42 (5) 831 - 840 0010-938X 2000/05 
    Porous anodic oxide formation on an Al-1.4wt%Fe alloy containing finely dispersed Al6Fe particles has been examined by transmission electron microscopy of ultramicrotomed sections, with particular attention directed towards the local film formation over the Al6Fe particles. It was found that anodic oxide formation over the Al6Fe phases involves initial oxidation of aluminium and interfacial enrichment of iron, with the enrichment confined to a thin layer, about 1-2 nm thick, in the Al6Fe phase immediately beneath the oxide. With EDX analysis, using an electron probe of 0.8 nm diameter, the composition of the iron-enriched layer has been determined to be about Al80Fe20. Additionally, close examination of the iron-enriched layer, using an ultra-high resolution transmission electron microscope, has revealed that the layer has a heavily distorted structure with the occasional presence of ordered domains, only 1 MI diameter, with the Al6Fe structure. No evidence was obtained to suggest the presence of nano-sized iron clusters in the enriched layer. These observations are discussed in terms of the Gibbs free energy criteria for alloy oxidation proposed recently by several of the authors. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • Zhou, X, GE Thompson, H Habazaki, MA Paez, K Shimizu, P Skeldon, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 147 (5) 1747 - 1750 0013-4651 2000/05 
    The morphological development of oxygen bubbles in amorphous, anodic alumina is examined during anodizing an Al-1 atom % Cu alloy. Using transmission electron microscopy, a sequence of stripped films reveals the dynamic evolution of numerous bubbles in the thickening film. The formation of the bubbles is associated with the enrichment of copper in the alloy due to growth of the anodic oxide. Evidently the alumina exhibits a liquid-like behavior under the electric field, assisted by inherent free-volume, which accommodates nucleation, growth, clustering, and coalescence of bubbles, without damage to the film. Bubbles nucleate throughout growth of the film, close to the alloy/film interface, but growth of pre-existing bubbles appears favored. The bubbles, which number about 1 x 10(14) m(-2), are in pressure equilibrium, with typical pressures of several hundred megapascals. The bubbles, with dimensions up to a few tens of nanometers, are obstacles to ionic transport, which leads to nonuniformity of film thickness and interfacial roughness. (C) 2000 The Electrochemical Society. S0013-4651(99)10-073-9. All rights reserved.
  • DB Lee, H Habazaki, A Kawashima, K Hashimoto
    CORROSION SCIENCE 42 (4) 721 - 729 0010-938X 2000/04 
    The oxidation behavior of an amorphous 58Nb-38Al-4Si (at.%) coating sputter-deposited on a titanium substrate has been studied in air at temperatures of 973-1173 K, The oxidation of the coated specimens follows a familiar parabolic rate law for a long time of oxidation at all temperatures examined, in contrast to the paralinear kinetics of uncoated titanium. Even though the coated specimen has higher oxidation rates than the amorphous Nb-Al-Si alloy itself, the amorphous Nb-Al-Si coating is highly effective in providing protection against the oxidation of titanium, The cross-sectional observation and energy-dispersive X-ray spectrometer analysis of the oxidized specimen reveal that titanium diffuses outward in the coating and is also present in the inner part of the oxide scale. The oxide scales formed on the coated specimens primarily consist of TiO2, AlNbO4 and kappa-Al2O3 The presence of less protective TiO2 within the oxides appears to decrease the oxidation resistance of the coating, but is not significantly detrimental. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • Y Kihn, GE Thompson, G Galaup, P Skeldon, Zhou, X, K Shimizu, H Habazaki
    CORROSION SCIENCE 42 (3) 533 - 544 0010-938X 2000/03 
    Anodic films developed on aluminium alloys, Al-Cr for example, are frequently characterised morphologically by transmission electron microscopy, with precise composition, and valence stales of relevant species determined by comparatively broad beam techniques, e.g, Rutherford backscattering spectroscopy, X-ray absorption spectroscopy using synchrotron radiation, etc. Here, the combination of transmission electron microscopy with electron energy loss spectroscopy has been utilized for morphological, compositional and structural probing at the necessary resolution in a single instrument. Fur the Al-Cr alloy, anodizing results in interfacial enrichment of chromium in a thin alloy layer immediately beneath the anodic him, upon achieving a steady-stale enrichment, chromium is oxidized and incorporated into the alumina film as Cr3+-O units. The Cr3+ species have reduced outward mobility relative to Al3+ ions under the high electric field across the anodic film. Further, oxygen gas development is associated with oxidation and incorporation of chromium, such gas, detected readily by EELS, is present in gas-filled voids within the film section. The presence of oxygen-filled voids evidently influences the outward mobility of chromium species detected from fine volumes of film material. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • N Margadant, P Skeldon, M Textor, GE Thompson, J Wan, H Habazaki, K Shimizu, ND Spencer, GC Wood
    CORROSION SCIENCE 42 (3) 405 - 419 0010-938X 2000/03 
    Al-0.028 at.% Ga alloy, either just electropolished or subsequently anodized, was examined for gallium enrichment in the alloy using Rutherford buckscattering spectroscopy. Unlike with alkaline etching, no significant enrichment of gallium, namely <5 x 10(17) Ga atoms m(-2), was developed by electropolishing in perchloric acid:ethanol, which is suggested to be associated with activation of the alloy in the acid bath. In contrast, during anodizing in ammonium pentaborate electrolyte, gallium is accumulated to 400 V at 50 A m(-2) progressively in a thin alloy layer beneath the anodic film, with initial formation of essentially gallium-free alumina. The number of gallium atoms accumulated in the enriched alloy layer per. unit area of alloy/film interface increases linearly with the anodizing voltage at 1.0 x 10(16) Ga atoms m(-2) V-1. At anodizing voltages above similar to 150 V, the films become detached locally from the alloy. The detachment evidently coincides with the formation of fine voids at the alloy/film interface, observed in the transmission electron microscope, possibly initiated by localized oxidation of gallium-rich regions of alloy. (C) 2000 Elsevier Science Ltd, All rights reserved.
  • M Mehmood, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 42 (2) 361 - 382 0010-938X 2000/02 
    The nanocrystalline heterogeneity has been introduced into sputter-deposited Cr-Nb alloys by heat treatment in order to clarify the effect of alloy heterogeneity on the corrosion resistance of the alloys. The as-deposited amorphous Cr-Nb alloys are spontaneously passive in 6 and 12 M HCl and show higher corrosion resistance than chromium and niobium. The heat treatment leads to the formation of two phase mixtures of bcc Cr and Cr2Nb, Cr2Nb and niobium-rich amorphous phase, Cr2Nb and bcc Nb, and chromium-rich amorphous phase and bcc Nb, depending on the alloy composition and the heat treatment conditions. It has been found that the Cr2Nb phase has high corrosion resistance, comparable to that of the amorphous alloys. The formation of nanocrystalline bcc Cr or bcc Nb phases results in the increase in the initial passive current density. However, the long time potentiostatic polarization has revealed that the steady state anodic current density of the heat-treated alloys is similar to that of the as-deposited alloys as a consequence of preferential dissolution of less corrosion-resistant phases. Accordingly, the high corrosion resistance of the amorphous Cr-Nb alloys is sustained even after the introduction of nanocrystalline heterogeneity. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    SURFACE AND INTERFACE ANALYSIS 29 (2) 151 - 154 0142-2421 2000/02 
    Amorphous Ni-P-plated aluminium disks for magnetic data storage have been analysed by glow discharge optical emission spectroscopy (GDOES) depth profiling. The distribution of impurities, related to the fabrication processes, have been disclosed within the NI-P layers and at the Ni-P/aluminium interface. Examination of sputter craters by AFM and surface roughness measurements indicate that the sputtering of the amorphous Ni-P layer proceeds without significant microscopic roughening, Copyright (C) 2000 John Whey & Sons, Ltd.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    SURFACE AND INTERFACE ANALYSIS 29 (2) 155 - 159 0142-2421 2000/02 
    The influence of Ar pressure on depth resolution during glow discharge optical emission spectroscopy (GDOES) depth profiling has been examined through the use of 358 nm thick anodic alumina films grown over flat aluminium surfaces. The films are ideal standards for the present purpose, being amorphous and highly uniform in thickness, with a flat and sharply-defined metal/film interface. The depth resolution is influenced strongly by the Ar pressure, which, in turn, is related to the shapes of the craters generated by cathodic sputtering. For a given power, an optimum Ar pressure results in a flat-bottomed crater and the highest depth resolution is realized. In the present example, the highest depth resolution, expressed in terms of width of the transition of the aluminium profile at the metal/film interface, i,e, similar to 7 nm, was achieved at a pressure gauge voltage of 5.60 V (0.41 mbar) and a power of 40 W, Increase or decrease of Ar pressure from the optimum leads to rapid degradation of depth resolution. Copyright (C) 2000 John Wiley & Sons, Ltd.
  • Z Ashitaka, GE Thompson, P Skeldon, GC Wood, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 147 (1) 132 - 139 0013-4651 2000/01 
    Thr effects of heat-treatment, electropolishing, alkaline etching, and anodizing on the distributions of lead in 100 mu m thick, two-phase aluminium foils, containing 100, 500 1000,;md 10,000 ppm le;lead, have been examined by scanning electron microscopy and Rutherford backscattering spectroscopy. Heat-treatment at 823 K for 20 ks resulted in segregation of similar to 3 to 15% of the lend to within approximately 500 nm of the surfaces of the foils. The enrichments, dependent upon foil composition, were largely retained in the near-surface regions during subsequent alkaline etching. but electropolishing caused depletion of lead. with respect to the bulk composition, over a depth up to about 500 nm, associated with loss of lead-rich particles, No significant enrichments were developed during subsequent anodizing of electropolished foils. In contrast, following anodizing of etc foils, lead was enriched both in the metal layers immediately adjacent to the metal/anodic: film interfaces and at the surfaces of the anodic films. Further, lead oxide or hydroxide particulates associated with anodic oxidation of lead particles, decorated the foil surfaces. It is suggested that lead species are present throughout anodic film material formed above matrix regions of metal. where they migrate outward faster than Al3+ ions to form a layer of lead-rich oxide at the film/electrolyte interface. The anodizing process resulted in loss of roughly 50% of the of original enrichment of the etched foil. (C) 2000 The Electrochemical Society. S0013-4651(99)06-069-3. All rights reserved.
  • K Fujimura, T Matsui, H Habazaki, A Kawashima, N Kumagai, K Hashimoto
    ELECTROCHIMICA ACTA 45 (14) 2297 - 2303 0013-4686 2000 
    MnO2-type manganese-molybdenum oxides have been anodically deposited under various conditions on IrO2-coated titanium substrates, and the durability of the oxide anodes for oxygen evolution in seawater electrolysis has been examined. When sufficiently thick oxides are deposited, all the oxide anodes containing 8 mol% or more molybdenum in cationic percentage show an initial oxygen evolution efficiency of almost 100% at a constant current density of 1000 A.m(-2) in 0.5 M NaCl solution at pH 12 and 30 degrees C. However, the oxygen evolution efficiency decreases gradually during the electrolysis mainly due to the exfoliation of oxides. It has been found that the exfoliation is remarkably suppressed when the oxide is deposited under vigorous oxygen evolution at high temperature of 90 degrees C, high current density of 600 A.m(-2) and low electrolyte pH of 0. The anode prepared under this condition reveals an oxygen evolution efficiency of more than 99.6% even after 1500 h of the electrolysis at 1000 A.m(-2). The anodic deposition at lower temperatures at and below 50 degrees C results in the electrochemical dissolution as permanganate ions during the electrolysis. Such dissolution does not occur for the oxides deposited at 90 degrees C, even when the electrolysis is performed at 10000 A.m(-2) at which the potential of the anode exceeds 3 V from the equilibrium potential of the formation of permanganate from MnO2. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • H Habazaki, K Ito, K Hon-yashiki, A Kawashima, K Hashimoto, S Mrowec
    HIGH TEMPERATURE CORROSION AND MATERIALS CHEMISTRY 99 (38) 258 - 269 2000 
    Cr-Ta alloys highly resistant to high temperature sulfidation and oxidation have been prepared by sputter deposition The sulfidation of the Cr-Ta alloys follows a familiar parabolic rate law, thus being diffusion controlled, The parabolic rate constants of the alloys are remarkably lower than those of chromiun, and decrease gradually with increasing alloy tantalum content. The sulfidation rates of the tantalum-rich alloys are close to that of tantalum. The sulfide scales formed on the Cr-Ta alloys consists of two layers, comprising an outer Cr2S3 layer and an inner TaS2 layer. The diffusional transport of matter in the inner layer should be a rate-determining step. The oxidation of the Cr-40Ta ahoy follows a parabolic rate law, and the oxidation rate is almost comparable to that of the typical chromia-forming alloys. The formation of an outer Cr2O3 layer should be responsible for the high oxidation resistance of this alloy.
  • S Meguro, T Sasaki, H Katagiri, H Habazaki, A Kawashima, T Sakaki, K Hashimoto
    FUNDAMENTAL ASPECTS OF ELECTROCHEMICAL DEPOSITION AND DISSOLUTION, PROCEEDINGS 99 (33) 211 - 218 0275-0171 2000 
    Tailoring of active nickel alloy cathodes for hydrogen evolution in a hot concentrated hydroxide solution was attempted by electrodeposition. Electrodeposited iron is naturally more active for hydrogen evolution than nickel, but Ni-Fe alloys show further high activity for hydrogen evolution, although the rate-determining step being assumed as proton discharge is not changed. The carbon addition to iron or nickel remarkably enhances the activity for hydrogen evolution and changes the mechanism of hydrogen evolution. Ternary Ni-Pe-C alloys show the highest activity for hydrogen evolution, and the Tafel slope of hydrogen evolution is about 30 mV/decade, suggesting the rate-determining step of desorption of adsorbed hydrogen by recombination. XPS analysis reveals that the charge transfer occurs from nickel to iron in alloys and the carbon addition particularly enhances the charge transfer. Accelerated proton discharge due to enhanced charge transfer from nickel to iron is responsible for the high activity of the Ni-Fe-C alloys for hydrogen evolution.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    ELECTROCHIMICA ACTA 45 (11) 1805 - 1809 0013-4686 2000 
    The migration rate of sulphate ions, incorporated into anodic alumina from the electrolyte, has been determined by analysis of films, containing a boron species marker, by glow discharge optical emission spectroscopy. The relative distributions of boron and sulphur species in the depth profiled film indicate that the inward migration of sulphate anions proceeds at a rate of about 0.62 times that of O2- ions. However, significant broadening of the sulphur profile with depth of migration was observed, which is attributed to statistical fluctuation of jump distances. The factors determining the rates of inward migration of anion species in amorphous anodic oxides are considered with respect to influences of ionic size, ionic charge and local film structure, although there is at present no general explanation of behaviours. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • M Yamasaki, H Habazaki, A Kawashima, K Asami, E Akiyama, K Hashimoto
    HIGH TEMPERATURE CORROSION AND MATERIALS CHEMISTRY 99 (38) 180 - 191 2000 
    In order to control the oxidation products of amorphous Ni-Zr and Ni-Zr-rare earth element alloys, which have an important role in the catalytic activities of the amorphous alloy-derived catalysts, their oxidation behavior was examined as a function of nickel and samarium contents. The faster oxidation occurs for the nickel-rich Ni-Zr binary allays in comparison with the zirconium-rich alloys. The addition of samarium further accelerates the oxidation, due to the formation of the poor protective oxide scale. The oxides formed from amorphous Ni-Zr and Ni-Zr-Sm alloys an nano-grained zirconia as well as NiO. The zirconia consists of metastable tetragonal and monoclinic phases. The relative amount of the tetragonal phase increases with an increase in the alloy nickel content. The suppression of grain growth of zirconia by the fine dispersion of NiO results in the formation of the metastable tetragonal phase. The addition of samarium to the Ni-Zr alloys further promotes the formation of the tetragonal phase as a result of the stabilization of the tetragonal phase by doping of samarium ions.
  • AC Crossland, H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X, CJE Smith
    CORROSION SCIENCE 41 (10) 1945 - 1954 0010-938X 1999/10 
    Flaws in anodic alumina films are localized sites where the film material is modified morphologically, structurally, or chemically compared with adjacent regions of uniform amorphous alumina. The flaws are preferred sites of pitting and dielectric breakdown, which are of importance to the corrosion resistance and electronic applications of aluminium respectively. Although flaws have been categorized in general terms as either mechanical or residual, there is no detailed understanding of the precise origin and nature of flaws and their mechanisms of influence in pitting and dielectric breakdown. Consideration is given here to the formation of oxygen bubbles within anodic alumina, by oxidation of O2- ions in the vicinity of the metal/film interface, which are suggested to be one type of residual flaw. The compositions of impurities or second phase particles, which may lead to generation of oxygen bubbles, are examined in the light of systematic investigations of anodizing of binary aluminium alloys. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 41 (9) 1849 - 1869 0010-938X 1999/09 
    Amorphous Fe-Cr-Ni-Ta alloys containing 7-75 at.% tantalum were successfully prepared by the D.C. magnetron sputtering method by using a target of commercial Type 304 stainless steel and high purity tantalum discs. The corrosion behavior of the Fe-Cr-Ni-Ta alloys in 12 M HCl at 30 degrees C was investigated by immersion tests, electrochemical measurements and XPS analysis, and compared with that of Cr-Ta binary alloys. The corrosion rate of the sputter-deposited Fe-Cr-Ni-Ta alloys containing more than 19 at.% tantalum was more than six orders of magnitude lower than that of bulk Type 304 stainless steel and even lower than that of sputter-deposited tantalum metal, although the corrosion rate of the alloys was higher than that of the Cr-Ta alloys. The open circuit potentials of the Fe-Cr-Ni-Ta alloys are located in the passive regions of both chromium and tantalum, and all the alloys are spontaneously passivated. XPS analysis revealed that the passive films formed on the alloys by immersion in 12 M HCl were significantly rich in tantalum and chromium cations, The films were deficient in iron cation and the formation of homogeneous double oxyhydroxides containing mainly chromium and tantalum should be responsible for the high corrosion resistance of the alloys. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • AA El-Moneim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 267 (2) 285 - 293 0921-5093 1999/07 
    New series of nanocrystalline and amorphous single phase binary Mn-Zr and Mn-Cr and ternary Mn-Zr-Cr manganese-base alloys are successfully prepared by DC magnetron sputtering. Electrochemical measurements in combination with XPS analysis are used for examining the effect of single and binary additions of zirconium and chromium metals on the passivity and breakdown of manganese-base alloys in borate-boric acid solutions of pH 8.4 containing 0.01-1 M NaCl. Significant improvement in the resistance to passivity breakdown is observed when chromium and zirconium are added simultaneously to manganese instead of single addition of zirconium or chromium metals. The beneficial effect of simultaneous addition of zirconium and chromium is based mainly on the synergistic interaction between chromium and zirconium cations in the homogeneous double oxyhydroxide passive films formed on the alloy by open circuit immersion. (C) 1999 Elsevier Science S.A. All rights reserved.
  • H Habazaki, K Hon-yashiki, K Ito, H Mitsui, A Kawashima, K Asami, K Hashimoto, S Mrowec
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 267 (2) 267 - 276 0921-5093 1999/07 
    In order to tailor novel alloys resistant to high temperature corrosion in multicomponent sulfidizing-oxidizing environments, amorphous or nanocrystalline Al-refractory metal alloys with and without silicon and Cr-refractory metal alloys have been prepared by sputter deposition. The sulfidation and oxidation behavior of the alloys has been studied as a function of temperature in sulfur vapor pressure of 10(3) Pa and in oxygen of 2 x 10(4) Pa, respectively. The sulfidation of these alloys generally follows a parabolic rate law, being thus diffusion controlled. The sulfidation rates of Al-refractory metal and Cr-refractory metal alloys are several orders of magnitude lower than those of conventional high temperature alloys and comparable to or even lower than those of the corresponding refractory metals. The sulfide scales formed on these alloys consist of two layers, comprising an outer Al2S3 or Cr2S3 layer and an inner refractory metal disulfide layer. The formation of the inner layer is attributed to the excellent sulfidation resistance of these alloys. The oxidation resistance of Al-refractory metal alloys is not sufficiently high, but the addition of silicon improves remarkably their oxidation resistance by synergistic effect of aluminum and silicon. Although the Cr-Mo alloys possess poor oxidation resistance, due to the formation of volatile molybdenum oxide, the oxidation resistance of the Cr-Nb and Cr-Ta alloys is as high as that of typical chromia-forming alloys. (C) 1999 Elsevier Science S.A. All rights reserved.
  • K Hashimoto, M Yamasaki, K Fujimura, T Matsui, K Izumiya, M Komori, AA El-Moneim, E Akiyama, H Habazaki, N Kumagai, A Kawashima, K Asami
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 267 (2) 200 - 206 0921-5093 1999/07 
    CO2 emissions which induce global warming, increase with the growth of the economic activity. It is, therefore, impossible to decrease emissions only by energy savings and by improvements of the energy efficiency. Global CO2 recycling can solve this problem and supply abundant renewable energy. Global CO2 recycling consists of three districts: (i) in deserts, all necessary electricities are generated by solar cells; (ii) on coasts close to the deserts, the electricity is used for production of H-2 by seawater electrolysis, H-2 is converted to CH4 by the reaction with CO2 and liquefied CH4 is transported to energy consuming districts; (iii) at energy consuming district, after CH4 is used as a fuel, CO2 is recovered, liquefied and transported to the coasts close to the deserts. A CO2 recycling plant for substantiation of our idea has been built on the roof of our Institute (IMR) in 1996, using key materials tailored by us. The key materials necessary for global CO2 recycling are the anode and cathode for seawater electrolysis and the catalyst for CO2 methanation. Since the quantities of CO2 to be converted far exceed an industrial level, the system must be very simple and the rate of conversion must be very fast. These requirements are satisfied in our global CO2 recycling system. When global CO2 recycling is conducted on a large scale, the energies and costs required to form liquefied CH4 in our global CO2 recycling system are almost the same as those for production of LNG from natural gas wells. A project for field experimenting the global CO2 recycling using pilot plants in Egypt has been planned in cooperation with Egyptian scientists, engineers and industries. (C) 1999 Elsevier Science S.A. All rights reserved.
  • K Hon-yashiki, H Habazaki, E Akiyama, A Kawashima, K Asami, K Hashimoto, S Mrowec
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 267 (2) 277 - 284 0921-5093 1999/07 
    Al-Nb-Mo ternary alloys of about 5 mu m thickness have been deposited on quartz substrates using a sputter deposition technique, and their sulfidation and oxidation behavior has been compared with the Al-Nb, Al-Mo and Nb-Mo binary alloys. The sulfidation of the ternary alloys follows two-stage parabolic kinetics at temperatures of 1073-1273 K in sulfur pressure of 10(3) Pa. The steady-state sulfidation is significantly slower than the initial sulfidation. An interesting fact is that the steady-state sulfidation rates of the ternary alloys are further lower than those of the Al-Nb and Al-Mo binary alloys. In particular, an increase in niobium content in the ternary alloys leads to a decrease in the sulfidation rate. Similarly to the AI-Nb and Al-Mo binary alloys, apparently two-layered scales are formed on the ternary alloys, consisting of an outer Al2S3 layer and an inner refractory metal sulfide layer. The detailed analysis of the inner layer reveals that the inner barrier layer is not a single layer but consisting of an outer thin NbS2 layer and inner major layer of MoS2 containing Nb3S4. The formation of the inner barrier layer consisting of two layers in which diffusing matters and directions are different is attributed to the higher sulfidation resistance of the ternary alloys than those of Al-Nb and Al-Mo binary alloys. The steady-state sulfidation rates of the ternary alloys are also lower than those of the Nb-Mo binary alloys, because the two layered niobium sulfide-molybdenum sulfide doped with Al3+ ions is more protective than the individual NbS2 and MoS2 sulfides doped with Al3+ ions. The oxidation resistance of the aluminum-rich Al-Nb-Mo alloys is better than the AI-Nb and AI-Mo alloys, although the resistance of the former alloys is still not sufficient. (C) 1999 Elsevier Science S.A. All rights reserved.
  • A Kawashima, T Sakaki, H Habazaki, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 267 (2) 246 - 253 0921-5093 1999/07 
    Nickel-molybdenum-oxygen alloy cathodes prepared by are ion plating technique are found to have excellent catalytic activity and durability in the electrolysis of 32.5 wt.% NaOH at 90 degrees C. The catalytic activity is strongly affected by the molybdenum and oxygen content in the alloys. The optimized compositions are between 10 and 20 at.% molybdenum and 5 and 10 at.% oxygen, giving a hydrogen overpotential of less than 100 mV at 4 x 10(3) A m(-2). Furthermore, the cathodes exhibit excellent stability compared with the currently used nickel-sulphur cathode. The decrease in the overpotential by the oxygen addition is attributed to the increase in effective surface area and the enhancement of the rate determining electrochemical desorption of adsorbed hydrogen. (C) 1999 Elsevier Science S.A. All rights reserved.
  • M Yamasaki, M Komori, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 267 (2) 220 - 226 0921-5093 1999/07 
    Nickel catalysts supported on nano-grained oxides have been prepared from amorphous Ni-Zr-Sm and Ni-Zr-Mm (Mm: misch metal) alloys and crystalline Ni-Sm and Ni-Mm alloys. These catalysts show higher catalytic activity for methanation of carbon dioxide than a conventionally prepared zirconia supported nickel catalyst. The catalytic activity of Ni-Zr-5 at% Sm catalysts increases with increase in nickel content, and is higher than the samarium-free Ni-Zr catalysts containing the same amount of nickel. The stabilization of tetragonal zirconia and the increase in the number of active surface nickel sites by addition of samarium to the nickel-rich catalysts leads to enhancement of catalytic activity. In the Ni-Zr-5 at% him catalysts, only the activity of the catalyst containing 60 at% nickel is enhanced in comparison with misch metal-free Ni-Zr catalysts. It is also found that Ni-Sm and Ni-Mm catalysts show activities as high as that of Ni-Zr catalyst, suggesting that samarium and misch metal oxides also act as good catalyst supports for methanation catalysts. (C) 1999 Elsevier Science S.A. All rights reserved.
  • P Skeldon, Zhou, X, GE Thompson, GC Wood, H Habazaki, K Shimizu
    CORROSION 55 (6) 561 - 565 0010-9312 1999/06 
    During anodizing of certain binary Al alloys, the growing anodic oxide film detaches from the alloy substrate, subsequently allowing access of the electrolyte to the underlying bare metal and re-anodizing at a high current density. An Al-3% Li alloy was shown to reveal these phenomena, which are associated with the development of voids at the alloy/film interface as the film thickens. The development of voids, assisting the film detachment, was attributed to the reduced volume of lithium oxide (Li2O) formed at the alloy/film interface and compared to that of alumina (Al2O3).
  • AC Crossland, GE Thompson, P Skeldon, CJE Smith, H Habazaki, K Shimuzu
    TRANSACTIONS OF THE INSTITUTE OF METAL FINISHING 77 95 - 98 0020-2967 1999/05 
    The growth of anodic films on non-equilibrium Al-16.2 at.% Mn-2-7 at. Ce alloy has been examined in ammonium pentaborate, sodium hydroxide and sulphuric acid electrolytes, providing a pH range from 0.2 to 12. Barrier-type anodic films are developed during anodizing to high voltages, the film growth resulting in formation of a main film material, comprising most of the film thickness, composed of units of Al2O3, MnO and CeO2. The Mn2+ and Ce4+ ions migrate outward faster then Al3+ ions, enabling formation of a thin, manganese-rich and cerium-rich, outermost film layer during anodizing in alkaline conditions. This layer sustains barrier film growth to high pH by allowing ingress of O2- but preventing ejection of Al3+ ions to the electrolyte. In sulphuric acid electrolyte, the outer film layer does not form. Furthermore, the outer 50% of the film contains a reduced amount of cerium, possibly due to transient porosity. However, the film remains relatively resistant to the acid electrolyte, thus hindering the transition to growth of porous film material.
  • J De Laet, Zhou, X, P Skeldon, GE Thompson, GC Wood, H Habazaki, K Takahiro, S Yamaguchi, K Shimizu
    CORROSION SCIENCE 41 (2) 213 - 227 0010-938X 1999/02 
    The anodic oxidation of dilute Al-Cr alloys, containing 0.8 and 1.7 at% Cr, has been investigated in order to understand the oxidation behaviour of the alloying element and its influences on the film composition and morphology. The alloys reveal two stages of oxidation: an initial stage, in which only aluminium atoms are oxidized to form a chromium-free anodic alumina film, and a subsequent stage, in which both aluminium and chromium are oxidized, in their approximate alloy proportions, with generation of a chromium-contaminated anodic alumina film. In the first stage, chromium is enriched in a thin layer of alloy, immediately beneath the anodic film, to an amount corresponding to a layer of average thickness 1.5 nm and of average composition, Al-20 at% Cr. Following the oxidation of chromium, oxygen is produced electrochemically within the film at or near the alloy/film interface, probably associated with the development of chromium-rich clusters in the enriched alloy layer and, subsequently, formation of semiconducting chromium-rich oxide. Thus, the film material formed at the alloy/film interface by inward migration of O2- ions contains many oxygen-filled bubbles with associated high pressures. The chromium species present in the film migrate outward more slowly than Al3+ ions. Hence, a layer of chromium-free anodic alumina, which thickens as the film grows, is maintained adjacent to the film/electrolyte interface. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • P Skeldon, GE Thompson, GC Wood, Zhou, X, H Habazaki, K Shimizu
    CORROSION SCIENCE 41 (2) 291 - 304 0010-938X 1999/02 
    The anodizing behaviour of sputter-deposited Al-4at.% Au-1 at.% Cu and Al-1.6 at.% W-0.6 at.% Zn alloys has been examined by Rutherford backscattering spectroscopy and transmission electron microscopy. Initially, a uniform, amorphous alumina film, free of copper and gold species, is formed on the Al-Au-Cu alloy; at the same time, a thin alloy layer, beneath the anodic film, is enriched in copper and gold. The uniform film growth is eventually terminated by generation of oxygen at gold-rich particles at, or near, the alloy/film interface, leading to bubble formation, subsequent rupture of the film and release of oxygen. Film growth on the Al-W-Zn alloy causes mainly enrichment of tungsten in the alloy, with the limited enrichment of zinc contrasting with the behaviour of Al-Zn alloys. Uniform film growth proceeds to high voltages with incorporation of mobile tungsten and zinc species into the film. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • Zhou, X, H Habazaki, E Shimizu, P Skeldon, GE Thompson, GC Wood
    PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 455 (1982) 385 - 399 1364-5021 1999/02 
    The growth of anodic oxide films on metals and alloys is of both theoretical value, in particular with relation to the mechanism of ionic transport in amorphous materials, and practical interest, especially in the surface treatment of metals and alloys and the use of anodic films in electronics applications. Most previous work has focused on uniform film growth, with formation of either an essentially single-layered or a duplex oxide. The present work, employing transmission electron microscopy and Rutherford backscattering spectroscopy, addresses the generation of metallic and gaseous phases in association with the usual film growth, and reveals the ability of the labile amorphous film to accommodate these non-oxide phases. Thus, anodizing of a thin Al-0.47 at.% Au alloy, deposited upon an electropolished aluminium substrate, is shown to result in formation of gold atom clusters of ca. 1-5 nm size and fine oxygen bubbles, at high pressures, which are contained by the growing amorphous alumina film. The generation of the phases originates from enrichment of gold in a thin layer of the alloy, probably containing gold-rich precursor clusters, during the oxidation of the alloy layer and the subsequent enforced incorporation of gold atom clusters into the anodic film by the electropolishing film on the aluminium. The final clusters are essentially immobile following incorporation into the growing anodic film. At the time of, and briefly after, the incorporation of clusters into the film, oxygen gas is produced by oxidation of O2- ions from the alumina, which occurs at the cluster-alumina interface prior to electrical isolation of the cluster due to undermining by further film growth. The resultant oxygen bubbles generated within the alumina expand as the film grows, driven by the high gas pressure and assisted by the effective plasticity of the labile amorphous alumina under the electric field.
  • K Hashimoto, M Mehmood, XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami
    PROCEEDINGS OF THE SYMPOSIUM ON CRITICAL FACTORS IN LOCALIZED CORROSION III 98 (17) 245 - 255 1999 
    The change in the corrosion resistance in concentrated hydrochloric acids with precipitation of nanocrystalline phases into sputter-deposited homogeneous amorphous or nanocrystalline Zr-Cr and Nb-Cr alloys was studied. In general, phases consisting of chromium and other effective elements are spontaneously passive and the corrosion resistance increases with increasing chromium content of the phases, but the bcc chromium phase itself is actively dissolved in concentrated hydrochloric acids. When less chromium-containing phases of about 20nm in diameter are precipitated, the corrosion resistance of the alloys increases because a more protective passive film with a higher chromium content can cover entire surface including the surface of the precipitates as a result of an increase in the chromium content of the matrix. However, if the average size of the precipitates exceeds about 20 nm, the corrosion resistance decreases because the chromium-enriched passive film cannot cover the surface of the grown less chromium precipitates. By contrast, the precipitation of the bcc chromium phase decreases the corrosion resistance, because of lowering of the passivating ability of the matrix regardless of the size of the precipitates, as a result of a decrease in the chromium content of the matrix.
  • Morlidge, JR, P Skeldon, GE Thompson, H Habazaki, K Shimizu, GC Wood
    ELECTROCHIMICA ACTA 44 (14) 2423 - 2435 0013-4686 1999 
    The development of gel layers during anodizing, and their influence on the efficiency of growth of anodic films, has been examined for formation of films at constant current density on aluminium in saturated potassium antimonate electrolyte and 0.1 M sodium molybdate, sodium silicate and sodium tungstate electrolytes. The gels are produced immediately above the growing anodic films by the reaction of H+ ions, generated at the film/gel interface, with the electrolyte anions to form uniform layers of hydrated oxide. The gels can enhance the efficiency of film growth by reducing, or eliminating, field-assisted ejection of Al3+ ions from the film to the electrolyte. The thicknesses of the gel layers increase at constant rates with thickening of the anodic films, although the efficiencies of gel formation per se are relatively low. The thickest gels are obtained following anodizing in antimonate electrolyte possibly reflecting a more favorable rate of gel formation, relative to its rate of dissolution, than that for other gel layers. The gel layers may shrink and crack on drying, most noticeably for the gels formed in antimonate and tungstate electrolytes. The gel layers formed in molybdate electrolyte appear, by comparison, highly resistant to cracking. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • K Shimizu, GM Brown, H Habazaki, G Kobayashi, P Skeldon, GE Thompson, GC Wood
    SURFACE AND INTERFACE ANALYSIS 27 (1) 24 - 28 0142-2421 1999/01 
    Anodic alumina films with precisely known distributions of incorporated species have been used as standards for glow discharge optical emission spectrometry (GDOES) depth profiling analysis to quantify depth resolution. It is evident that the depth resolution of GDOES is excellent and is comparable with, or better than, secondary ion mass spectrometry depth profiling of similar films. Further, the sensitivity for detection of elements is also high, given the amounts of impurity species detected successfully. Thus, GDOES, with its further ability of routine and rapid analysis of films (organic, inorganic or metallic) of thicknesses up to several hundreds of microns, has significant potential in studies of the corrosion and filming behaviour of materials. (C) 1999 John Wiley & Sons, Ltd.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    ELECTROCHIMICA ACTA 44 (13) 2297 - 2306 0013-4686 1999 
    The impurity distributions in the barrier anodic films formed on aluminium in a wide variety of electrolytes have been investigated by glow discharge optical emission spectroscopy (GDOES) depth profiling. The depth profiles obtained were compared, wherever available, with those obtained by other techniques. It was found that GDOES profiling is an extremely powerful and reliable technique for depth profiling analysis of thin, non-conducting alumina films. Surface charging is insignificant and the sputtering rate of the film is kept constant throughout the analysis, giving rise to excellent depth resolution which is comparable to, or better than, secondary ion mass spectrometry (SIMS) depth profiling analysis. Further sensitivity is also high, given the amount of impurity species being detected successfully. Thus, GDOES is expected to play a great role in depth profiling analysis of non-conducting anodic alumina films or other films where SIMS depth profiling is only of limited use due to ion beam bombardment-induced sample surface charging which has significant influence on the sputtering rate of the films. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • GE Thompson, H Habazaki, K Shimizu, M Sakairi, P Skeldon, Zhou, X, GC Wood
    AIRCRAFT ENGINEERING AND AEROSPACE TECHNOLOGY 71 (3) 228 - 238 1748-8842 1999 
    Anodizing is used widely in the surface treatment of aluminium alloys for aerospace applications. Considers recent advances in understanding of the influences of alloying elements in anodizing of aluminium alloys and, in particular, their applicability to second phase particles during anodizing of commercial alloys. Through more precise knowledge of the response of second phase materials to anodic polarization, improved anodizing and related surface treatment processes may be developed in order to enhance the performance of aluminium alloys.
  • GE Thompson, P Skeldon, GC Wood, Zhou, X, U Kreissig, E Wieser, H Habazaki, K Shimizu
    SURFACE AND INTERFACE ANALYSIS 27 (1) 57 - 62 0142-2421 1999/01 
    The influences of magnesium upon the formation of barrier-type anodic films on an Al-4.5 at.% Mg-0.05 at.% Cu alloy have been examined by elastic recoil detection analysis, Rutherford backscattering spectroscopy and analytical transmission electron microscopy. The results reveal that magnesium species are distributed uniformly throughout the anodic alumina film, with magnesium species migrating outwards in the film approximately twice as fast as Al3+ ions. Upon reaching the film surface, the magnesium species are ejected into the electrolyte under the particular conditions of anodizing, whereas Al3+ ions are retained within the film. The oxidation of magnesium results in voids at the alloy/film interface, which are probably associated with the low Pilling-Bedworth ratio of Mg/MgO relative to that of Al/Al2O3. The voids are formed in the presence of a high enrichment of copper (to 1.0 x 10(19) Cu atoms m(-2)) in the alloy region immediately beneath the anodic film, with copper species (which migrate outward faster than Al3+ ions) present throughout the anodic film. (C) 1999 John Wiley & Sons, Ltd.
  • Felhosi, I, H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    CORROSION SCIENCE 40 (12) 2125 - 2139 0010-938X 1998/12 
    The formation of Voids at the alloy/anodic film interface and the enrichments of alloying elements in a thin alloy layer immediately beneath the anodic film as a consequence of anodizing have been examined for Al-0.28 at.% In alloy and Al-0.5 at.% Cu alloys containing similar to 0.11 at.% Cd, similar to 0.07 at.% In or similar to 0.27 at.% Sn. Fine voids are formed for the indium- and tin-containing alloys for the selected conditions of anodizing, which is suggested to be associated with the relatively low Pilling-Bedworth ratios of the alleging element oxides incorporated into the anodic films. Thus, the formation of voids is dependent upon oxidation of the alloying element. Consequently, no voids were resolved for the cadmium-containing alloy for which limited or no oxidation of cadmium occurred. The enrichment of the binary alloy was equivalent to 3.5 at.% In, with enrichments of the ternary alloys to the ranges 11-16 at.% Cu and 2-7 at.% Cd, In or Sn respectively, for an assumed 2 nm thick enriched layer. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
  • J Bhattarai, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (11) 1897 - 1914 0010-938X 1998/11 
    Nano-crystalline single phase bce solid solution of sputter-deposited tungsten-rich W-Nb alloys are passivated spontaneously in all hydrochloric acid solutions examined, and their corrosion rates are dependent upon the concentration of HCl solutions at 30 degrees C. The corrosion rate of the tungsten-rich W-Nb alloys in 12 M HCl is lower than that in 6 M HCl, although the initial corrosion rate measured for less than about 24 h in 12 M HCl is higher than that in 6 M HCl. XPS and AFM results reveal that the more aggressive nature of 12 M than 6 M HCl solution enhances fast formation of more stable and protective passive films, consisting of tungsten-rich double oxyhydroxide of tungsten and niobium ions due to fast dissolution of niobium. This is responsible for higher corrosion resistance in 12 M HCl than that in 6 M HCl solution at 30 degrees C. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • F Echeverria, P Skeldon, GE Thompson, GC Wood, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 145 (9) 3011 - 3015 0013-4651 1998/09 
    The growth of anodic films on gallium phosphide has been investigated by transmission electron microscopy using ultramicrotomed sections of anodized specimens and Rutherford backscattering spectroscopy. The films were grown at constant current density, either 450 or 850 mu A cm(-2), in aqueous 0.1 M sodium tungstate electrolyte at 293 K. Two-layered amorphous films, consisting of an outer layer composed of Ga2O3 and an inner layer composed of units of Ga2O3 and P2O5 in the ratio of about 1:3.0, are formed by outward migration of cation species and inward migration of O2- ions. For film formation at 100% efficiency the outer layer represents about 34% of the film thickness. The layering is developed due to the faster migration outward of Ga3+ ions compared with that of P5+ ions. The films are highly soluble in the tungstate electrolyte at the termination of anodizing. However, following the initial period of film nucleation, the films are formed at relatively high efficiency, probably due to the presence or a protective gel layer, composed of hydrated WO3 at the film/electrolyte interface.
  • AA El-Moneim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (9) 1491 - 1512 0010-938X 1998/09 
    The effect alloying tantalum and chromium on the corrosion resistance of amorphous manganese-base alloys was studied by weight-loss, electrochemical and XPS techniques. Amorphous alloys were formed in a wide composition range by the addition of tantalum to manganese-chromium alloys. The corrosion rates of Mn-Ta-Cr alloys in 1 M H2SO4 open to air at 30 degrees C were about four and six orders of magnitude lower than those of MnTa and Mn-Cr alloys containing the same amount of manganese, respectively, and decreased with increasing alloy chromium content. Thus, additions of chromium and tantalum to manganese were synergistically effective in enhancing the corrosion resistance of Mn Ta-Cr alloys. The beneficial effect of chromium in the presence of tantalum is explained in terms of enhancement passivity and cathodic reactions of the alloys. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
  • AA El-Moneim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (9) 1513 - 1531 0010-938X 1998/09 
    Amorphous Mn-Nb alloys are prepared by D.C. magnetron sputter deposition method in a wide composition range. The effects of niobium addition on the corrosion behaviour of manganese are evaluated in a berate buffer solution of pH 8.4 containing 0.1 M NaCl by using weight-loss measurement, electrochemical and XPS techniques. A clear improvement of the corrosion resistance of these alloys compared with electro-deposited manganese is found. The alloys containing 24 at.% or more Nb are spontaneously passive. Their corrosion rates are about three to four orders of magnitude lower than that of manganese. The alloys containing 40 at.% or more Nb show almost the same corrosion rate as that of niobium. XPS analysis reveals that niobium is concentrated in air-formed films, and the films formed after open circuit immersion are further enriched in niobium. The improvement of the corrosion resistance by alloying with niobium is explained in terms of the formation of niobium-rich passive films composed of double oxyhydroxides of Mn2+ and Nb5+ ions. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
  • JCS Fernandes, MGS Ferreira, JC Soares, CM Jesus, CM Rangel, P Skeldon, GE Thompson, Zhou, X, H Habazaki, K Shimizu
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 31 (17) 2083 - 2090 0022-3727 1998/09 
    Amorphous anodic oxide films have been formed at high efficiency on aluminium implanted with 3.0 x 10(20) W ions m(-2) in order to study the behaviour of tungsten during film growth. The initial film is composed mainly of alumina because the outer layer of aluminium above the main implanted region of the substrate is oxidized. During this period, tungsten atoms, present in low concentrations in the aluminium, accumulate in a thin metal layer just beneath the anodic film. Subsequently, the main tungsten-implanted region is oxidized, with incorporation of tungsten and aluminium species into the anodic film at the metal-film interface in proportion to their concentrations in the metal. The incorporated tungsten species migrate outwards in the anodic film at about 0.34 times the rate of Al3+ ions. After oxidation of the main tungsten-containing region, more dilute regions of metal containing about 1 at% W are consumed, with oxidation of aluminium and tungsten in the presence of a highly tungsten-enriched metal layer. The enrichment is initially equivalent to 15 +/- 4 at% W, assuming that the enriched layer is 2 nm thick. However, rater, as the metal-film interface reaches regions of metal containing about 0.1 at% VV, the enriched layer contains significantly more tungsten than is usual for such dilute metal regions, indicating that tungsten is transported with the metal-film interface from metal regions of higher prior tungsten concentration as the film thickens.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (9) 1587 - 1604 0010-938X 1998/09 
    The sputter-deposited Cr-Ta alloys show extremely high corrosion resistance in 12M HCl. The open circuit potentials of the Cr-Ta alloys are located in the passive regions of both chromium and tantalum, and all Cr-Ta alloys are spontaneously passivated. XPS analysis indicates that the composition and thickness of the air-formed film are the same as those of spontaneously passivated film, and the composition of the passive films becomes constant after prolonged immersion. The film consists of a double oxyhydroxide of chromium and tantalum cations. The formation of the homogeneous double oxyhydroxide film consisting of both chromium and tantalum cations by air oxidation is responsible for the extremely high corrosion resistance of the Cr-Ta alloys in comparison with the corrosion resistance of chromium and tantalum metals. (C) 1998 Elsevier Science Ltd. Ali rights reserved.
  • H Habazaki, M Yamasaki, BP Zhang, A Kawashima, S Kohno, T Takai, K Hashimoto
    APPLIED CATALYSIS A-GENERAL 172 (1) 131 - 140 0926-860X 1998/08 
    The activity and durability of the catalysts prepared by the oxidation-reduction treatment of amorphous Co-15 at% Zr, Ni-40 at% Zr and Ni-30 at% Zr-10 at% Sm alloys have been investigated for simultaneous methanation of carbon monoxide and carbon dioxide, It has been found that the Ni-30Zr-10Sm catalyst shows the highest activity among the catalysts examined, and the activity of the Co-15Zr catalyst is lower than those of the nickel-based catalysts, in agreement with the activity for the solo methanation of carbon dioxide. On all the catalysts, carbon monoxide reacts preferentially with hydrogen, and is completely converted into methane at and above 523 K. The remaining hydrogen further reacts with carbon dioxide to form methane. The methanation rate in the H-2-CO-CO2 mixed gas is higher than that in H-2-CO2 mixed gas without CO. This is probably related to the prevention of the formation of surface carbon by the disproportionation reaction of carbon monoxide due to the presence of carbon dioxide. The activity of the Ni-40Zr catalyst at 573 K gradually decreases with reaction time. It has been found that tetragonal ZrO2, the presence of which is responsible for the high activity, is transformed to thermodynamically more stable monoclinic ZrO2 during the catalytic reaction. In contrast to the Ni-40Zr catalyst, the Ni-30Zr-10Sm catalyst sustains the initial high activity, and no structural change is observed during the durability test regardless of the presence of a small amount of hydrogen sulfide. (C) 1998 Elsevier Science B.V, All rights reserved.
  • F Echeverria, P Skeldon, GE Thompson, Walton, JR, H Habazaki, K Shimizu
    ELECTROCHEMICAL AND SOLID STATE LETTERS 1 (1) 24 - 26 1099-0062 1998/07 
    A new method, employing atomic force microscopy, for the examination of thin oxide layers is described. The approach utilizes the relief created on diamond-cut surfaces of sections through thin oxide films attached to a substrate, which reveals the main features of the films. The example considered is that of the anodic film formed on a GaP substrate. The film thickness and the two-layered nature of the anodic film are disclosed clearly over relatively long lengths of the semiconductor/film interface, with relevant dimensions in good agreement with those determined by transmission electron microscopy (C) 1998 The Electrochemical Society, Inc. S1099-0062(98)02-065-3.
  • H Habazaki, K Takahiro, S Yamaguchi, K Shimizu, P Skeldon, GE Thompson, GC Wood
    PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES 78 (1) 171 - 187 0141-8610 1998/07 
    A sputter-deposited Ti-20 at.% W alloy has been anodized at high efficiency in order to examine the influence of alloy species on the structure of anodic films on titanium. Interestingly, amorphous oxide films develop on the alloy to voltages of about 200V, in contrast with crystalline film formation on relatively pure titanium at voltages less than 20V. The amorphous films consist of an outer TiO2 layer and an inner layer containing units of TiO2 and WO3. The layered films form as a consequence of the migration of Ti4+ ions about 2.4 times faster than that of W6+ ions, probably owing to the relative strengths of the W6+-O and Ti4+-O bonds. Film growth proceeds by migration of both the O2- and/or OH- ions and the metal cations, typical of amorphous anodic films, with the transport number of cations, determined using a silicon species marker, of 0.39. During anodizing above about 200V, local regions of thicker film material develop, possibly owing to nucleation and growth of crystalline material. The voltage eventually reaches a maximum value of about 340V associated with copious oxygen evolution from the specimen and an extensively flawed film surface.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 40 (7) 1229 - 1238 0010-938X 1998/07 
    The incorporation of electrolyte species into anodic oxide films formed on tungsten in H2SO4 and H3PO4 solutions, which is shown to be anomalously low compared with that into films formed on other valve metals, has been examined by secondary ion mass spectrometry and by transmission electron microscopy of ultramicrotomed sections. For films formed in relatively dilute, i.e. 0.1 M, solutions, levels of anion incorporation are so low that their distributions in the films could not be revealed. In contrast, for the film formed in more concentrated, i.e. 14.7 M, H3PO4 solution, the presence of PO43- anions in approximately the outer half of the film is disclosed by SIMS, although the anion incorporation is at a low level such that the duplex nature of the films is revealed only faintly by transmission electron microscopy. EDX analysis indicates an atomic ratio of phosphorus and tungsten in the PO43--doped layer of about 0.01. Further, electron-beam-induced crystallization of the amorphous anodic film to monoclinic WO3 indicated no significant differences in the susceptibilities of film layers to crystallization. (C) 1998 Elsevier Science Ltd. All rights reserved
  • AC Crossland, GE Thompson, P Skeldon, GC Wood, CJE Smith, H Habazaki, K Shimizu
    CORROSION SCIENCE 40 (6) 871 - 885 0010-938X 1998/06 
    The anodic oxidation of Al-Ce alloys, containing up to 27 at.% Ce, has been investigated in ammonium pentaborate and sodium hydroxide electrolytes of pH 8.3 and 12.0 respectively. Cerium ions and Al3+ ions are incorporated into the mainly amorphous anodic oxide films at the alloy/film interface in proportion to the concentration of the respective elements in the bulk alloys. The cerium ions migrate outward in the films more rapidly than Al3+ ions, by factors from about 1.4 to 2.5, increasing with reduction of the cerium content of the alloy. The more rapid migration of cerium ions leads to the formation of a layer of relatively pure cerium oxide, or for dilute alloys a cerium-enriched layer of alumina, adjacent to the alloy/film interface, which thickens as the films grows. The films can be grown at relatively high efficiency under alkaline conditions, at least to pH 12, which would not normally support usual anodic film growth on high purity aluminium. The sustained film growth to high pH is due to the anodic inhibition provided by the outer cerium-rich layer of film, which prevents the direct ejection of Al3+ ions from the film to the electrolyte. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 40 (6) 963 - 973 0010-938X 1998/06 
    The anodic films formed at 1 mA cm(-2) on tantalum in concentrated H3PO4 (85%) and H2SO4 (95%) solutions at 25 degrees C have been examined directly in the transmission electron microscope employing ultramicrotomed sections. In the former electrolyte, duplex films comprising an outer PO43--doped layer, constituting about 70% of the film thickness, and an inner relatively pure Ta2O5 layer are developed, contrasting with the uniformly SO42--doped films developed during anodizing in concentrated H2SO4. The doped layers contain high concentrations of PO43- and SO42- ions, with compositions represented by Ta2O5(1-x)(PO4)(10x/3) and Ta2O5(1-x)(SO4)(5x), where x = 0.27 and 0.30 respectively. The increased incorporation of electrolyte species relative to films formed in dilute electrolytes significantly enhances the resistivity of the film material with an associated reduction in the dielectric constant. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • J Bhattarai, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (4-5) 757 - 779 0010-938X 1998/04 
    A series of nanocrystalline or amorphous single solid solutions of W-Ta alloys are prepared by D.C. magnetron sputtering. The passivation behavior of these alloys is studied by immersion test, electrochemical measurements and X-ray photoelectron spectroscopy (XPS) analysis. The W-Ta alloys are passivated spontaneously and show significantly high corrosion resistance in 12 M HCl at 30 degrees C. Their corrosion rates are about two orders of magnitude lower than that of sputter-deposited tungsten and are lower than that of sputter-deposited tantalum. XPS analysis shows that tantalum is concentrated in both the air-formed films and the passive films formed spontaneously on the alloys after long time immersion in 12 M HCl. The surface films are composed of double oxyhydroxides of Ta5+ and W4+ ions. The formation of spontaneous passive film composed of a double oxyhydroxide of tungsten and tantalum ions is responsible for high corrosion resistance of the W-Ta alloys in concentrated hydrochloric acid solution. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (4-5) 821 - 838 0010-938X 1998/04 
    The corrosion behavior of sputter-deposited Cr-Nb alloys in 12 M HCl solution was investigated by electrochemical and XPS methods. All of the Cr-Nb alloys are spontaneously passivated in 12 M HCl solution open to air at 30 degrees C. The open circuit potentials for chromium-rich alloys containing 42 at% or less niobium are located in the passive region of chromium and niobium, but those for niobium-rich alloys containing 52 at% or more niobium are located in the active region of chromium. XPS analysis reveals that the passive film consists of a double oxyhydroxide of chromium and niobium. The formation of the passive film consisting of double oxyhydroxide of chromium and niobium is responsible for the high corrosion resistance of the Cr-Nb alloys. The passive films formed on the chromium-rich alloys are slightly rich in chromium, and are not appreciably different from the air-formed films before immersion. Angle-resolved XPS analysis indicates no concentration gradient of Cr3+ and Nb5+ ions in depth of the passive films on the chromium-rich alloys. On the other hand. the air-formed film on the niobium-rich alloys is not stable in 12 M HCl and converted to the passive film in which niobium is slightly enriched. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
  • J Bhattarai, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (2-3) 155 - 175 0010-938X 1998/02 
    Nanocrystalline, single bcc solid solutions of W-Cr alloys have been prepared by DC magnetron sputtering over a wide composition range. The passivation behavior of these alloys was studied by electrochemical measurements, X-ray photoelectron spectroscopy (LPS) and atomic force microscopy (AFM). The W-Cr alloys are passivated spontaneously and showed significantly high corrosion resistance in 12M HCl solution at 30 degrees C. Their corrosion rates are about one order of magnitude lower than that of sputter-deposited tungsten and about five orders of magnitude lower than that of chromium metal even after prolonged immersion. XPS analysis showed that tungsten is enriched in the spontaneously passivated films formed on the alloys after long immersion time, and the passive films on the W-Cr alloys are found to be composed of double oxyhydroxide of tungsten and chromium ions. Angle-resolved XPS measurements reveal that tungsten and chromium ions are homogeneously distributed in the spontaneously passivated films. The synergistic effect of tungsten and chromium in forming the double oxyhydroxide is responsible for the higher corrosion resistance of the W-Cr alloys than of the alloy component metals. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • AA El-Moneim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (2-3) 235 - 250 0010-938X 1998/02 
    Amorphous Mn-ZI alloys were prepared by DC magnetron sputtering in a wide composition range. The electrochemical behavior in borate-boric acid solutions of pH 8.4 containing 0.01-1 M NaCl was investigated in combination with XPS analysis. All alloys were spontaneously passive. Their pitting potential increased with increasing zirconium content, and the alloys with 75-87 at.% zirconium possess higher pitting resistance than zirconium. The high passivating ability was attributed to the formation of a homogeneous double oxyhydroxide film composed of major Zr4+ and minor Mn2+. The formation of zirconium-enriched passive film results from preferential oxidation of zirconium with a consequent enrichment of manganese in the exterior of the underlying alloy surface. The formation of a zirconium oxyhydroxide film containing a few percent of manganese cations on zirconium-rich alloys is responsible for a significantly thinner film thickness and higher pitting resistance in comparison with zirconium. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • K Izumiya, E Akiyama, H Habazaki, N Kumagai, A Kawashima, K Hashimoto
    MATERIALS TRANSACTIONS JIM 39 (2) 308 - 313 0916-1821 1998/02 
    Manganese-tungsten oxide electrodes have high efficiency for oxygen evolution in seawater electrolysis. Manganese oxide, tungsten oxide and manganese-tungsten oxides were coated on the IrO2-coated titanium (IrO2/Ti electrode) by thermal decomposition. The oxygen evolution efficiencies at 200 A.m(-2) of the manganese oxide and tungsten oxide electrodes in 0.5 M NaCl solution at pH 8 and 30 degrees C were 70 and 68%, respectively. The efficiency for oxygen evolution is enhanced by small amounts of mutual additions into manganese oxide or tungsten oxide. In particular, the efficiencies of alpha-Mn2O3-type oxide with 15 mol% W6+ and WO3-type oxide with 10 mol% Mn2+ go up to over 92 and 86%, respectively Further increase in additives leads to the formation of MnWO4 and to a significant decrease in the oxygen evolution efficiency.
  • J Bhattarai, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 (1) 19 - 42 0010-938X 1998/01 
    Amorphous W-Nb alloys containing 52-78 at% niobium have been prepared successfully by DC magnetron sputtering. The W-Nb alloys are passivated spontaneously and show high corrosion resistance in both 6 and 12 M HCl solutions at 30 degrees C. In particular, their corrosion rates in 12 M HCl solution are about one order of magnitude lower than those of tungsten and niobium. Analysis by X-ray photoelectron spectroscopy (XPS) shows that tungsten is slightly enriched in the spontaneously passive films formed on the alloys after immersion for a long time in HCl solutions at 30 degrees C, and the passive films are composed of double oxyhydroxides of tungsten and niobium ions. Angle-resolved XPS measurements reveal that tungsten and niobium ions are homogeneously distributed throughout the passive films. The formation of the spontaneous passive film composed of the homogeneous double oxyhydroxide of tungsten and niobium ions is responsible for the high corrosion resistance of the W-Nb alloys. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, TJ Konno, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES 77 (1) 267 - 272 0141-8610 1998/01 
    Anodic oxidation of many dilute aluminium alloys results in alloy layers about 1-2 nm thick, just beneath the anodic film, suggested to contain clusters rich in alloying elements, although direct evidence of their existence is lacking. The present high-resolution transmission electron microscopy study discloses discrete Al2Au nanocrystals in the gold-enriched layer on anodized AI-Au alloys containing 0.4 and 3.8 at.% Au. For the single-phase 0.4 at.% Au alloy, the nanocrystals form as a consequence of enrichment of gold in the alloy through initial oxidation of aluminium atoms. For the 3.8 at.% Au alloy, composed of fee aluminium and Al2Au phases, the nanocrystals are derived from the bulk alloy by the retreat inwards of the alloy-film interface and are also produced following preferential oxidation of aluminium in the fee matrix phase.
  • H Habazaki, T Yoshida, M Yamasaki, M Komori, K Shimamura, E Akiyama, A Kawashima, K Hashimoto
    ADVANCES IN CHEMICAL CONVERSIONS FOR MITIGATING CARBON DIOXIDE 114 261 - 266 0167-2991 1998 
    The nano-grained Ni/ZrO2 catalysts containing rare earth element oxides were prepared by oxidation-reduction pretreatment of amorphous Ni-(40-x) at% Zr-x at% rare earth element (Y, Ce and Sm; x=1 - 10) alloy precursors. The conversion of carbon dioxide on the catalysts containing 1 at% rare earth elements was almost the same as that on the rare earth element-free catalyst, but the addition of 5 at% or more rare earth elements increased remarkably the conversion at 473 K. In contrast to the formation of monoclinic and tetragonal ZrO2 during pretreatment of amorphous Ni-Zr alloys containing 1 at% rare earth elements, tetragonal ZrO2, which is generally stable only at high temperatures, was predominantly formed during the pretreatment of the catalysts containing 5 at% or more rare earth elements. The surface area of the catalysts increased with the content of rare earth element. Thus, the increase in the surface area and stabilization of tetragonal ZrO2 seem to be responsible for the improvement of catalytic activity of the Ni-Zr alloy-derived catalysts by the addition of rare earth elements.
  • K Hashimoto, K Izumiya, K Fujimura, M Yamasaki, E Akiyama, H Habazaki, A Kawashima, M Komori, K Shimamura, N Kumagai
    PROCEEDINGS OF CORROSION 98 - RESEARCH TOPICAL SYMPOSIUM ON CORROSION IN ADVANCED MATERIALS AND SYSTEMS 1 - 14 1998 
    CO2 emissions, which induce global warming, increase with the development of economic activity. It is impossible to ask the CO2 emission decrease based on suppression of the economic activity. Global CO2 recycling can solve this problem. The global CO2 recycling consists of three district: The electricity is generated by solar cells on deserts. At coasts close to the deserts, the electricity transmitted from the deserts is used for H-2 production by seawater electrolysis and H-2 is used for CH4 production by the reaction with CO2. CH4 is liquefied and transported to energy consuming districts where, after CH4 is used as a fuel, CO2 is recovered, liquefied and transported to the coast close to the deserts. Since 90% of city gases in Japan is liquefied natural gas (LNG) that consists mostly of CH4, CH4 produced in the global CO2 recycling on be used immediately as the city gas. A CO2 recycling plant for substantiation of our idea has been built on the roof of our Institute (IMR) in 1996. Rey materials necessary for the global CO2 recycling are the anode and cathode for seawater electrolysis and the catalyst for CO2 conversion. All of them have been tailored by us. Since quantities of CO2 to be converted far exceed an ordinary industrial level, the system must be very simple, the rate of conversion must be very fast and precious metals must not be used for the system. All these requirements are satisfied in the global CO2 recycling. When the global CO2 recycling is conducted in a large scale, the energies and costs required to form liquefied CH4 in the global CO2 recycling are almost the same as those for production of LNG from natural gas wells. The project to examine feasibility of the global CO2 recycling has been planned in Egypt in cooperation of Egyptian and Japanese scientists, engineers and industries.
  • K Hashimoto, J Bhattarai, XY Li, PY Park, JH Kim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Shimamura
    PROCEEDINGS OF THE SYMPOSIUM ON PASSIVITY AND ITS BREAKDOWN 97 (26) 369 - 383 1998 
    Cr-Ti, Cr-Zr, Cr-Nb, Cr-Ta, Mo-Cr, Mo-Ti, Mo-Zr, Mo-Nb, Mo-Ta, W-Cr, W-Ti, W-Zr, W-Nb and W-Ta alloys prepared by sputter deposition are extremely corrosion-resistant due to spontaneous passivation in 6 and 12 M HCl at 30 degrees C. They are composed of either amorphous single phase or nanocrystalline single solid solution. Spontaneously passivated films are composed of double oxyhydroxides of both alloy component cations, which have higher corrosion resistance than that of passive oxyhydroxide films of alloy component metals. Molybdenum suffers transpassive dissolution at open circuit potentials of the alloys. This results in concentration gradient in the film, while homogeneous passive firms are formed on chromium- and tungsten-valve metal alloys. Corrosion-resistant coatings on inner walls of narrow tubes are successfully performed by magnetron sputtering.
  • K Izumiya, E Akiyama, H Habazaki, N Kumagai, A Kawashima, K Hashimoto
    ELECTROCHIMICA ACTA 43 (21-22) 3303 - 3312 0013-4686 1998 
    The oxygen evolution efficiency in seawater electrolysis has been examined for manganese oxide and manganese-tungsten oxide electrodes anodically deposited on iridium oxide-coated titanium substrates as a function of pH of the deposition electrolytes and tungsten content in the oxides. The oxygen evolution efficiency in 0.5 M NaCl solution at 30 degrees C On the MnO2 electrodes increases with a decrease in pH of the deposition electrolyte. The tungsten-containing electrodes show significantly higher efficiency for oxygen evolution. The tungsten addition enhances oxygen evolution and suppresses chlorine evolution, and hence 99.6% efficiency for oxygen evolution was obtained at 200 A m(-2) on the oxide with the molar ratio W6+/(Mn4+ + W6+) of 0.16. The anodically deposited manganese oxide consists of nanocrystalline gamma-MnO2. The manganese-tungsten oxides are also composed of a single orthorhombic nanocrystalline gamma MnO2-type phase, in which Mn4+ and W6+ ions are homogeneously distributed, even when cationic fraction of tungsten in the oxide is 0.16. The Tafel slopes of the MnO2 and (Mn-W)O-X electrodes for oxygen evolution are both higher than those for chlorine evolution. The MnO2 and (Mn-W)O-X electrodes anodically deposited at lower pH and the (Mn-W)O-X electrodes with higher tungsten content have smaller grain size and higher surface roughness. The surface roughening of the oxides leading to the decrease in the electrode potential under the galvanostatic condition accelerates the oxygen evolution reaction and suppresses chlorine evolution. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • M Mehmood, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    ELECTROCHEMICAL METHODS IN CORROSION RESEARCH VI, PTS 1 AND 2 289-2 629 - 639 0255-5476 1998 
    Sputter-deposited amorphous Cr-60Zr and Cr-67Zr alloys are spontaneously passive in 6 M HCl and sputter-deposited amorphous Al-Cr alloys are spontaneously passive in 0.1 M HCl. They suffer pitting by anodic polarization. The change in the pitting susceptibility by introduction of heterogeneity to the homogeneous amorphous alloys by crystallization heat treatment at 400-700 degrees C for 30 min is studied. Heat treatment of the Cr-Zr alloys results in two stage crystallization, (i) precipitation of hepzirconium phase and (ii) massive transformation from amorphous phase to intermetallic compound, Cr2Zr. Since the precipitation of the hcp zirconium phase depends on the zirconium content of alloys, the average size of the hcp zirconium phase in the Cr-60Zr alloy specimens heated to 700 degrees C is less than 20 nm, while heating of the Cr-67Zr alloy to 600 degrees C results in precipitation of the hcp zirconium phase larger than 20 nm in diameter. Heat treatment of Al-43Cr alloy leads to formation of a two phase mixture of Al17Cr9 and bcc Cr(Al). The size of nanocrystalline two phase mixture is about 15 nm when heated at 550 degrees C but becomes 20-30 nm by heating at 600 degrees C. The heat treatment gives rise to the ennoblement of pitting potential in spite of the formation of nanocrystalline phases. This is due to the fact that the formation of the hcp zirconium or Al17Cr9 phase leads to an increase in the chromium content of the matrix phase which is able to form thin, protective chromium-rich passive films covering entire heterogenous alloy surfaces. However, when the average size of the less corrosion-resistant phases exceeds 20 nm, the protective chromium-rich passive films cannot completely cover the less corrosion-resistant phases and the pitting resistance decreases.
  • P Sheldon, GE Thompson, GC Wood, Xhou, X, H Habazaki, K Shimizu
    DIELECTRIC MATERIAL INTEGRATION FOR MICROELECTRONICS 98 (3) 350 - 361 1998 
    The formation of anodic oxide films is reviewed, based on recent studies in the authors' laboratories of aluminium alloys, to highlight features developed during anodizing that may influence the electrical properties of oxide films and alloy/film interfaces in general. In particular, the development of the following are considered: alloy layers containing greatly enhanced concentrations of the alloying element, created as a consequence of anodic film growth; clusters enriched in alloying element atoms within the enriched alloy layer; line-scale heterogeneity of the oxide composition due: to oxidation of clusters at the alloy/film interface; incorporation of metal particles into oxide films; generation of oxygen gas within oxide films, with formation of high pressure bubbles; roughening of the alloy/film and film/electrolyte interfaces due to the presence of oxygen bubbles and their rupture; void formation at, or close to the alloy/film interface and subsequent detachment of the anodic film from the substrate.
  • M Yamasaki, H Habazaki, T Yoshida, M Komori, K Shimamura, E Akiyama, A Kawashima, K Asami, K Hashimoto
    ADVANCES IN CHEMICAL CONVERSIONS FOR MITIGATING CARBON DIOXIDE 114 451 - 454 0167-2991 1998 
    Nano-grained Ni/ZrO2 and Ni/ZrO2-Sm2O3 catalysts were prepared from amorphous Ni-Zr and Ni-Zr-Sm alloys by oxidation-reduction treatment. Their catalytic activity for methanation of carbon dioxide was examined as a function of precursor alloy composition and temperature. The addition of samarium is effective in enhancing the activity of the nickel-rich catalysts, but not effective for the zirconium-rich catalysts. The surface area and hydrogen uptake of the nickel-rich catalysts are increased by the samarium addition, In addition, tetragonal zirconia, the formation of which is beneficial to the catalytic activity, is stabilized and formed predominantly by the addition of samarium to the nickel-rich catalysts, although monoclinic zirconia is also formed in the zirconium-rich catalysts. As a consequence, the higher conversion of carbon dioxide is obtained on the Ni-Zr-Sm catalysts with relatively high nickel contents.
  • H Habazaki, P Skeldon, GE Thompson, J Wan, GC Wood, Zhou, X, J DeLaet, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 144 (12) 4217 - 4222 0013-4651 1997/12 
    The anodic oxidation of Al-4 atom percent (a/o) Cr [7.4 weight percent (w/o) Cr] and Al-10 a/o Cr (17.6 w/o Cr) sputtered-deposited alloy films was investigated by transmission electronmicroscopy and by x-ray absorption studies. The oxidation behavior of both alloys is explained by initial formation of a chromium-free anodic alumina film with accumulation of chromium in a thin underlying alloy layer. On sufficient enrichment of the alloy, chromium and aluminum are oxidized at the alloy/film interface in their approximate alloy proportions. The resultant Cr3+ ions migrate outward through the film more slowly than Al3+ ions. Oxidation of chromium is followed by production of what is probably oxygen gas within the film, which is likely to generate a high pressure, leading to film rupture and gas release. Consequently, a complex, irregular film morphology, associated with voids, channels and cracks, develops. X-ray absorption studies reveal that Cr(VI) species are detected in significant quantities only after the mechanical breakdown of the film. Such species probably form as a result of the high electrochemical potential of the alloy that is freshly exposed to the environment following film rupture.
  • K Izumiya, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto, N Kumagai
    JOURNAL OF APPLIED ELECTROCHEMISTRY 27 (12) 1362 - 1368 0021-891X 1997/12 
    Utilizing the fact that the equilibrium potential of oxygen evolution is lower than that of chlorine evolution, oxygen evolution in seawater electrolysis was enhanced by decreasing the polarization potential under galvanostatic conditions through increasing the effective surface area of manganese oxide electrodes. Electrodes were prepared by a thermal decomposition method. IrO2-coated titanium (IrO2/Ti electrode) was used as the substrate on which manganese oxide was coated (MnOX/IrO2/Ti electrode). Subsequently, oxide mixtures of manganese and zinc were coated (MnOX-ZnO/MnOX/IrO2/Ti electrode). The effective surface area of the MnOX-ZnO/MnOX/IrO2/Ti electrodes was increased by selective dissolution of zinc (leaching) into hot 6 M KOH. The oxygen evolution efficiency of the MnOX/IrO2/Ti electrode was 68-70%. Leaching of zinc from the MnOX-ZnO/MnOX/IrO2/Ti electrodes with 25 mol% or less zinc led to a significant increase in the oxygen evolution efficiency. The maximum efficiency attained was 86% after leaching of zinc from the MnOX-25 mol% ZnO/MnOX/IrO2/Ti electrode. However, large amounts of zinc addition, such as 40 mol% or more are detrimental because of a decrease in the oxygen evolution efficiency. This is due to the formation of a double oxide, ZnMnO3, which is hardly dissolved in hot 6 M KOH.
  • M Yamasaki, H Habazaki, T Yoshida, E Akiyama, A Kawashima, K Asami, K Hashimoto, M Komori, K Shimamura
    APPLIED CATALYSIS A-GENERAL 163 (1-2) 187 - 197 0926-860X 1997/12 
    Finely grained Ni/ZrO2 catalysts were prepared from amorphous Ni-Zr alloy precursors by oxidation and subsequent reduction pretreatment, and the catalytic activity for CO2 methanation was examined as a function of precursor alloy composition and temperature. The catalysts thus prepared produce exclusively methane, apart from water as a by-product. The conversion of CO2 increases with temperature in the range of 373-573 K. Among the catalysts examined, the maximum methanation rate is obtained on the catalysts prepared from the amorphous alloy precursors containing 40 and 50 at% zirconium. Further, the methanation rates of all the catalysts prepared from the amorphous alloy precursors are higher than that of a 3 at% Ni/ZrO2 catalyst prepared by wet impregnation. The number of surface nickel atoms, determined by hydrogen chemisorption, increases with zirconium content in the catalysts, while, interestingly, the turnover number decreases with increasing zirconium content. In the catalysts prepared from the amorphous alloys, two types of zirconia are present: metastable tetragonal and stable monoclinic zirconia. The former zirconia phase is present predominantly in the catalyst prepared from the Ni-30 at% Zr alloy, but the relative amount of this oxide phase, with respect to the total amounts of zirconia, gradually decreases with an increase in zirconium content of alloys. Thus, the higher turnover number of the catalysts with higher nickel content can be attributed to nickel supported on metastable tetragonal zirconia. Increasing nickel content of the precursor alloys leads to an increase in tetragonal zirconia and to a decrease in the number of surface nickel atoms on the catalysts. This is responsible for the fact that the maximum conversion appears at medium contents of zirconium in the precursor alloys. (C) 1997 Elsevier Science B.V.
  • AA El-Moneim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 (10-11) 1965 - 1979 0010-938X 1997/10 
    Amorphous Mn-Ta alloys were successfully prepared by DC magnetron sputter deposition in a wide composition range. Their corrosion behaviour was investigated in 0.5 M NaCl solution of pH 11.5 at 30 degrees C by electrochemical measurements and XPS analysis. The corrosion rates of these alloys were significantly lower than that of manganese metal, and decreased with increasing alloy tantalum content. The alloys containing 30 at.% or more tantalum were spontaneously passive and showed a wide passive region exceeding the potential of transpassive region of manganese. XPS analysis revealed that the spontaneously passivated films were not composed of a mixture of manganese and tantalum oxyhydroxide and consisted of a double oxyhydroxide containing Mn2+ and Ta5+ cations. The passive films are enriched in tantalum ions in almost the entire film except the top-most surface where manganese hydroxide is precipitated. The passive double oxyhydroxide film with an almost fixed composition grows with anodic polarization potential, revealing that both tantalum and manganese are effective in forming the barrier type oxyhydroxide film. The formation of tantalum-enriched double oxyhydroxide film is responsible for the high corrosion resistance of the alloys. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 144 (10) 3492 - 3495 0013-4651 1997/10 
    The present study examines anodic oxidation of a dilute Zr-W alloy for which enrichment of tungsten in the alloy is expected from thermodynamic considerations. However, no significant enrichment of tungsten, with an upper limit determined by the resolution of the analysis of about 1 x 10(18) tungsten atom m(-3), is developed during formation of the anodic film. The relative lack of enrichment is attributed to the crystalline structure and growth mechanism of the film on the Zr-W alloy The film is composed of zirconia, contaminated by tungsten species through its thickness, which develops mainly at the alloy/film interface by inward migration of oxygen ions via short-circuit paths.
  • K Izumiya, E Akiyama, H Habazaki, N Kumagai, A Kawashima, K Hashimoto
    MATERIALS TRANSACTIONS JIM 38 (10) 899 - 905 0916-1821 1997/10 
    Manganese oxide electrodes with some additives enhance oxygen evolution efficiency in seawater electrolysis. Electrodes were prepared by a thermal decomposition method. IrO2-coated titanium (IrO2/Ti electrode) was used as the substrate on which manganese oxide (MnOX/IrO2/Ti) and oxide mixtures of manganese and iridium, ruthenium, platinum, iron, cobalt, nickel, tin, lanthanum, cerium or molybdenum ((Mn-M)O-X/IrO2/Ti electrode, M: additives) were coated. The oxygen evolution efficiency of the MnOX/IrO2/Ti electrode was 68-70%. The addition of small amounts of nickel, cobalt, iron or tin enhanced the oxygen evolution efficiency. However the addition of excess amounts of these elements and additions of noble metals, cerium or lanthanum were detrimental for the oxygen evolution.Among the additives examined, molybdenum was the most effective additional element to increase the oxygen evolution efficiency. The addition of a small amount of molybdenum leads to a remarkable increase in the oxygen evolution efficiency up to 91%. The formation of a single phase Mn2O3 with molybdenum ions seems to be responsible for the high efficiency for oxygen evolution.
  • P Skeldon, GE Thompson, GC Wood, Zhou, X, H Habazaki, K Shimizu
    PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES 76 (4) 729 - 741 0141-8610 1997/10 
    The composition of the barrier anodic film formed at 50 Am-2 to 200 V on solution-treated Al-1 at.% Cu alloy in ammonium pentaborate electrolyte at 293 K has been investigated by Rutherford backscattering spectroscopy and nuclear reaction analysis. The film contains about 14% more oxygen in comparison with that expected for an anodic alumina film as usually formed on high purity aluminium under similar conditions. The excess oxygen is attributed to the electrochemical production of oxygen near the alloy-film interface during growth of the firm. The formation of the oxygen is probably linked to the oxidation of copper in a thin alloy layer, highly enriched in copper, immediately beneath the anodic him. Most of the oxygen appears to reside in bubbles, of dimensions from about 5 to 250 nm, within the inner part of the film, which are revealed in the transmission electron microscope. The estimated pressure of the oxygen gas within the bubbles is approximate to 150 MPa.
  • BP Zhang, A Kawashima, H Habazaki, K Asami, K Hashimoto
    CORROSION SCIENCE 39 (10-11) 2005 - 2018 0010-938X 1997/10 
    The pitting behavior of amorphous Ni-Zr alloys prepared by melt-spinning was thoroughly investigated by placing an emphasis on the effect of the microstructure and surface composition. It was found that the alloy ribbons showed different pitting corrosion behavior along the thickness direction from the dull side to the shiny side in de-aerated 0.5 M H2SO4 solution with 0.1 M NaCl. The dull side surface was most susceptible to pitting corrosion, but it became difficult to occur if the as-prepared dull side surface was removed by mechanical polishing. The shiny side surface of all the alloys passivated spontaneously and the pitting potential increased with an increase in alloy zirconium content. TEM observation indicated that all the shiny side surfaces were wholly amorphous, while some microcrystalline phases existed in the amorphous matrix in the dull side. The crystalline phases formed in the dull side were identified as Ni3Zr and NiZr2 for the Ni-30Zr and Ni-70Zr alloys, respectively. The presence of both the microcrystalline phases in the amorphous matrix and the irregular surface morphology of the dull side were responsible for the origin of the pitting corrosion of the dull side surface. The high corrosion resistance of the shiny side surface was attributed to the high protectiveness of the passive film and the structural homogeneity of the alloy. (C) 1997 Elsevier Science Ltd.
  • H Mitsui, H Habazaki, K Hashimoto, S Mrowec
    CORROSION SCIENCE 39 (9) 1571 - 1583 0010-938X 1997/09 
    The effect of silicon addition on the sulfidation and oxidation behavior of sputter-deposited AI-Ta alloys was investigated as a function of alloy composition and temperature. The sulfidation kinetics of Al-Ta-Si alloys generally followed a parabolic rate law, and the sulfidation resistance of Al-Ta alloys was improved by the addition of adequate amounts of silicon. The excess addition of silicon to Al-Ta alloys decreased the resistance to high temperature sulfidation. In the case of high tantalum alloys containing about 80 at. % Ta, the dense and columnar sulfide scale of tantalum disulfide was formed on the alloys, and the formation of this protective scale led to the excellent resistance to high temperature sulfidation. The effect of silicon addition on the oxidation behavior of Al-Ta alloys was rather complicated. In general, the oxidation rate of Al-Ta alloys was also decreased by the addition of adequate amounts of silicon, although the excess addition was harmful to the oxidation resistance of these alloys. In the case of high aluminum alloys containing about 30 at % Ta, continuous aluminum-rich oxide scale and the porous underlying alloy were formed after oxidation, and these voids in the underlying alloy were assumed to accelerate oxidation. However, at 1073 K, the rapid weight loss, which was observed in binary Al-Ta alloys during oxidation, was suppressed by silicon addition. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 453 (1963) 1593 - 1609 1364-5021 1997/08 
    The inter-relationships of alloy composition, film composition and ionic transport for formation of amorphous anodic oxide films are addressed quantitatively through systematic study of sputter-deposited Al-Ta alloys containing up to 39 at.% Ta. The work reveals the dependence of electric field, ionic transport number, incorporation of species into the anodic film at the alloy-film interface and mobility and distribution of species within the anodic film on alloy composition. Anodic oxidation, at high current efficiency, of alloys containing 2.8, 15, 32 and 39 at.% tantalum results in formation of two-layered anodic films by migration of cations outwards and by migration of anions inwards: an outer layer, 20% or less of the total film thickness, composed of relatively pure alumina and an inner layer containing units of Al2O3 and Ta2O5 distributed relatively homogeneously. Two-layered films develop due to the slower migration rate of Ta5+ ions relative to Al3+ ions in the inner layer of the growing anodic films, which changes progressively from about 0.6 for dilute alloys to about 0.9 for Al-39 at.% Ta. The average nm V-1 ratios, total transport numbers of cations and average Pilling-Bedworth ratios for the films change almost linearly with alloy composition between the values for anodic alumina and anodic tantala. A tantalum-enriched layer, about 1 nm thick, is formed in the Al-2.8 at.% Ta and Al-15 at.% Ta alloys just beneath the anodic film, indicating prior oxidation of aluminium in the initial stages of anodizing. In contrast, aluminium and tantalum in the alloys containing more than 30 at.% tantalum are immediately incorporated into anodic films in their alloy proportions, without development of a tantalum-enriched layer, at the available resolution. Boron species, incorporated from the electrolyte into the outer parts of the films, are immobile in films on alloys up to 15 at.% Ta but migrate outwards in other films, possibly due to the increased Lorentz field. Though the inter-relationships between film parameters and alloy composition are established for Al-Ta alloys specifically, the findings are considered to be equally relevant to amorphous anodic oxides formed on alloys and semiconductors generally.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 (8) 1365 - 1380 0010-938X 1997/08 
    X-ray photo-electron spectroscopy (XPS) has been used to examine spontaneously passivated films formed on sputter-deposited Cr-Zr alloys in 6 M HCl solution open to air at 30 degrees C, for a better understanding of the high corrosion resistance of these alloys. The open circuit potentials of the Cr-Zr alloys are located in the passive regions of both chromium and zirconium, and all of the Cr-Zr alloys examined are spontaneously passivated. An increase in chromium content of the alloys enhances the cathodic activity for oxygen reduction and content of the alloys enhances the cathodic activity for oxygen reduction and decreases the anodic current density with a consequent ennoblement of the open circuit potential. XPS analysis indicates that the air-formed films on these alloys are composed of homogeneous double oxyhydroxide consisting of both chromium and zirconium ions. The cationic composition of the film is almost the same as the alloy composition although slight enrichment of zirconium occurs. The air-formed film is protective enough to lead to spontaneous passivation of these alloys. The immersion for a long period of time results in a slight deficiency in zirconium in the exterior of the passive film as a result of gradual dissolution of zirconium. At the same time, the total amount of chromium in the passive film increases. The passive film consists of double oxyhydroxide of chromium and zirconium, in which the cationic composition is almost the same as the alloy composition. The formation of the passive film consisting of double oxyhydroxide of chromium and zirconium is responsible for the higher corrosion resistance of these Cr-Zr alloys in comparison with chromium and zirconium metals. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 30 (13) 1833 - 1841 0022-3727 1997/07 
    The anodic oxidation of Al-Au alloys, containing 0.4, 3.8 and 11 at% Au, has been examined by high-resolution transmission electron microscopy and Rutherford backscattering spectroscopy. Oxidation proceeds initially by the formation of an anodic alumina film containing few, or no, gold species. The alloy layer just beneath the anodic film is then enriched progressively in gold as a consequence of the initial formation of relatively pure alumina. Upon sufficient enrichment of gold in the alloy, oxygen gas is produced at, or near, the alloy/film interface. At, or about, the same time, gold-rich clusters a few nanometres in size are incorporated into the film at the alloy/film interface. The necessary enrichment of the alloy for the production of oxygen gas is dependent upon the alloy composition: > 2 x 10(19), 8.5 x 10(19) and 1.7 x 10(20) gold atoms m(-2) for the 0.4, 3.8 and 11 at% Au alloys respectively. The extensive generation of oxygen within the film at, or near, the alloy/film interface, leads to the formation of oxygen-filled bubbles within the anodic alumina, which may subsequently rupture and release oxygen gas.
  • H Habazaki, P Skeldon, GE Thompson, GC Wood, K Shimizu
    JOURNAL OF MATERIALS RESEARCH 12 (7) 1885 - 1891 0884-2914 1997/07 
    The mechanism of ionic transport in the amorphous anodic film formed on Al-40 at. % Sm alloy has been examined by transmission electron microscopy and Rutherford backscattering spectroscopy. The film consists of an outer layer, about 6% of the total film thickness, composed of relatively pure Sm2O3 and an inner layer containing units of Al2O3 and Sm2O3 distributed homogeneously at the available resolution. The anodic film material is formed by migration of O2-/OH- ions inward and migration of cations outward, with a cation transport number about 0.29. The two-layered film develops as a consequence of faster migration of Sm3+ ions than Al3+ ions in the film.
  • E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 226 920 - 924 0921-5093 1997/06 
    The corrosion behavior of amorphous Al-Ti-Ni, Al-Cr-Ti and Al-Cr-Mo alloys in 1 M I-ICI and that of amorphous Al-Ti-ME alloys in chloride containing neutral solution is investigated. The amorphous Al-Ti-Ni, Al-Ti-Cr and Al-Cr-Mo alloys are passivated spontaneously even in 1 M HCl and show lower corrosion rates and higher pitting potentials in comparison with Al-Ti and Al-Cr binary alloys. Al-Ti-Mg alloys containing relatively low concentration of magnesium possess a better resistance against pitting corrosion. X-ray photoelectron spectroscopy measurement reveals that titanium and chromium are enriched in the passive films formed on Al-Ti-Ni, Al-Ti-Mg and Al-Cr-Mo alloys, respectively. Angle-resolved XPS measurements were performed in order to characterize the in-depth distribution of constituents in the passive films formed on amorphous Al-Ti-Ni, Al-Ti-Mg and Al-Cr-Mo alloys in the passive films of which, passivating elements are enriched. (C) 1997 Elsevier Science S.A.
  • K Ito, H Habazaki, H Mitsui, E Akiyama, A Kawashima, K Asami, K Hashimoto, S Mrowec
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 226 910 - 914 0921-5093 1997/06 
    Cr-Nb and Cr-Mo alloys have been sputter-deposited on to quartz substrate, and their sulfidation and oxidation behavior has been studied as a function of temperature and alloy composition in He-S-2 and Ar-O-2 atmospheres. The sulfidation of these alloys follows a parabolic rate law, being diffusion controlled. The sulfidation rates of Cr-Nb alloys decrease with increasing niobium content in the alloy, and the sulfidation resistance of the high niobium alloys is comparable with that of niobium. The sulfidation resistance of Cr-Mo alloys is independent of alloy composition, being comprable with that of molybdenum. The sulfide scales formed on these alloys consist of two layers, comprising an outer chromium sulfide layer and an inner layer composed mainly of refractory metal sulfides. The formation of the refractory metal sulfide scales is responsible for the high sulfidation resistance to sulfide corrosion. Under the oxidation condition the Cr-Mo alloys are rapidly oxidized due to the formation of volatile molybdenum oxide. The oxidation of Cr-Nb alloys proceeds accompanying partial breakdown and the restoration of the scales, but the average oxidation rates are almost the same as their sulfidation rates. Consequently, the Cr-Nb alloys possess high resistance to both sulfidation and oxidation at high temperatures. (C) 1997 Elsevier Science S.A.
  • A Kawashima, E Akiyama, H Habazaki, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 226 905 - 909 0921-5093 1997/06 
    Binary Ni-Mo and Ni-W alloy coatings with good adhesion to nickel substrate are successfully prepared by d.c. magnetron sputter deposition method. These alloy electrodes are found to be active hydrogen evolution electrocatalysts in 1 M NaOH solution at 30 degrees C. Ni-Mo alloy electrodes exhibit the highest activity, which is higher than that of smooth platinum electrode. Leaching treatment in hot concentrated caustic solution for Ni-Mo alloys significantly enhances the activity. (C) 1997 Elsevier Science S.A.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    THIN SOLID FILMS 300 (1-2) 131 - 137 0040-6090 1997/05 
    Binary, non-equilibrium Al-29at%Nb, Al-44at%Ta, Al-19at%Ti, Al-25at%Ti and Al-32at%Zr alloys were prepared by magnetron sputtering and subsequently anodized at high Faradaic efficiency to grow barrier-type anodic films. Examination in the transmission electron microscope revealed amorphous anodic films of relatively uniform compositions across the film thicknesses, except for a layer of relatively pure alumina, of about 5% of the film thickness, present at the film/electrolyte interface of the AI-Ta alloy. The film compositions, from Rutherford backscattering spectroscopy, indicate that the alloy constituents are oxidized in their alloy proportions to form films comprising intimately mixed units of the various oxides, namely alumina, niobia, titania, tantala and zirconia. The films grow by co-operative transport of metal and oxygen ions under the electric field with formation of film material by both migration of metal ions outwards and of oxygen, and possibly hydroxyl, ions inwards. The average migration rates of Al3+, Nb5+, Ti4+ and Zr4+ ions are similar, to within 10%, but Ta5+ ions migrate more slowly than Al3+ ions. The results of the study show that a wide range of compositions of amorphous oxide films can be readily formed by anodic oxidation of appropriate alloys, including compositions containing units of normally crystalline anodic oxides, namely TiO2 and ZrO2. (C) 1997 Elsevier Science S.A.
  • A Kawashima, WP Yu, BP Zhang, H Habazaki, K Asami, K Hashimoto
    MATERIALS TRANSACTIONS JIM 38 (5) 443 - 450 0916-1821 1997/05 
    The pitting corrosion behavior of the melt spun amorphous Ni-Zr alloys with 30-75 at% zirconium, the crystalline are-melted counterparts and the sputter-deposited Ni-Zr alloys with 20-84 at% zirconium was examined by electrochemical measurements in deaerated 0.5 kmol/m(3) H2SO4 with and without 0.1 kmol/m(3) NaCl at 303 K. In the sulfuric acid solution without Cl-, these alloys were spontaneously passive and their potentiodynamic behavior was similar to each other. In the Cl--containing solution, all the melt-spun amorphous alloys suffered pitting during anodic polarization and the pitting potential decreased with an increase in zirconium content. On the other hand, the crystalline are-melted low zirconium alloys suffered pitting but no pitting observed for the crystalline alloys containing 70 at% zirconium or more. In addition, the pitting potential increased with the zirconium content of crystalline alloys. All the sputter-deposited alloys did not suffer pitting regardless of the amorphous and crystalline structures. Therefore, the melt-spun amorphous alloys were the most susceptible to pitting corrosion. A marked difference was observed in the pitting behavior between the shiny side (top side) and the dull side (wheel side) surfaces of the melt-spun ribbon. The pits initiated from the dull side surface. Thus, the dull side surface could be responsible for such an unusual pitting behavior of the melt spun ribbon.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 (5) 935 - 948 0010-938X 1997/05 
    Among sputter-deposited Cr-Ti alloys, 30-65 at% Ti alloys are amorphized. The Cr-Ti alloys with 22 at% or less Ti are bcc single phase alloys. Regardless of the crystallinity, the open circuit potentials of sputter-deposited Cr-Ti alloys are located in the passive regions of both titanium and chromium in 6 M HCl solution open to air at 30 degrees C, and all Cr-Ti alloys are spontaneously passivated. X-ray photo-electron spectroscopy (XPS) analysis reveals that the spontaneously formed passive film as well as air-formed film is slightly rich in titanium ions mainly because of preferential oxidation of titanium. According to angle-resolved XPS measurement, no concentration gradient of Cr3+ and Ti4+ ions has been detected in depth of the passive film. Analysis of binding energies of core electrons of Cr3+ and Ti4+ cations shows that Cr3+ and Ti4+ cations are located very closely in the film so as to show the electronic interaction, and the film is not composed of a heterogeneous mixture of chromium and titanium oxyhydroxides but of homogeneous double oxyhydroxide consisting of Cr3+ and Ti4+ cations. The formation of the homogeneous double oxyhydroxide film containing both Cr3+ and Ti4+ cations is responsible for extremely higher corrosion resistance of the homogeneous single phase Cr-Ti alloys in 6 M HCl open to air at 30 degrees C in comparison with the corrosion resistance of chromium and titanium metals. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, P Skeldon, GE Thompson, Zhou, X, J DeLaet, GC Wood
    CORROSION SCIENCE 39 (4) 719 - 730 0010-938X 1997/04 
    By anodizing of a thin layer of Al-0.5 at.% Cr alloy, ca. 54 nm thick, superimposed on electropolished superpure aluminium, chromium species are incorporated into the anodic alumina as a thin band ca. 3 nm thick. This allows the relative mobility of chromium species, with respect to aluminium ions, to be determined, providing key information to assist development of insight into ionic transport processes in amorphous anodic films under high electric fields. During anodizing of the thin alloy film, chromium atoms are not oxidized and are accumulated in a layer of alloy, ca. 2 nm thick, immediately beneath the anodic film as a consequence of prior oxidation of aluminium. When the alloy film is totally consumed by anodizing, all the chromium atoms in the enriched layer are oxidized and incorporated immediately into the anodic film, forming a thin chromium species-containing band of ca. 3 nm thickness. With further anodizing, the incorporated chromium species band migrates outwards without widening. From chemical sectioning of the anodic film and XPS surface analysis, the chromium species are present as Cr3+ ions in the anodic film. The relative migration rate of Cr3+ ions, with respect to Al3+ ions, determined from the precise location of the chromium species-containing layer, using transmission electron microscopy and Rutherford backscattering spectroscopy, is 0.74. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    CORROSION SCIENCE 39 (4) 731 - 737 0010-938X 1997/04 
    The enrichment of alloying elements as a consequence of formation of amorphous anodic films on relatively dilute, metastable binary aluminium alloys, prepared by magnetron sputtering, has been determined quantitatively employing Rutherford backscattering spectroscopy for a range bf alloying elements. The measurements relate to the enrichments that must be developed in order for oxidation of the alloying element at the alloy/film interface to proceed. The enrichments, occurring in a thin layer of alloy of 1-5 nm thickness immediately beneath the anodic film, can be correlated with the Gibbs free energy per equivalent for formation of the alloying element oxides relative to that of alumina. The enrichment increases progressively, approximately linearly, for alloying elements associated with oxides of increasingly higher Gibbs free energy per equivalent, with no enrichment for alloying elements associated with oxides of lower Gibbs free energy per equivalent. A thermodynamic approach per se is insufficient to explain the enrichment phenomenon completely. (C) 1997 Elsevier Science Ltd.
  • AC Crossland, GE Thompson, J Wan, H Habazaki, K Shimizu, P Skeldon, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 144 (3) 847 - 855 0013-4651 1997/03 
    The growth of barrier-type anodic films on amorphous Al-Mo alloys, containing 16 to 40 atom percent Mo, in borate electolyte was investigated by analytical transmission electron microscopy, Rutherford backscattering spectroscopy, secondary ion mass spectrometry, and extended x-ray absorption spectroscopy. During growth at 1 and 5 mA cm(-2), two-layered amorphous oxide films formed at high efficiency by outward migration of cations and inward migration of oxygen ions; the outer layer is composed of units of alumina contaminated by boron species derived from the electrolyte and the inner layer contains units of both Al2O3 and MoO3 distributed uniformly at the resolution of the analyses. At 0.1 mA cm(-2) the films form at reduced faradaic efficiency, which results in a decreased thickness of the outer alumina layer. The two-layered films develop as a consequence of faster migration of Al3+ ions than Mo6+ ions within the inner layers of the films. New film material forms at the alloy/film and film/electrolyte interfaces and at the interface between the inner and outer layers. At the alloy/film interface, a thin layer of alloy is highly enriched in molybdenum as a consequence of anodic oxidation. Due to the mechanism of film growth, a high concentration of boron accumulates in a sublayer of film material just above the inner/outer layer interface.
  • K Hashimoto, E Akiyama, H Habazaki, A Kawashima, M Komori, K Shimamura, N Kumagai
    SCIENCE REPORTS OF THE RESEARCH INSTITUTES TOHOKU UNIVERSITY SERIES A-PHYSICS CHEMISTRY AND METALLURGY 43 (2) 153 - 160 0040-8808 1997/03 
    On the basis of tailoring of amorphous alloy electrodes for seawater electrolysis to form H-2 and amorphous alloy catalysts for conversion of CO2 to CH4, we are proposing global CO2 recycling: At deserts; power generation by solar energy, at coasts close to the deserts; production of H-2 by electrolysis of seawater, production of CH4 by the reaction of H-2 and CO2 transported, and at energy consuming districts; combustion of CH4, recovery of CO2 and transportation of liquefied CO2 to the coast close to the deserts. Since Egyptian scientists agree with us to do collaboration, the energy balance and the amount of reduction of CO2 emission in the global CO2 recycling between Middle East and Japan are estimated for the operation of a 1 GW CH4-combustion power plant. The energy consumed in a year up to liquefaction of CH4 including that corresponding to the repayment of solar power plant is almost the same as that spent up to obtaining LNG. The energy necessary for the global CO2 recycling is only 8.7% higher than the energy necessary for LNG combustion for power generation without control of CO2 emission. The extra energy is for recovery, liquefaction and transportation of CO2. The reduction of CO2 emission by the global CO2 recycling is 79% of CO2 emission from an LNG combustion power plant, that is, 2.62 Mtons/year.
  • K Hashimoto, BP Zhang, BM Im, HJ Lee, E Akiyama, H Habazaki, A Kawashima, K Asami
    SCIENCE REPORTS OF THE RESEARCH INSTITUTES TOHOKU UNIVERSITY SERIES A-PHYSICS CHEMISTRY AND METALLURGY 43 (2) 145 - 151 0040-8808 1997/03 
    Phosphorus contained in amorphous metal-metalloid alloys is often beneficial in enhancing the corrosion resistance particularly in strong acids. On the basis of investigations conducted so far, the beneficial role of phosphorus is comprehensively summarized. Immersion of amorphous metal-phosphorus alloys containing passivating elements leads to the formation of elemental phosphorus layer on the topmost surface of the alloy as a result of initial alloy dissolution. The elemental phosphorus layer has high cathodic activity for oxygen and proton reduction and acts as the diffusion barrier against alloy dissolution. These beneficial effects ennoble the open circuit potential, and when the open circuit potential attains the passive region of the alloy spontaneous passivation occurs. An increase in the protectiveness of the passive film by ageing further ennobles the open circuit potential. At the high open circuit potential elemental phosphorus is no longer stable and dissolves into the solution. The passive film thus formed generally consists of passive oxyhydroxide and the phosphorus content in the film is rather low.
  • M Komori, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    APPLIED CATALYSIS B-ENVIRONMENTAL 11 (3-4) 243 - 255 0926-3373 1997/03 
    The effects of hydrofluoric acid (HF) treatment and bulk structure of precursor alloys on the catalytic decomposition of nitrogen monoxide have been investigated. Alloy catalysts were prepared from Ni-40valve metal (Ta, Nb, Ti and Zr)-1Pd alloys by the HF treatment and subsequent preoxidation at 750 degrees C. The tantalum-containing catalyst without previous HF treatment shows the highest activity among the catalysts examined, while the preparation of the active catalysts from other amorphous alloys requires HF treatment for surface roughening and for surface enrichment of palladium prior to the pre-oxidation treatment. The catalyst prepared from the amorphous Ni-40Ta-1Pd alloy is superior to the conventionally prepared Pd/Al2O3 catalyst, in spite of the fact that the BET surface area of the latter catalyst is two orders of magnitude higher than that of the Ni-Ta-Pd catalyst. The catalyst prepared from the amorphous Ni-40Ta-Pd alloy shows a better performance for the NO decomposition in comparison with the catalyst prepared from the crystalline counterpart, because the amorphous precursor becomes a more irregular and more microporous catalyst.
  • MW Tan, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 (3) 589 - 603 0010-938X 1997/03 
    Open circuit immersion immediately after potentiostatic polarization is carried out to investigate the effect of molybdenum addition on the stability of the passive films formed on amorphous Fe-8Cr-13P-7C alloys by polarization in de-aerated 1 M HCl at -100 mV(SCE), which is in the passive region of both chromium and molybdenum. The open circuit potentials of both molybdenum-free and -containing alloys decrease with immersion time after polarization, apart from the passive potential region of chromium but in the passive region of molybdenum. The passive film formed on molybdenum-free alloy by polarization for 10 min and 2.5 h is disrupted by open circuit immersion for 30 min, and the alloy was corroded seriously, whereas molybdenum-containing alloys passivated by polarization for 10 min remains in the passive state during subsequent immersion for 5 h. Regardless of polarization time and molybdenum addition, the cationic fraction of chromium in the surface film decreases continuously with immersion. Open circuit immersion leads to an increase in the concentration of molybdenum ion in the film on the alloys polarized previously for 10 min and a remarkable enrichment of molybdenum ion occurs after prolonged immersion, showing the formation and stabilization of molybdenum-enriched passive film. On the other hand, the enrichment of molybdenum ion during immersion is more difficult in the film on the alloys polarized previously for 2.5 h than that on the alloys polarized previously for 10 min. (C) 1997 Elsevier Science Ltd.
  • HW Wang, R DuranRomero, H Habazaki, P Skeldon, GE Thompson, GC Wood, K Shimizu
    SURFACE & COATINGS TECHNOLOGY 89 (3) 262 - 269 0257-8972 1997/03 
    The composition, structure and morphology of the molybdenum sulphide, which forms at the anodic film surface during anodizing of aluminium in thiomolybdate electrolyte, have been determined from Rutherford backscattering spectroscopy, electron microscopy and X-ray diffraction. The sulphide consists of a fragile layer of amorphous of microcrystalline MoS3 that is attached loosely to the surface of the anodic film. The layer is formed near or at the film surface by the reaction between thiomolybdate ions, from the electrolyte, and H+ ions, produced by film growth. The presence of the sulphide layer on the film surface does not affect significantly the growth of a typical barrier-type alumina film, which, as generally occurs, is contaminated in part of its thickness by a low concentration of sulphur-containing species derived from electrolyte anions. (C) 1997 Elsevier Science S.A.
  • J Bhattarai, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 (2) 355 - 375 0010-938X 1997/02 
    Amorphous W-Zr alloys containing 23-76 at% zirconium have been successfully prepared by DC magnetron sputtering. The W-Zr alloys are spontaneously passive and show significantly high corrosion resistance in 6 and 12 M HCL solutions. In particular, their corrosion resistance in 12 M HCl is higher than that of the alloy constituents. The pitting resistance of zirconium is greatly improved by alloying with tungsten. XPS analysis showed that zirconium is enriched in both the air-formed films and the passive films in HCl solutions. From angular-dependent XPS measurements, the passive films on W-Zr alloys are found to be composed of the double oxyhydroxide of tungsten and zirconium ions, although there are some concentration gradients of tungsten and zirconium ions. The formation of the homogeneous double oxyhydroxide of tungsten and zirconium ions acts synergistically in improving the corrosion resistance of W-Zr alloys in HCl solutions open to air at 30 degrees C. (C) 1997 Elsevier Science Ltd.
  • AA ElMoneim, BP Zhang, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 (2) 305 - 320 0010-938X 1997/02 
    Amorphous Mn-Ti alloys were successfully prepared by DC magnetron sputter-deposition in a wide composition range. Corrosion experiments and anodic potentiodynamic polarization measurements performed in 0.5 M NaCl at pH 5.5 and 11.5, open to air at 30 degrees C, show improved the corrosion resistance of the alloys compared with manganese. Alloying of 12 at.% or more titanium to manganese was very effective in increasing the corrosion resistance in aerated alkaline solution containing chloride ions. X-ray photo-electron spectroscopic analysis of spontaneously passivated films formed in alkaline medium revealed that titanium ions were enriched in the passive films. The passive films formed on Mn-Ti alloys at pH 11.5 were composed of a homogeneous double oxyhydoxide of tetravalent titanium and divalent manganese. It is concluded that the presence of oxidized manganese and titanium in the form of a homogeneous double oxyhydroxide is responsible for the corrosion resistance of the Mn-Ti alloys. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 39 (2) 339 - 354 0010-938X 1997/02 
    Anodic film formation, at high Faradaic efficiency, on sputter-deposited Al-(1.9-22) at% W-(0.6-0.3) at%Cu alloys has been examined, using transmission electron microscopy and Rutherford backscattering spectroscopy, in order to understand the enrichment and oxidation of alloying elements at the alloy/film interface. Anodic oxidation of the Al-1.9 at% W-0.8 at%Cu alloy results in initial prior oxidation of aluminium atoms and the accumulation of both tungsten and copper atoms in an alloy layer, about 2 nm thick, immediately beneath the amorphous alumina film, similar to enrichment behaviour in dilute binary Al-Cu and AI-W alloys. Tungsten atoms are then oxidized and incorporated into the film at about 12 V, and copper atoms are oxidized and incorporated subsequently, at about 150 V. After initial incorporation of tungsten into the anodic film, the concentration of tungsten atoms in the enriched layer decreases, in association with the progressive accumulation of copper atoms in the layer, until the steady-state composition for incorporation of both tungsten and copper atoms is achieved. In contrast to this relatively dilute alloy, tungsten enrichment, but no significant enrichment of copper, occurs following anodic oxidation of ternary alloys containing 15 at%, or more, tungsten. For each of the ternary alloys of the study, the compositions of the enriched alloy layers can be interpreted using the compositions of the enriched alloy layers of corresponding binary alloys. The anodic film compositions and morphologies are dependent upon the anodizing voltage, and are related readily to the delayed oxidation of alloying elements through enrichment, and the subsequent mobility of incorporated copper and tungsten ions. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, Zhou, X, K Shimizu, P Skeldon, GE Thompson, GC Wood
    ELECTROCHIMICA ACTA 42 (17) 2627 - 2635 0013-4686 1997 
    Transmission electron microscopy of ultramicrotomed sections and Rutherford backscattering spectroscopy have been used to quantify the significantly faster mobility of copper ions compared with Al3+ ions in anodic alumina films. To determine the migration rate of copper ions, an Al-0.4 at % Cu alloy film of ca. 35 nm thickness has been sputter deposited onto an electropolished superpure aluminium substrate; the specimen comprising the alloy layer superimposed on aluminium was then anodized at a constant current density to various voltages at high current efficiency. The anodic oxidation of the alloy film results in the prior oxidation of aluminium and the accumulation of copper in a layer of alloy, ca. 2 nm thick, just beneath the anodic film; consequently, no copper is incorporated into the alumina film during anodizing of the alloy. At ca. 49 V for the particular alloy thickness, the alloy film is totally consumed by anodizing and the copper-enriched layer beneath the anodic film is incorporated abruptly into the film, because of the presence of an air-modified electropolishing film sandwiched between the alloy and aluminium regions. With further anodizing, the incorporated copper ions migrate outwards at a rate ca. 3.2 times that of Al3+ ions. The method employed provides a novel approach to determining the precise mobility of foreign ions incorporated into anodic alumina. (C) 1997 Elsevier Science Ltd.
  • H Habazaki, Zhou, X, K Shimizu, P Skeldon, GE Thompson, GC Wood
    THIN SOLID FILMS 292 (1-2) 150 - 155 0040-6090 1997/01 
    The migration rate of zinc ions in growing anodic alumina films has been determined as part of a systematic study for understanding the ionic transport processes in anodic films under a high electric field. An Al-0.2 at% Zn alloy, about 35 nm thick, sputter-deposited onto an electropolished, high purity aluminium substrate has been anodized at a constant current density to various voltages at high current efficiency. During anodizing of the alloy, zinc atoms are accumulated in a layer of alloy, about 2 nm thick, just beneath the anodic film as a consequence of prior oxidation of the aluminium atoms. No zinc ions are incorporated into the anodic alumina film during anodizing of the alloy. When the alloy film is almost totally consumed by anodizing, zinc atoms in the enriched alloy layer are oxidized and incorporated immediately into the anodic film as a result of the presence of an air-modified, electropolishing film on the aluminium substrate. During further anodizing, zinc ions migrate outwards; the migration rate of the zinc ions is about 2.3 times that of Al3+ ions. The migration rate of the zinc ions is slower than that of the Cu2+ ions incorporated into the anodic films during anodizing of dilute Al-Cu alloys, although the strengths of the single Zn2+-O and Cu2+-O bonds and the radii and valences of Zn2+ and Cu2+ ions are similar.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    TRANSACTIONS OF THE INSTITUTE OF METAL FINISHING 75 18 - 23 0020-2967 1997/01 
    The anodic oxidation of aluminium alloys is reviewed and discussed with reference to recent results of the authors on the anodizing of model binary aluminium alloys. Attention is given primarily to the oxidation of alloying elements at the alloy/film interface during the formation of barrier-type anodic films. However, the findings are also considered to be applicable to the formation of porous anodic films. The enrichments of alloy layers of about 1-5 nm thickness is revealed to be a relatively common occurrence following anodizing of aluminium alloys. The enrichments, present in the alloy just beneath the anodic film, are a direct consequence of the formation of the anodic film on the alloy. The influence of alloy composition on the enrichments of the alloying element within the alloy is highlighted, and correlated with the Gibbs free energy per equivalent for formation of the alloying element oxide. The development of enriched alloy layers is not confined to anodizing and is found following other surface treatments including chemical polishing, electropolishing and alkaline etching.
  • H Mitsui, H Habazaki, K Hashimoto, S Mrowec
    CORROSION SCIENCE 39 (1) 9 - 26 0010-938X 1997/01 
    In order to improve the oxidation and sulfidation resistance of binary Al-Nb alloys at high temperatures, the effect of silicon addition on the sulfidation and oxidation behavior of sputter-deposited Al-Nb-Si alloys was studied as a function of temperature (1073 to 1273 K) and alloy composition in HeS2 and Ar-O-2 atmospheres. The sulfidation of the ternary alloys follows a parabolic rate law, although two-stage parabolic behavior is definitely observed for Al-54Nb-20Si. The steady-state sulfidation rates of this alloy are one order of magnitude lower than those of niobium at the temperatures examined. The sulfidation rate decreases with increasing alloy silicon content for alloys containing about 50 at.% niobium, but is almost independent of silicon content for high aluminum alloys. A duplex sulfide scale, comprising an outer aluminum sulfide layer containing small amounts of silicon and an inner niobium sulfide layer, is formed on all the alloys studied. It is assumed that the improved sulfidation resistance of Al-Nb alloys by addition of silicon is responsible for the decrease in the amount of aluminum in the alloy, which is preferentially sulfidized and whose ions have extremely high diffusibility in the protective niobium sulfide layer. The oxidation resistance of Al-Nb alloys is also improved by the addition of silicon, particularly when the niobium content is about 50 at.%. A 'pest phenomenon', observed during oxidation of Al-Nb binary alloys, is not found for the present ternary alloys. The oxidation of the alloys containing about 50 at.% niobium follows a parabolic kinetic, in contrast to the linear kinetics for the oxidation of binary alloys. The oxidation rates of the former alloys are almost comparable to that of chromia-forming alloys, though still higher than those of alumina-forming alloys due to the formation of NbAlO4 in the scale. Rapid oxidation after an incubation period is observed for Al-Nb-Si alloys with high aluminum content. Copyright (C) 1996 Elsevier Science Ltd
  • H Mitsui, H Habazaki, K Hashimoto, S Mrowec
    CORROSION SCIENCE 39 (1) 59 - 76 0010-938X 1997/01 
    As a part of a systematic study to elucidate oxidation and sulfidation resistance of Al-refractory metal alloys at high temperatures, the behavior of sputter-deposited Al-(33-80) at.%Ta alloys has been examined at temperatures ranging from 1073 K to 1273 K in HeS2 atmosphere and in Ar-O-2 atmosphere. The sulfidation kinetics of these alloys follow a parabolic rate law in an early sulfidation stage, although, in some cases, the sulfidation rates are decreased after prolonged sulfidation. The sulfidation resistance of these alloys is comparable to that of high purity tantalum and remarkably higher than those of typical high temperature alloys. The sulfide scales on these alloys comprise an outer aluminum-rich layer and an inner tantalum-rich layer. The formation of a protective inner tantalum sulfide layer is responsible for the excellent resistance to high temperature sulfidation. The oxidation kinetics of the Al-Ta alloys change with alloy composition and temperature. The oxidation of Al-33Ta initially follows a parabolic rate law, but after a particular period of oxidation, rapid oxidation is observed at high temperatures above 1173 K. In contrast, the oxidation rates of higher tantalum alloys decrease with oxidation time, although the oxidation rates in the early stage are higher than those of Al-33Ta. At the temperatures below 1123 K a rapid weight loss during oxidation was observed for the Al-Ta alloys. This seems to result from disintegration of these alloys due to the pest phenomenon. Copyright (C) 1996 Elsevier Science Ltd
  • Zhou, X, GE Thompson, H Habazaki, K Shimizu, P Skeldon, GC Wood
    THIN SOLID FILMS 293 (1-2) 327 - 332 0040-6090 1997/01 
    The average thickness and composition of the copper-enriched alloy layer that is present at the alloy / oxide interface during anodic oxidation of an electropolished Al-0.9 at.% Cu alloy at a constant current density of 50 A m(-2) have been determined by Rutherford backscattering spectroscopy and transmission electron microscopy. The copper-enriched layer, of about 2 nm thickness, has an average composition of Al-40 at.% Cu and contains about 5.4x10(15) Cu atoms cm(-2), The average composition and thickness of the layer do not change significantly during anodizing from 10 to 200 V. The essentially steady-state, copper-enriched layer is established mainly by the prior electropolishing of the alloy. As a consequence of the pre-enrichment of copper, both aluminium and copper atoms are oxidized immediately at the alloy/film interface on subsequent anodizing. Owing to the importance of copper enrichment in AI-Cu alloys to the oxidation of copper atoms, alloy pre-treatment has an important role in determining the initial oxidation behaviour. (C) 1997 Elsevier Science S.A.
  • MW Tan, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 (12) 2137 - 2151 0010-938X 1996/12 
    The effect of open circuit immersion on the passivation behavior of amorphous Fe-8Cr-Mo-13P-7C alloys with 0, 2 and 6 at.% molybdenum by potentiostatic polarization in de-aerated 1 M HCl was investigated. The polarization was made at 400 mV (SCE) which is in the passive region of chromium but in the transpassive region of molybdenum, whereas the open circuit potential of these alloys is in the passive region of molybdenum but in the active region of chromium. Open circuit immersion of molybdenum-bearing alloys results in the formation of molybdenum-enriched passive film, but passivation at 400 mV is based on the formation of chromium-enriched passive film and the molybdenum-enriched film formed by open circuit immersion is converted to the chromium-enriched film at 400 mV. Polarization at 400 mV immediately after immersion leads to rapid enrichment of chromium to the level of 50% cations within 100 s, but polarization after open circuit immersion of molybdenum-bearing alloys for 10 min results in a gradual increase in chromium content to the level of 50% of cations in 5 h. The current density of molybdenum-bearing alloys after open circuit immersion is always higher than that of the alloys polarized immediately after immersion. Open circuit immersion of molybdenum-free alloy for 10 min gives rise to serious damage of the alloy surface and hence prevents passivation even if prolonged polarization is carried out. Copyright (C) 1996 Elsevier Science Ltd
  • DB Lee, H Mitsui, H Habazaki, A Kawashima, K Hashimoto
    CORROSION SCIENCE 38 (11) 2031 - 2042 0010-938X 1996/11 
    The sulfidation behavior of amorphous 58 at.%Nb-38 at.%Al-4 at.%Si and 59 at.%Nb-35 at.%Al-6 at.%Si coatings sputter-deposited on a stainless steel substrate of SUS 304 has been studied at 1 kPa sulfur vapor pressure over the temperature range of 973-1173 K. The scales formed on the coating were bilayered, primarily consisting of an outer non-protective layer of Al2S3 and an inner barrier layer of NbS2. Beneath the coating the formation of (Fe, Cr, Ni) depleted, Al enriched zone was observed, which resulted from the mutual diffusion between the coating and the substrate. The coating improved effectively the sulfidation resistance of the stainless steel, although elements in the substrate diffused outwards in the coating and small amounts of their ions were contained in the sulfide scales. The high sulfidation resistance of the coated specimens seems attributable to the formation of a protective NbS2 scale, instead of less protective FeNb2S4, even in the presence of iron, incorporated by outward diffusion from the substrate, in the coating. Copyright (C) 1996 Elsevier Science Ltd
  • H Habazaki, P Skeldon, D Ghidaoui, SB Lyon, K Shimizu, GE Thompson, GC Wood
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 29 (10) 2545 - 2553 0022-3727 1996/10 
    The anodic film formed in aqueous tungstate electrolyte at 2.5 A m(-2), to about 295 nm thickness, on n(+)-type GaAs at high faradaic efficiency, about 94%, has been examined by analytical transmission electron microscopy, using ultramicrotomed film sections, Rutherford backscattering spectroscopy, x-ray photoelectron spectroscopy, electron probe micro-analysis and scanning electron microscopy. The film is revealed to be amorphous and to comprise a uniform distribution of units of Ga2O3 and As2O3 across the main film thickness, with possible gallium enrichment in the outermost 10 nm or so of the film. Gallium and arsenic are incorporated into the anodic film at the alloy/film interface in the substrate proportions, without development of a layer enriched either in gallium or in arsenic just beneath the anodic film. The formation ratio for the film is about 2.01 nm V-1. The film, formed by migration both of cations and of anions across its thickness, is enriched in arsenic relative to the substrate composition, the level of enrichment suggesting that Ga3+ ions migrate outwards in the film about 2.4 times faster than do As3+ ions, based on a cation transport number of 0.2. The Ga3+ ions may be ejected, to the electrolyte, under the electric field, on reaching the film/electrolyte interface, with limited formation of an outer layer of essentially Ga2O3 at the film/electrolyte interface, or form a layer of Ga2O3, up to about 10% of the total film thickness, which is thinned after anodizing by exposure to the electrolyte and the rinse water. Significantly, the outer layer of film material developed by the faster migrating Ga3+ ions prevents loss of As3+ ions from the film during film growth. However, during prolonged exposure to aqueous conditions in the absence of the field, the film becomes enriched in gallium species due to preferential dissolution of arsenic species. The high faradaic efficiency of film growth is a consequence of the presence of a tungsten-enriched layer, probably a gel composed of hydrated tungsten oxide, which develops at the film/electrolyte interface during film growth. No significant presence of tungsten species within the bulk of the anodic film is detected.
  • CA NunezLopez, H Habazaki, P Skeldon, GE Thompson, H Karimzadeh, P Lyons, TE Wilks
    CORROSION SCIENCE 38 (10) 1721 - 1729 0010-938X 1996/10 
    In order to investigate the role of silicon carbide in microgalvanic corrosion of magnesium-based metal matrix composites (MMCs), a high-purity MMC was specially prepared by magnetron sputtering magnesium on to a substrate surface impregnated with silicon carbide particles. The corrosion of the model MMC was then studied by microscopic examination following immersion for up to 36 h in 3.5 wt% NaCl solution at the corrosion potential and by potentiodynamic polarization. The MMC revealed a comparatively low corrosion current density, about 10 mu A cm(-2), and corrosion proceeded in a relatively uniform manner across the macroscopic surface of the specimen. Of most relevance to the purpose of the work, there was no evidence of microgalvanic corrosion around silicon carbide particles, indicating that the particles had virtually no influence on corrosion of the MMC. Copyright (C) 1996 Elsevier Science Ltd
  • PY Park, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 (10) 1649 - 1667 0010-938X 1996/10 
    Mo-Ti alloys composed of a single bcc solid solution have been prepared by a sputter deposition technique. The corrosion resistance of the Mo-Ti alloys in 12 M HCl is extremely high, being superior to that of molybdenum and titanium metals. The Mo-Ti alloys are spontaneously passivated in 12 M HCl. The corrosion potential of these alloys is slightly lower than that of molybdenum. The spontaneously passivated film on the alloys is significantly enriched in tetravalent molybdenum, as a consequence of preferential dissolution of titanium. The angle-resolved XPS analysis reveals that there is a compositional gradient in the passive film; molybdenum ions are concentrated in the exterior of the passive films while the concentration of titanium increases in the interior of the films. Copyright (C) 1996 Elsevier Science Ltd
  • PY Park, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 (10) 1731 - 1750 0010-938X 1996/10 
    Single bcc phase Mo-Nb alloys are successfully prepared by sputter deposition. These alloys are spontaneously passivated and show significantly high corrosion resistance in 12 M HCl. Their corrosion rates are lower than those of molybdenum and niobium. XPS analysis revealed that the passive films formed on Mo-Nb alloys by open circuit immersion in 12 M HCl are composed of outer niobium-enriched oxyhydroxide and inner molybdenum-enriched oxyhyroxide with a concentration gradient. The concentration gradient in the passive film on Mo-Nb stems from the fact that the corrosion potential of these alloys is close to or rather exceeds the potential for the transpassive dissolution of molybdenum. Copyright (C) 1996 EIsevier Science Ltd
  • M Komori, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    APPLIED CATALYSIS B-ENVIRONMENTAL 9 (1-4) 93 - 106 0926-3373 1996/09 
    Active catalysts for the direct decomposition of nitrogen monoxide were prepared from amorphous Ni-40Ta-Pd alloys by HF-treatment and subsequent pre-oxidation. The pre-oxidized catalyst consists of NiO, Ta2O5 and PdO, and PdO is decomposed to fee Pd by heating at temperatures higher than 600 degrees C. At further higher temperatures NiO and Ta2O5 are transformed to a very fine gained double oxide NiTa2O6. The catalysts thus formed consist of three layers and show high catalytic activity for the decomposition of nitrogen monoxide in a wide temperature range from 550 to 850 degrees C. The catalytic behavior is affected by the structural change in the catalyst. With the transformation from NiO and Ta2O5 to NiTa2O6, the catalytic activity and the nitrogen formation selectivity increase significantly. TEM observation of ultramicrotomed cross-sections revealed that finely dispersed palladium supported on very fine-grained NiTa2O6 is formed in the interface between the outer and intermediate layers. High catalytic activities and high nitrogen formation selectivities of the Ni-40Ta-Pd alloys are attributable to the formation of the NiTa2O6-supported palladium catalyst.
  • H Mitsui, H Habazaki, K Asami, K Hashimoto, S Mrowec
    CORROSION SCIENCE 38 (9) 1431 - 1447 0010-938X 1996/09 
    The sulfidation and oxidation behavior of sputter-deposited Al-(27-54 at. %)Nb alloys has been investigated as a function of temperature (1073-1473 K) and alloy composition in He-S-2 atmospheres with partial sulfur pressures (pS(2)) ranging from 5 x 10(1) to 1 x 10(4) Pa and in an Ar-O-2 atmosphere with partial oxygen pressure (pO(2)) of 2 x 10(4) Pa at a total pressure of 10(5) Pa. Sulfidation of these alloys follows parabolic kinetics over the whole temperature and pressure ranges studied. The sulfidation rate increases with sulfur pressure and aluminum content in the alloy, the apparent activation energy for the reaction being virtually independent of alloy composition. The scale consists of two layers. The outer layer is composed mainly of aluminum sulfide, while the inner layer is built up of niobium sulfide. It is presumed that the rate-determining step for the overall reaction is the outward diffusion of both aluminum and niobium ions through the inner niobium sulfide layer. Therefore a higher aluminum content in the alloy is harmful for the sulfidation resistance of Al-Nb alloys. The oxidation resistance of these alloys increases with aluminum content in the alloy, although even high aluminum alloys such as Al-30Nb show lower oxidation resistance than typical alumina-forming alloys. Oxidation of Al-30Nb does not follow parabolic kinetics, but follows linear kinetics, because of the formation of a nonprotective scale composed of Al2O3 and NbAlO4. At lower temperatures these alloys break up during oxidation or during the cooling period to room temperature. This seems to be due to the ''pest phenomenon''. Copyright (C) 1996 Elsevier Science Ltd
  • Zhou, X, H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 38 (9) 1563 - 1577 0010-938X 1996/09 
    As part of a systematic study of anodic oxidation of aluminium alloys, focused on the importance of initial enrichment of thin layers of alloy to the oxidation of alloying elements at the alloy/film interface, the behaviour of Al/Zn alloys is considered, which is also of relevance to surface treatment of commercial aluminium alloys. The alloys investigated, by a combination of transmission electron microscopy and Rutherford backscattering spectroscopy, are bulk Al-0.90 at% Zn alloy, in the electropolished condition, and Al-0.23 at% Zn alloy, produced by magnetron sputtering. Following anodic oxidation at 50 A m(-2), both alloys reveal zinc enrichments immediately beneath the amorphous anodic films, in thin layers of alloy which contain average concentrations of about 1.8 x 10(19) and 4.6 x 10(19) Zn atoms m(-2), respectively. For the Al-0.9 at% Zn alloy, the enrichment is sufficient for zinc atoms to be oxidized at the alloy/film interface and, hence, for zinc ions to be incorporated into the mainly alumina film. The incorporated zinc ions migrate outwards in the anodic film about 2.3 times faster than Al3+ ions. For the Al-0.23 at% Zn alloy, the enrichment is insufficient for oxidation of zinc atoms to proceed and, hence, no significant amount of zinc ions was detected in the film. The oxidation behaviour of zinc in Al-Zn alloys is generally similar to that of copper in dilute Al-Cu alloys, although the incorporation of zinc ions into the anodic films does not create the high population density of flaws found in films on Al-Cu alloys following incorporation of copper ions. Further, anodic film material on Al-Zn alloys becomes detached from the substrate at a particular condition of the alloy/film interface which, in the present work, occurs at an anodizing voltage of about 100 V for the Al-0.90 at% Zn alloy. Following detachment of the film, most of the zinc in the zinc-enriched alloy layer is lost from the exposed alloy surface and the enrichment reforms during subsequent regrowth of the anodic film. Copyright (C) 1996 Elsevier Science Ltd
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 143 (8) 2465 - 2470 0013-4651 1996/08 
    The anodic oxidation at high faradaic efficiency of sputter-deposited Al-W alloys, containing 0.1 to 5 atom percent (a/o) W, has been examined using transmission electron microscopy and Rutherford backscattering spectroscopy. The oxidation is revealed to proceed in essentially two stages, with initial formation of relatively pure anodic alumina, neglecting minor contamination from the electrolyte, and subsequent formation of tungsten-contaminated alumina. In the initial stage, tungsten accumulates progressively in a layer of alloy, about 1.5 nm thick, just under the essentially pure anodic alumina film. The accumulation attains levels corresponding to average compositions of the enriched layer of 2.5, 25, and 30 a/o W for bulk alloy compositions of 0.1, 1.8, and 5 a/o W, respectively. The transition from accumulation of tungsten in the enriched alloy layer to incorporation of tungsten species into the anodic film is considered to be related to development of tungsten-rich clusters of critical size within the enriched layer. Subsequently, aluminum and tungsten atoms are incorporated into the anodic film in their alloy proportions in the presence of a steady-state enrichment of the alloy at the alloy/film interface. Due to the discrete nature of the incorporation process, tungsten is distributed nonuniformly, on a fine scale, within the region of tungsten-contaminated alumina: The average migration rate of tungsten species in the film is about 0.38 that of Al3+ ions, thus resulting in films consisting of an outer layer of relatively pure anodic alumina and an inner layer of tungsten-contaminated alumina.
  • HJ Lee, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 (8) 1269 - 1279 0010-938X 1996/08 
    The addition of a large amount of phosphorus, such as 20 at%, to arc-melted crystalline and rapidly quenched amorphous Ni-10Ta alloys greatly enhances the corrosion resistance in 12 M HCl at 30 degrees C. The corrosion rate of the rapidly quenched amorphous Ni-10Ta-20P alloy after immersion for 168 h is about one order of magnitude lower than that of the are-melted crystalline counterpart. The open circuit potentials of both alloys are initially ennobled by accumulation of elemental phosphorus having a high activity for the cathodic oxygen reduction. The open circuit potential is further ennobled by spontaneous passivation. The ennoblement of the open circuit potential of the amorphous alloy is faster than that of the crystalline counterpart, because of faster passivation as a result of the formation of a tantalum-enriched passive film. Copyright (C) 1996 Elsevier Science Ltd.
  • H Habazaki, MA Paez, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    CORROSION SCIENCE 38 (7) 1033 - 1042 0010-938X 1996/07 
    The anodic oxidation of Al-0.9 at%Cu alloy has been investigated, focusing on the effect of a mechanical polishing pre-treatment on incorporation of copper ions into the anodic film and the accumulation of copper atoms in the alloy just beneath the alloy/film interface. For the particular alloy and anodizing conditions, a relatively pure alumina film is formed to thickness of about 170 nm with associated progressive accumulation of copper atoms in the alloy at the alloy/film interface. The thickness of the copper-enriched layer is about 2 nm and the average composition approaches about 42 at%Cu. Only on achieving this level of enrichment are copper ions incorporated into the anodic film. The copper ions are more mobile than aluminium ions and hence, are able to reach the film/electrolyte interface during subsequent film growth. Copyright (C) 1996 Elsevier Science Ltd.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES 73 (3) 445 - 460 0141-8637 1996/03 
    Anodic oxidation of a non-equilibrium Al-1.9 at.% W alloy has been studied in order to investigate the mechanism of incorporation of metal ions into the anodic film at the alloy-film interface. Initially a relatively tungsten-free anodic alumina film is formed on the alloy to a thickness of about 28 nm, corresponding to an anodizing voltage of about 23 V. During growth of the alumina film, tungsten atoms are accumulated in a similar to 1.5 nm layer of alloy, just beneath the anodic film, that becomes enriched in tungsten to an average composition of about Al-25 at.% W. At this critical condition of the interface, tungsten and aluminium are then incorporated into the anodic film in their alloy proportions by a mechanism having similarities with the anodizing of layered valve metals, forming oxides of differing ionic resistivity, but on a nanoscale. Transient fingers, composed of relatively pure WO3 or a tungsten-enriched mixture of units of WO3 and Al2O3, develop at discrete sites, of about 1-2 nm separation, along the interface and penetrate the higher-resistivity, labile alumina. The sites are regions of alloy of higher than average tungsten concentration, probably associated with tungsten-rich clusters of a critical size. Owing to the limited thickness of the enriched layer of alloy, individual fingers are restricted to lengths of similar to 5 nm. Comparatively pure alumina is formed at sites along the alloy/film interface between the fingers at which the critical size of cluster has not been reached. By this mechanism, tungsten is incorporated discontinuously into the anodic film at local sites, with alternating local depletion of tungsten in the enriched layer by formation of the finger from a tungsten-rich cluster of critical size, and subsequent enrichment of tungsten, to redevelop clusters, by oxidation of aluminium. The average rate of incorporation of tungsten is constant since fingers form continually along the interface which, through the incorporation mechanism, is finely roughened. By inference, the flow of ionic current normal to the alloy-film interface fluctuates at particular sites along the interface during incorporation of tungsten into the film. The incorporated tungsten migrates outwards in the anodic film, under the influence of the electric field, at an average rate of about 37% of the rate of Al3+ ions. The initially non-uniform distribution of tungsten in the anodic film, due to the discrete nature of incorporation, is smoothed, but not eliminated, by the ionic transport processes, involving Al3+ and O2-/OH- ions and tungsten species, within the film. As a result of the initial development of the tungsten-rich layer at the alloy/film interface, prior to incorporation of tungsten into the film, the distribution of tungsten in the film is dependent upon the film thickness. For relatively thick films, formed to voltages much greater than 23 V, the outer similar to 30% of the film thickness is composed of relatively pure alumina, while the inner similar to 70% of the film is composed of a mixture of units of Al2O3 and WO3.
  • K Hashimoto, H Habazaki, E Akiyama, H Yoshioka, JH Kim, PY Park, A Kawashima, K Asami
    SCIENCE REPORTS OF THE RESEARCH INSTITUTES TOHOKU UNIVERSITY SERIES A-PHYSICS CHEMISTRY AND METALLURGY 42 (1) 99 - 105 0040-8808 1996/03 
    Tailoring corrosion-resistant new alloys has recently been performed mostly by sputter deposition technique. This technique is suitable to form a single phase solid solution even when the boiling point of a component is lower than the melting point of the rest of components and/or when a component is immiscible to another component in the liquid state. Sputter-deposited chromium alloys with valve metals, such as titanium, zirconium, niobium and tantalum are composed of amorphous single phase in wide composition ranges. Molybdenum-valve metal alloys consist mostly of fine-grained bcc single phases. These alloys have very high corrosion resistance in concentrated hydrochloric acids which is higher than that of alloy constituting elements. The corrosion resistance increases with increasing chromium content of chromium-valve metal alloys, while the corrosion resistance decreases with increasing molybdenum content of molybdenum-valve metal alloys. Their corrosion resistance is based on spontaneous passivation. The passive films formed on amorphous chromium-valve metal alloys consist of double oxyhydroxides of chromic ion and valve metal cations. The passive films formed on molybdenum-valve metal alloys are heterogeneous. The exterior of the films is rich in valve metal cations and the interior is rich in tetra valent molybdenum.
  • A Kawashima, H Habazaki, K Asami, K Hashimoto
    SCIENCE REPORTS OF THE RESEARCH INSTITUTES TOHOKU UNIVERSITY SERIES A-PHYSICS CHEMISTRY AND METALLURGY 42 (1) 91 - 98 0040-8808 1996/03 
    Amorphous alloy electrodes for fuel cells have been reviewed. This includes the performance of the electrodes for electro-oxidation of methanol and its derivatives, hydrogen and some hydrocarbons, and reduction of oxygen. These electrodes show a very high activity and durability for the oxidation of the fuels and reduction of oxygen. The characterization of the electrocatalysts prepared from the amorphous alloys has also presented.
  • HJ Lee, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 (3) 469 - 485 0010-938X 1996/03 
    The corrosion resistance of arc-melted Ni-10Ta-P alloys containing 0, 10 and 20 at% phosphorus in 12 M HCl solution at 30 degrees C was investigated. The alloys containing 0 and 10 at% phosphorus suffer severe corrosion. The addition of 20 at% phosphorus to crystalline Ni-10Ta alloy results in a three-orders-of-magnitude decrease in the corrosion rate. The open circuit potentials of the Ni-10Ta alloys containing 0 and 10 at% phosphorus stay almost constant in the active region of nickel, while the open circuit potential of the Ni-10Ta-20P alloy increases almost linearly in the initial 2 h. The Ni-10Ta alloy consists of intermetallic Ni8Ta and immersion in 12 M HCl results in faceting dissolution. Ni-10Ta-10P alloy is composed of major Ni8Ta and Ni3P phases acid minor Ni2Ta and Ni2P phases. Immersion of Ni-10Ta-10P alloy leads to preferential dissolution of the Ni8Ta phase and to continuous thickening of the corrosion product film consisting mostly of tantalum as cations. Ni-10Ta-20P alloy consists of Ni2Ta, Ni3P, Ni2P and NiP phases. Immersion of Ni-10Ta-20P alloy gives rise to initial increase in elemental phosphorus on the surface as a result of selective dissolution of nickel and selective oxidation of tantalum. The formation of elemental phosphorus with a high cathodic activity is responsible for the initial ennoblement of the open circuit potential and for the formation of the passive film in which tantalum is highly concentrated. The higher corrosion resistance of Ni-10Ta-20P alloy than Ni-10Ta-10P alloy is attributable to the formation of the Ni2Ta phase with a higher tantalum content than the Ni8Ta phase which is the readily corroded major intermetallic phase in the Ni-10Ta-10P alloy.
  • H Mitsui, H Habazaki, E Akiyama, A Kawashima, K Asami, K Hashimoto, S Mrowec
    MATERIALS TRANSACTIONS JIM 37 (3) 379 - 382 0916-1821 1996/03 
    The sulfidation and oxidation behavior of sputter-deposited Al-Mo, Al-Nb, Al-Ta and Al-W binary alloys has been investigated under isothermal-isobarometric conditions at the temperature ranging from 1073 to 1273 K. High temperature sulfidation was carried out in He-S-2 atmosphere with sulfur vapor pressure kept constant at 1 kPa, and high temperature oxidation was carried out in Ar-O-2 atmosphere with oxygen pressure fixed to 20 kPa. In sulfidation tests, these alloys showed superior high temperature sulfidation resistance to the known metallic materials, and the sulfidation rates of these alloys were comparable to those of refractory metals. The sulfide scales of these alloys were composed of bilayer, and it was revealed that the formation of the inner protective sulfide scale of refractory metal was responsible for the lower sulfidation rate of these alloys. The oxidation rates of these alloys were much lower than that of corresponding refractory metals, but higher than those of typical alumina-forming alloys because of the formation of refractory metal oxides or their double oxides with aluminum.
  • H Habazaki, P Skeldon, GE Thompson, GC Wood, K Shimizu
    PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES 73 (2) 297 - 308 0141-8637 1996/02 
    Nominally uniform and amorphous sputter-deposited binary alloys (Al-Ta, Al-Nb, Al-Zr, Al-Ti) prepared by conventional magnetron sputtering of valve metals are shown in reality to comprise fine scale, multilayered alloy films for particular conditions of deposition. The layers, each about 1 nm thick, are the result of a periodic modulation of the composition of the alloy him during the deposition process, leading to layers relatively enriched and depleted in the alloying element compared with the mean composition of the alloy. During subsequent anodizing at high Faradaic efficiency, amorphous anodic films, that are mainly uniform in thickness, composition and structure, are formed on the sputter-deposited alloys indicating that the heterogeneity of the substrate is not imparted to the bulk of the anodic film material. This is apparently due to the smoothing effect of the ionic transport processes during anodic him growth. However, near to the alloy film/anodic him interface, significant variations in the composition of the anodic film, associated with the heterogeneity of the substrate, are evident, suggesting that the variation in substrate composition is of importance to the formation and subsequent composition of relatively thin anodic films and the inner regions of thick ones. Consideration is given to the use of multilayered alloy films as investigative probes of anodic him growth, in particular of the migration of Al3+ ions and cations of the alloying element under the electric field, and the formation of anodic film material at the alloy film/anodic film interface. Of wider relevance, the heterogeneity of the substrate would be of critical importance to the use of sputter-deposited alloys in studies of dealloying, passivation and pitting as well as in the practical use of such sputter-deposited materials.
  • MA Paez, TM Foong, CT Ni, GE Thompson, K Shimizu, H Habazaki, P Skeldon, GC Wood
    CORROSION SCIENCE 38 (1) 59 - 72 0010-938X 1996/01 
    Barrier-type anodic film formation on a bulk A1-3.5wt% Cu alloy has been examined by analytical transmission electron microscopy. Anodic alumina Nm formation proceeds in the usual way, with Al3+ egress and O2- ingress across the pre-existing film under the high electric field. Copper species are incorporated into the alumina Nm at the alloy/film interface and have a greater mobility under the held than outwardly mobile aluminium cations; the absence of any enrichment of copper species at the film/electrolyte interface also suggests their direct ejection into the electrolyte. The incorporation of copper species into the alumina film is related to clustering processes at the alloy/film interface which lead to a significant interfacial enrichment of copper and its local oxidation in the form of relatively short-lived copper oxide fingers. The generation of fine clusters and their preferential oxidation, with subsequent reformation as a result of the anodic oxidation of the adjacent aluminium matrix, explain the relatively narrow region of copper enrichment at the alloy/film interface.
  • H Habazaki, P Skeldon, K Shimizu, GE Thompson, GC Wood
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 28 (12) 2612 - 2618 0022-3727 1995/12 
    The anodic oxidation of amorphous Al-32 at% Zr alloy films at high current efficiency results in amorphous anodic films, comprising a mixture of Al2O3 and ZrO2 units, of uniform composition and thickness. The use of an immobile xenon marker reveals that the films develop, under the high field, at the alloy/film and film/electrolyte interfaces by the inward transport of O2- and OH- ions and the outward transport of cations respectively. This mechanism is typical of growth of amorphous anodic films involving the cooperative transport of cations and anions. The total transport number of cations is about 0.35. Zirconium and aluminium are incorporated into the anodic films, in their alloy proportions, without the development of significant enrichments or depletions of zirconium at the alloy/film interface. Zr4+ ions, which are immobile in the usual crystalline anodic zirconia, migrate outwards at about the same rate as Al3+ ions. Boron species, incorporated into the films from the electrolyte, are immobile and are distributed uniformly in the film material formed at the film/electrolyte interface by outward migration of cations.
  • H Habazaki, K Shimizu, MA Paez, P Skeldon, GE Thompson, GC Wood, Xhou, X
    SURFACE AND INTERFACE ANALYSIS 23 (13) 892 - 898 0142-2421 1995/12 
    The mechanism of oxidation of copper at the alloy/film interface, and the subsequent migration of copper ions in barrier-type films, has been examined for anodizing of an Al-1.5 wt.% Cu alloy with a prior chemical polishing treatment Both chemical polishing and anodizing result in formation of a thin layer of alloy at the alloylfilm interface, of similar to 2 nm thick, that is highly enriched in copper, The layer is present immediately beneath the different types of him formed by chemical polishing and subsequent anodizing, and contains in both cases similar to 6 x 10(19) Cu atoms m(-2). The amount of copper contained within the enriched layer of alloy is not significantly dependent upon the anodizing voltage. During anodic film growth, both aluminium and copper ions are incorporated into the film at the alloylfilm interface, on average in their alloy proportions, However, the film is depleted in copper relative to the alloy because copper ions in the him migrate faster than Al3+ ions and, on reaching the film/electrolyte interface, are ejected directly to solution, The mechanism of oxidation of copper is proposed to depend upon the formation, through prior oxidation of aluminium, of copper-rich clusters in the enriched layer of alloy at the alloy/film interface, Individual clusters are oxidized only on achieving a critical size. Consequently, copper is incorporated into the him discontinuously both in time and in position along the alloy/film interface. The films contain a high population density of flaws, which affects the film composition, the uniformity of ionic current, the faradaic efficiency of him growth, and the detailed distributions of copper ions within the films, However, the general features of film growth are compatible with the usual growth mechanism of anodic alumina, with transport numbers of Al3+ and O2-/OH- ions of similar to 0.4 and similar to 0.6, respectively.
  • T MORI, A KAWASHIMA, E AKIYAMA, H HABAZAKI, K ASAMI, K HASHIMOTO
    JOURNAL OF APPLIED ELECTROCHEMISTRY 25 (10) 953 - 961 0021-891X 1995/10 
    Active electrode materials for a new zinc electrowinning process, in which the thermodynamic cell voltage is about half that of the conventional process by replacing oxygen evolution by anodic oxidation of SO2 produced in the zinc smelting process have been studied. Immersion in HF solution and subsequent cyclic voltammetry (CV) in sulfuric acid are known to be effective surface activation treatments of the amorphous alloy electrodes. The galvanostatic cathodic reduction (CR) treatment was applied to obtain further activation for sulfite oxidation for HF- and CV-treated electrodes prepared from amorphous nickel-valve metal-platinum group metal alloys. This treatment has been found to be effective in enhancing the activity. Among the amorphous Ni-40Nb alloys containing platinum group elements, the platinum-containing electrode showed the highest catalytic activity, which was higher than that of platinized platinum. Furthermore, the electrocatalytic activities of CR-treated electrodes prepared from amorphous alloys containing platinum and rhodium, and platinum and ruthenium were higher than that of the electrode containing only platinum. According to XPS analysis of the amorphous Ni-40Nb-1Pt-1Ru alloy specimen the enrichment of platinum and ruthenium occurred by CV treatment, and a small amount of oxidized platinum and ruthenium species remained on the electrode surfaces, but most of them were cathodically reduced to the metallic state by CR treatment. High catalytic activities for sulfite oxidation can be attributed to the metallic state of platinum and ruthenium contained in the alloy electrodes, even though the activity of these electrocatalysts is higher than that of pure Pt or Ru.
  • H HABAZAKI, P SKELDON, K SHIMIZU, GE THOMPSON, GC WOOD
    CORROSION SCIENCE 37 (9) 1497 - 1509 0010-938X 1995/09 
    Al-30 at% Mo alloy films, of excellent adherence, compositional and thickness uniformity have been sputter-deposited on to electropolished and anodized aluminium substrates. Anodic oxidation of the amorphous alloy films results in anodic oxide which is free from molybdenum species in the outer regions and enriched in molybdenum species in the inner regions. The development of the film can be readily interpreted from current knowledge of the mobilities of aluminium, oxygen/hydroxyl and molybdenum species gained from anodizing of relatively pure aluminium in molybdate solution. However, unlike the previous situation which leads to relatively low levels of incorporated molybdate species, significant incorporation results from alloy oxidation which influences markedly anodic oxide resistivity and field strength during anodic oxidation.
  • BM IM, M KOMORI, BT LEE, E AOYAGI, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HIRAGA, K HASHIMOTO
    CORROSION SCIENCE 37 (9) 1411 - 1422 0010-938X 1995/09 
    The formation of a single amorphous Fe-Cr-P phase was strongly related to the amount of phosphorus addition. The structure of the melt-spun Fe-8Cr-P alloys containing 16.5 at% or more phosphorus was confirmed to be amorphous by X-ray diffraction (XRD). However, high-resolution transmission electron microscopy (TEM) revealed that a microcrystalline bcc Fe phase was dispersed in the amorphous matrix of the Fe-8Cr-16.5P and Fe-8Cr-18P alloys. The corrosion behavior of Fe-Cr-P alloys is significantly sensitive to the presence of microcrystallites in the amorphous matrix. A thick corroded layer was formed on the Fe-8Cr-16.5P and Fe-8Cr-18P alloys by immersion in 9M H2SO4 A TEM image for the thick corroded layer of the Fe-8Cr-16.5P alloy showed that the microcrystalline bcc Fe phase was preferentially dissolved away in the solution and that the amorphous Fe-Cr-P phase remained on the surface of the alloy without dissolution. Accordingly, the thick corroded layer corresponds to the amorphous Fe-Cr-P phase which is covered with the passive film. The addition of 20 at% phosphorus is necessary to form an almost complete amorphous structure and to provide the high corrosion resistance even in 9M H2SO4.
  • HJ LEE, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 37 (8) 1313 - 1324 0010-938X 1995/08 
    The corrosion behavior of Ni-10Ta-P alloys in 12 M HCl solution was investigated. An increase in the alloy phosphorus content improves the corrosion resistance of the Ni-10Ta-P alloys. Ni-1oTa-15P and Ni-10Ta-20P alloys with sufficient phosphorus additions are spontaneously passivated due to the formation of a stable passive film in which tantalum ions are accumulated, comprising more than 70% of cations just after immersion. The composition and thickness of the film on these alloys are almost unchanged during prolonged immersion. By contrast, Ni-10Ta-5P and Ni-10Ta-10P alloys with insufficient phosphorus additions are not passivated spontaneously and continue to dissolve actively. Thus, a tantalum-enriched him cannot be formed for initial short periods of immersion. A large amount of dissolution of Ni-10Ta-5P and Ni-10Ta-10P alloys results in accumulation of tantalum ions on the alloy surface, and tantalum species precipitate and are concentrated in corrosion products on the alloy surface. Accordingly, the concentration of tantalum ions in the corrosion product film is increased slowly to more than 90% of cations, which is significantly higher than that in the stable passive film formed on the alloys with high phosphorus additions.
  • K HASHIMOTO, PY PARK, JH KIM, H YOSHIOKA, H MITSUI, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, Z GRZESIK, S MROWEC
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 198 (1-2) 1 - 10 0921-5093 1995/07 
    Tailoring new corrosion-resistant alloys has recently been performed mostly by the sputter deposition technique. This technique is suitable for forming a single-phase solid solution even when the boiling point of one component is lower than the melting points of the other components and/or when one component is immiscible with another component in the liquid state. Aluminium-refractory metal, chromium-valve metal and molybdenum-chromium-nickel alloys have been successfully prepared in a single amorphous phase. Amorphous aluminium-refractory metal alloys are corrosion resistant in 1 M HCl and chromium-valve metal alloys are spontaneously passive in 12 M HCl, showing a better corrosion resistance in comparison with the alloy components. The amorphous aluminium-refractory metal alloys also have an extraordinarily high hot corrosion resistance. Their sulphidation resistance at higher temperatures is far higher than any other known metallic materials and their oxidation resistance is comparable to chromia- or alumina-forming alloys.
  • BM IM, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 37 (5) 709 - 722 0010-938X 1995/05 
    The corrosion resistance of amorphous Fe-8Cr-P alloys depends very strongly on the amount of phosphorus addition. The corrosion rates of crystalline Fe-8Cr-7P and Fe-Cr-13P alloys in 9 M H-2 SO4 solution at 30 degrees C are extremely high in comparison with those of amorphous Fe-8Cr-P alloys with 16.5 at% or more phosphorus. An increase in the phosphorus content improves the corrosion resistance. The amorphous Fe-8Cr-16.5P and Fe-8Cr-18P alloys which are composed of very fine bce phase dispersed in the amorphous matrix turn black after immersion for about 10 min, while the amorphous Fe-8Cr-20P alloy maintains the metallic luster after immersion for 168 b. Intense spectra of elements in the metallic state are observed in XPS analysis even though the specimen surface turns black. This metallic species found by XPS corresponds to the amorphous Fe-Cr-P phase which is not corroded. The thick corroded layer formed on Fe-8Cr-16.5P and Fe-8Cr-18P alloys seems to be the amorphous alloy phase after dissolution of the microcrystalline bce Fe, the amorphous Fe-Cr-P phase being covered with a passive him. The amorphous Fe-8Cr-20P alloy does not show initial active dissolution, and the corrosion loss Of this alloy is very small. Therefore, at least 20 at% addition of phosphorus to the Fe-8Cr allay is necessary to form the completely amorphous structure and to provide the high corrosion resistance.
  • HJ LEE, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 37 (2) 321 - 330 0010-938X 1995/02 
    The addition of 3 at% phosphorus to amorphous Ni-30Ta alloy results in two orders of magnitude decrease in the corrosion rate in 12 M HCl at 30 degrees C. The amorphous Ni-30Ta-P alloys with 2 at% or more phosphorus were spontaneously passive. The open circuit potential of the phosphorus-free amorphous Ni-30Ta alloy decreases with time and becomes constant in the active region of nickel. By contrast, the open circuit potentials of the phosphorus-containing alloys increase with time of immersion. XPS analysis reveals that surface films on the Ni-30Ta alloys are composed exclusively of Ta5+ ions as cations regardless of the presence of phosphorus. The film formed on the amorphous Ni-30Ta alloy is significantly thicker than that on the amorphous Ni-30Ta-5P ahoy. The thick surface film on the Ni-30Ta alloy consists of a high concentration of OH- ions, while the passive film on the Ni-30Ta-5P alloy contains a high concentration of O2- ions.
  • PY PARK, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 37 (2) 307 - 320 0010-938X 1995/02 
    Amorphous Mo-Zr alloys were prepared in a wide composition range of 40-80 at% zirconium by a magnetron sputtering method. The sputter-deposited Mo-Zr alloys exhibit lower corrosion rates than those of molybdenum and zirconium in 12 M HCl solution open to air at 30 degrees C. The corrosion resistance of Mo-Zr alloys increases with increasing alloy zirconium content, but molybdenum and zirconium improve the corrosion resistance synergistically. Mo-Zr alloys containing 60 at% or more zirconium exhibit a passive region in a wide potential range without transpassive dissolution of molybdenum. The presence of zirconium suppresses both the cathodic reaction for hydrogen evolution and the anodic reduction. The air-formed film is composed of a double oxyhydroxide of zirconium and molybdenum. Spontaneously passivated films on the alloys containing less than and more than 40 at% of zirconium are composed of molybdenum-enriched and zirconium-enriched oxyhydroxides, respectively. They seem to consist of a bilayer structure; the outer zirconium and inner molybdenum oxyhydroxides. Weak points in each layer in the bilayered passive film seem to be protected mutually by another layer. This appears to be responsible for the high corrosion resistance of the Mo-Zr alloys in comparison with alloy constituents.
  • E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    PASSIVATION OF METALS AND SEMICONDUCTORS 185- 809 - 818 0255-5476 1995
  • H HABAZAKI, P SKELDON, GE THOMPSON, GC WOOD, K SHIMIZU
    PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES 71 (1) 81 - 90 0141-8637 1995/01 
    The formation of barrier-type anodic films on sputter-deposited amorphous Al-30W (at.%) alloy has been studied for the first time to elucidate ionic transport mechanisms across the film and associated interfaces. The film, grown with high Faradaic efficiency at 50 A m-2 to 150 V in aqueous 0.01 M ammonium pentaborate electrolyte at 293 K, comprises two main layers of relatively uniform composition and with flat, parallel and sharp interfaces: an outer layer, representing about 15% of the film thickness and composed of tungsten-free anodic alumina, and an inner layer containing both aluminium and tungsten in an amorphous structure based on groupings of Al2O3 and WO3. The two layers form as a consequence of the slower migration of tungsten species in the film compared with that of Al3+ ions. The inner layer has, as expected on compositional grounds, a lower ionic resistivity than the outer layer; yet, contrary to predictions, film formation proceeds in a uniform manner, i.e. without current channelling. Aluminium and tungsten are incorporated into the film at the alloy-film interface in their alloying proportions within the limitations of the measurements.
  • K Hashimoto, PY Park, JH Kim, E Akiyama, H Habazaki, A Kawashima, K Asami
    PASSIVATION OF METALS AND SEMICONDUCTORS 185- 779 - 788 0255-5476 1995
  • B. M. Im, E. Akiyama, H. Habazaki, A. Kawashima, K. Asami, K. Hashimoto
    Corrosion Science 36 (9) 1537 - & 0010-938X 1994/09 [Refereed][Not invited]
     
    The corrosion behavior of the amorphous Fe-8Cr-metalloid alloys containing phosphorus as a metalloid element is largely affected by the amount of phosphorus. Immersion tests in concentrated 9 M H2SO4 solution open to air at 30°C show that the corrosion resistance of amorphous Fe-8Cr-20P alloy is very much higher than that of amorphous Fe-8Cr-13P-7C alloy. The corrosion loss of the amorphous Fe-8Cr-20P alloy is hardly detected by a microbalance even though the open circuit potential is initially in the active region of chromium. By contrast, the amorphous Fe-8Cr-13P-7C alloy shows active dissolution initially and the corrosion loss of this alloy increases gradually with immersion time. Only 30 mV difference in the initial open circuit potentials is responsible for the difference in the passivation behavior, with spontaneous passivation of the Fe-8Cr-20P alloy without initial active dissolution and delayed spontaneous passivation of the Fe-8Cr-13P-7C alloy with initial active dissolution. The presence of phosphorus ennobles the open circuit potentials of Fe-8Cr-13P-7C and Fe-8Cr-20P alloys sharply from the active region to the passive region of chromium by suppressing the anodic dissolution and accelerating the cathodic reactions of hydrogen evolution and oxygen reduction. XPS analysis indicates that the chromium content in the passive film increases with time of immersion following the ennoblement of the open circuit potential. The passivity of the Fe-8Cr-20P alloy which has a higher corrosion resistance than that of the Fe-8Cr-13P-7C alloy is maintained by the passive film in which chromium is less enriched in comparison with the passive film on the Fe-8Cr-13P-7C alloy. Phosphorus and chromium enhance synergistically the corrosion resistance. Phosphorus stimulates passivation and chromium forms the passive oxyhydroxide film. © 1994.
  • H. Habazaki, K. Takahiro, S. Yamaguchi, K. Hashimoto, J. Dabek, S. Mrowec, M. Danielewski
    Materials Science and Engineering A 181-182 (C) 1099 - 1103 0921-5093 1994/05/15 [Refereed][Not invited]
     
    High temperature corrosion of sputter-deposited amorphous Al(34-46)Mo and Al31Mo(6-16)Si alloys has been studied as a function of temperature (973-1273 K) in sulfur vapor (103 Pa), as well as in oxygen and air. The sulfidation process follows parabolic kinetics, so is diffusion controlled. Over the whole temperature range studied, the discussed alloys showed excellent resistance to sulfide corrosion, their sulfidation rates being comparable with the oxidation rates of chromia-forming materials. The oxidation resistance of binary AlMo alloys has been found to be satisfactory, but only at temperatures not exceeding 1073 K. Above the melting point of MoO3 (1069 K), the scale, consisting mainly of Al2O3 with about 5% MoO3, becomes unprotective because of the evaporation of MoO3. However, ternary AlMoSi alloys show excellent resistance to oxidizing environment up to about 1200 K, their oxidation rates being comparable with those of Al2O3 formers. No traces of molybdenum have been found in the Al2O3 scale on these alloys. © 1994.
  • H HABAZAKI, H MITSUI, K ASAMI, S MROWEC, K HASHIMOTO
    ADVANCED MATERIALS '93, I - A & B 14 (A & B) 309 - 312 1994
  • H MITSUI, H HABAZAKI, K ASAMI, K HASHIMOTO, S MROWEC
    ADVANCED MATERIALS '93, I - A & B 14 (A & B) 243 - 246 1994
  • K ASAMI, SC CHEN, H HABAZAKI, K HASHIMOTO
    CORROSION SCIENCE 35 (1-4) 43 - 49 0010-938X 1993 
    Passive films formed on pure Ti and crystalline and amorphous Ti-Ni alloys containing from 30 to 60 at% Ti in a sulfuric acid solution were studied by XPS and photoelectrochemical methods. The photocurrent increased with applied anodic potential. The band-gap energies in the surface films were in the range of 3.2-3.4 eV which decreased with increasing applied potential. In the surface film, Ti ions were enriched. The Ti in the film consisted of Ti4+, Ti3+ and Ti2- ions. The ratios between them on a specimen were independent of the applied potential, although the thickness of the surface film itself increased with the increasing potential. The surface films on pure Ti and Ti-Ni alloys contained OH-type oxygen.
  • K HASHIMOTO, N KUMAGAI, H YOSHIOKA, JH KIM, E AKIYAMA, H HABAZAKI, S MROWEC, A KAWASHIMA, K ASAMI
    CORROSION SCIENCE 35 (1-4) 363 - 370 0010-938X 1993 
    This is a review of laser and electron beam processing and sputter deposition for the preparation of corrosion-resistant amorphous surface alloys and of the characteristics of thus prepared surface alloys. Amorphous surface alloys with a large surface area were prepared by repetition of instantaneous melting of a very restricted volume of the surface by irradiation with a CO2 laser or electron beam and subsequent self quenching by the cold bulk substrates. The materials consisting of the amorphous surface alloys and bulk crystalline metals are quite suitable for corrosion-resistant materials with other specific properties. Sputter deposition was used for preparation of various amorphous alloys such as Al-Ti, Al-Zr, Al-Nb, Al-Ta, Al-Cr, Al-Mo, Al-W, Cr-Ti, Cr-Zr, Cr-Nb, Cr-Ta, Cu-Nb and Cu-Ta. The corrosion resistance of amorphous aluminum alloys was very high and could be changed from that comparable to 304 stainless steels to that far exceeding corrosion-resistant nickel-base alloys by changing the alloying element and its concentration. The corrosion rates of amorphous chomium-valve metal alloys are several orders of magnitude lower than those of alloy constituting elements. The amorphous Al-Mo alloys show high resistance to both sulfidation and oxidation at high temperatures. Sputter deposition is a potential method to produce new materials with specific properties.
  • K ASAMI, SC CHEN, H HABAZAKI, A KAWASHIMA, K HASHIMOTO
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 134 1025 - 1028 0921-5093 1991/03 
    In dilute sulphuric solution, amorphous and crystalline Ni-Ti alloys with titanium content greater-than-or-equal-to 40 at.% had almost the same anodic behavior and photoelectrochemical properties in so far as they had the same composition, i.e. they were spontaneously passivated and showed a positive photocurrent. Band-gap energies of the surface film on amorphous and crystalline Ni-Ti alloys were all about 3.3 eV although they were dependent on the applied potential. The thickness of the surface film formed on amorphous and crystalline Ni-40Ti alloys was, in the range of several nanometers, within the potential region examined. It increased with potential. In the surface film Ti4+ ions were concentrated relative to the bulk alloy composition.
  • H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 134 1033 - 1036 0921-5093 1991/03 
    The active and passive current densities in the low-potential region of amorphous Fe-8Cr-Mo-13P-7C alloys in 1M HCl aqueous solution decrease with increasing molybdenum content in the alloy. Hence, the addition of molybdenum improves the corrosion resistance and passivating ability. X-ray photoelectron spectroscopy (XPS) and electrochemical investigations reveal that the quantity of chromium dissolved during potentiostatic passivation gradually decreases with an increase in molybdenum content in the alloy. As a result, the surface film formed on the molybdenum-containing alloy is rapidly enriched in chromic ions during passivation. By contrast, the enrichment of chromic ions in the surface film on the alloy without molybdenum is relatively slow, although the concentration of chromic ions in the passive film is almost the same as or higher than that in the passive film formed on the molybdenum-containing alloy after prolonged polarization. When a sufficient quantity of molybdenum is added, almost no chromium is dissolved during potentiostatic polarization in the passive region and passivation takes place by transformation of the air-formed film to the passive film as a result of preferential dissolution of a small quantity of iron.
  • K HASHIMOTO, N KUMAGAI, H YOSHIOKA, H HABAZAKI, A KAWASHIMA, K ASAMI, BP ZHANG
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 133 22 - 25 0921-5093 1991/03 
    This is a review of studies performed by the authors after RQ6 on the subjects in the field of the chemical properties of rapidly quenched metals. This includes corrosion-resistant alloys, the effects of alloy homogeneity and structural relaxation on corrosion behavior, electrocatalytic materials for electrolysis of seawater and fuel cells, and catalysts for the oxidation of carbon monoxide.
  • R NISHIMURA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 134 1074 - 1077 0921-5093 1991/03 
    The passivation behavior of hydrogen-charged iron-based amorphous alloys (Fe-xCr-13P-7C, x = 5, 10 and 15) and a nickel-based amorphous alloy (Ni-15Cr-16P-4B) has been investigated in a sulphuric acid solution at 303 K using the electrochemical method. The specimens were first hydrogen charged at a constant current density of 2 x 10(-3) A cm-2 for different charging times and immediately were polarized for passivation at a constant potential of 0.445 V SHE-1 on the iron alloys and 0.645 V SHE-1 on the nickel alloy for 1 h in the same solution. For the iron-based amorphous alloys, the passive current and the amount of charge passed during the polarization drastically changed at a charging time of 3-4 h, which was called the critical charging time. After the critical charging time, the surface changed from shiny to black in color. The black film reduces the corrosion resistance in the sense that it interferes with the passivation. The Ni-15Cr-16P-4B amorphous alloy examined for comparison exhibited no such critical charging time.

MISC

  • 常温でも働く水素分離膜の開発
    青木 芳尚, 倉 千晴, 國貞 雄治, 朱 春宇, 幅崎 浩樹  クリーンエネルギー  27-  (6)  44  -51  2018  [Not refereed][Not invited]
  • 青木芳尚, 青木芳尚, 幅崎浩樹  セラミックス  52-  (2)  82‐86  -86  2017/02/01  [Not refereed][Not invited]
  • 窒化チタン微結晶膜におけるヒドリドイオン伝導の発現とそれによる常温水素膜分離
    青木芳尚, 倉千晴, 國貞雄治, 朱春宇, 幅崎浩樹  真空技術協会誌  132-  32  -41  2017  [Not refereed][Not invited]
  • Marcin Pisarek, Hiroki Habazaki, Aleksander Krupski, Pawel Kulesza, Maria Janik-Czachor  APPLIED SURFACE SCIENCE  388-  605  -607  2016/12  [Refereed][Not invited]
  • HABAZAKI Hiroki  Journal of the Surface Finishing Society of Japan  67-  (10)  508  -514  2016  [Not refereed][Not invited]
  • NODA HIROYUKI, TSUJI ETSUSHI, MOTOHASHI TERUKI, AOKI YOSHITAKA, KOYAMA YUKINORI, MORI MASAHIRO, UCHIMOTO YOSHIHARU, ARAI HAJIME, HABAZAKI HIROKI  電池討論会講演要旨集  56th-  472  2015/11/10  [Not refereed][Not invited]
  • KATAOKA FUMITAKA, SHAHZAD KHURRAM, TSUJI ETSUSHI, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  131st-  265  2015/02/20  [Not refereed][Not invited]
  • HIRAGA TAKUYA, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  131st-  51  2015/02/20  [Not refereed][Not invited]
  • 井上佳士, 辻悦司, 本橋輝樹, 青木芳尚, 谷田肇, 内本喜晴, 荒井創, 幅崎浩樹  電気化学秋季大会講演要旨集(CD-ROM)  2015-  2015
  • TSUJI ETSUSHI, NODA HIROYUKI, MOTOHASHI TERUKI, AOKI YOSHITAKA, HABAZAKI HIROKI  電池討論会講演要旨集  55th-  466  2014/11/19  [Not refereed][Not invited]
  • AOKI YOSHITAKA, KOBAYASHI SHOHEI, TSUJI ETSUSHI, HABAZAKI HIROKI, YASHIRO KEIJI, KAWADA TATSUYA  固体イオニクス討論会講演要旨集  40th-  187  -188  2014/11/16  [Not refereed][Not invited]
  • 辻 悦司, 幅崎 浩樹  静電気学会誌  38-  (6)  254  -259  2014/11  [Not refereed][Not invited]
  • NAKAYAMA KATSUTOSHI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  日本学術会議材料工学連合講演会講演論文集  58th-  460  -461  2014/10/27  [Not refereed][Not invited]
  • KOBAYASHI KOHEI, TSUJI ETSUSHI, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2014-  90  2014/09/27  [Not refereed][Not invited]
  • MATSUURA SHIKI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2014-  13  2014/09/27  [Not refereed][Not invited]
  • 菊地竜也, 吉田雅純, 夏井俊悟, 幅崎浩樹, 鈴木亮輔  電気化学秋季大会講演要旨集  2014-  91  2014/09/27  [Not refereed][Not invited]
  • TSUJI ETSUSHI, HIRATA NAOTO, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  130th-  212  2014/09/10  [Not refereed][Not invited]
  • HABAZAKI HIROKI, TSUJI ETSUSHI, AOKI YOSHITAKA  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  75th-  ROMBUNNO.19A-A4-3  2014/09/01  [Not refereed][Not invited]
  • 幅崎浩樹, 片岡文崇, 辻悦司, 青木芳尚, 永田晋二  東北大学金属材料研究所新素材共同研究開発センター共同利用研究報告書  2013-  70  -71  2014/06  [Not refereed][Not invited]
  • KONNO YOSHIKI, TSUJI ETSUJI, AOKI YOSHITAKA, OTSUKA TOSHIAKI, HABAZAKI HIROKI  電気化学会大会講演要旨集  81st-  136  2014/03/29  [Not refereed][Not invited]
  • NODA HIROYUKI, TSUJI ETSUSHI, MOTOHASHI TERUKI, AOKI YOSHITAKA, TAKEGUCHI TATSUYA, HABAZAKI HIROKI  電気化学会大会講演要旨集  81st-  449  2014/03/29  [Not refereed][Not invited]
  • KOBAYASHI KOHEI, TSUJI ETSUSHI, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  電気化学会大会講演要旨集  81st-  93  2014/03/29  [Not refereed][Not invited]
  • KIKUTANI KAZUMASA, AOKI YOSHITAKA, TSUJI ETSUSHI, HABAZAKI HIROKI  電気化学会大会講演要旨集  81st-  43  2014/03/29  [Not refereed][Not invited]
  • KOBAYASHI SHOHEI, AOKI YOSHITAKA, TSUJI ETSUSHI, HABAZAKI HIROKI  日本化学会講演予稿集  94th-  (2)  636  2014/03/12  [Not refereed][Not invited]
  • KURA CHIHARU, AOKI YOSHITAKA, TSUJI ETSUSHI, NAGATA SHINJI, HABAZAKI HIROKI  日本化学会講演予稿集  94th-  (3)  1000  2014/03/12  [Not refereed][Not invited]
  • KIMURA TAIKI, TSUJI ETSUSHI, AOKI YOSHITAKA, YANO TAKAYOSHI, HASSEL A. W, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  129th-  145  2014/03/03  [Not refereed][Not invited]
  • NAKAYAMA YUKI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  129th-  236  2014/03/03  [Not refereed][Not invited]
  • NAKAYAMA KATSUTOSHI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  129th-  239  2014/03/03  [Not refereed][Not invited]
  • YAMASAKI TAKENORI, TSUJI ETSUSHI, AOKI YOSHITAKA, PARK SOO-GIL, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  129th-  211  2014/03/03  [Not refereed][Not invited]
  • KATAOKA FUMITAKA, TSUJI ETSUSHI, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  129th-  250  2014/03/03  [Not refereed][Not invited]
  • KOBAYASHI KOHEI, TSUJI ETSUSHI, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.2C10  2014/01/28  [Not refereed][Not invited]
  • HIRATA NAOTO, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.2C19  2014/01/28  [Not refereed][Not invited]
  • SATO HINA, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.1C19  2014/01/28  [Not refereed][Not invited]
  • KOBAYASHI SHOHEI, AOKI YOSHITAKA, TSUJI ETSUSHI, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.P45  2014/01/28  [Not refereed][Not invited]
  • OBA HIROSHI, AOKI YOSHITAKA, TSUJI ETSUSHI, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.2C12  2014/01/28  [Not refereed][Not invited]
  • KURE KAMBUN, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.2C11  2014/01/28  [Not refereed][Not invited]
  • MATSUURA SHIKI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.1C20  2014/01/28  [Not refereed][Not invited]
  • NODA HIROYUKI, TSUJI ETSUSHI, MOTOHASHI TERUKI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集(CD-ROM)  2014-  ROMBUNNO.1C07  2014/01/28  [Not refereed][Not invited]
  • HABAZAKI Hiroki, FUJII Takashi, NAKAYAMA Katsutoshi, TSUJI Etsushi, AOKI Yoshitaka  Jitsumu Hyomen Gijutsu  65-  (9)  426  -431  2014  [Not refereed][Not invited]
  • HABAZAKI HIROKI, NAKAYAMA KATSUTOSHI, TSUJI ETSUSHI, AOKI YOSHITAKA  日本学術会議材料工学連合講演会講演論文集  57th-  215  2013/11/25  [Not refereed][Not invited]
  • KURE KAMBUN, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2013-  64  2013/09/27  [Not refereed][Not invited]
  • TSUJI ETSUSHI, KAKEDA KO, KIRIU MASAHIKO, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2013-  243  2013/09/27  [Not refereed][Not invited]
  • KIMURA TAIKI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI, YANO TAKAYUKI  表面技術協会講演大会講演要旨集  128th-  158  2013/09/10  [Not refereed][Not invited]
  • NAKAYAMA KATSUTOSHI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  128th-  162  -163  2013/09/10  [Not refereed][Not invited]
  • 吉田雅純, 吉田雅純, 菊地竜也, 夏井俊悟, 幅崎浩樹, 鈴木亮輔  日本金属学会講演概要(CD-ROM)  153rd-  ROMBUNNO.596  2013/09/03  [Not refereed][Not invited]
  • 幅崎 浩樹  電気化学および工業物理化学 : denki kagaku  81-  (7)  583  -583  2013/07/05  [Not refereed][Not invited]
  • YE KE, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  東北大学金属材料研究所金属ガラス総合研究センター共同利用研究報告書  2012-  15  -16  2013/06  [Not refereed][Not invited]
  • 熊谷直和, 橋本功二, 泉屋宏一, 高野裕之, 加藤善大, 幅崎浩樹, 秋山英二, 山崎倫昭  Hits技報  74-  (1)  33  -41  2013/05  [Not refereed][Not invited]
  • KONNO YOSHIKI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  材料と環境講演集  2013-  275  -276  2013/04/30  [Not refereed][Not invited]
  • 幅崎 浩樹  表面  51-  (4)  170  -181  2013/04  [Not refereed][Not invited]
  • TSUJI ETSUSHI, TAGUCHI YOSHIAKI, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学会大会講演要旨集  80th-  359  2013/03/29  [Not refereed][Not invited]
  • HABAZAKI HIROKI, ISHIZUKA MASATOSHI, TSUJI ETSUSHI, AOKI YOSHITAKA, SAKAGUCHI NORIHITO, NAGATA SHINJI  電気化学会大会講演要旨集  80th-  147  2013/03/29  [Not refereed][Not invited]
  • KURE KAMBUN, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  127th-  192  2013/03/06  [Not refereed][Not invited]
  • HIRATA NAOTO, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  127th-  200  -201  2013/03/06  [Not refereed][Not invited]
  • SATO HINA, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  127th-  189  -190  2013/03/06  [Not refereed][Not invited]
  • 幅崎 浩樹  旭硝子財団助成研究成果報告  1  -4  2013  [Not refereed][Not invited]
  • NONAKA RYO, AOKI YOSHITAKA, TSUJI ETSUSHI, HABAZAKI HIROKI  電池討論会講演要旨集  53rd-  438  2012/11/13  [Not refereed][Not invited]
  • TAGUCHI YOSHIAKI, HIRATA NAOTO, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  日本学術会議材料工学連合講演会講演論文集  56th-  369  2012/10/29  [Not refereed][Not invited]
  • ISHIZUKA MASATOSHI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  126th-  69  2012/09/12  [Not refereed][Not invited]
  • 瀬尾眞浩, 伏見公志, 坂入正敏, 幅崎浩樹, 中山武典  材料と環境討論会講演集  59th-  183  -184  2012/09/10  [Not refereed][Not invited]
  • YE KE, AOKI YOSHITAKA, HABAZAKI HIROKI, NAGATA SHINJI  東北大学金属材料研究所金属ガラス総合研究センター共同利用研究報告書  2011-  12  -13  2012/06  [Not refereed][Not invited]
  • 瀬尾眞浩, 伏見公志, 幅崎浩樹, 稲葉雅之, 横溝臣智, 早川敬済, 中山武典  材料と環境講演集  2012-  167  -168  2012/04/11  [Not refereed][Not invited]
  • FUJII TAKASHI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  125th-  188  2012/03/01  [Not refereed][Not invited]
  • S. Ono, H. Habazaki  CORROSION SCIENCE  53-  (11)  3521  -3525  2011/11  [Refereed][Not invited]
     
    The pit growth process on (1 0 0) aluminium under anodic pulse current in a mixed solution of 1 M HCl and 0.1 M H2SO4 at 30 degrees C has been evaluated using potential transient measurements and pit size distributions obtained by scanning electron microscopy. Sustained pit growth is observed for all pits during the initial anodic potential rise before reaching a steady-state etch potential, whereas a substantial fraction of the pits passivate at the steady-state etch potential. The pit growth rate during the initial potential rise is 3.4 mu m s(-1), which is similar to that at the steady-state etch potential. The growth rates of active pits are potential-independent. (C) 2011 Elsevier Ltd. All rights reserved.
  • Takashi Fujii, Yoshitaka Aoki, Hiroki Habazaki  LANGMUIR  27-  (19)  11752  -11756  2011/10  [Refereed][Not invited]
     
    Hierarchical dual pillar surfaces with optimized pillar intervals are fabricated by a novel combined process of the c oblique angle magnetron sputtering deposition of Al-Nb alloys and their anodizing. The pillar intervals are controlled by the deposition angle and cell size of a scalloped substrate for oblique angle deposition. Anodizing of the deposited pillar surfaces develops a nanopillar oxide layer, producing the hierarchical dual pillar surfaces. After being coated with a fluoroalkyl phosphate layer to reduce the surface free energy, hierarchical surfaces with submicrometer pillar intervals greater than 400 nm show super liquid repellency even for hexadecane with a low surface tension of 27.5 mN m(-1), although the submicrometer pillar surfaces with smaller submicrometer pillar intervals and without nanopillars were not super-oil-repellent. In contrast, the dual pillar surfaces show superhydrophobicity regardless of the submicrometer pillar intervals. Thus, the present study demonstrates the importance of the pillar intervals (gap size between pillars) to realize the superoleophobicity.
  • Shun Koyama, Yoshitaka Aoki, Shinji Nagata, Hiroki Habazaki  JOURNAL OF SOLID STATE ELECTROCHEMISTRY  15-  (10)  2221  -2229  2011/10  [Refereed][Not invited]
     
    Zr-Al alloys containing up to 26 at.% aluminum, prepared by magnetron sputtering, have been anodized in 0.1 mol dm(-3) ammonium pentaborate electrolyte, and the structure and dielectric properties of the resultant anodic oxide films have been examined by grazing incidence X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, and AC impedance spectroscopy. The anodic oxide film formed on zirconium consists of monoclinic and tetragonal ZrO(2) with the former being a major phase. Two-layered anodic oxide films, comprising an outer thin amorphous layer and an inner main layer of crystalline tetragonal ZrO(2) phase, are formed on the Zr-Al alloys containing 5 to 16 at.% aluminum. Further increase in the aluminum content to 26 at.% results in the formation of amorphous oxide layer throughout the thickness. The anodic oxide films become thin with increasing aluminum content, while the relative permittivity of anodic oxide shows a maximum at the aluminum content of 11 at.%. Due to major contribution of permittivity enhancement, the maximum capacitance of the anodic oxide films is obtained on the Zr-11 at.% Al alloy, being 1.7 times than on zirconium at the formation voltage of 100 V.
  • TAGUCHI GIEI, YANG SHU, KONNO SHOKI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  材料と環境討論会講演集  58th-  181  -182  2011/09/16  [Not refereed][Not invited]
  • SAH SANTOSH PRASAD, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2011-  230  2011/09/09  [Not refereed][Not invited]
  • TSUNEKAWA SO, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  124th-  106  2011/09/09  [Not refereed][Not invited]
  • TAGUCHI YOSHIAKI, TSUJI ETSUSHI, AOKI YOSHITAKA, KAWAKITA JIN, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  124th-  105  2011/09/09  [Not refereed][Not invited]
  • KONNO YOSHIKI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2011-  229  2011/09/09  [Not refereed][Not invited]
  • FUJII TAKASHI, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  124th-  103  2011/09/09  [Not refereed][Not invited]
  • MISAWA TAKAHIRO, HABAZAKI HIROKI, AOKI YOSHITAKA, TSUJI ETSUSHI, ONO SHOJI  電気化学秋季大会講演要旨集  2011-  197  2011/09/09  [Not refereed][Not invited]
  • KOYAMA SHUN, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2011-  198  2011/09/09  [Not refereed][Not invited]
  • Shu Yang, Hiroki Habazaki, Takashi Fujii, Yoshitaka Aoki, Peter Skeldon, George E. Thompson  ELECTROCHIMICA ACTA  56-  (22)  7446  -7453  2011/09  [Refereed][Not invited]
     
    We report the fabrication of superhydrophobic surfaces with a hierarchical morphology by self-organized anodizing process. Simply by anodizing of niobium metal in hot phosphate-glycerol electrolyte, niobium oxide microcones, consisting of highly branched oxide nanofibers, develop on the surface. The size of the microcones and their tip angles are controlled by changing the applied potential difference in anodizing and the water content in the electrolyte. Reduction of the water content increases the size of the microcones, with the nanofibers changing to nanoparticles. The size of microcones is also reduced by increasing the applied potential difference, without influencing the tip angle. The hierarchical oxide surfaces are superhydrophilic, with static contact angles close to 0 degrees. Coating of the anodic oxide films with a monolayer of fluoroalkyl phosphate makes the surfaces superhydrophobic with a contact angle for water as high as 175 degrees and a very small contact angle hysteresis of only 2 degrees. The present results indicate that the larger microcones with smaller tip angles show the higher contact angle for water. (C) 2011 Elsevier Ltd. All rights reserved.
  • SAH SANTOSH PRASAD, TSUJI ETSUSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  日本化学会北海道支部夏季研究発表会講演要旨集  2011-  104  2011/07/01  [Not refereed][Not invited]
  • NONAKA RYO, AOKI YOSHITAKA, TSUJI ETSUSHI, HABAZAKI HIROKI  日本化学会北海道支部夏季研究発表会講演要旨集  2011-  86  2011/07/01  [Not refereed][Not invited]
  • Takashi Fujii, Yoshitaka Aoki, Hiroki Habazaki  APPLIED SURFACE SCIENCE  257-  (19)  8282  -8288  2011/07  [Refereed][Not invited]
     
    A combined process of oblique angle magnetron sputtering and anodizing has been developed to tailor superhydrophobic surfaces with hierarchical morphology. Isolated submicron columns of single-phase Al-Nb alloys are deposited by magnetron sputtering at several oblique deposition angles on a scalloped substrate surface, with the gaps between columns increasing with an increase in the deposition angle from 70 degrees to 110 degrees. Then, the columnar films have been anodized in hot phosphate-glycerol electrolyte to form a nanoporous anodic oxide layer on each column. Such surfaces with submicron-/nano-porous structure have been coated with a fluoroalkyl phosphate layer to reduce the surface energy. The porous surface before coating is superhydrophilic with a contact angle for water is less than 10 degrees, while after coating the contact angles are larger than 150 degrees, being superhydrophobic. The beneficial effect of dual-scale porosity to enhance the water repellency is found from the comparison of the contact angles of the submicron columnar films with and without nanoporous oxide layers. The larger submicron gaps between columns are also preferable to increase the water repellency. (C) 2011 Elsevier B. V. All rights reserved.
  • Hiroki Habazaki, Shun Koyama, Yoshitaka Aoki, Norihito Sakaguchi, Shinji Nagata  ACS APPLIED MATERIALS & INTERFACES  3-  (7)  2665  -2670  2011/07  [Refereed][Not invited]
     
    Anodic oxide films with nanocrystalline tetragonal ZrO2 precipitated in an amorphous oxide matrix were formed on Zr-Si and Zr-Al alloys and had significantly enhanced capacitance in comparison with those formed on zirconium metal. The capacitance enhancement was associated with the formation of a high-temperature stable tetragonal ZrO2 phase with high relative permittivity as well as increased ionic resistivity, which reduces the thickness of anodic oxide films at a certain formation voltage. However, there is a general empirical trend that single-phase materials with higher permittivity have lower ionic resistivity. This study presents a novel material design based on a nanocrystalline-amorphous composite anodic oxide film for capacitor applications.
  • M. Tauseef Tanvir, T. Fujii, Y. Aoki, K. Fushimi, H. Habazaki  APPLIED SURFACE SCIENCE  257-  (19)  8295  -8300  2011/07  [Refereed][Not invited]
     
    For electrolytic capacitor application of the single-phase Ti alloys containing supersaturated silicon, which form anodic oxide films with superior dielectric properties, porous Ti-7 at% Si columnar films, as well as Ti columnar films, have been prepared by oblique angle magnetron sputtering on to aluminum substrate with a concave cell structure to enhance the surface area and hence capacitance. The deposited films of both Ti and Ti-7 at% Si have isolated columnar morphology with each column revealing nanogranular texture. The distances between columns are similar to 500 nm, corresponding to the cell size of the textured substrate and the gaps between columns are 100-200 nm. When the porous Ti-7 at% Si film is anodized at a constant current density in ammonium pentaborate electrolyte, the growth of a uniform amorphous oxide film continues to similar to 35 V, while it is limited to less than 6 V on the porous Ti film. The maximum voltage of the growth of uniform amorphous oxide films on the Ti-7 at% Si films is similar for both the flat and porous columnar films, suggesting little influence of surface roughness on the amorphous-to-crystalline transition of growing anodic oxide under the high electric field. Due to the suppression of crystallization to sufficiently high voltages, the anodic oxide films formed on the porous Ti-7 at% Si film shows markedly improved dielectric properties, in comparison with those on the porous Ti film. (C) 2011 Elsevier B. V. All rights reserved.
  • Michiaki Yamasaki, Shogo Izumi, Yoshihito Kawamura, Hiroki Habazaki  APPLIED SURFACE SCIENCE  257-  (19)  8258  -8267  2011/07  [Refereed][Not invited]
     
    Highly corrosion-resistant nanocrystalline Mg-Zn-Y-Al multi-phase alloys have been prepared by consolidation of rapidly solidified (RS) ribbons. The relation between corrosion behavior and microstructure evolution of Mg-Zn-Y-Al alloys with a long period stacking ordered phase has been investigated. In order to clarify the influence of rapid solidification on the occurrence of localized corrosion such as filiform corrosion, several Mg96.75Zn0.75Y2Al0.5 (at.%) alloys with different cooling rates are fabricated by the gravity casting, copper mould injection casting and melt-spinning techniques and their corrosion behavior and microstructures are examined by the salt water immersion test, electrochemical measurements, GDOES, XRD, SEM and TEM. To clarify the effect of aluminium addition on the improvement in corrosion resistance of the alloys, several Mg97.25-xZn0.75Y2Alx alloys with different aluminium contents are fabricated by consolidating RS ribbons and the formation of corroded films on the Mg-Zn-Y-Al alloys have been investigated. Rapid solidification brings about the grain refinement and an increase in the solid solubility of zinc, yttrium and aluminium into the magnesium matrix, enhancing microstructural and electrochemical homogeneity, which in turn enhanced corrosion resistance. The addition of aluminium to magnesium can modify the structure and chemical composition of surface films and improves the resistance to local breakdown of the films. (C) 2011 Elsevier B. V. All rights reserved.
  • S. Yang, Y. Aoki, H. Habazaki  APPLIED SURFACE SCIENCE  257-  (19)  8190  -8195  2011/07  [Refereed][Not invited]
     
    Nanoporous niobium oxide films with microcone-type surface morphology were formed by anodizing at 10 V in glycerol electrolyte containing 0.6 mol dm(-3) K(2)HPO(4) and 0.2 mol dm(-3) K(3)PO(4) in a temperature range of 428-453 K. The microcones appeared after prolonged anodizing, but the required time was largely reduced by increasing electrolyte temperature. The anodic oxide was initially amorphous at all temperatures, but crystalline oxide nucleated during anodizing. The anodic oxide microcones, which were crystalline, appeared on surface as a consequence of preferential chemical dissolution of initially formed amorphous oxide. The chemical dissolution of an initially formed amorphous layer was accelerated by increasing the electrolyte temperature, with negligible influence of the temperature on the morphology of microcones up to 448 K. (C) 2011 Elsevier B. V. All rights reserved.
  • FAN Ye, YE Ke, 青木芳尚, 幅崎浩樹, 永田晋二  東北大学金属材料研究所金属ガラス総合研究センター共同利用研究報告書  2010-  50  -51  2011/06  [Not refereed][Not invited]
  • Yoshitaka Aoki, Hiroki Habazaki, Toyoki Kunitake  SOLID STATE IONICS  192-  (1)  93  -96  2011/06  [Refereed][Not invited]
     
    Amorphous hafnium silicate, a-Hf0.1Si0.9Ox, thin film with thickness of 32, 41, 55, 80, 110, 120, 180 and 320 nm was prepared by multiple spin-cast process and the proton conductivity across the films was measured at intermediate temperatures (100-400 degrees C) in dry atmosphere. The morphologically- and compositionally-uniform films were prepared on a substrate as confirmed by SEM. RBS and XPS measurements. a-Hf0.1Si0.9Ox thin film clearly revealed the H/D isotope effect on ionic conductivity, indicating that protonic conduction is dominant in the measured temperature range. The films did not reveal thickness-dependent proton conductivity in dry air and the sigma at given temperatures is almost constant at any thickness. No increment of sigma in a-Hf0.1Si0.9Ox thin films by reduction of thickness might be related to the absence of the highly-conductive acid network with mesoscopically-sized length because of the relatively low concentration of Bronsted acid sites inside films. (C) 2010 Elsevier B.V. All rights reserved.
  • S. Tsunekawa, Y. Aoki, H. Habazaki  SURFACE & COATINGS TECHNOLOGY  205-  (19)  4732  -4740  2011/06  [Refereed][Not invited]
     
    Ti-15V-3Al-3Cr-35n (Ti-15-3) is one of the important practical titanium alloys with high cold deformability and high mechanical strength, but its wear resistance is poor. This paper reports the formation of wear-resistant and adhesive ceramic coatings on Ti-15-3 by two-step plasma electrolytic oxidation (PEO). The PEO of Ti-15-3 has been carried out first in alkaline aluminate electrolyte to form a wear-resistant oxide layer and then in acid electrolyte containing both phosphoric acid and sulfuric acid to improve adhesion of the coating. The coating formed in the alkaline aluminate electrolyte is more than 10 mu m thick, and highly crystalline. The main phase is Al2TiO5. This coating shows high wear resistance, but is not adherent to substrate due to the development of a number of voids and pores in the oxide layer close to the substrate. A new oxide layer with amorphous structure is formed next to the substrate in the subsequent PEO in the acid electrolyte, during which the voids are filled with a new oxide formed in the acid electrolyte, reducing the porosity. As a consequence, the adhesion of the coating is markedly improved without deteriorating the high wear resistance. (C) 2011 Elsevier B.V. All rights reserved.
  • 瀬尾眞浩, 伏見公志, 青木芳尚, 幅崎浩樹, 稲葉雅之, 横溝臣智, 早川敬済, 中山武典  材料と環境講演集  2011-  185  -188  2011/05/20  [Not refereed][Not invited]
  • S. J. Garcia-Vergar, I. S. Molchan, F. Zhou, H. Habazaki, D. Kowalski, P. Skeldon, Andg. E. Thompson  SURFACE AND INTERFACE ANALYSIS  43-  (5)  893  -902  2011/05  [Refereed][Not invited]
     
    The effect of tungsten species on the incorporation and migration of phosphorus species within anodic alumina is investigated. The study employs barrier anodic films, formed on a sputtering-deposited Al-15at.% W alloy in phosphate electrolytes. The films consist of either an outer tungsten-containing region and an inner tungsten-free region, or a tungsten-containing region only. Phosphorus species are shown to migrate inward in the tungsten-containing alumina more slowly than in the tungsten-free alumina. In contrast, the outward migration of tungsten species is relatively unaffected by the presence of phosphorus species. The relevance of the results to the use of tungsten tracers for the study of porous film growth is discussed. Copyright (C) 2010 John Wiley & Sons, Ltd.
  • Santosh Prasad Sah, Yasuhiro Tatsuno, Yoshitaka Aoki, Hiroki Habazaki  CORROSION SCIENCE  53-  (5)  1838  -1844  2011/05  [Refereed][Not invited]
     
    Single pulse anodizing of aluminium micro-electrode has been employed to study the behaviour of dielectric breakdown and subsequent oxide formation on aluminium in alkaline silicate and pentaborate electrolytes. Current transients during applying pulse voltage have been measured, and surface has been observed by scanning electron microscopy. Two types of current transients are observed, depending on the electrolyte and applied voltage. There is a good correlation between the current transient behaviour and the shape of discharge channels. In alkaline silicate electrolyte, circular open pores are healed by increasing the pulse width, but such healing is not obvious in pentaborate electrolyte. (C) 2011 Elsevier Ltd. All rights reserved.
  • S. Yang, Y. Aoki, P. Skeldon, G. E. Thompson, H. Habazaki  JOURNAL OF SOLID STATE ELECTROCHEMISTRY  15-  (4)  689  -696  2011/04  [Refereed][Not invited]
     
    Growth of porous anodic alumina films has been examined at 10 V in hot phosphate-containing glycerol electrolyte containing 0.1 to 0.57 mass% water. The growth rate of the films is highly dependent upon the water content of the electrolyte, reducing markedly at a water content of 0.1 mass%, an opposite trend to that found previously for the formation of porous films on titanium and niobium. Chemical dissolution of the anodic alumina is also suppressed in electrolyte of low water content. GDOES depth profiles revealed that an increased water content of the electrolyte promoted the incorporation of phosphorus species into the films, although chemical dissolution reduced the amounts of phosphorus in the outer regions. Carbon species also appeared to be present in films, particularly at lower water content. Using a niobium oxide outer layer to suppress chemical dissolution resulted in films that were about 1.2 times the thickness of the consumed aluminium for an electrolyte containing 0.25 mass% water. The expansion suggests a possible contribution of field-assisted flow of film material in the growth of the porous anodic film.
  • TAGUCHI YOSHITERU, AOKI YOSHITAKA, HABAZAKI HIROKI, KAWAKITA JIN  電気化学会大会講演要旨集  78th(CD-ROM)-  ROMBUNNO.1H29  2011/03/29  [Not refereed][Not invited]
  • KOYAMA SHUN, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  123rd-  125  -126  2011/03/07  [Not refereed][Not invited]
  • TSUNEKAWA SO, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  123rd-  95  2011/03/07  [Not refereed][Not invited]
  • 幅崎浩樹, 恒川聡, 三浦吉幸, SAH S. P, 青木芳尚, 伏見公志  表面技術協会講演大会講演要旨集  123rd-  330  -333  2011/03/07  [Not refereed][Not invited]
  • Yoshitaka Aoki, Hiroki Habazaki, Shinji Nagata, Aiko Nakao, Toyoki Kunitake, Shu Yamaguchi  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY  133-  (10)  3471  -3479  2011/03  [Refereed][Not invited]
     
    The finite size effect of proton conductivity of amorphous silicate thin films, a-M0.1Si0.9Ox (M = Al, Ga, Hf, Ti, Ta, and La), was investigated. The proton conductivity across films, sigma, was measured in dry air by changing the thickness in the range of 10-1000 nm. sigma of the films with M = Al, Ga, and Ta was elevated in a power law by decreasing thickness into less than a few hundred nanometers, and the increment was saturated at a thickness of several 10's of nanometers. On the other hand, a of the films with M = Hf, Ti, and La was not related to the decrease of the thickness in the range of >10 nm. Thickness-dependent conductivity of the former could be numerically simulated by a percolative resistor network model that involves the randomly distributed 3 4 5 6 7 8 2 3 4 5 6 7 8 array of two kinds of resistors R-1 and R-2 (R-1 > R-2) in the form of a simple cubic-type lattice. High-resolution TEM clarified that a-M0.1Si0.9Ox films involved heterogeneous microstructures made of the condensed domain and the surrounding uncondensed matrix due to the fluctuation of glass networks on the nanometer scale. The condensed domain had a wormlike shape with an average length of several 10's of nanometers and performed the role of the proton conduction pathway penetrating through the poorly conducting matrix. It was concluded that the thickness-dependent conductivity could be identical to finite-size scaling of the percolative network of the interconnected domains in the nanometer range.
  • KOMIYAMA SHOZO, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2011-  78  2011/02/01  [Not refereed][Not invited]
  • TAGUCHI YOSHIAKI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2011-  155  2011/02/01  [Not refereed][Not invited]
  • FUKUNAGA YUKI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2011-  53  2011/02/01  [Not refereed][Not invited]
  • Y. Aoki, Y. Fukunaga, H. Habazaki, T. Kunitake  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  158-  (8)  B866  -B870  2011  [Refereed][Not invited]
     
    Novel thin film fuel cell based on the 100 nm-thick electrolyte of amorphous ZrP(2.6)O(x), working at 400 degrees C, was demonstrated. The hydrogen permeable membrane fuel cell (HMFC) using a Pd foil as a nonporous solid anode was fabricated. Ni interlayer of several hundreds nm thickness was introduced between the Pd anode and the ZrP(2.6)O(x) electrolyte in order to suppress the deterioration of the electrolyte nanofilm by the deformation of the Pd anode during hydrogen absorption. In the ZrP(2.6)O(x) electrolyte the transport number of proton was unity at 400 degrees C as determined by an EMF measurement. The modification of the Ni anode surface by an ultrathin Pt or Pd layer effectively decreased the anode/electrolyte interfacial polarization. Consequently, the HMFC revealed the OCV of 1.0 V and the maximum power density of 1.8 mW cm(-2) at 400 degrees C. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3595388] All rights reserved.
  • Y. Aoki, S. Hirata, H. Habazaki  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  158-  (4)  P41  -P44  2011  [Refereed][Not invited]
     
    The proton conductivity sigma across 100 nm thick, amorphous aluminum phosphate thin films under anhydrous conditions was investigated. The densely packed glass films were uniformly formed without formation of pinholes and clacks over the electrode substrate by multiple spin-coating with a mixed precursor sol, as checked by transmission electron microscopy. X-ray absorption spectroscopy, and Fourier transform infrared indicated that the Al-rich films were mainly composed of alumina and phosphate mixed glass phase, but the P-rich films involved a large amount of the aluminum metaphosphate glass moiety. sigma abruptly changed with Al/P ratio owing to this variation of glass network structure. The Al-rich films revealed the large activation energy E-a of about 1.0 eV, but the P-rich films revealed the small E-a of about 0.2 eV above 200 degrees C and they kept the value on the order of 10(-5) S cm(-1) at the temperatures. Consequently, the sigma of P-rich films were one order of magnitude higher than that of the others at around 300 degrees C. (C) 2011 Electrochemical Society. [DOI: 10.1149/1.3551572] All rights reserved.
  • Koji Fushimi, Takatoshi Shimada, Hiroki Habazaki, Hidetaka Konno, Masahiro Seo  ELECTROCHIMICA ACTA  56-  (4)  1773  -1780  2011/01  [Refereed][Not invited]
     
    Depassivation-repassivation of iron surfaces in boric-borate solutions were investigated by using the micro-indentation test. A pair of current peaks due to repair of the passive film following rupture of the film were observed during a series of indenter drives, i.e., loading and unloading of the indenter. The shape of the current peak depended on environmental conditions (conductivity and pH of the solution) and substrate conditions (mechanical processing history, alloyed element) as well as indentation conditions (repetition, maximum depth, and maximum load). Plastic deformation of the surface was accompanied by surface depassivation, while no depassivation occurred during the elastic deformation, indicating that the passive film on iron has a ductile property. The solution conditions did not affect the scale of depassivation but affected the rate of repassivation. Dislocations in the substrate made surface depassivation difficult but enhanced reactivity during the repassivation. The test also revealed that type-312L stainless steel has high corrosion resistance in a concentrated NaCl solution. (C) 2010 Elsevier Ltd. All rights reserved.
  • Ke Ye, Yoshitaka Aoki, Etsushi Tsuji, Shinji Nagata, Hiroki Habazaki  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  158-  (11)  C385  -C390  2011  [Refereed][Not invited]
     
    Novel proton-conducting amorphous anodic ZrO2-WO3-SiO2 films, 200 nm thick, are prepared by anodizing of sputter-deposited Zr37W47Si16 at 100 V with current decay for 1.8 ks in 0.1 mol dm(-3) phosphoric acid electrolyte at 20 degrees C. The resultant anodic films have been characterized using electrochemical impedance spectroscopy, transmission electron microscopy, glow discharge optical emission spectroscopy and Rutherford backscattering spectroscopy. The addition of silicon species to the anodic ZrO2-WO3 film significantly enhanced the thermal stability. Even after thermal treatment at 300 degrees C in dry Ar atmosphere, the anodic ZrO2-WO3-SiO2 films revealed stable proton conductivity in the temperature range of 50-225 degrees C, while the anodic ZrO2-WO3 on the Zr43W57 loses the proton conductivity by annealing at 250 degrees C. The anodic film on the Zr37W47Si16 consisted of two layers, comprising an outer thin ZrO2 layer, free from tungsten and silicon species, and an inner main layer containing all zirconium, tungsten and silicon species. The results in this study suggest that the conductivity deterioration at high annealing temperatures is associated with the diffusion-induced formation of a poorly-conducting layer near the alloy/anodic oxide interface. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.068111jes] All rights reserved.
  • F. Zhou, A. K. Mohamed Al-Zenati, A. Baron-Wiechec, M. Curioni, S. J. Garcia-Vergara, H. Habazaki, P. Skeldon, G. E. Thompson  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  158-  (6)  C202  -C214  2011  [Refereed][Not invited]
     
    The growth of anodic alumina in sulphuric acid is investigated at constant current on bulk and sputtering-deposited aluminium. The ratio of the thickness of the film to the thickness of oxidized aluminium is shown to increase with increase of the current density (from 0.5 to 50 mA cm(-)2) and with decrease of the electrolyte temperature (from 20 to 0 degrees C). In addition, the sulphur content of the films and the efficiency of film formation increase. It is suggested that pores are generated primarily by dissolution at current densities below similar to 2 mA cm(-2), with flow of film material dominating at higher current densities. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3578028] All rights reserved.
  • FUKUNAGA YUKI, AOKI YOSHITAKA, HABAZAKI HIROKI  電池討論会講演要旨集  51st-  315  2010/11/08  [Not refereed][Not invited]
  • Hiroki Habazaki, Yoshiki Konno, Yoshitaka Aoki, Peter Skeldon, George E. Thompson  JOURNAL OF PHYSICAL CHEMISTRY C  114-  (44)  18853  -18859  2010/11  [Refereed][Not invited]
     
    The growth of porous anodic films on iron has been examined at a constant current density of 50 A m(-2) in 0.1 mol L-1 NH4F-elhylene glycol electrolytes containing 0.1-1.5 mol L-1 water. Nanoporous films are formed in all the electrolytes, with the growth rate increasing with the decrease in the water content of the electrolyte. A barrier layer, in which a high electric field is applied during anodizing, thickens in proportion to the formation voltage at a ratio of 1.9 nm V-1, regardless of the water content of the electrolyte. However. there is a transition water content between 0.3 and 0.5 mol L-1. at which growth behavior changes. Above the transition level, the formation voltage is constant after an initial voltage rise, with the constant voltage slightly rising with a decrease in water content. In contrast, the formation voltage increases continuously to more than 150 V when the water contents are below the transition level. The anodic films are poorly crystalline and contain a significant amount of fluoride species. A high enrichment of fluoride species occurs near the metal/film interface when the water content in the electrolyte is below the transition level. Such enrichment is not as significant, or possibly absent, in electrolytes of increased water content.
  • FUJII TAKASHI, AOKI YOSHITAKA, HABAZAKI HIROKI  日本学術会議材料工学連合講演会講演論文集  54th-  364  2010/10/25  [Not refereed][Not invited]
  • HABAZAKI HIROKI, TANVIR M.T, AOKI YOSHITAKA  日本学術会議材料工学連合講演会講演論文集  54th-  363  2010/10/25  [Not refereed][Not invited]
  • Takashi Fujii, Yoshitaka Aoki, Koji Fushimi, Takeshi Makino, Shoji Ono, Hiroki Habazaki  NANOTECHNOLOGY  21-  (39)  395302  2010/10  [Refereed][Not invited]
     
    Nanopillar films of Al-Nb alloys have been fabricated on substrates with a regular concave cell structure by oblique angle physical vapor deposition. The concave cell structure of the substrate increases the shadow region for the flux of depositing atoms, assisting the formation of an isolated nanopillar on each cell. Depending upon the alloy composition and deposition angle, the pillar shape changes from horn-like nanopillars through triangular nanoprisms to nanoplates. The Al-Nb alloy nanoplate films with wide gaps between plates are of interest as electrodes for capacitor applications. The dielectric oxide film formed on the nanoplate film showed a capacitance more than ten times larger than that on the respective flat film, due to the enlarged surface area.
  • Yoshitaka Aoki, Kota Ogawa, Hiroki Habazaki, Toyoki Kunitake, Yuanzhi Li, Shinji Nagata, Shu Yamaguchi  CHEMISTRY OF MATERIALS  22-  (19)  5528  -5536  2010/10  [Refereed][Not invited]
     
    Amorphous zirconium phosphate thin films, a-ZrP2.5Ox, revealed unique proton conductivity transition induced by reducing thickness due to the formation of highly conductive, hydrated nanolayer. The dense films made of a metaphosphate glass phase were uniformly formed over the electrode substrate by multiple spin-coating with a mixed precursor sol. as checked by TEM and RBS. When thickness d was larger than 60 nm, the proton conductivity across film and the activation energy E were not variable with d. sigma abruptly increased 200 times and E-a decreases from 0,9 to 0.7 eV when d decreased from 60 to 40 nm. and it became thickness-independent again in d < 40 nm. a of 100 mm-thick film is increased to the similar value as that of the 40 nm thick by annealing at 400 degrees C in H2O/air. It was concluded that the conductivity transition could be associated with the hydration of metaphosphate nanolayer. The hydrated. high-conductive phase was very stable Only when the thickness was less than 100 nm. Therefore, the films of more than hundreds nm thickness cannot change to the high-conducting hydrated phase throughout the film thickness. These unprecedented behaviors could not be explicable with a simple model based on the core space charge or continuum structural relaxation at hetrointerface.
  • AOKI YOSHITAKA, HARADA AKITOSHI, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2010-  75  2010/09/02  [Not refereed][Not invited]
  • AOKI YOSHITAKA, MISAWA TAKAHIRO, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2010-  183  2010/09/02  [Not refereed][Not invited]
  • TSUNEKAWA SO, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2010-  67  2010/09/02  [Not refereed][Not invited]
  • TERAOKA MASANOBU, AOKI YOSHITAKA, PARK SOO-GIL, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  122nd-  110  -111  2010/08/20  [Not refereed][Not invited]
  • KONNO YOSHIKI, AOKI YOSHITAKA, NAGATA SHINJI, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  122nd-  112  2010/08/20  [Not refereed][Not invited]
  • MISAWA TAKAHIRO, AOKI YOSHITAKA, HABAZAKI HIROKI  日本化学会北海道支部夏季研究発表会講演要旨集  2010-  45  2010/06/25  [Not refereed][Not invited]
  • KOYAMA SHUN, AOKI YOSHITAKA, HABAZAKI HIROKI, NAGATA SHINJI, KIMURA HISAMICHI  東北大学金属材料研究所金属ガラス総合研究センター共同利用研究報告書  2009-  13  -14  2010/06  [Not refereed][Not invited]
  • S. Ono, H. Habazaki  CORROSION SCIENCE  52-  (6)  2164  -2171  2010/06  [Refereed][Not invited]
     
    The AC etch process effectively expands the surface area of aluminium foil as compared with DC etch process. This study explored the effect of cathodic half-cycle. The cathodic half-cycle enhanced passivation of pits developed during the preceding anodic half-cycle, making pit nucleation random. Anodic pulse without cathodic half-cycle produced hollows, due to preferential pit nucleation on pits produced in the preceding anodic half-cycle. The open circuit before the cathodic half-cycle does not largely influence the etch factor, but etch film formation is largely suppressed. The precipitation of aluminium hydroxide may not have a crucial role in porous layer formation. (C) 2010 Elsevier Ltd. All rights reserved.
  • KONNO SHOKI, AOKI YOSHITAKA, NAGATA SHINJI, KIMURA HISAMICHI, HABAZAKI HIROKI  材料と環境講演集  2010-  357  -358  2010/04/26  [Not refereed][Not invited]
  • 瀬尾眞浩, 伏見公志, 青木芳尚, 幅崎浩樹, 中山武典  材料と環境講演集  2010-  345  -346  2010/04/26  [Not refereed][Not invited]
  • F. Zhou, D. J. LeClere, S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, H. Habazaki  SURFACE AND INTERFACE ANALYSIS  42-  (4)  247  -251  2010/04  [Refereed][Not invited]
     
    Porous anodic alumina films have been much studied recently due to interest in the application of the self-ordered porosity in nanotechnological systems. Experimental investigations have identified anodising regimes that generate pores with a relatively high degree of long-range order. However, the growth mechanism of the films, and its relation to the ordering of pores, is only partially understood. In the present work, the growth processes are studied over a range of current densities for films formed in oxalic acid. The films are formed on sputtering-deposited substrates containing tungsten nanolayers that provide W(6+) tracer species in the films. The distributions of tracer species are observed by scanning and transmission electron microscopes and the amounts of tracer species quantified by Rutherford backscattering spectroscopy. It is shown that the tungsten tracer remains within an inner region of the cells, with a tungsten-free region being present next to the pore walls during the growth of the anodic films. Further, the thickness of the anodic film relative to that of oxidised metal increases with increasing current density, which is associated with an increase in the efficiency of film formation. This behaviour is consistent with the formation of pores by flow of film material in the barrier layer to the pore wall regions. Copyright (C) 2010 John Wiley & Sons, Ltd.
  • Atsushi Naganuma, Koji Fushimi, Kazuhisa Azumi, Hiroki Habazaki, Hidetaka Konno  CORROSION SCIENCE  52-  (4)  1179  -1186  2010/04  [Refereed][Not invited]
     
    Crevice corrosion of iron was evaluated using the multichannel electrode method in which 10 individual working electrodes (WEs) of pure iron were embedded in resin, placed in an artificial crevice in the range from 0.5 mm to 2.0 mm, and immersed in 0.51 mol dm(-3) NaCl solution. The WEs were connected to an electronic circuit which allowed galvanic coupling between them and measurement of their individual coupling current or open circuit potential. Time-transient of the spatial distribution of coupling current and open circuit potential showed sequential transition of the coupling current on WEs at the middle position of the crevice from cathode to anode. The WE near the opening of the crevice initially showed a large anodic current, then a decreasing the anodic current corresponding to the current transition of other WEs, and finally a large cathodic current coupled with the other anodic WEs in the crevice. The transition of coupling current was explained by the change in pH and concentration of dissolved oxygen in the crevice. Thickness of the gap of the artificial crevice affected the transition behavior of coupling current distribution. For example, slower current transition with smaller coupling current was found in the case of a narrower gap. Such properties were related to the introduction and consumption of dissolved oxygen in the crevice solution and the circulation of gap solution from/to the outside of the crevice. (C) 2010 Elsevier Ltd. All rights reserved.
  • H. Habazaki, M. Teraoka, Y. Aoki, P. Skeldon, G. E. Thompson  ELECTROCHIMICA ACTA  55-  (12)  3939  -3943  2010/04  [Refereed][Not invited]
     
    The present study reveals the formation of porous anodic films on titanium at an increased growth rate in hot phosphate/glycerol electrolyte by reducing the water content. A porous titanium oxide film of 12 mu m thickness, with a relatively low content of phosphorus species, is developed after anodizing at 5 V for 3.6 ks in 0.6 mol dm(-3) K2HPO4 +0.2 mol dm(-3) K3PO4/glycerol electrolyte containing only 0.04% water at 433K. The growth efficiency is reduced by increasing the formation voltage to 20V, due to formation of crystalline oxide, which induces gas generation during anodizing. The film formed at 20V consists of two layers, with an increased concentration of phosphorus species in the inner layer. The outer layer, comprising approximately 25% of the film thickness, is developed at low formation voltages, of less than 10 V, during the initial anodizing at a constant current density of 250 A m(-2). The pore diameter is not significantly dependent upon the formation voltage, being similar to 10 nm. (C) 2010 Elsevier Ltd. All rights reserved.
  • HARADA AKITOSHI, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学会大会講演要旨集  77th-  457  2010/03/26  [Not refereed][Not invited]
  • OGAWA KOTA, AOKI YOSHITAKA, HABAZAKI HIROKI, YAMAGUCHI SHU  電気化学会大会講演要旨集  77th-  310  2010/03/26  [Not refereed][Not invited]
  • AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学会大会講演要旨集  77th-  311  2010/03/26  [Not refereed][Not invited]
  • TSUNEKAWA SO, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学会大会講演要旨集  77th-  453  2010/03/26  [Not refereed][Not invited]
  • KOYAMA SHUN, AOKI YOSHITAKA, NAGATA SHINJI, KIMURA HISAMICHI, HABAZAKI HIROKI  電気化学会大会講演要旨集  77th-  277  2010/03/26  [Not refereed][Not invited]
  • FUKUNAGA YUKI, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学会大会講演要旨集  77th-  483  2010/03/26  [Not refereed][Not invited]
  • S. Koyama, Y. Aoki, S. Nagata, H. Kimura, H. Habazaki  ELECTROCHIMICA ACTA  55-  (9)  3144  -3151  2010/03  [Refereed][Not invited]
     
    Sputter-deposited zirconium and Zr-16 at.% Si alloy have been anodized to various voltages at several formation voltages in 0.1 mol dm(-3) ammonium pentaborate electrolyte at 298 K for 900 s. The resultant anodic films have been characterized using X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy, and electrochemical impedance spectroscopy. The anodic oxide films formed on Zr-16 at.% Si are amorphous up to 30 V, but the outer part of the anodic oxide films crystallizes at higher formation voltages. This is in contrast to the case of sputter-deposited zirconium, on which the crystalline anodic oxide films, composed mainly of monoclinic ZrO2, are developed even at low formation voltages. The outer crystalline layer on the Zr-16 at.% Si consists of a high-temperature stable tetragonal phase of ZrO2. Due to immobile nature of silicon species, silicon-free outermost layer is formed by simultaneous migrations of Zr4+ ions outwards and O2- ions inwards. An intermediate crystalline oxide layer, in which silicon content is lower in comparison with that in the innermost layer, is developed at the boundary of the crystalline layer and amorphous layer. Capacitances of the anodic zirconium oxide are highly enhanced by incorporation of silicon due to reduced film thickness, even though the permittivity of anodic oxide decreases with silicon incorporation. (C) 2010 Elsevier Ltd. All rights reserved.
  • S. J. Garcia-Vergara, H. Habazaki, P. Skeldon, G. E. Thompson  ELECTROCHIMICA ACTA  55-  (9)  3175  -3184  2010/03  [Refereed][Not invited]
     
    The behaviours of hafnium, molybdenum and hafnium tracer species in porous anodic alumina films are compared in order to investigate the relationship between the migration rate of alloying element species and their amounts and distributions in the films. The study employs substrates consisting of a thin layer of Al-Hf, Al-Mo or Al-Nd alloy deposited by magnetron sputtering on to electropolished aluminium, with a top layer of aluminium deposited above the alloy layer. The substrates are then anodized at constant current density in phosphoric acid to incorporate the tracer species into the porous anodic film. The tracer distributions in the film are investigated by scanning electron microscopy, and the amounts of tracer quantified by Rutherford backscattering spectroscopy. The distributions of the species within the films differ for the three tracer species. Molybdenum species, which migrate slower than Al3+ ions, are retained within the films, since they are unable to migrate to the pore base regions of the films. In contrast, hafnium and neodymium species, which respectively migrate at rates similar to and faster than Al3+ ions, are able to reach the pore base regions where they are lost to the electrolyte; the loss of the faster migrating-neodymium species is greater than that of hafnium species. The behaviours are related to the influence of flow of the alumina within the barrier layer on the transport of the tracer species. (C) 2010 Elsevier Ltd. All rights reserved.
  • KOMIYAMA SHOZO, AOKI YOSHITAKA, NAGATA SHINJI, KIMURA HISAMICHI, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  121st-  238  -239  2010/02/26  [Not refereed][Not invited]
  • FUJII TAKASHI, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  121st-  236  -237  2010/02/26  [Not refereed][Not invited]
  • TATSUNO YASUHIRO, SAH S. P, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  121st-  252  2010/02/26  [Not refereed][Not invited]
  • KOYAMA SHUN, AOKI YOSHITAKA, NAGATA SHINJI, KIMURA HISAMICHI, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  121st-  240  -241  2010/02/26  [Not refereed][Not invited]
  • HABAZAKI Hiroki  表面技術 = The journal of the Surface Finishing Society of Japan  61-  (2)  159  -160  2010/02/01  [Not refereed][Not invited]
  • SHIMIZU Kenn-ichi, HABAZAKI Hiroki  Journal of the Surface Finishing Society of Japan  61-  (2)  157  -158  2010/02/01  [Not refereed][Not invited]
  • A. Suleiman, P. Skeldon, G. E. Thompson, F. Echeverria, M. J. Graham, G. I. Sproule, S. Moisa, T. Quance, H. Habazaki  CORROSION SCIENCE  52-  (2)  595  -601  2010/02  [Refereed][Not invited]
     
    Amorphous anodic oxide films on InAlP have been grown at high efficiency in sodium tungstate electrolyte. The films are shown to comprise an outer layer containing indium species, an intermediate layer containing indium and aluminium species and an inner layer containing indium, aluminium and phosphorus species. The layering correlates with the influence on cation migration rates of the energies of In3+-O, Al3+-O and P5+-O bonds. which increase in this order. The film surface becomes increasingly rough with increase of the anodizing voltage as pores develop in the film, which appear to be associated with generation of oxygen gas. (C) 2009 Elsevier Ltd. All rights reserved.
  • Yoshitak Aoki, Hiroki Habazaki, Toyoki Kunitake  SOLID STATE IONICS  181-  (3-4)  115  -121  2010/02  [Refereed][Not invited]
     
    Ceramic electrolytes operating in the temperature range of 200 to 500 degrees C under dry atmosphere are a key material for the next-generation fuel cell and related applications. We discovered that nanometer-thick films of amorphous hafnium silicate (HfnSi1-nOx) exhibited efficient ionic conduction at 100-400 degrees C in dry air. When the fraction of hafnium doping was around 0.1, the nanofilm showed a low area-specific-resistance (<0.15 Omega cm(2)) at around 350 degrees C that was small enough for the practical fuel cell application. The sub-100 nm-thick membranes of Hf0.13Si0.87Ox, could be fabricated on porous Pt/alumina substrate to provide gas concentration cells. The electromotive force observed with H-2 concentration cell indicated that the ceramic nanomembrane acted as predominant proton conductor without permeation of H-2 gas. In addition, the Hf0.13Si0.87Ox and Zr0.11Si0.89Ox membranes responded to the change of O-2 pressures in O-2 concentration cells, while the Al0.16Si0.84Ox and Ce0.06Si0.94Ox membranes did not produce the electrical voltage by gradient of O-2 pressure. We conclude that Hf0.13Si0.87Ox nanomembrane is promising as electrolyte material for fuel cells and related ionics devices. (C) 2009 Published by Elsevier B.V.
  • HORIGUCHI TAKUMI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2010-  37  2010/01/26  [Not refereed][Not invited]
  • HARADA AKIHISA, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2010-  113  2010/01/26  [Not refereed][Not invited]
  • HIRATA SHUHEI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2010-  112  2010/01/26  [Not refereed][Not invited]
  • FUKUNAGA YUKI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2010-  36  2010/01/26  [Not refereed][Not invited]
  • TATSUNO YASUHIRO, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2010-  21  2010/01/26  [Not refereed][Not invited]
  • KONNO YOSHIKI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2010-  114  2010/01/26  [Not refereed][Not invited]
  • F. Zhou, D. J. LeClere, S. J. Garcia-Vergara, T. Hashimoto, I. S. Molchan, H. Habazaki, P. Skeldon, G. E. Thompson  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  157-  (12)  C437  -C443  2010  [Refereed][Not invited]
     
    Al-W nanolayers have been used previously to investigate the mechanism of formation of porous anodic films on aluminum in phosphoric acid. The present study considers the interactions of the tungsten tracer species and phosphorus species in the films and the consequence to the transport of the tracer. The findings showed that phosphorus species migrate inward and pass through the nanolayer of outwardly migrating tungsten species. Further, the migration behaviors indicated negligible influence of either species on the migration of the other. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3499218] All rights reserved.
  • Takatoshi Yamamoto, Koji Fushimi, Hiroki Habazaki, Hidetaka Konno  ELECTROCHIMICA ACTA  55-  (3)  1232  -1238  2010/01  [Refereed][Not invited]
     
    Depassivation-repassivation behavior on a pure iron surface in borate buffer solution was examined under potentiostatic control by a micro-indentation test. Current peaks emerge during both downward and upward drives of the indenter due to depassivation which is caused by plastic deformation of the substrate but not elastic deformation and repassivation. The total electric charge of the current peaks is proportional to the maximum load. The total electric charge also increases with increase in intermission time of the indentation, indicating that the passive film is ruptured even during stress relaxation. It is estimated from the electric charge balance that 82% and 18% of the film rupture occurs during the downward drive and intermission, respectively, and that no rupture occurs during the upward drive. Furthermore, the film-ruptured area is estimated to be 80% of the plastic deformed surface area. The partial retainment of the passive film on iron suggests that the ductility of the passive film is higher than that of the substrate. (c) 2009 Elsevier Ltd. All rights reserved.
  • Santosh Prasad Sah, Yoshitaka Aoki, Hiroki Habazaki  MATERIALS TRANSACTIONS  51-  (1)  94  -102  2010/01  [Refereed][Not invited]
     
    Plasma electrolytic oxidation of AZ80 magnesium alloy in alkaline aluminate electrolytes develops MgAl2O4-based highly crystalline oxide coatings with the morphology changing largely with phosphate concentration in electrolyte. The thickness of the coatings increases with phosphate concentration from 5 mu m in phosphate-free electrolyte to similar to 70 mu m in the electrolyte containing 0.1 mol.dm(-3) phosphate after anodizing for 900 s. The formation of the latter thick coating is associated with intense sparking during, anodizing. The thick coatings formed in the electrolytes containing 0.075 and 0.1 mol.dm(-3) phosphate are highly cracked. In contrast, the coating formed in the electrolyte containing 0.05 mol.dm(-3) phosphate is relatively uniform, showing the highest corrosion protection in 0.5 mol.dm(-3) NaCl solution. The coatings consist of two layers, comprising an outer thick layer with high concentration of aluminum and an inner thin magnesium-rich layer. [doi:10.2320/matertrans.M2009226]
  • F. La Mantia, M. Santamaria, F. Di Quarto, H. Habazaki  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  157-  (7)  C258  -C267  2010  [Refereed][Not invited]
     
    The influence of thermal aging, at intermediate temperature (1 h at 250 degrees C) and in different environments, on the electronic and solid-state properties of stabilized 160 nm thick amorphous anodic niobia, grown on magnetron-sputtered niobium metal, has been studied. A detailed physicochemical characterization of the a-Nb(2)O(5)/0.5 M H(2)SO(4) electrolyte junction has been carried out by means of photocurrent and electrochemical impedance spectroscopy as well as by differential admittance (DA) measurements. A change in the optical bandgap (3.45 eV) of niobia film has been observed after aging (3.30 eV) at 250 degrees C in air for 1 h. A cathodic shift (0.15-0.2 V) in the flatband potential of the junction has been observed. The frequency dependence of DA data agrees with expectations of the theory of amorphous semiconductor Schottky barrier. The fitting of both components of DA allowed to get information on the distribution of the electronic density of states as a function of energy and distance from the metal oxide interface. The DA measurements evidenced for vacuum-treated niobia film an insulating to semiconductor transition. These findings can help to explain the large changes in the measured values of capacitance, after aging, and the larger leakage current observed in niobia electrolytic capacitors. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3428396] All rights reserved.
  • S. Koyama, Y. Aoki, N. Sakaguchi, S. Nagata, H. Habazaki  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  157-  (12)  C444  -C451  2010  [Refereed][Not invited]
     
    Capacitance enhancement of anodic oxide films on zirconium by adding silicon is reported here with correlation to the phase transformation of the oxide. The anodic oxide film formed on zirconium consists mainly of monoclinic ZrO2, which changes to tetragonal ZrO2 phase on the Zr-5.5 atom % Si. Further increase in the silicon contents to 10 and 16 atom % results in the formation of amorphous oxide up to 30 V, above which two-layered films, comprising an outer crystalline tetragonal-phase oxide layer and an inner amorphous layer, are developed. The relative thickness of the outer crystalline layer to the total film thickness increases with formation voltage. The highest capacitance of the anodic oxide films is obtained on the Zr-10 atom % Si. The changes in capacitance, permittivity and formation ratio of anodic oxide films with alloy composition are discussed with phase transformation and growth process of anodic oxides. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3503592] All rights reserved.
  • AOKI YOSHITAKA, HABAZAKI HIROKI  固体イオニクス討論会講演要旨集  35th-  168  -169  2009/12/07  [Not refereed][Not invited]
  • S. J. Garcia-Vergara, D. Le Clere, T. Hashimoto, H. Habazaki, R. Skeldon, G. E. Thompson  ELECTROCHIMICA ACTA  54-  (26)  6403  -6411  2009/11  [Refereed][Not invited]
     
    Improved methods are presented for investigating the flow of anodic alumina during the formation of porous anodic films on aluminium in phosphoric acid. In particular, the use of tungsten nanolayer tracers with increased flatness is shown to result in enhanced definition of the influences of flow on the tracer distribution, as observed by electron microscopy. Additionally, taper sectioning of films, by ultramicrotomy, and parallel sectioning of films, by sputtering using an Ar+ ion plasma, enable tungsten distributions across cells to be determined. In the case of an Al-3.5 at.%W alloy, the flow results in an inner alumina layer lining the pore walls that is relatively free of tungsten species and an outer cell layer of comparatively high tungsten content. Both sectioning procedures also show the presence of fine cell boundary bands of relatively high tungsten content, which are suggested to result from the transport of tungsten. enriched in the alloy immediately beneath the film, toward the cell boundary by the alloy/film interface. (c) 2009 Elsevier Ltd. All rights reserved.
  • M. Tauseef Tanvir, Y. Aoki, H. Habazaki  THIN SOLID FILMS  517-  (24)  6711  -6716  2009/10  [Refereed][Not invited]
     
    The present work demonstrates the formation of porous niobium films with separated columnar structures by oblique angle magnetron sputtering for capacitor application. The mobium films deposited on textured aluminium substrates, which had concave cell structures with the cell sizes ranging from 125 nm to 550 nm, consist of isolated columns of niobium with wider gaps between columns developing on the substrates with larger cell sizes. The surface areas of the deposited films. evaluated by the capacitance of the anodic films formed at several voltages, increased with an increase in the cell size of substrate. The surface area decreases with an increase in the formation potential of anodic films from 2 V to 10 V vs Ag/AgCl, because the gaps are filled with anodic oxide as a consequence of the large Pilling-Bedworth ratio of 2.6 for the Nb/Nb2O5 system. The reduction of the surface area is suppressed when the substrate with larger cell size is used, due to the formation of niobium columns with wider gaps, which are not filled with anodic oxide. The high surface area even at higher formation voltages of the anodic films is a requisite for capacitor application. (C) 2009 Elsevier B.V. All rights reserved.
  • S. Ono, H. Habazaki  CORROSION SCIENCE  51-  (10)  2364  -2370  2009/10  [Refereed][Not invited]
     
    Pit propagation on high purity aluminium electrode in 2 M HCl solutions with and without H(2)SO(4) under an alternating current (AC) has been examined. Pit development and potential transients were dependent on the H(2)SO(4) concentration. In the sulfate-free etchant, most pits developed from the pretreated surface, with little tendency to form clusters of pits. With increasing H(2)SO(4) concentration the size of the pit clusters increased. There is an optimal H(2)SO(4) concentration, which is 0.01 M H(2)SO(4) in this study, to form a deep etched layer of uniform thickness with high surface area. At H(2)SO(4) concentrations higher than 0.01 M, the pit propagation proceeded on limited foil surface sites and deep etched regions were formed locally, since sulfate ions assisted passivation and reduced the number of pit nucleation sites on foil surface. Analysis of potential transients during the anodic half-cycle supports the hypothesis that sulfate ions retarded the pit nucleation. (C) 2009 Elsevier Ltd. All rights reserved.
  • Yoshitaka Aoki, Hiroki Habazaki, Toyoki Kunitake  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY  131-  (40)  14399  -14406  2009/10  [Refereed][Not invited]
     
    Amorphous aluminosilicate nanofilms, a-Al0.1Si0.9Ox, exhibit unique size-enhancement of the proton conductivity along the thickness direction because of the presence of the zeolite-like, acid site network with the mesoscopically sized dimension inside glass matrix. The dense films with the thickness of 22-1400 nm were uniformly formed over the electrode substrate in nanometer thickness precision by multiple spin-coating with a mixed precursor Sol. XANES measurements indicated that the basic framework of a-Al0.1Si0.9Ox films was similar to the zeolitic one, consisting of the corner-linkage Of SiO4 and AlO4 tetrahedral units. These films revealed the complex temperature- and humidity-dependency of proton conductivity by the existence of two kinds of protonic carriers: Bronsted acidic protons and Lewis acidic protons. The Bronsted acidic protons could be persistent in amorphous films at around 500 degrees C, as checked by thermal desorption spectroscopy, so that the film exhibited the humidity-independent proton conductivity at temperatures above 300 degrees C. Furthermore, the conductivity across the film a increased in a power low by reduction of the film thickness of to less than 120 nm as sigma proportional to d-(tau), and it was saturated when the thickness become less than 40 nm. The observed scaling index tau was 2.2 in agreement with the value of the theoretical index (2.3) of cluster size scaling in a three-dimensional percolation system. This conduction behavior is explicable by finite size-scaling of the highly conductive pathway based on the interconnected Bronsted acid centers in the range of a few tens to hundreds of nanometers.
  • 瀬尾眞浩, 伏見公志, 青木芳尚, 幅崎浩樹, 中山武典  材料と環境討論会講演集  56th-  157  -158  2009/09/11  [Not refereed][Not invited]
  • KOMIYAMA SHOZO, AOKI YOSHITAKA, IZUMI TOMOO, HABAZAKI HIROKI  電気化学秋季大会講演要旨集  2009-  254  2009/09/10  [Not refereed][Not invited]
  • TERAOKA MASANOBU, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  120th-  60  2009/09/07  [Not refereed][Not invited]
  • KOWALSKI DAMIAN, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  120th-  68  2009/09/07  [Not refereed][Not invited]
  • Y. Oikawa, T. Minami, H. Mayama, K. Tsujii, K. Fushimi, Y. Aoki, P. Skeldon, G. E. Thompson, H. Habazaki  ACTA MATERIALIA  57-  (13)  3941  -3946  2009/08  [Refereed][Not invited]
     
    Porous anodic niobium oxide with a pore size of similar to 10 nm was formed at 10 V in glycerol electrolyte containing 0.6 mol dm(3) K2HPO4 and 0.2 mol dm(-3) K3PO4 at 433 K. After prolonged anodizing for 5.4 ks, niobium oxide microcones develop on the surface. X-ray diffraction patterns of the anodized specimens revealed that the initially formed anodic oxide is amorphous, but an amorphous-to-crystal-line transition occurs during anodizing. As a consequence of the preferential chemiccal dissolution of the initially formed amorphous oxide, due to different solubility of the amorphous and crystalline oxides, crystalline oxide microcones appear on the film surface after prolonged anodizing. The surface is superhydrophilic. After coating with fluorinated alkylsilane, the surface becomes superhydrophobic with a contact angle of 158 degrees for water. The surface is also oil repellent, with a contact angle as high as 140 degrees for salad oil. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • Takatoshi Yamamoto, Koji Fushimi, Masahiro Seo, Shiro Tsuri, Tetsuo Adachi, Hiroki Habazaki  CORROSION SCIENCE  51-  (7)  1545  -1553  2009/07  [Refereed][Not invited]
     
    Repassivation behavior of type-312L stainless steel containing 6% of molybdenum was examined in NaCl solution using in situ micro-indentation technique, together with type-304 and 316L stainless steels. High stability of the passive film formed on the type-312L stainless steel was also examined by depth profiling analysis of passive films using glow discharge optical emission spectroscopy (GDOES). In 0.9 mol dm(-3) NaCl solution at 296 K the type-304 and 316L stainless steels are passive only up to 0.3 V (SHE), above which pitting corrosion occurs. In contrast, no pitting corrosion occurs on type-312L stainless steel. Despite the significant difference of the pitting corrosion resistance, the repassivation kinetics of the three stainless steels, examined by micro-indentation at 0.3 V (SHE), is similar. The presence of molybdenum in the stainless steel does not influence the repassivation kinetics. The charge required to repassivate the ruptured type-312L stainless steel surface increases approximately linearly with the potential, even though the passivity-maintaining current increased markedly at potentials close to the transpassive region. Repassivation occurs without accompanying significant dissolution of steel, regardless of the stability of passive state. Depth profiling analyses of the passive films on the type-312L stainless steels formed at several potentials revealed that molybdenum species enrich in the outer layer of the passive film, below which chromium-enriched layer is present. The permeation of chloride ions may be impeded by the outer layer containing molybdate, enhancing the resistance against the localized corrosion of the type-312L stainless steel. (C) 2008 Elsevier Ltd. All rights reserved.
  • M. Uemura, T. Yamamoto, K. Fushimi, Y. Aoki, K. Shimizu, H. Habazaki  CORROSION SCIENCE  51-  (7)  1554  -1559  2009/07  [Refereed][Not invited]
     
    Thin passive films formed on highly corrosion-resistant type-312L stainless steel, containing 20 mass% chromium and 6 mass% molybdenum, in 2 mol dm(-3) HCl solution at 293 K have been analyzed by glow discharge optical emission spectroscopy (GDOES). The stainless steel does not suffer pitting corrosion even in this aggressive solution, showing a wide passive potential region. The depth profiles obtained clearly show a two-layer structure of the air-formed and passive films: an outer iron-rich layer and an inner layer highly enriched in chromium. Alloy-constituting molybdenum is deficient in the inner layer of the passive films and is enriched in the outer layer, particularly at the active dissolution potential. The molybdenum species in the outer layer may retard the active dissolution of stainless steel, promoting the formation of stable passive films highly enriched in chromium. Chloride ions are present only at the outermost part of the passive films, not penetrating into the interior part. (C) 2008 Elsevier Ltd. All rights reserved.
  • M. Tauseef Tanvir, Y. Aoki, H. Habazaki  APPLIED SURFACE SCIENCE  255-  (20)  8383  -8389  2009/07  [Refereed][Not invited]
     
    In the present study, porous Nb-Si alloy films with isolated nano-column morphology have been successfully developed by oblique angle magnetron sputtering on to aluminum substrate with concave cell structure. The deposited films are amorphous with the 15 at% silicon supersaturated into niobium. The porous Nb-15 at% Si films, as well as niobium films with similar morphology, are anodized at several voltages up to 50 V in 0.1 mol dm (3) ammonium pentaborate electrolyte. Due to the presence of sufficient gaps between neighboring columns, the gaps are not filled with anodic oxide, despite the large Pilling-Bedworth ratio (for instance, 2.6 for Nb/Nb2O5) and hence, a linear correlation between the reciprocal of capacitance and formation voltage is obtained for the Nb-15 at% Si. From the comparison with the anodic films formed on porous niobium films, it has been found that silicon addition improves the thermal stability of anodic niobium oxide; the change in capacitance and increase in leakage current become small for the Nb-Si. The findings indicate the potential of oblique angle deposition to tailor porous non-equilibrium niobium alloy films for high performance niobium-base capacitor. (C) 2009 Elsevier B.V. All rights reserved.
  • M. Nakajima, Y. Miura, K. Fushimi, H. Habazaki  CORROSION SCIENCE  51-  (7)  1534  -1539  2009/07  [Refereed][Not invited]
     
    Spark anodizing of titanium, Ti-6Al-4V and Ti-15V-3Al-3Cr-3Sn in alkaline aluminate electrolyte produces highly crystalline anodic films consisting mainly of Al2TiO5 with alpha- and gamma-Al2O3 as minor oxide phases, irrespective Of Substrate composition. However, the apparent efficiency for film formation decreases in the following order: Ti-6Al-4V, titanium and Ti-15V-3Al-3Cr-3Sn. A large amount of aluminium species are incorporated from the electrolyte, probably by plasma-chemical reaction, and become distributed throughout the film thickness. This distribution indicates that the electrolyte penetrates near to the film/substrate interface through the discharge channels. Thus, the outwardly migrating aluminium ions under a high electric field can be present even in the inner part of the anodic films. Voids are developed at the film/substrate interface. particularly on the vanadium-containing alloys, reducing the adhesion of the anodic film to the substrate. (C) 2008 Elsevier Ltd. All rights reserved.
  • 瀬尾眞浩, 青木芳尚, 伏見公志, 幅崎浩樹, 稲葉雅之, 横溝臣智, 早川敬済, 中山武典  材料と環境講演集  2009-  243  -244  2009/05/08  [Not refereed][Not invited]
  • S. J. Garcia-Vergara, T. Hashimoto, P. Skeldon, G. E. Thompson, H. Habazaki  ELECTROCHIMICA ACTA  54-  (13)  3662  -3670  2009/05  [Refereed][Not invited]
     
    Formation of porous anodic films on sputtering-deposited aluminium incorporating Al-Hf tracer layers has been examined at constant current in sulphuric and phosphoric acids. Hafnium was selected as the tracer species since the migration rates of Hf4+ and Al3+ ions are similar in barrier-type anodic alumina. The distribution of hafnium in the films was determined using ion beam analysis, scanning electron microscopy and transmission electron microscopy. Increases in the anodizing voltage and barrier layer thickness accompany the oxidation of hafnium and the migration of Hf4+ ions through the barrier layer region of the porous film. Hf4+ and Al3+ ions that migrate to the pore bases are lost to the electrolyte. Other Hf4+ ions are incorporated into the cell walls. For films formed in phosphoric acid, with relatively thick barrier layers, channelling of the ion current leads to accelerated outward transport of Hf4+ ions toward the pore base, while a U-shaped inner edge of the hafnium distribution beneath the pores is associated with more slowly transported hafnium species. The tracer behaviours for films formed in both acids are consistent with the transport of Hf4+ ions in the barrier layer regions by a combination of flow of film material and ion migration, the flow being a key factor in the development of the pores. The percentage losses of Hf4+ and Al3+ ions from the films to the electrolyte are relatively Similar, correlating with their similar migration rates, and contrast with the retention in the film of slow migrating WG+ ions, found previously, due to a more dominant role of flow. (C) 2009 Elsevier Ltd. All rights reserved.
  • OGAWA KOTA, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学会大会講演要旨集  76th-  298  2009/03/29  [Not refereed][Not invited]
  • TERAOKA MASANOBU, AOKI YOSHITAKA, HABAZAKI HIROKI  電気化学会大会講演要旨集  76th-  461  2009/03/29  [Not refereed][Not invited]
  • AOKI YOSHITAKA, HABAZAKI HIROKI, KUNITAKE TOYOKI  電気化学会大会講演要旨集  76th-  298  2009/03/29  [Not refereed][Not invited]
  • 伏見公志, 山本俊佑, 幅崎浩樹, 金野英隆  電気化学会大会講演要旨集  76th-  88  2009/03/29  [Not refereed][Not invited]
  • KOMIYAMA SHOZO, AOKI YOSHITAKA, IZUMI TOMOO, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  119th-  40  -41  2009/03/02  [Not refereed][Not invited]
  • KOYAMA SHUN, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  119th-  105  -106  2009/03/02  [Not refereed][Not invited]
  • 堀口匠, 青木芳尚, 伏見公志, 幅崎浩樹  表面技術協会講演大会講演要旨集  119th-  299  -300  2009/03/02  [Not refereed][Not invited]
  • Koji Fushimi, Shunsuke Yamamoto, Hidetaka Konno, Hiroki Habazaki  CHEMPHYSCHEM  10-  (2)  420  -426  2009/02  [Refereed][Not invited]
     
    Convective mass transfer in a flowing-electrolyte-type droplet cell (f-DC) is investigated for quantitative analysis of an electrode process and precise electrofabrication of microstructures using this device. The limiting current in the f-DC was expressed theoretically and its practical equation is investigated experimentally by cyclic voltammetry in solutions containing a redox mediator. The limiting-current equation in the f-DC derived experimentally could be expressed as a sum of hydrodynamic and stagnant terms. The current derived from the latter term of the f-DC is ten times larger than that in a conventional stagnant cell, thus indicating that the convective mass transfer in the cell would be changed dramatically at a small volumetric flow rate.
  • FUJII TAKASHI, AOKI YOSHITAKA, MAKINO TAKESHI, ONO SHOJI, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2009-  32  2009/01/26  [Not refereed][Not invited]
  • OGAWA KOTA, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2009-  166  2009/01/26  [Not refereed][Not invited]
  • KOYAMA SHUN, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2009-  36  2009/01/26  [Not refereed][Not invited]
  • TERAOKA MASANOBU, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2009-  167  2009/01/26  [Not refereed][Not invited]
  • MIURA YOSHIYUKI, AOKI YOSHITAKA, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2009-  28  2009/01/26  [Not refereed][Not invited]
  • KOMIYAMA SHOZO, AOKI YOSHITAKA, IZUMI TOMOO, HABAZAKI HIROKI  化学系学協会北海道支部冬季研究発表会講演要旨集  2009-  165  2009/01/26  [Not refereed][Not invited]
  • F. La Mantia, M. Santamaria, H. Habazaki, F. Di Quarto  ECS Transactions  19-  (3)  411  -422  2009  [Not refereed][Not invited]
     
    The effect of thermal treatment for lh at 250°C in air or under vacuum on the electronic structure of thick amorphous anodic niobia was characterized by electrochemical impedance, differential admittance (DA) and photocurrent spectroscopy (PCS). The analysis of anodized niobia has revealed that it behaves as a pure dielectric. The thermal treatment in air increases the value of its differential capacitance. The effect is stronger when the thermal treatment is carried out in vacuum, and can be cancelled by re-anodizing the oxide to its initial formation potential. The frequency dependence of the sample treated in vacuum exhibited behavior typical of a semiconducting amorphous material. PCS measurements were used to derive the optical band gap value and to confirm the location of the flat band potential that was derived from admittance data. © The Electrochemical Society.
  • FUJII Takashi, AOKI Yoshitaka, FUSHIMI Koji, MAKINO Takeshi, ONO Shoji, HABAZAKI Hiroki  J. Surf. Finish. Soc. Jpn.  60-  (3)  166  -169  2009  [Not refereed][Not invited]
  • Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION  48-  (41)  7582  -7585  2009  [Refereed][Not invited]
  • H. Habazaki, Y. Oikawa, K. Fushimi, Y. Aoki, K. Shimizu, R. Skeldon, G. E. Thompson  ELECTROCHIMICA ACTA  54-  (3)  946  -951  2009/01  [Refereed][Not invited]
     
    Niobium has been anodized at a constant current density to 10 V with a current decay in 0.8 mol dm(-3) K(2)HPO(4)-glycerol electrolyte containing 0.08-0.65 mass% water at 433 K to develop porous anodic oxide films. The film growth rate is markedly increased when the water content is reduced to 0.08 mass%; a 28 mu m-thick porous film is developed in this electrolyte by anodizing for 3.6 ks, while the thickness is 4.6 and 2.6 mu m in the electrolytes containing 0.16 and 0.65 mass% water respectively. For all the electrolytes, the film thickness changes approximately linearly with the charge passed during anodizing, indicating that chemical dissolution of the developing oxide is negligible. SIMS depth profiling analysis was carried for anodic films formed in electrolyte containing similar to 0.4 mass% water with and without enrichment of H(2) (18)O. Findings disclose that water in the electrolyte is a predominant source of oxygen in the anodic oxide films. The anodic films formed in the electrolyte containing 0.65 mass% water are practically free from phosphorus species. Reduction in water content increased the incorporation of phosphorus species. (c) 2008 Elsevier Ltd. All rights reserved.
  • M. Fogazza, M. Santamaria, F. Di Quarto, S. J. Garcia-Vergara, I. Molchan, P. Skeldon, G. E. Thompson, H. Habazaki  ELECTROCHIMICA ACTA  54-  (3)  1070  -1075  2009/01  [Refereed][Not invited]
     
    The growth of barrier-type anodic films at high efficiency on a range of sputtering-deposited Al-Hf alloys, containing from 1 to 95 at.% Hf. has been investigated in ammonium pentaborate electrolyte. The alloys encompassed nanocrystalline and amorphous structures, the latter being produced for alloys containing from 26 to 61 at.% Hf. Except at the highest hafnium content, the films were amorphous and contained units of HfO2 and Al2O3 distributed relatively uniformly through the film thickness. Boron species were confined to outer regions of the films. The boron distributions suggest that the cation transport number decreases progressively with increasing hafnium concentration in the films, from similar to 0.4 in anodic alumina to similar to 0.2 for a film on an Al-61 at.% Hf alloy. The distributions of Al3+ and Hf4+ ions in the films indicate their similar migration rates, which correlates with the similarity of the energies of Al3+ -O2- and Hf4+ -O2- bonds. For an alloy containing similar to 95 at.% Hf. the film was largely nanocrystalline, with a thin layer of amorphous oxide, of non-uniform thickness, at the film surface. The formation ratios for the films on the alloys changed approximately in proportion to the hafnium content of the films between the values for anodic alumina and anodic hafnia, similar to 1.2 and 1.8 nm V-1 respectively. (c) 2008 Elsevier Ltd. All rights reserved.
  • AOKI YOSHITAKA, HABAZAKI HIROKI, KUNITAKE TOYOKI  固体イオニクス討論会講演要旨集  34th-  57  -58  2008/12/03  [Not refereed][Not invited]
  • Masahiro Seo, Koji Fushimi, Hiroki Habazaki, Takenori Nakayama  CORROSION SCIENCE  50-  (11)  3139  -3146  2008/11  [Refereed][Not invited]
     
    The effect of Pb(2+) on polarization behavior of nickel has been investigated in 0.1 M NaClO(4) + 10(-2) M HClO(4) + x M PbO solutions (x = 0, 10(-5), 10(-4), 10(-3)) at room temperature. The cyclic voltammogram has suggested that Pb(2+) degrades the stability of the passive film on Ni. The corrosion potential of Ni shifted to the more noble direction and the anodic current peak of Ni dissolution decreased with increasing Pb(2+) concentration in solution, indicating that Pb(2+) suppresses significantly the anodic dissolution. The under-potential deposition (UPD) of lead on Ni in the potential range more noble than -0.215 V (SHE) corresponding to the equilibrium potential of the Pb(2+) (10(-3) M)/Pb electrode was confirmed by XPS and GDOES analyses. The anodic Tafel slope, b(+), of Ni dissolution changed from b(+) = 40 mV decade(-1) in the absence of Pb(2+) to b(+) = 17 mV decade(-1) in the presence of 10(-4) or 10(-3) M Pb(2+), which was ascribed to the increase in active sites of Ni surface emerged as a result of electrodesorption of Pb adatoms. The roles of Pb adatoms in active dissolution and active/passive transition of Ni were discussed from the above results, (C) 2008 Elsevier Ltd. All rights reserved.
  • H. Habazaki, T. Ogasawara, K. Fushimi, K. Shimizu, S. Nagata, T. Izumi, R. Skeldon, G. E. Thompson  ELECTROCHIMICA ACTA  53-  (28)  8203  -8210  2008/11  [Refereed][Not invited]
     
    The present work demonstrates effective inhibition of field crystallization of amorphous anodic niobium oxide by incorporation of silicon species from substrate. The field crystallization, detrimental for capacitor application of niobium, occurs during anodizing of magnetron sputtered niobium at 100V in 0.1 mol dm(-3) ammonium pentaborate electrolyte at 333 K, while amorphous structure of the anodic oxide is totally retained during anodizing of magnetron sputtered Nb-12 at%Si. Even after prior thermal treatment in air, which accelerates field crystallization of anodic oxide on niobium, no crystallization occurs on the Nb-12 at%Si. Through examination of the crystallization behaviours of anodic films formed on a thin Nb-12 at%Si layer superimposed on a niobium layer as well as, on a thin niobium layer superimposed on an Nb-12 at%Si layer, it has been confirmed that air-formed oxide or thermal oxide becomes a nucleation site for crystallization. Modification of the air-formed or thermal oxide by incorporation of silicon species inhibits the nucleation of crystalline oxide. The modification, however, does not influence the growth of crystalline oxide. The growth is suppressed by continuous incorporation of silicon species into anodic film from the substrate during anodizing. (C) 2008 Elsevier Ltd. All rights reserved.
  • S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, H. Habazaki  CORROSION SCIENCE  50-  (11)  3179  -3184  2008/11  [Refereed][Not invited]
     
    The behaviour of Nd3+ ions is examined in porous anodic alumina films formed at 5 mA cm(-2) in 0.4 M phosphoric acid at 293 K on aluminium substrates that contain a buried 5 nm-thick tracer band of Al-Nd alloy. The Nd3+ ions migrate outward in the barrier region about twice as fast as Al3+ ions. The neodymium was located in the anodic film by transmission electron microscopy and scanning electron microscopy, and quantified by Rutherford backscattering spectroscopy. The Nd3+ ions migrated to the cell walls and to pore base, depending upon their location in the substrate relative to the alumina cells and pores. Nd3+ ions that reached the pore base were lost to the electrolyte. The outward transport of the Nd3+ ions was greatest beneath the pores and least at the cell boundaries, resulting in transformation of the planar tracer layer of the substrate to a roughly hemispherical shape in the film. The behaviour contrasts with that of a tracer band of slowly migrating W6+ ions, which reveals an approximately inverse distribution, while W6+ ions are retained within the film. (C) 2008 Elsevier Ltd. All rights reserved.
  • KOYAMA SHUN, AOKI YOSHITAKA, HABAZAKI HIROKI  表面技術協会講演大会講演要旨集  118th-  215  2008/08/20  [Not refereed][Not invited]
  • 及川祐樹, 伏見公志, 青木芳尚, 幅崎浩樹  表面技術協会講演大会講演要旨集  118th-  214  2008/08/20  [Not refereed][Not invited]
  • 立野靖博, 伏見公志, 青木芳尚, 幅崎浩樹  表面技術協会講演大会講演要旨集  118th-  224  -225  2008/08/20  [Not refereed][Not invited]
  • 立野靖博, 伏見公志, 青木芳尚, 幅崎浩樹  日本化学会北海道支部研究発表会講演要旨集  2008-  131  2008/07/19  [Not refereed][Not invited]
  • 堀口匠, 青木芳尚, 伏見公志, 幅崎浩樹  日本化学会北海道支部研究発表会講演要旨集  2008-  130  2008/07/19  [Not refereed][Not invited]
  • M. Santamaria, F. Di Quarto, H. Habazaki  CORROSION SCIENCE  50-  (7)  2012  -2020  2008/07  [Refereed][Not invited]
     
    A photoelectrochemical investigation on thin (<= 13 nm) mixed oxides grown on sputter-deposited Ti-Zr alloys of different composition by air exposure and by anodizing (formation voltage, U-F = 4 V/SCE) was carried out. The experimental results showed that the optical band gap, E-g(opt), increases with increasing Zr content in both air formed and anodic films. Such behaviour is in agreement with the theoretical expectation based on the correlation between the band gap values of oxides and the difference of electronegativity of their constituents. The flat band potential of the mixed oxides was found to be almost independent on the Ti/Zr ratio into the film and more anodic with respect to those estimated for oxide grown on pure Zr. The semiconducting or insulating character of the investigated films was strongly influenced by the forming conditions and the alloy composition. (C) 2008 Elsevier Ltd. All rights reserved.
  • M. Tauseef Tanvir, K. Fushimi, Y. Aoki, H. Habazaki  MATERIALS TRANSACTIONS  49-  (6)  1320  -1326  2008/06  [Refereed][Not invited]
     
    Niobium films with isolated columnar morphology have been prepared by oblique angle magnetron sputtering for capacitor application. Anodizing of the deposited mobium to form dielectric mobium oxide reduces the surface roughness, since the gaps between the neighboring columns are filled with the oxide due to large Pilling-Bedworth ratio for Nb/Nb2O5. To increase the gaps between neighboring columns, the influences of the angle of mobium flux to substrate and substrate surface roughness on the columnar morphology of the deposited films have been investigated using scanning electron microscopy and the electrochemical measurements. The deposition on the textured rough substrate surface and at higher angle of the mobium flux from normal to the substrate surface fabricates the mobium films with higher surface roughness.
  • A. Suleiman, T. Hashimoto, P. Skeldon, G. E. Thompson, F. Echeverria, M. J. Graham, G. I. Sproule, S. Moisa, H. Habazaki, P. Bailey, T. C. Q. Noakes  CORROSION SCIENCE  50-  (5)  1353  -1359  2008/05  [Refereed][Not invited]
     
    Anodizing of InSb at 5mAcm(-2) in sodium tungstate electrolyte is shown to produce barrier-type amorphous oxide at relatively low voltages, to about 40 V, and porous-type amorphous oxide at increased voltages. The barrier-type amorphous oxide, consisting of units of In2O3 and Sb2O3, distributed relatively uniformly throughout the film, develops at a formation ratio of 2.2 +/- 0.2 nmV(-1). The outer 15-20% of the film also contains tungsten species. The relatively high efficiency of barrier film growth reduces significantly with transition to porous oxide, which is associated additionally with generation of oxygen at the film surface. The final oxide, at 65V, comprises pores, of typical diameter 80nm, orientated approximately normal to the substrate and extending from a barrier region to the film surface. (c) 2008 Elsevier Ltd. All rights reserved.
  • Y. Liu, M. A. Arenas, S. J. Garcia-Vergara, T. Hashimoto, P. Skeldon, G. E. Thompson, H. Habazaki, P. Bailey, T. C. Q. Noakes  CORROSION SCIENCE  50-  (5)  1475  -1480  2008/05  [Refereed][Not invited]
     
    Enrichment of copper beneath amorphous anodic films on relatively dilute, solid-solution Al-Cu alloys is necessary before copper can be oxidized and incorporated into the oxide layer. A similar enrichment arises during electropolishing, which also develops an amorphous oxide. In these cases, external polarization is applied, usually generating a relatively high oxidation rate. In contrast, enrichment behaviour at the corrosion potential has received less attention. The present study examines the corrosion of Al-Cu alloys, containing up to 6.7 at.% Cu, in 0.1 M sodium hydroxide solution at 293 K. Copper is again found to enrich in the alloy, similarly to behaviour with anodic polarization. However, following enrichment, discrete copper-rich particles appear to be generated in the corrosion product. These are suggested to be nanoparticles of copper, since the corrosion potentials of the alloys are low relative to that required for oxidation of copper. The corrosion rate increases with increase of both time and copper content of the alloy, probably associated with a greater cathodic activity due to an increasing number of nanoparticles. The corrosion proceeds with loss of aluminium species to the sodium hydroxide solution, but with retention of copper in the layer of hydrated alumina corrosion product. (c) 2008 Elsevier Ltd. All rights reserved.
  • 瀬尾眞浩, 伏見公志, 幅崎浩樹, 中山武典  材料と環境講演集  2008-  213  -214  2008/04/25  [Not refereed][Not invited]
  • 瀬尾眞浩, 伏見公志, 幅崎浩樹, 世木隆, 河野研二, 横溝臣智, 稲葉雅之, 中山武典  材料と環境講演集  2008-  317  -318  2008/04/25  [Not refereed][Not invited]
  • 清水 健一, 三谷 智明, 幅崎 浩樹  工業材料  56-  (4)  72  -82  2008/04  [Not refereed][Not invited]
  • AOKI YOSHITAKA, HABAZAKI HIROKI, KUNITAKE TOYOKI  電気化学会大会講演要旨集  75th-  235  2008/03/29  [Not refereed][Not invited]
  • Masahiko Kiriu, Koji Fushmi, Hidetaka Konno, Hiroki Habazak  ELECTROCHEMISTRY  76-  (3)  197  -202  2008/03  [Not refereed][Not invited]
     
    Nanocarbons with brush-type morphology have been prepared by liquid phase carbonization of poly(acrylamide) (PAA) or poly(vinylchloride) (PVC) in pores of template. The template used is dc etched aluminum foil that is further anodized in sulfuric acid electrolyte. The nanocarbons derived from PAA contain nitrogen, whose content decreases with increasing heat treatment temperature. At each heat treatment temperature, the specific surface area as well as pore structure is similar for both the nanocarbons derived from PAA and PVC. Nevertheless, the markedly large electrochemical capacitance, measured in 1 mol dm(-3) sulphuric acid, is obtained for the PAA-derived nanocarbons, compared with that from PVC, due to pseudocapacitance arising from nitrogen species in the former nanocarbons. Despite the specific surface area of less than 250 m(2) g(-1), the PAA-derived nanocarbons reveal the capacitance as large as similar to 130 F g(-1). The capacitance per specific surface area is found to increase almost linearly with the content of nitrogen. It is also found that the capacitance per specific surface area of the nanocarbons with the brush-type morphology is larger than that of the carbon nanofilaments prepared similarly using a template of porous anodic alumina on plain aluminum foil.
  • Koji Fushimi, Hiroki Habazaki  ELECTROCHIMICA ACTA  53-  (8)  3371  -3376  2008/03  [Refereed][Not invited]
     
    Anodic dissolution behavior of titanium in NaCl-containing ethylene glycol has been examined to obtain electropolished titanium surface. During anodic polarization in 1 mol dm(-3) NaCl ethylene glycol solution at 293 K, the titanium electrode covered with oxide dissolves with gas evolution at potentials higher than 10 V (Ag/AgCl) while it is in passive state at potentials lower than 5 V. However, after removal of the oxide layer by pre-polarization at gas-evolving potentials, no gas evolution is observed, and the titanium electrode shows a limiting dissolution current as tetravalent species at potentials higher than 5 V, producing a smooth surface. The polarization of the rotating disk titanium electrode reveals that the kinetics of the mass transfer reaction for electropolishing of titanium is controlled by titanium species dissolved into the solution, not by chloride ions or water containing in the solution. Repetition of dynamic polarization gives a well-electropolished surface. (C) 2007 Elsevier Ltd. All rights reserved.
  • 伏見公志, 安住和久, 幅崎浩樹, 釣之郎  表面技術協会講演大会講演要旨集  117th-  112  2008/02/29  [Not refereed][Not invited]
  • 植村元宣, 青木芳尚, 伏見公志, 幅崎浩樹  表面技術協会講演大会講演要旨集  117th-  111  2008/02/29  [Not refereed][Not invited]
  • 瀬尾眞浩, 藤祐輔, 伏見公志, 幅崎浩樹, 中山武典  表面技術協会講演大会講演要旨集  117th-  113  -114  2008/02/29  [Not refereed][Not invited]
  • 及川祐樹, 南貴之, 眞山博幸, 辻井薫, 青木芳尚, 伏見公志, 幅崎浩樹  表面技術協会講演大会講演要旨集  117th-  268  -269  2008/02/29  [Not refereed][Not invited]
  • 藤井隆志, 青木芳尚, 伏見公志, 幅崎浩樹, 牧野猛, 小野昭二  表面技術協会講演大会講演要旨集  117th-  270  2008/02/29  [Not refereed][Not invited]
  • 三浦吉幸, 青木芳尚, 伏見公志, 幅崎浩樹, 高沢祐之  表面技術協会講演大会講演要旨集  117th-  271  -272  2008/02/29  [Not refereed][Not invited]
  • 長沼淳, 伏見公志, 安住和久, 幅崎浩樹, 金野英隆  表面技術協会講演大会講演要旨集  117th-  129  -130  2008/02/29  [Not refereed][Not invited]
  • E. Matykina, R. Arrabal, P. Skeldon, G. E. Thompson, H. Habazaki  THIN SOLID FILMS  516-  (8)  2296  -2305  2008/02  [Refereed][Not invited]
     
    The influence of grain orientation on oxygen generation during anodizing of chemically polished titanium at 20 mA cm(-2) in 0.026 M Na3PO4 and 0.02 M Na4P2O7 is investigated in the pre-sparking region using scanning electron, atomic force and transmission electron microscopies. The findings reveal preferential oxygen generation in the anodic film on titanium grains that tend to a basal-like orientation. The resultant oxygen-filled voids that develop within the film increase in size and coalesce with progress of anodizing. Their presence leads to formation of blisters and the eventual film rupture due to release of the high-pressure gas. In contrast, relatively few voids, and hence smoother film, develop on grains of prism-like orientation. The differing rates of oxygen generation are attributed to the grain orientation dependence of the amorphous-to-crystalline transition of anodic titania, with rutile being identified at sites of oxygen-filled voids in films formed in 0.02 M Na4P2O7. There may also be small contributions to oxygen generation from influences of substrate impurities incorporated into the film. The grain orientation also affected the rate of chemical polishing of the titanium in HF/HNO3, which was faster on basal-like planes. (c) 2007 Elsevier B.V. All rights reserved.
  • Q. Lu, J. Alberch, T. Hashimoto, S. J. Garcia-Vergara, H. Habazaki, P. Skeldon, G. E. Thompson  CORROSION SCIENCE  50-  (2)  548  -553  2008/02  [Refereed][Not invited]
     
    The growth of a nanoporous anodic oxide oil titanium and a Ti-20 at.% W alloy, both deposited by magnetron sputtering, ill a glycerol/phosphate electrolyte at 453 K is reported. The oxide formed on titanium is a mixture of amorphous titania and anatase. However, that on the alloy is amorphous only and forms at increased efficiency, about 27%. The amorphous structure is considered to be stabilized by incorporated units Of WO3, which are distributed uniformly throughout the anodic film. The growth of the porous oxides is suggested to be associated with loss of film species at the film/electrolyte interface at the base of pores, with new oxide forming exclusively at the metal/film interface by inward migration of O2- ions. (c) 2007 Elsevier Ltd. All rights reserved.
  • 桐生雅彦, 青木芳尚, 伏見公志, 金野英隆, 幅崎浩樹  三学協会北海道支部研究発表会講演要旨集  2008-  41  2008/01/21  [Not refereed][Not invited]
  • 植村元宣, 青木芳尚, 伏見公志, 幅崎浩樹  三学協会北海道支部研究発表会講演要旨集  2008-  29  2008/01/21  [Not refereed][Not invited]
  • 及川祐樹, 青木芳尚, 伏見公志, 幅崎浩樹  三学協会北海道支部研究発表会講演要旨集  2008-  40  2008/01/21  [Not refereed][Not invited]
  • 伏見公志, 中島美穂, 幅崎浩樹, 豊武孝太郎  アルミニウム研究会誌  (1)  39  -40  2008  [Not refereed][Not invited]
  • 幅崎浩樹, 伏見公志, 清水健一  アルミニウム研究会誌  (1)  25  2008  [Not refereed][Not invited]
  • 及川祐樹, 伏見公志, 幅崎浩樹  アルミニウム研究会誌  (1)  24  2008  [Not refereed][Not invited]
  • 及川祐樹, 青木芳尚, 伏見公志, 幅崎浩樹  アルミニウム研究会誌  (5)  92  2008  [Not refereed][Not invited]
  • T. Yamamoto, K. Fushimi, H. Habazaki, H. Konno, S. Miura  ECS Transactions  16-  (52)  133  -140  2008  [Not refereed][Not invited]
     
    The effects of grain orientation and cold-rolling on the depassivation-repassivation behavior of polycrystalline irons were examined in pH8.4 borate buffer solution using in-situ micro-indentation technique. The depassivation rate on the passive iron surface during the downward drive of the indenter (penetration of an indenter tip into iron surface) depended on the grain orientation the highest rate was obtained on {100} surface, on which a possible main slip plane of {110} was normal to the surface. In contrast, the total electric charge required for repassivation during the downward and subsequent upward drives was not influenced by the grain orientation. The electric charge for repassivation was strongly influenced by the rolling reduction that changed the dislocation density at the specimen surface. There was a linear correlation between the electric charge normalized by residual dent area and the square root of the dislocation density. ©The Electrochemical Society.
  • M. Seo, N. Kikuchi, K. Fushimi, H. Habazaki, T. Narita, T. Nakayama  ECS Transactions  16-  (52)  109  -116  2008  [Not refereed][Not invited]
     
    The anodic behavior of nickel has been investigated in deaerated acidic perchlorate solution containing 10-4 M Pb2+ at room temperature. The addition of Pb2+ in solution shifted the corrosion potential or the potential of anodic current peak to the more noble direction and suppressed the anodic dissolution of nickel. The Tafel slope of anodic dissolution decreased from 37 mV decade-1 to 13 mV decade -1 due to the addition of Pb2+. The uderpotential deposition (UPD) of Pb on nickel was discussed with relation to the effect of Pb2+ on anodic behavior of nickel. ©The Electrochemical Society.
  • Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki  ECS Transactions  16-  (48)  57  -65  2008  [Not refereed][Not invited]
     
    Amorphous Nb2O5 film of 167 nm thickness was fabricated by anodic oxidation of sputter deposited niobium and characterized by TEM, GD-OES and AFM. The electric properties of the anodic films with sputter-deposited circular gold electrodes were studied by AC impedance spectroscopy in ambient gas atmospheres of air, argon, oxygen or hydrogen in the temperature range of 25 - 200°C. The amorphous Nb2O5 showed the character of n-type semiconductor. The conductivity of the film, following the Arrhenius behaviour, was independent of the oxygen partial pressure, but was largely dependent on hydrogen partial pressure. The conductivity of the Nb2O5 film at room temperature in dry hydrogen was 2.2 orders of magnitude as high as that in air. The enhanced conductivity could be associated with partial reduction of Nb5+ in dry hydrogen atmosphere. The addition of water vapor to hydrogen atmosphere reduced conductivity probably due to suppressing the reduction of Nb 2O5. ©The Electrochemical Society.
  • K. Fushimi, K. Takakura, H. Habazaki, H. Konno, K. Azumi, S. Tsuri  ECS Transactions  16-  (52)  291  -296  2008  [Not refereed][Not invited]
     
    The combination of the potentiometric pH measurement and potentiostatic polarization was carried out for the type-312L and 316L austenitic stainless steels during decreasing pH by dropping hydrochloric acid in sodium chloride solution. The acidification changed the surface condition of the austenitic stainless steels. The significant acidity of the solution induced a rapid increase in the anodic current passing through the steel at a critical pH, pHdepass. The value of pHdepass was increased by elevating the solution temperature or concentrating the chloride ions in solution. In the potential - pHdepass diagram, the surface condition could be classified into four domains immunity, active, passive and transpassive/pitting states. The boundary between the active and passive states was strongly dependent on solution pH but independent of potential, indicating that the depassivation of the steel surface proceeded with a chemical reaction participating protons rather than the electrochemical one. ©The Electrochemical Society.
  • Y. Aoki, H. Habazakia, T. Kunitake  ECS Transactions  16-  (51)  407  -412  2008  [Not refereed][Not invited]
     
    AlxSi1-xOn, films exhibit a drastic change of proton conductivity across the film by reducing its thickness to less than 100 nm. The temperature- and humidity-dependence of conductivity of the sub-100 nm films is quite different from those of the thicker films. Furthermore, in the former thickness range, the value of conductivity markedly increases with reducing the film thickness, and its thickness dependence follows a power law with a fixed index of -2.1. This size-scaling effect can be explained by the percolation conductivity model that the probability for percolating of the conductive moiety in AlxSi1-xOn, films increases with decreasing the thickness. ©The Electrochemical Society.
  • FUSHIMI Koji, SAKAIRI Masatoshi, HABAZAKI Hiroki  Journal of the Surface Finishing Society of Japan  59-  (12)  863  -868  2008  [Not refereed][Not invited]
  • M. Santamaria, F. Di Quarto, H. Habazaki  ELECTROCHIMICA ACTA  53-  (5)  2272  -2280  2008/01  [Refereed][Not invited]
     
    A photoelectrochemical investigation on anodic films of different thickness grown on sputter-deposited Zr and Zr-20at.%Ti was carried out. The estimated optical band gap and flat band potential of thick (U-F >= 50 V) anodic films were related to their crystalline structure and compared with those obtained for thinner (U-F <= 8 V/SCE) anodic oxides having undetermined crystalline structure. The E,, values obtained by photocurrent spectroscopy were also compared with the experimental band gap estimated by other optical ex situ techniques and with the available theoretical estimates of the zirconia electronic structures in an attempt to reconcile the wide range of band gap data reported in the literature. Finally, the optical band gap and flat band potential values obtained for tetragonal Zr0.8Ti0.2O2 mixed oxide were compared with that expected on the basis of a correlation between E-g and the film composition. (c) 2007 Elsevier Ltd. All rights reserved.
  • D. J. LeClere, A. Velota, P. Skeldon, G. E. Thompson, S. Berger, J. Kunze, P. Schmuki, H. Habazaki, S. Nagata  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  155-  (9)  C487  -C494  2008  [Refereed][Not invited]
     
    Using a sputtering-deposited titanium substrate, incorporating six equally spaced nanolayers of Ti-W alloy, the volume and composition changes accompanying the formation of porous anodic films on titanium in 0.5 wt % NH(4)F in glycerol are investigated. The findings reveal amorphous films with nanotubes of TiO(2), containing fluoride ions and possibly glycerol derivatives. Tungsten and titanium species are lost to the electrolyte at differing rates during anodizing, leading to an enrichment of tungsten in the film relative to the composition of the substrate. The spacing of tungsten-containing bands in the film is similar to 2.3 that of the original alloy layers during growth of the major pores. The generation of the nanotubes can be explained either by field-assisted flow of film material within the barrier layer to the pore walls, with cation and anion transport numbers of anodic titania in the barrier layer region similar to those of barrier films and with field-assisted ejection of Ti(4+) ions to the electrolyte, or by field-assisted dissolution, but with a reduction in cation transport number. (C) 2008 The Electrochemical Society.
  • H. Habazaki, M. Yamasaki, T. Ogasawara, K. Fushimi, H. Konno, K. Shimizu, T. Izumi, R. Matsuoka, P. Skeldon, G. E. Thompson  THIN SOLID FILMS  516-  (6)  991  -998  2008/01  [Refereed][Not invited]
     
    Thermal treatment of anodized niobium and oxygen-containing niobium has been carried out to elucidate the thermal degradation mechanism of niobium, capacitors and to clarify the influence of oxygen dissolved in niobium. on thermal degradation. The capacitance and leakage current of the anodized specimens increase with thermal treatment above 423 K in air, although the oxygen content in the substrate has no significant effect up to 523 K. At increased temperatures, the changes in capacitance and leakage current are suppressed with increasing oxygen content. The anodic film formed on the Nb-50 at.% O substrate thickens significantly during thermal treatment at 623 K in air, while only a slight reduction of the thickness is evident for those on the niobium and Nb-20 at.% O substrates. In contrast, vacuum thermal treatment at 623 K causes thinning of the anodic film on niobium, with evidently no change in the film thickness on the Nb-50 at.% 0 substrate. These are interpreted in terms of oxygen diffusion from the anodic film to the substrate as well as thermal oxide growth. (C) 2007 Elsevier B.V. All rights reserved.
  • S. J. Garcia-Vergara, M. Curioni, F. Roeth, T. Hashimoto, P. Skeldon, G. E. Thompson, H. Habazaki  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  155-  (7)  C333  -C339  2008  [Refereed][Not invited]
     
    An Al-1 atom % Au gold alloy is employed to investigate the incorporation of a nonoxidized alloying element into porous anodic alumina films formed in phosphoric acid and sulfuric acid electrolytes. Gold is shown to enrich in the alloy in the initial stages of film growth, when a gold-free film is formed. On sufficient enrichment of the alloy, gold nanoparticles are incorporated into the film above an enriched alloy layer containing nanocrystals of Al2Au. The formation of the nanoparticles is accompanied by a reduced rate of film growth due to generation of oxygen. The gold is incorporated into the films preferentially at the cell boundary regions of the scalloped alloy/film interface. Elongated and approximately circular nanoparticles are observed in film sections, the former type being particular to films formed in sulfuric acid electrolyte. The incorporation of gold into the film commences earlier than predicted for a planar alloy/film interface. The behavior suggests that transport of gold occurs within the enriched alloy layer, possibly associated with the stresses at the alloy/film interface due to film growth processes. (c) 2008 The Electrochemical Society.
  • Koji Fushimi, Shunsuke Yamamoto, Ryota Ozaki, Hiroki Habazaki  ELECTROCHIMICA ACTA  53-  (5)  2529  -2537  2008/01  [Refereed][Not invited]
     
    The scanning-droplet-cell (SDC), recently used for studying electrochemistry of electrodes in micro-areas, was modified to a flowing electrolyte type one (f-SDC), in which fresh electrolyte was continuously supplied oil the surface to be examined. The f-SDC with a coaxial double capillary structure could avoid the contamination of electrolyte by species dissolved front the measuring electrode surface. In the present study, the f-SDC technique was applied successfully to obtain profiles of the corrosion potential for the cross-sections of aluminium-alloy brazing sheets, used for the heat exchanger of the automobile. The brazing sheets consist of an Al-Zn alloy sacrificial anode layer, an Al-Mn-Cu core layer and an Al-Si brazing filler. The profiles of the corrosion potential, important to evaluate the corrosion protection performance of the sacrificial anode, revealed that the potential gradient arising from the sacrificial anode to the core layer is mainly controlled by zinc, which diffuses from the former layer to the latter during the cladding treatment and the post-heat treatment. (c) 2007 Elsevier Ltd. All rights reserved.
  • Yoshitaka Aoki, H. Habazaki, Toyoki Kunitake  ELECTROCHEMICAL AND SOLID STATE LETTERS  11-  (11)  P13  -P16  2008  [Refereed][Not invited]
     
    AlxSi1-xOn films exhibit a drastic change of proton conductivity across the film by reducing their thickness to less than 100 nm. The temperature and humidity dependence of conductivity of the sub-100 nm films is quite different from those of the thicker films. Furthermore, in the former thickness range, the value of conductivity markedly increases with reducing the film thickness, and its thickness dependence follows a power law with a fixed index of -2.1. This size-scaling effect can be explained by the percolation conductivity model that the probability for percolating of the conductive moiety in AlxSi1-xOn films increases with decreasing the thickness.
  • Yoshitaka Aoki, H. Habazaki, Toyoki Kunitake  ELECTROCHEMICAL AND SOLID STATE LETTERS  11-  (11)  P13  -P16  2008  [Refereed][Not invited]
     
    AlxSi1-xOn films exhibit a drastic change of proton conductivity across the film by reducing their thickness to less than 100 nm. The temperature and humidity dependence of conductivity of the sub-100 nm films is quite different from those of the thicker films. Furthermore, in the former thickness range, the value of conductivity markedly increases with reducing the film thickness, and its thickness dependence follows a power law with a fixed index of -2.1. This size-scaling effect can be explained by the percolation conductivity model that the probability for percolating of the conductive moiety in AlxSi1-xOn films increases with decreasing the thickness.
  • 幅崎 浩樹  化学と工業 = Chemistry and chemical industry  60-  (12)  1178  -1178  2007/12/01
  • H. Habazaki, Y. Oikawa, K. Fushimi, K. Shimizu, S. Nagata, P. Skeldon, G. E. Thompson  ELECTROCHIMICA ACTA  53-  (4)  1775  -1781  2007/12  [Refereed][Not invited]
     
    Porous anodic films, with pore size of similar to 10 nm, have been developed by anodizing of magnetron sputtered Ti-25 at. % Si alloy at constant formation voltages in glycerol electrolyte containing dibasic potassium phosphate at 433 K. The films, of amorphous structure, contain titanium and silicon species, as units of TiO2 and SiO2, throughout the film thicknesses, with negligible amounts of phosphorus species. The silicon is enriched in the film relative to the composition of the alloy, the level of enrichment suggesting that anion migration is increased in comparison with amorphous film growth at ambient temperature. In contrast to the behaviour of the alloy, essentially barrier films were formed on commercially pure titanium in the glycerol electrolyte, when a main anodic reaction was generation of oxygen, which was probably promoted by the development of anatase. (c) 2007 Elsevier Ltd. All rights reserved.
  • 桐生雅彦, 青木芳尚, 伏見公志, 金野英隆, 幅崎浩樹  炭素材料学会年会要旨集  34th-  370  -371  2007/11/28  [Not refereed][Not invited]
  • S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, H. Habazaki  SURFACE AND INTERFACE ANALYSIS  39-  (11)  860  -864  2007/11  [Refereed][Not invited]
     
    A tungsten tracer introduced into a sputtering-deposited aluminium substrate was employed to investigate pore development in anodic films formed at 3 mA cm(-2) in 0.25 M chromic acid electrolyte at 313 K. The anodized specimens were observed by transmission electron microscopy (TEM), with compositions of films determined by Rutherford backscattering spectroscopy (RBS). The anodic films were found to be similar in thickness to that of the aluminium layer consumed during anodizing and revealed the feathered pore morphology that is a characteristic of the electrolyte. The anodizing efficiency was similar to 45-48%, with tungsten tracer species, in addition to aluminium species, being lost to the electrolyte at the pore base. These findings, together with the relatively uniform distribution of tungsten species within the film, are consistent with field-assisted dissolution of the alumina playing a major role in the development of pores. The films contrast with those formed in phosphoric and sulphuric acid electrolytes, for which feathering of pores is absent, the tracer distribution is inverted and the film thickness exceeds that of the consumed metal, features indicative of the influence of material flow in pore development. Copyright (C) 2007 John Wiley & Sons, Ltd.
  • 長沼淳, 伏見公志, 安住和久, 幅崎浩樹, 金野英隆  材料と環境討論会講演集  54th-  207  -210  2007/10/15  [Not refereed][Not invited]
  • H. Habazaki, M. Kiriu, M. Hayashi, H. Konno  MATERIALS CHEMISTRY AND PHYSICS  105-  (2-3)  367  -372  2007/10  [Refereed][Not invited]
     
    Platelet structure carbon nanofilaments of similar to 30 nm in diameter have been prepared by heating a mixture of porous anodic alumina template and poly(vinyl)chloride (PVC) powders in an argon atmosphere, and the change in their structure and morphology with heat treatment temperature, ranging from 600 to 2800 degrees C, has been examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen gas adsorption measurements. The diameter of the carbon nanofilaments formed does not change with heat treatment temperature, being in agreement with the pore diameter of the template, while their length is reduced with the temperature. The platelet-type orientation of graphene layers is evident even at 600 degrees C with the layer structure further developing with increasing heat treatment temperature. The carbon nanofilaments formed at lower temperatures have micropores, while those formed at higher temperatures do not have porosity. Highly graphitized carbon nanofilaments have been obtained after heat treatment at 2800 degrees C, with another characteristic structural feature being presence of loops at the edge of graphene layers formed at 2800 degrees C. (c) 2007 Elsevier B.V. All rights reserved.
  • S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, H. Habazaki  SURFACE & COATINGS TECHNOLOGY  201-  (24)  9506  -9511  2007/10  [Refereed][Not invited]
     
    The study investigates the behaviour of tungsten species during anodizing of a metastable solid-solution Al-3.5 at.%W alloy at a current density of 5 mA cm(-2) in 0.4 M phosphoric acid at 293 K in order to elucidate the development of pores in anodic alumina. Quantitative measurements of film compositions, by ion beam analysis, have been employed to determine the loss of film species, with film morphologies examined by transmission electron microscopy. The findings indicate anodizing efficiencies, from the period of embryo cell formation to major pore growth.. in the range 58-74%. The reduced efficiency is due to loss of aluminium, species to the electrolyte. Notably, tungsten species are retained within the anodic films. The anodizing behaviour is consistent with cell and pore development due to flow of material in the barrier layer, under the influences of field-assisted plasticity and film growth stresses. The flow, in combination with the slow migration of tungsten species in the anodic alumina, leads to alumina cells with an outer tungsten-free region and an inner tungsten-containing region. (c) 2007 Elsevier B.V. All rights reserved.
  • S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, H. Habazaki  CORROSION SCIENCE  49-  (10)  3772  -3782  2007/10  [Refereed][Not invited]
     
    The generation of pores is investigated in anodic films formed at 5 mA cm(-2) on aluminium in 0.4 M sulphuric acid electrolyte at 293 K. The study follows the behaviour of a fine tungsten tracer layer, initially located in the aluminium, during anodizing. Significantly, the tungsten is incorporated into the anodic film with negligible loss of the tracer to the electrolyte. The findings indicate that pores develop primarily due to flow of film material in the barrier layer under the influences of the stresses of film growth. The flow of material from beneath pores toward the cell walls is accommodated by the increased thickness of the anodic film relative to that of the oxidized metal by a factor of about 1.35. (c) 2007 Elsevier Ltd. All rights reserved.
  • S. J. Garcia-Vergara, H. Habazaki, P. Skeldon, G. E. Thompson  NANOTECHNOLOGY  18-  (41)  415605  2007/10  [Refereed][Not invited]
     
    Porous anodic films on aluminium have attracted much recent attention with a view to the generation of templates with ordered nanoporosity. The present work addresses the mechanism of film formation and pore development, through examination of films formed in phosphoric acid, with focus on the influence of current density on anodizing efficiency. The findings are consistent with the development of porosity by flow of film material, rather than by film dissolution. Flow of the film material contributes to the film being much thicker than the oxidized aluminium. Notably, the thickness enhancement is promoted at higher rates of film growth, which lead to reduced losses of aluminium species to the electrolyte as the efficiency increases from similar to 0.67 to similar to 0.93 between current densities of 5 and 30 mA cm(-2). Accordingly, an increased amount of oxidized aluminium is available for film formation, such that the film thickness rises from similar to 1.38 to 1.86 times that of the oxidized aluminium.
  • 三浦吉幸, 伏見公志, 幅崎浩樹, 高沢祐之  表面技術協会講演大会講演要旨集  116th-  68  -69  2007/09/11  [Not refereed][Not invited]
  • 及川祐樹, 伏見公志, 幅崎浩樹  表面技術協会講演大会講演要旨集  116th-  72  -73  2007/09/11  [Not refereed][Not invited]
  • 伏見公志, 幅崎浩樹  表面技術協会講演大会講演要旨集  116th-  67  2007/09/11  [Not refereed][Not invited]
  • 藤井隆志, 伏見公志, 幅崎浩樹, 牧野猛, 小野昭二  表面技術協会講演大会講演要旨集  116th-  52  2007/09/11  [Not refereed][Not invited]
  • 山本隆登志, 伏見公志, 幅崎浩樹  表面技術協会講演大会講演要旨集  116th-  275  2007/09/11  [Not refereed][Not invited]
  • M. Tauseef Tanvir, K. Fushimi, K. Shimizu, S. Nagatac, P. Skeldon, G. E. Thompson, H. Habazaki  ELECTROCHIMICA ACTA  52-  (24)  6834  -6840  2007/08  [Refereed][Not invited]
     
    Amorphous anodic titania, stabilised by incorporation of silicon species, is shown to grow to high voltages on sputter-deposited, single-phase Ti-Si alloys during anodizing at a constant current density in ammonium pentaborate electrolyte. The films comprise two main layers, with silicon species confined to the inner layers. An amorphous-to-crystalline transition occurs at similar to 60V on the Ti-6 at.% Si alloy, while the transition is suppressed to voltages above 140 V on alloys with 12 and 26 at.% silicon. The crystalline oxide, nucleated at a depth of similar to 40% of the film thickness, is associated with the presence of a precursor of crystalline oxide in the pre-existing air-formed oxide. The modified structure of the air-formed oxide due to increased incorporation of silicon species suppresses the amorphous-to-crystalline transition until the onset of dielectric breakdown. The transport numbers of cations and anions during growth of the anodic oxides are independent of the concentration of silicon species in the inner layer, despite the marked change in the field strength. (c) 2007 Elsevier Ltd. All rights reserved.
  • F. Monfort, E. Matykina, A. Berkani, P. Skeldon, G. E. Thompson, H. Habazaki, K. Shimizu  SURFACE & COATINGS TECHNOLOGY  201-  (21)  8671  -8676  2007/08  [Refereed][Not invited]
     
    The mechanism of coating growth during sparking anodizing of aluminium is probed by use of an electrolyte containing both silicate and phosphate ions, with subsequent determination of the locations of silicon and phosphorus species through the coating thickness. Importantly, the main alumina-based layer of the coating contains incorporated silicon and phosphorus species of differing distributions. Phosphorus species are primarily found in a region next to the metal, representing roughly about 30% of the layer thickness. Silicon species are located mainly above this region to the layer surface. New coating material is added in discreet amounts associated with breakdown events, which provide short-circuit paths through the layer. The growth processes within the discharge region result in separation of the silicate- and phosphate-derived species, which may relate to their different mobilities, dependent upon factors such as charge, size and bonding with other species. Further, silicon-rich material is deposited at the surface of the alumina-based layer, which is often encountered in spark anodizing in silicate electrolyte. (c) 2006 Elsevier B.V All rights reserved.
  • H. Habazaki, T. Onodera, K. Fushimi, H. Konno, K. Toyotake  SURFACE & COATINGS TECHNOLOGY  201-  (21)  8730  -8737  2007/08  [Refereed][Not invited]
     
    Spark anodizing of a bcc solid solution Ti-15% V-3% Al-3% Cr-3% Sn alloy has been performed in an alkaline electrolyte containing aluminate and phosphate using dc-biased ac anodizing to form a wear-resistant coating on the alloy. The coating consists mainly of Al2TiO5, with rutile and gamma-Al2O3 being present as minor oxide phases. Depth profiles of the coating, examined by glow discharge optical emission spectroscopy, have revealed that aluminium species, highly enriched in the coating, distribute uniformly in the coating, while phosphorus species, incorporated from the electrolyte, are located mainly in the inner part of the coating near the coating/alloy interface. The location of the phosphorus species should be associated with the porous nature of the coating, allowing access of the electrolyte directly to the inner parts of the coating. The porosity of the coating is reduced by anodizing to high voltages. The marked improvement of the wear resistance by the coating has been demonstrated from a pin-on-disc wear test. (c) 2006 Elsevier B.V. All rights reserved.
  • Koji Fushimi, Takatoshi Yamamoto, Kazuhisa Azumi, Masahiro Seo, Hiroki Habazaki  ELECTROCHIMICA ACTA  52-  (24)  6901  -6910  2007/08  [Refereed][Not invited]
     
    During in situ micro-indentation of passive iron in pH 8.4 borate solution, a couple of anodic current peaks emerged; the first peak during loading and the second peak during unloading. The current transients, associated with rupture and repair of the passive film, were influenced by the indentation conditions. For instance, the current peak height, the cur-rent peak area and the time required for complete repassivation are strongly dependent on indentation rate. A numerical model was proposed to correlate the current transient during loading with mechanical deformation of the passive surface. The comparison between the current transient measured experimentally and that estimated from the load transient suggested that the ruptured area of passive film was about 10% of the surface area deformed by the contact with the indenter. (c) 2007 Published by Elsevier Ltd.
  • 藤井隆志, 伏見公志, 幅崎浩樹, 牧野猛, 小野昭二  日本化学会北海道支部研究発表会講演要旨集  2007-  145  2007/07/21  [Not refereed][Not invited]
  • 及川祐樹, 伏見公志, 幅崎浩樹  日本化学会北海道支部研究発表会講演要旨集  2007-  146  2007/07/21  [Not refereed][Not invited]
  • Takatoshi Yamamoto, Koji Fushimi, Masahiro Seo, Shiro Tsuri, Tetsuo Adachi, Hiroki Habazaki  ELECTROCHEMISTRY COMMUNICATIONS  9-  (7)  1672  -1676  2007/07  [Refereed][Not invited]
     
    Micro-indentation test was performed for passive iron surface in deaerated pH 8.4 borate solution to correlate the passive film breakdown with mechanical deformation of substrate. Loading and unloading of a conical micro-indenter to the passive surface were repeated 10 times at an identical position. Elastic-plastic deformation occurred during the first indentation, while elastic deformation is predominant during the second and following indentations. The anodic current appears at the commencement of the first loading, with the maximum current generated at the maximum load. A more obvious current peak appears when the indenter just lost the contact with the iron surface during the first unloading. The current peaks observed during the subsequent indentations decreased markedly compared with the first indentation. Thus, the passive film breakdown by elastic deformation of iron substrate is less significant compared with that by plastic deformation under the present conditions. There is a linear correlation between the electric charge required for repassivation of the ruptured passive film and the work for plastic deformation. (C) 2007 Elsevier B.V. All rights reserved.
  • H. Habazaki, K. Fushimi, K. Shimizu, P. Skeldon, G. E. Thompson  ELECTROCHEMISTRY COMMUNICATIONS  9-  (5)  1222  -1227  2007/05  [Refereed][Not invited]
     
    The rapid inward migration of fluoride ions in growing anodic titanium oxide under a high electric field has been elucidated by anodizing a Ti-12 at% silicon alloy, where film growth proceeds at nearly 100% efficiency in selected electrolytes. Further, incorporated silicon species in the anodic film are immobile, acting as marker species. The migration rate of fluoride ions is determined precisely by three-stage anodizing, consisting of initial anodic film formation at a constant current density to 50 V in ammonium pentaborate electrolyte, subsequent incorporation of fluoride ions by reanodizing to 55 V in ammonium fluoride electrolyte and, finally, anodizing again in ammonium pentaborate electrolyte at high current efficiency. The resultant films were analyzed by glow discharge optical emission spectroscopy to reveal the depth distribution of fluoride ions and the location of the silicon marker species. The fluoride ions migrate inward at twice the rate of O2- ions. Consequently, anodizing of titanium in fluoride-containing electrolytes develops a fluoride-rich layer that separates the alloy substrate from the anodic oxide, with eventual detachment of the film from the substrate. (c) 2007 Elsevier B.V. All rights reserved.
  • S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, H. Habazaki  THIN SOLID FILMS  515-  (13)  5418  -5423  2007/05  [Refereed][Not invited]
     
    The growth of porous anodic films at 60 V in an alkaline 0.13 M borax electrolyte at 333 K is examined using sputtering-deposited aluminium substrates, with a fine band of incorporated tungsten tracer. The findings reveal amorphous alumina films containing approximately conical major pores incorporating finer secondary pores, with film thicknesses similar to that of the oxidized aluminium. Further, the distribution of the tungsten tracer within the film is mainly consistent with its expected migration behaviour in anodic alumina. The results indicate that pore development under the present growth conditions is dominated by field-assisted dissolution of anodic alumina, with an efficiency of film growth of about 50%. The findings are in contrast with those of porous anodic films formed in phosphoric acid electrolyte, which are significantly thicker than the layer of oxidized metal. (C) 2007 Elsevier B.V. All rights reserved.
  • 山本隆登志, 伏見公志, 瀬尾眞浩, 幅崎浩樹, 釣之郎, 足達哲男  材料と環境講演集  2007-  369  -370  2007/04/25  [Not refereed][Not invited]
  • 伏見公志, 幅崎浩樹, 大谷良行, 兒島洋一  材料と環境講演集  2007-  455  -458  2007/04/25  [Not refereed][Not invited]
  • 山本俊佑, 伏見公志, 幅崎浩樹, 尾崎良太  材料と環境講演集  2007-  371  -372  2007/04/25  [Not refereed][Not invited]
  • SHIMIZU Kenichi, TACHIBANA Sigeaki, MITANI Tomoaki, HABAZAKI Hiroki  Microscopy  42-  (1)  45  -49  2007/03/30  [Not refereed][Not invited]
  • 及川祐樹, 伏見公志, 清水健一, 幅崎浩樹  電気化学会大会講演要旨集  74th-  420  2007/03/29  [Not refereed][Not invited]
  • Hidetaka Konno, Takahiro Morishita, Chuanyun Wan, Takashi Kasashima, Hiroki Habazaki, Michio Inagaki  CARBON  45-  (3)  477  -483  2007/03  [Refereed][Not invited]
     
    Two low molecular weight silicone compounds, a cyclic type having vinyl groups and a chain-type having Si-H bonds, a catalyst for curing, and a catalyst regulator were mixed. The mixture was impregnated into exfoliated graphite (EG) by sorption, and cured in air at 200 degrees C. By this process cross-linked silicone coatings were formed on graphite flakes. The composites of Si-C-O glass-like compounds and EG were synthesized by heat treatment of this precursor at 1000-1400 degrees C for 1 h in argon. The composites formed at 1000-1300 degrees C were amorphous by XRD and had practically the same chemical composition: Si 44-45, C 27-29, 0 25-26, H < 0.5, all in mass%. The Si-29 MAS-NMR spectra indicated that the compound formed at 1000 degrees C was mainly composed of siloxane bonds and amorphous silica, whereas in the compound formed at 1300 degrees C, Si-C bonds and amorphous silica were predominant. The insertion/extraction characteristics of lithium ions for the electrode prepared with composite:poly(vinylidene fluoride) = 90:10 mass%) were examined in 1 mol L-1 LiCIO4 solution of ethylene carbonate:diethyl carbonate = 50:50 vol%. High, 650-700 mA h g(-1), capacities and steady cycle performance at 50 mA g(-1) were achieved with the composites formed at 1250-1300 degrees C. Capacities of the composites formed at 1200 degrees C and lower were initially higher but decreased with increasing number of cycles. The composites formed at 1350 degrees C showed good cycle performance but the capacity was about 500 mA h g(-1) due to the formation of beta-SiC. Except for the first cycle, the capacity-potential characteristics were similar to those of hard carbons and the coulomb efficiency was 95-100%. For all the composites the capacity was larger than that of graphite (372 mA h g(-1)) in the range of 50-200 mA g(-1). Due to the large insertion capacity of the first cycle, the efficiency was low (60-70%) at first. By short-circuiting the working electrode to the lithium foil counter electrode for a certain period, the irreversible capacity of the first cycle was almost eliminated. It indicates that direct doping of lithium ions into composites is a promising way to increase the efficiency of the first cycle. (c) 2006 Elsevier Ltd. All rights reserved.
  • Koji Fushimi, Kirsten A. Lill, Hiroki Habazaki  ELECTROCHIMICA ACTA  52-  (12)  4246  -4253  2007/03  [Refereed][Not invited]
     
    Corrosion behavior of Fe-3 at.% Si alloy in 0.01 mold m(-3) HCl solution was investigated by using scanning electrochemical microscopy (SECM) as well as general electrochemistry. The rate of corrosion coupled with hydrogen evolution was initially 0.44 A m(-2) but decreased significantly with time. Localized hydrogen evolution on the specimen surface was probed by an SECM system in which a force sensor was mounted to determine the probe height from the specimen surface. SECM images revealed that hydrogen evolution took place heterogeneously on the specimen surface depending on crystallographic orientation of substrate single grains in the initial stage and then became relatively homogeneous. Finally, a heterogeneous hydrogen distribution corresponding to the appearance of localized corrosion sites was observed. (c) 2006 Elsevier Ltd. All rights reserved.
  • 瀬尾眞浩, 萩生真知子, 伏見公志, 幅崎浩樹, 千葉誠  表面技術協会講演大会講演要旨集  115th-  125  -126  2007/02/22  [Not refereed][Not invited]
  • 及川祐樹, 伏見公志, 幅崎浩樹  表面技術協会講演大会講演要旨集  115th-  168  2007/02/22  [Not refereed][Not invited]
  • 長沼淳, 伏見公志, 安住和久, 幅崎浩樹  表面技術協会講演大会講演要旨集  115th-  346  -347  2007/02/22  [Not refereed][Not invited]
  • 幅崎浩樹, 伏見公志, 清水健一  表面技術協会講演大会講演要旨集  115th-  169  2007/02/22  [Not refereed][Not invited]
  • 伏見公志, 中島美穂, 幅崎浩樹, 豊武孝太郎  表面技術協会講演大会講演要旨集  115th-  183  -184  2007/02/22  [Not refereed][Not invited]
  • F. Monfort, A. Berkani, E. Matykina, P. Skeldon, G. E. Thompson, H. Habazaki, K. Shimizu  CORROSION SCIENCE  49-  (2)  672  -693  2007/02  [Refereed][Not invited]
     
    Spark anodizing of aluminium at 5 A dm(-2) in sodium metasilicate/potassium hydroxide electrolytes is studied, with particular emphasis on the mechanism of coating growth, using transmission electron microscopy and surface analytical techniques, with coatings typically 10 gm, or more, thick. Two-layered coatings develop by deposition of an outer layer based on amorphous silica, associated with low levels of alkali-metal species, at the coating surface and growth of an inner, mainly alumina-based, layer, with an amorphous region next to the metal/coating interface. Formation of crystalline phases in the inner layer, mainly gamma-Al2O3, with some alpha-Al2O3 and occasional delta-Al2O, is assisted by local heating, and possibly also by ionic migration processes, arising from the rapid coating growth at sites of breakdown. Due to local access of electrolyte species in channels created by breakdown events, the silicon content in the inner coating-regions varies widely, ranging from negligible levels to about 10 at.%. Silica deposition at the coating surface and formation of Al2SiO5 and Al6Si2O13 phases is promoted by increased time of anodizing and concentration of metasilicate in the electrolyte. However, at sufficiently high concentration of metasilicate and pH, when more extreme voltage fluctuations accompany breakdown, the two-layered nature of coatings is replaced by a mixture of aluminium-rich and silicon-rich regions throughout the coating thickness. (c) 2006 Elsevier Ltd. All rights reserved.
  • H. Habazaki, T. Ogasawara, H. Konno, K. Shimizu, S. Nagata, P. Skeldon, G. E. Thompson  CORROSION SCIENCE  49-  (2)  580  -593  2007/02  [Refereed][Not invited]
     
    Influences of electrolyte, pre-thermal treatment and substrate composition have been examined to elucidate the mechanism of field crystallization of anodic niobia formed on magnetron-sputtered niobium. The field crystallization occurs during anodizing at 100 V in 0.1 mol dm(-3) ammonium pentaborate electrolyte at 333 K, with the crystalline oxide growing more rapidly than the amorphous oxide, resulting in petal-like defects. The nucleation of crystalline oxide is accelerated by pre-thermal treatment of the niobium at 523 K in air, while vacuum treatment hinders nucleation. Notably field-crystallization is also absent in 0.1 mol dm(-3) phosphoric acid electrolyte or when anodizing Nb-10at.%N and Nb-29at.%W alloys in the ammonium pentaborate electrolyte. The behaviour is explained by the role of the air-formed oxide in providing nucleation sites for field crystallization at about 25% of the thickness of the subsequently formed anodic film, the location being due to the growth mechanism of the anodic oxide and the nature of crystal nuclei. Incorporation of tungsten, nitrogen and phosphorus species to this depth suppresses the field crystallization. However, boron species occupy a relatively shallow layer and are unable to affect the nucleation sites. (c) 2006 Elsevier Ltd. All rights reserved.
  • 小笠原健, 伏見公志, 瀬尾眞浩, 幅崎浩樹, 松岡良輔, 泉知夫  三学協会北海道支部研究発表会講演要旨集  2007-  28  2007  [Not refereed][Not invited]
  • 植村元宣, 山本隆登志, 伏見公志, 釣之郎, 足達哲男, 幅崎浩樹  三学協会北海道支部研究発表会講演要旨集  2007-  18  2007  [Not refereed][Not invited]
  • 中島美穂, 伏見公志, 豊武孝一郎, 幅崎浩樹  三学協会北海道支部研究発表会講演要旨集  2007-  21  2007  [Not refereed][Not invited]
  • 長沼淳, 伏見公志, 安住和久, 幅崎浩樹  三学協会北海道支部研究発表会講演要旨集  2007-  6  2007  [Not refereed][Not invited]
  • 三浦吉幸, 伏見公志, 幅崎浩樹  三学協会北海道支部研究発表会講演要旨集  2007-  15  2007  [Not refereed][Not invited]
  • 清水 健一, 三谷 智明, 幅崎 浩樹  工業材料  55-  (1)  90  -95  2007/01  [Not refereed][Not invited]
  • Akihiro Sudoh, Hidetaka Konno, Hiroki Habazaki, Hajime Kiyono  TANSO  2007-  (226)  8  -12  2007  [Not refereed][Not invited]
  • Hidetaka Konno, Shu'ya Sato, Ken'ichi Kimura, Hiroki Habazaki  JOURNAL OF THE EUROPEAN CERAMIC SOCIETY  27-  (1)  405  -412  2007  [Refereed][Not invited]
     
    A process to form different shapes of beta-SiC was developed using precursors composed of silicone compounds and urethane foam. Two types of low molecular weight silicone. a Pt catalyst for curing, and a catalyst regulator were impregnated into urethane foam chips with different porosities and bulk densities, and cured at 200 degrees C for 1 h in air. Formed precursors were converted into beta-SiC by pyrolysis at 1600 degrees C for 1-5 h in argon. Depending on the type of urethane foam, beta-SiC balloons and beta-SiC blocks with high porosities and low bulk densities were obtained. In addition, fine particles of beta-SiC smaller than 100 nm were also obtained by crushing the blocks. For a disk formed by 5 h pyrolysis at 1500 degrees C, N-2 gas permeability, electric conductivity, and oxidation resistance at 900 degrees C in air were measured. The results indicated that the disk may be used as a gas permeable heater. The process is simple, and the materials for this process are not hazardous and commercially available at low cost. (c) 2006 Elsevier Ltd. All rights reserved.
  • K. Hashimoto, K. Asami, A. Kawashima, H. Habazaki, E. Akiyama  CORROSION SCIENCE  49-  (1)  42  -52  2007/01  [Refereed][Not invited]
     
    Passivity of alloys containing corrosion-resistant elements were reviewed. Chromium and valve metals except aluminum form stable oxyhydroxide films even in aggressive hydrochloric acids. Molybdenum forms a passive Moo, film in the active region of stainless steels and hence decreases the active dissolution current. In the passive region of transition metals and valve metals, molybdenum is generally in the transpassive state and dissolved. However, if the outer oxyhydroxide film is stable the inner MoO2 film is protected by the outer oxyhydroxide film and the MoO2 film acts as the effective barrier against diffusion of matters through the film. Thus the passive current density of 30Cr-2Mo ferritic stainless steel is more than two orders of magnitude lower than that of 30Cr steel without molybdenum in 1M HCl. (c) 2006 Elsevier Ltd. All rights reserved.
  • 桐生雅彦, 幅崎浩樹, 伏見公志, 金野英隆  炭素材料学会年会要旨集  33rd-  266  -267  2006/12/01  [Not refereed][Not invited]
  • HABAZAKI Hiroki  The Journal of the Surface Finishing Society of Japan  57-  (11)  773  -775  2006/11/01
  • S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, H. Habazaki  ELECTROCHIMICA ACTA  52-  (2)  681  -687  2006/10  [Refereed][Not invited]
     
    The development of pores in a classical porous anodic film formed on aluminium in phosphoric acid solution is investigated. The study employs a tungsten tracer layer that is incorporated into the anodic film from the aluminium substrate, followed by detection of the tracer by transmission electron microscopy and Rutherford backscattering spectroscopy. Distortions of the tungsten layer on entry into the film and retention of tungsten species in the film are compatible with porosity arising mainly from flow of anodic oxide beneath the pore bases towards the cell walls. The behaviour is contrary to expectations of a dissolution model of pore formation. (c) 2006 Elsevier Ltd. All rights reserved.
  • 山本隆登志, 伏見公志, 幅崎浩樹, 瀬尾眞浩, 釣之郎, 足達哲男  表面技術協会講演大会講演要旨集  114th-  227  -228  2006/09/25  [Not refereed][Not invited]
  • 長沼淳, 伏見公志, 安住和久, 幅崎浩樹  表面技術協会講演大会講演要旨集  114th-  240  -241  2006/09/25  [Not refereed][Not invited]
  • 桐生雅彦, 幅崎浩樹, 伏見公志, 金野英隆  表面技術協会講演大会講演要旨集  114th-  298  -299  2006/09/25  [Not refereed][Not invited]
  • Y. Liu, M. A. Arenas, P. Skeldon, G. E. Thompson, H. Habazaki, K. Shimizu, P. Bailey, T. C. Q. Noakes  CORROSION SCIENCE  48-  (8)  1874  -1884  2006/08  [Refereed][Not invited]
     
    A mechanism of formation of copper nanoparticles is proposed for alkaline etching of a sputtering-deposited Al-30 at.%Cu alloy, simulating the equilibrium 0 phase of 2000 series aluminium alloys. Their formation involves enrichment of copper in the alloy beneath a thin alumina film, clustering of copper atoms, and occlusion of the clusters, due to growth of alumina around the clusters, to form nanoparticles. The proposed mechanism is supported by medium energy ion scattering, Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy of the alloy following immersion in the sodium hydroxide solution, which disclose the enrichment of copper and the generation of the nanoparticles in the etching product of hydrated alumina. The generation of the nanoparticles is dependent upon the enrichment of copper in the alloy in a layer of a few nanometres thickness, with no requirement for bulk de-alloying of the alloy. (c) 2005 Elsevier Ltd. All rights reserved.
  • H. Habazaki, M. Kiriu, H. Konno  ELECTROCHEMISTRY COMMUNICATIONS  8-  (8)  1275  -1279  2006/08  [Refereed][Not invited]
     
    Carbon nanofilaments (CNFs) with platelet structure have been prepared by liquid phase carbonization using porous anodic alumina template, and their lithium ion insertion/extraction properties have been examined as a function of heat treatment temperature and filament diameter. The CNFs heat-treated at 1000 degrees C reveal higher capacitance and higher rate capability compared with those heat-treated at higher temperatures. Further, it is found that higher reversible capacity is obtained for the CNFs with reduced diameter. The reversible capacity of highly graphitized CNFs formed at 2800 degrees C is less than 200 mA h g(-1) at a current density of 50 mA g(-1), being far lower than the theoretical capacity (372 mA h g(-1)) of graphite. A probable reason is the presence of loop at the edge of graphene layers. (c) 2006 Elsevier B.V. All rights reserved.
  • MORISHITA Takahiro, SUZUKI Rieko, TSUMURA Tomoki, HABAZAKI Hiroki, INAGAKI Michio  Tanso  0-  (223)  220  -226  2006/06/15  [Not refereed][Not invited]
     
    Porous carbons with high surface area were successfully prepared from thermoplastic precursors, such as poly (vinyl alcohol) (PVA), by the carbonization of mixtures with MgO precursor at 900°C in inert atmosphere. MgO in the carbonization products was dissolved out by using a diluted acid, either sulfuric or acetic acid. The carbon precursors with MgO precursors (reagent grade magnesium acetate and citrate) were mixed either in powder (powder mixing) or in aqueous solution (solution mixing). Pore structure of the resultant carbons depended strongly on the mixing method. The BET surface area of the carbons obtained through solution mixing could reach to very high value, such as 2000 m2/g, even though any activation process was not applied. The carbons prepared through solution mixing method were rich in mesopores. By changing the size of MgO particles formed by pyrolysis of MgO precursor, the size of mosopores could be controlled. It was experimentally shown that substrate MgO was easily recycled.
  • E. Matykina, M. Montuori, J. Gough, F. Monfort, A. Berkani, P. Skeldon, G. E. Thompson, H. Habazaki  TRANSACTIONS OF THE INSTITUTE OF METAL FINISHING  84-  (3)  125  -133  2006/05  [Refereed][Not invited]
     
    Spark anodising of titanium enables fabrication of coatings with potential biocompatibility. In the present study, coatings were produced in electrolytes containing various amounts of CaHPO(4), Ca(H(2)PO(4))(2), Na(6)P(6)O(18) and Ca(CH(3)COO)(2). The findings disclose formation of coatings with compositions, morphologies and structures dependent upon the growth conditions. Calcium and phosphorus species are distributed throughout most of the coating thickness, with typical Ca/P atomic ratios of similar to 0.45 and (Ca+P)/Ti atomic ratios in the range 1.0-2.6 in the near surface regions. Calcium contents in particular reduced towards the metal. Dissolution behaviour in physiological solution was investigated by potentiodynamic polarisation measurements and immersion tests, the latter indicating titanium loss rates of similar to 0.3 mu g cm(-2) day(-1). Preliminary adhesion studies using primary human osteoblast cells revealed favourable cell responses to the anodic coatings. Further, the deposition of hydroxyapatite by cathodic deposition in selected electrolytes indicates scope for additional tailoring of coating surfaces. More limited studies of Ti-6Al-4V alloy demonstrated coating formation broadly similar to that on titanium, but with incorporation of aluminium and vanadium species and increased loss rates of titanium, similar to 4 mu g cm(-2) day(-1), in immersion tests.
  • Y. Liu, M. A. Arenas, P. Skeldon, G. E. Thompson, P. Bailey, T. C. Q. Noakes, H. Habazaki, K. Shimizu  CORROSION SCIENCE  48-  (5)  1225  -1248  2006/05  [Refereed][Not invited]
     
    The anodic behaviour of sputtering-deposited Al-20at%Mg-20at.%Cu alloy is investigated during anodizing and potentiodynamic polarization treatments using transmission electron microscopy, X-ray photoelectron spectroscopy and medium energy ion scattering. The composition of the alloy is close to that of the S-phase in 2024 aluminium alloy. The anodizing behaviour in both 0.1 M ammonium pentaborate and 0.1 M sodium hydroxide electrolytes follows the behaviour of more dilute, solid-solution, aluminium alloys, with enrichment of copper developing in the alloy during the growth of an alumina-based initial oxide containing incorporated magnesium species. Oxygen gas is generated following sufficient enrichment of copper for its oxidation to proceed and hence, for copper species to enter the oxide film. The generation of oxygen gas causes extensive damage to the film, which limits the voltage to relatively low values. Potentiodynamic polarization in 0.1 M sodium hydroxide electrolyte revealed mainly passive behaviour following an initial period of corrosion during which the passive film is developed. In this initial period, copper enriches in the alloy, beneath an oxide film containing aluminium and magnesium species. The magnesium species migrate faster through the film than the aluminium species and form a surface layer of MgO/Mg(OH)(2), which protects against losses of aluminium species to solution and permits the establishment of the passive film. The steady open-circuit potential of the passivated alloy in the hydroxide solution is about -550 mV (SCE), compared with about -1940 mV (SCE) for aluminium. (c) 2005 Elsevier Ltd. All rights reserved.
  • 中島美穂, 伏見公志, 幅崎浩樹, 豊武孝太郎  電気化学秋季大会講演要旨集  2006-  218  2006  [Not refereed][Not invited]
  • 小笠原健, 幅崎浩樹, 伏見公志, 金野英隆, 清水健一, 永田晋二, 泉知夫  電気化学秋季大会講演要旨集  2006-  334  2006  [Not refereed][Not invited]
  • SHIMIZU Kenichi, MITANI Tomoaki, TACHIBANA Sigeaki, HABAZAKI Hiroki  J. Japan Inst. Light Metals  56-  (8)  454  -458  2006  [Not refereed][Not invited]
  • M Yamasaki, H Habazaki, K Asami, K Izumiya, K Hashimoto  CATALYSIS COMMUNICATIONS  7-  (1)  24  -28  2006/01  [Refereed][Not invited]
     
    In zirconia-supported nickel catalysts, the influence of the ZrO2 phase on the catalytic activity for CO2 methanation has been investigated by TPD. and TPR measurements. Ni/ZrO2 catalysts with various amounts of the tetragonal ZrO2 polymorph were prepared from amorphous Ni-Zr alloys by an oxidation-reduction treatment. The fraction of tetragonal ZrO2 in the Ni/ZrO2 catalysts increased with increasing nickel content of the amorphous alloy precursors. The methanation activity of Ni/ZrO2 was strongly influenced by the ZrO2 phase change. The tetragonal zirconia-supported nickel catalysts showed a higher turnover frequency for the methanation reaction and a greater CO2 adsorption than the monoclinic zirconia-supported nickel catalysts. (c) 2005 Elsevier B.V. All rights reserved.
  • A Suleiman, Y Liu, T Hashimoto, P Skeldon, GE Thompson, MJ Graham, T Quance, H Habazaki, K Shimizu, P Bailey, TCQ Noakes  CORROSION SCIENCE  48-  (1)  126  -136  2006/01  [Refereed][Not invited]
     
    The anodic oxidation of InAlAs is investigated by transmission electron microscopy, Rutherford backscattering spectroscopy and medium energy ion scattering in order to elucidate the mechanism of oxide growth. For this purpose, anodizing was carried out at 5 mA cm(-2) in 0.1 M sodium tungstate and 0.1 M ammonium pentaborate electrolytes at 293 K, which results in relatively efficient film growth over an initial voltage increment of about 70 V. In this period, an amorphous oxide develops with a formation ratio of 2.0 +/- 0.2 nm V-1. The film consists mainly of an outer layer of In2O3 and an inner layer of units of In2O3, Al2O3 and As2O3, the former representing about 14% of the film. There is suggestion of a fine, intermediate layer containing units of In2O3 and Al2O3 only. The layering correlates with the bond energies of the cation and oxygen species in the oxide and hence their relative migration rates. Further, for films formed in tungstate electrolyte, tungsten species are incorporated into the outer 40% of the film. Bubbles of oxygen gas are present in the film, probably developed within the In2O3 layer. At higher voltages, the film undergoes breakdown, with resulting major changes in the film morphology. (C) 2005 Elsevier Ltd. All rights reserved.
  • Konno Hidetaka, Abe Daisuke, Habazaki Hiroki  TANSO  2006-  (221)  8  -13  2006  [Not refereed][Not invited]
     
    Different metal alkoxides were impregnated into exfoliated graphite (EG) by sorption and hydrolyzed with steam. Thus formed precursors were pyrolyzed at 1500-1700°C for 1-10h in argon to form single- and multi-component carbides, such as ZrC, TiC, (Ti, Zr) C solid solutions, TiC-ZrC composites, and TiC-Fe composites. In this process, hydrolyzed metal alkoxides were converted mainly to oxides and/or oxyhydroxides on the surface of graphite sheet composing EG, and eventually they are reduced to carbide or metal by graphite carbon at elevated temperatures. The small reaction spaces in EG produce fine metal carbide particles only by the pyrolysis. The process is simple and low cost, and possible to be developed to synthesize other carbides and composites.
  • H Habazaki, T Ogasawara, H Konno, K Shimizu, S Nagata, K Asami, K Takayama, P Skeldon, GE Thompson  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  153-  (5)  B173  -B177  2006  [Refereed][Not invited]
     
    Solid-solution Nb-O films containing up to 50 atom % oxygen, prepared by magnetron sputtering, were used to investigate the influence of the oxygen on field crystallization during anodizing at 100 V in 0.1 mol dm(-3) ammonium pentaborate electrolyte at 333 K. The findings reveal that field crystallization is hindered dramatically by addition of 20 atom % oxygen to the substrate, while no crystallization occurs for a Nb-50 atom % O substrate. Prior thermal treatment accelerates field crystallization of niobium, but not the Nb-50 atom % O substrate. The thermal treatment is considered to promote generation of precursor sites for crystal nucleation. However, sufficient oxygen in the substrate may restrict precursor development and/or reduce the compressive stresses in the amorphous anodic niobia that can facilitate crystal growth. (c) 2006 The Electrochemical Society.
  • HABAZAKI Hiroki, FUSHIMI Koji, KONNO Hidetaka, SHIMIZU Kenn-ichi, ASAMI Katsuhiko, SKELDON P., THOMPSON G. E.  Jitsumu Hyomen Gijutsu  57-  (9)  676  -678  2006  [Not refereed][Not invited]
  • S. Fujimoto, B. MacDougall, H. Habazaki, E. Akiyama  ECS Transactions  1-  (4)  2005/12/01  [Not refereed][Not invited]
  • 幅崎 浩樹  工業材料  53-  (7)  1  -4  2005/07  [Not refereed][Not invited]
  • Zhou, X, GE Thompson, P Skeldon, K Shimizu, H Habazaki, GC Wood  CORROSION SCIENCE  47-  (5)  1299  -1306  2005/05  [Not refereed][Not invited]
     
    During anodising of Al-Cu alloys, copper species are incorporated into the anodic alumina film, where they migrate outward faster than Al3+ ions. In the present study of an Al-lat.% Cu alloy, the valence state of the incorporated copper species was investigated by X-ray photoelectron spectroscopy, revealing the presence of Cu2+ ions within the amorphous alumina film. However, extended X-ray irradiation led to reduction of units of CuO to Cu2O, probably due mainly to interactions with electrons from the X-ray window of the instrument and photoelectrons from the specimen. The XPS analysis employed films formed on thin sputtering-deposited alloy/electropolished aluminium specimens. Such an approach enables sufficient concentrations of copper species to be developed in the anodic film for their ready detection. (c) 2004 Elsevier Ltd. All rights reserved.
  • 幅崎 浩樹  表面技術  56-  (10)  604  -606  2005  [Not refereed][Not invited]
  • H. Habazaki, T. Ogasawara, H. Konno, K. Shimizu, K. Asami, S. Nagata, K. Takayama, P. Skeldon, G. E. Thompson  ECS Transactions  1-  (4)  343  -349  2005  [Not refereed][Not invited]
     
    Solid-solution Nb-O films, containing up to 50 at% oxygen, prepared by magnetron sputtering were used to investigate the influence of the oxygen on field crystallization during anodizing at 100 V in 0.1 mol dm-3 ammonium pentaborate electrolyte at 333 K. The findings reveal that field crystallization is hindered dramatically by addition of 20 at% oxygen to the substrate, while no crystallization occurs for an Nb-50 at% O substrate. Prior thermal treatment accelerates field crystallization of niobium, but not of the Nb-50 at% O substrate. The thermal treatment is considered to promote generation of pre-cursor sites for crystal nucleation. However, sufficient oxygen in the substrate may restrict pre-cursor development and/or reduce the compressive stresses in the amorphous anodic niobia that can facilitate crystal growth. copyright The Electrochemical Society.
  • Liu, Y., Arenas, A.M., Garcia-Vergara, S.G., Skeldon, P., Thompson, G.E., Shimizu, K. and Habazaki, H.: "Ageing effects in the growth of chromate conversion coatings on aluminium", Corros. Sci., 47: 145-150 (2005)*
    2005  [Not refereed][Not invited]
  • Habazaki, H., Ogasawara, T., Konno, H., Shimizu, K., Asami, K., Saito, K., Nagata, S., Skeldon, P. and Thompson, G.E.: "Growth of anodic oxide films on oxygen-containing niobium", Electrochim. Acta, 50: 5334-5339 (2005)*
    2005  [Not refereed][Not invited]
  • Habazaki, H., Shimizu, K., Nagata, S., Asami, K., Takayama, K., Oda, Y., Skeldon, P. and Thompson, G.E.: "Inter-relationship between structure and dielectric properties of crystalline anodic zirconia", Thin Solid Films, 479: 144-151 (2005)*
    2005  [Not refereed][Not invited]
  • Konno, H., Kinomura, T., Habazaki, H. and Aramata, M.: "Formation of oxidation resistant graphite flakes by ultrathin silicone coating", Surf. Coat. Technol., 194: 24-30 (2005)*
    2005  [Not refereed][Not invited]
  • T Kuranishi, H Habazaki, H Konno  SURFACE & COATINGS TECHNOLOGY  200-  (7)  2438  -2444  2005  [Not refereed][Not invited]
     
    Diffusion barrier layers of anodic alumina, introduced between an oxidation-resistant Al-Nb-Cr alloy and gamma-TiAl substrate, have been evaluated using scanning electron microscopy and electron probe microanalysis. Diffusion of titanium to the Al-Nb-Cr coating is obvious when the Al-Nb-Cr alloy coated directly on the TiAl substrate is oxidized at 900 degrees C for 168 h. The anodic alumina layer has been introduced by sputter-depositing aluminum and subsequent anodizing of the aluminum layer at a constant current density in 0.01 mol dm(-3) ammonium pentaborate electrolyte at 298 K. Then, the Al-Nb-Cr alloy is further sputter-deposited on the anodized specimens. It is clearly demonstrated that the thin anodic alumina layer, less than 500 nm thick, suppresses effectively the inter-diffusion between the oxidation-resistant alloy coating and the TiAl substrate, particularly when a thin aluminum layer is remained beneath the anodic alumina. Although microcracks are generated and the substrate is oxidized through the cracked regions for the coatings that contain the metallic aluminum layer, the oxidation of the substrate through the cracks is prevented by pre-oxidation treatment at 800 degrees C. (c) 2004 Elsevier B.V. All rights reserved.
  • Habazaki, H., Uozumi, M., Konno, H., Shimizu, K., Nagata, S., Takayama, K., Oda, Y., Skeldon, P. and Thompson, G.E.: "Influence of film composition on the structure and dielectric properties of anodic films on Ti-W alloys", J. Electrochem. Soc., 152: B・・・
    2005  [Not refereed][Not invited]
     
    Habazaki, H., Uozumi, M., Konno, H., Shimizu, K., Nagata, S., Takayama, K., Oda, Y., Skeldon, P. and Thompson, G.E.: "Influence of film composition on the structure and dielectric properties of anodic films on Ti-W alloys", J. Electrochem. Soc., 152: B263-B270 (2005)*
  • Liu, Y., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Chromate conversion coatings on aluminium-copper alloys", Corros. Sci., 47: 341-354 (2005)*
    2005  [Not refereed][Not invited]
  • Lu, Q., Hashimoto, T., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Nanoporous anodic niobium oxide formed in phosphate/glycerol electrolyte", Electrochem. Solid-State Lett., 8: B17-B20 (2005)*
    2005  [Not refereed][Not invited]
  • Lu, Q., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Composition and density of non-thickness-limited anodic films on aluminium and tantalum", Thin Solid Films, 471: 118-122 (2005)*
    2005  [Not refereed][Not invited]
  • Monfort, F., Berkani, A., Matykina, E., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "A tracer study of oxide growth during spark anodizing of aluminum", J. Electrochem. Soc., 152: C382-C387 (2005)*
    2005  [Not refereed][Not invited]
  • H Konno, T Morishita, S Sato, H Habazaki, M Inagaki  CARBON  43-  (5)  1111  -1114  2005  [Not refereed][Not invited]
  • Habazaki, H., Hayashi, M., Konno, H. and Inagaki, M.: "Synthesis of nano-carbon materials using a porous alumina template formed by anodizing of etched aluminum foil", J. Surf. Finish. Soc. Jpn., 56: 352-353 (2005)*
    2005  [Not refereed][Not invited]
  • Arenas, M.A., Iglesias-Rubianes, L., Liu, Y., Skeldon, P., Thompson, G.E., Habazaki, H., Shimizu, K., Bailey, P. and Noakes, T.C.Q.: "Behaviour of zinc in electropolished and etched Al-Zn alloys and effect on corrosion potential", Corros. Sci., 47: 232・・・
    2005  [Not refereed][Not invited]
     
    Arenas, M.A., Iglesias-Rubianes, L., Liu, Y., Skeldon, P., Thompson, G.E., Habazaki, H., Shimizu, K., Bailey, P. and Noakes, T.C.Q.: "Behaviour of zinc in electropolished and etched Al-Zn alloys and effect on corrosion potential", Corros. Sci., 47: 2321-2331 (2005)*
  • Konno, H., Matsuura, R., Kiyono, H., Sudoh, A., Habazaki, H. and Inagaki, M.: "Formation and characterization of carbon micro-spheres doped with boron and nitrogen", Tanso, 219: 221-225 (2005)*
    2005  [Not refereed][Not invited]
  • K Shimzu, H Fujitani, H Habazaki, P Skeldon, GE Thompson  CORROSION SCIENCE  46-  (10)  2549  -2561  2004/10  [Not refereed][Not invited]
     
    The potential of low-voltage, high-resolution scanning and scanning transmission electron microscopy (SEM/STEM) for morphological characterization of various surface insulating films on aluminium and its alloys has been assessed by examination of porous anodic films, barrier anodic films and corrosion product layers. The characterization shows clearly the value of the approaches, particularly the ability to image directly fine details of appropriately-prepared aluminium surfaces that have usually required examination by transmission electron microscopy (TEM). Such ready characterization assists mechanistic understanding of the contributions of the macroscopic surface and flaws or second phase to the filming and corrosion processes. Further, the approaches are applicable to other materials where such understanding was limited by the sample preparation routes available for TEM. (C) 2004 Elsevier Ltd. All rights reserved.
  • 清水 健一, 幅崎 浩樹, Gijbels Renaat  工業材料  52-  (9)  97  -101  2004/09  [Not refereed][Not invited]
  • 清水 健一, 幅崎 浩樹, Wirth Thomas  工業材料  52-  (8)  72  -75  2004/08  [Not refereed][Not invited]
  • HASHIMOTO Koji, KUMAGAI Naokazu, IZUMIYA Koichi, MEGURO Shinsaku, ASAMI Katsuhiko, HABAZAKI Hiroki, YAMASAKI Michiaki  Materia Japan  43-  (4)  318  -325  2004/04/20  [Not refereed][Not invited]
  • HABAZAKI Hiroki  The Journal of the Surface Finishing Society of Japan  55-  (1)  39  -41  2004/01/01
  • Liu, Y., Arenas, A.M., Garcia-Vergara, S.G., Skeldon, P., Thompson, G.E., Shimizu, K. and Habazaki, H.: "Ageing effects in the growth of chromate conversion coatings on aluminium", Corrosion Science, 47: 145-150 (2004)*
    2004  [Not refereed][Not invited]
  • Konno, H., Sato, S.y., Habazaki, H. and Inagaki, M.: "Formation of platelet structure carbon nanofilaments by a template method", Carbon, 42: 2756-2759 (2004)*
    2004  [Not refereed][Not invited]
  • H Konno, T Kinomura, H Habazaki, M Aramata  CARBON  42-  (4)  737  -744  2004  [Not refereed][Not invited]
     
    Utilizing micro-spaces of exfoliated graphite (EG), a process to synthesize fine beta-SiC particles was developed. Two types of low molecular weight silicone and a catalyst were impregnated into EG by sorption, and then heated in air to cure the compounds. Formed precursors were black flakes of a few millimeters in diameter. Only by the heat treatment of precursors at 1500 degreesC for 5 h or at 1550-1600 degreesC for 1 h in Ar, beta-SiC of a few tens to hundreds nanometers in size was obtained with the yield around 40 mass%. In the present process, EG play two important roles; one is as reaction spaces and the other is as a reductant that functions at elevated temperatures. Initially the cured silicone is coating the graphite sheets of EG as thin films of less than 1 mum, and above 1300 degreesC they start to decompose and form small particles of a few tens to 100 nm in diameter on the graphite sheets. These intermediate particles are composed of the Si-C-O composites and SiO2 and they spontaneously decompose to beta-SiC from around 1400 degreesC, and between 1400 and 1500 degreesC the reduction of remaining Si-C-O intermediates by graphite sheets occur and form well-crystallized fine beta-SiC particles. The process is simple and raw materials are not expensive so that it is promising for industrial applications. (C) 2004 Elsevier Ltd. All rights reserved.
  • Abulsain, M., Berkani, A., Bonilla, F.A., Liu, Y., Arenas, M.A., Skeldon, P., Thompson, G.E., Bailey, P., Noakes, T.C.Q., Shimizu, K. and Habazaki, H.: "Anodic oxidation of Mg-Cu and Mg-Zn alloys", Electrochimica Acta, 49: 899-904 (2004)*
    2004  [Not refereed][Not invited]
  • Aoki, Y., Habazaki, H. and Konno, H.: "Reducing gas sensing based on the redox interconversion of neodymium (III) chromate(V)", Chemistry Letters, 33: 992-993 (2004)*
    2004  [Not refereed][Not invited]
  • Garcia-Vergara, S., Colin, F., Skeldon, P., Thompson, G.E., Bailey, P., Noakes, T.C.Q., Habazaki, H. and Shimizu, K.: "Effect of Copper Enrichment on the Electrochemical Potential of Binary Al-Cu Alloys", Journal of the Electrochemical Society, 151: B1・・・
    2004  [Not refereed][Not invited]
     
    Garcia-Vergara, S., Colin, F., Skeldon, P., Thompson, G.E., Bailey, P., Noakes, T.C.Q., Habazaki, H. and Shimizu, K.: "Effect of Copper Enrichment on the Electrochemical Potential of Binary Al-Cu Alloys", Journal of the Electrochemical Society, 151: B16-B21 (2004)*
  • Habazaki, H., Konno, H., Shimizu, K., Nagata, S., Skeldon, P. and Thompson, G.E.: "Incorporation of transition metal ions and oxygen generation during anodizing of aluminum alloys", Corrosion Science, 46: 2041-2053 (2004)*
    2004  [Not refereed][Not invited]
  • Konno Hidetaka, Takahashi Yukihiro, Habazaki Hiroki  TANSO  214-  (214)  191  -193  2004  [Not refereed][Not invited]
     
    An organic solution of tris (acetylacetonato) iron (III) was impregnated by sorption into exfoliated graphite and dried at 180°C in air. By 1h treatment of this precursor at 900-1200°C in Ar (heating rate to each temperature: 400Kh-1), iron/graphite composites containing 33mass% Fe were obtained. In these composites fine α-Fe particles of several tens to hundreds nanometers were uniformly dispersed, though the surface of some particles may be oxidized by exposure to air. For the 1000°C product, magnetization assigned for iron was 154emu g-1, and the coercive force, Hc, 420Oe.
  • Shimizu, K., Payling, R., Habazaki, H., Skeldon, P. and Thompson, G.E.: "Rf-GDOES depth profiling analysis of a monolayer of thiourea adsorbed on copper", Journal of Analytical Atomic Spectrometry, 19: 692-695 (2004)*
    2004  [Not refereed][Not invited]
  • Lu, Q., Skeldon, P., Thompson, G.E., Masheder, D., Habazaki, H. and Shimizu, K.: "Transport numbers of metal and oxygen species in anodic tantala", Corrosion Science, 46: 2817-2824 (2004)*
    2004  [Not refereed][Not invited]
  • Lu, Q., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Composition and density of non-thickness-limited anodic films on aluminium and tantalum", Thin Solid Films, 471: 118-122 (2004)*
    2004  [Not refereed][Not invited]
  • Liu, Y., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Chromate conversion coatings on aluminium-copper alloys", Corrosion Science, 47: 341-354 (2004)*
    2004  [Not refereed][Not invited]
  • Liu, Y., Arenas, A.M., Garcia-Vergara, S.G., Skeldon, P., Thompson, G.E., Shimizu, K. and Habazaki, H.: "Ageing effects in the growth of chromate conversion coatings on aluminum", Corrosion Science, 47: 145-150 (2004)*
    2004  [Not refereed][Not invited]
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, H Habazaki, K Shimizu  CORROSION SCIENCE  45-  (12)  2905  -2913  2003/12  [Not refereed][Not invited]
     
    The ionic transport numbers in barrier anodic films, formed on an Al-5.7at.%W alloy in 0.1 M sodium tungstate electrolyte at 293 K, have been measured for current densities from 0.1 to 1000 mA cm(-2). For this purpose, a xenon marker was ion implanted with a fluence of 1.5 x 10(15) ions cm(-2) into a film formed to 10 V on the alloy, which was then further anodized to 150 V. The position of the marker layer in the final film was determined by transmission electron microscopy and Rutherford backscattering spectroscopy. The cation transport number was similar to0.38, with no dependence upon current density to an accuracy of similar to10%. (C) 2003 Elsevier Ltd. All rights reserved.
  • HABAZAKI Hiroki  材料と環境 : zairyo-to-kankyo  52-  (11)  586  -587  2003/11/15  [Not refereed][Not invited]
  • S Mato, G Alcala, P Skeldon, GE Thompson, D Masheder, H Habazaki, K Shimizu  CORROSION SCIENCE  45-  (8)  1779  -1792  2003/08  [Not refereed][Not invited]
     
    Strikingly different morphologies of amorphous anodic films on a Mg/40 at.%Ta alloy are shown to result from single-stage and sequential anodizing procedures. The alloy, prepared by magnetron sputtering, was anodized galvanostatically in ammonium pentaborate (pH 8.3) and sodium silicate (pH 12.6) electrolytes at 293 K and studied by transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. For one-step anodizing in the pentaborate electrolyte, a single-layered film, of approximate composition Ta2O5 (.) MgO, forms at a ratio of similar to1.8 nm V-1. In the silicate electrolyte, an outer, magnesium-rich layer, containing silicon species, also forms, with a ratio of 0.8 nm V-1. The outer layer can develop due to relatively fast migration of magnesium ions in the inner layer and the stabilization of the pH at the film surface, probably linked to generation of a silica gel that also limits loss of magnesium species to the electrolyte. Further thickening of the anodic film, in ammonium pentaborate electrolyte, produces fingers of low resistivity, inner oxide that penetrate the pre-existing, high resistivity outer layer.. with a bi-modal distribution of finger sizes. When fingers reach the film surface, magnesium ions are ejected to the electrolyte. The absence of fingers in films grown in sodium silicate electrolyte is possibly due to prevention, by the silica gel, of their initiation, (C) 2003 Published by Elsevier Science Ltd.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson  SURFACE AND INTERFACE ANALYSIS  35-  (7)  564  -574  2003/07  [Not refereed][Not invited]
     
    Previously, glow discharge optical emission spectroscopy (GDOES), both d.c. and r.f. has been used for depth profiling analysis of thick films several tens of microns thick, utilizing its high sputtering rates of >1 mum min(-1). Through selected examples, it is demonstrated here that r.f. GDOES also has enormous potential for depth profiling analysis of ultrathin films <10 nm thick, where AES and SIMS have dominant roles. The significant features of r.f. GDOES enabling such analysis arise from the nature of r.f. glow discharge sputtering where samples, both conducting and non-conducting, are sputtered very stably with Ar+ ions of low energies (<50 eV) and high current fluxes (of the order of 100 mA cm(-2)). The low Ar+ energy ensures that film sputtering proceeds without significant formation of altered layers, which is a prerequisite for successful depth profiling analysis of ultrathin films at high depth resolution. The high current fluxes allow sputtering to proceed at very high rates of >1 mum min(-1), thereby extending the limit of film thickness for analysis to 100 gm. Thus r.f. GDOES, with its unique ability to accommodate depth profiling analysis of films of a very wide thickness range, is expected to play an important role in the field of practical surface analysis. Copyright (C) 2003 John Wiley Sons, Ltd.
  • K Shimizu, N Kasahara, H Habazaki, P Skeldon, GE Thompson  SURFACE AND INTERFACE ANALYSIS  35-  (7)  611  -617  2003/07  [Not refereed][Not invited]
     
    The distributions of the additive-derived carbon and sulphur impurities in electroplated metallic layers are of great concern in plating industries. The amounts of carbon and sulphur impurities in the layers are normally <1 wt.% but they influence significantly the structure and properties of the layers. By analysis of the duplex nickel layers for corrosion protection of exterior automotive zinc die casting, it is demonstrated that radiofrequency glow discharge optical emission spectroscopy is a powerful and reliable technique for this purpose, allowing rapid depth profiling analysis with excellent sensitivities for the detection of carbon and sulphur, along with other impurities such as hydrogen and iron, and depth resolution. A freshly generated and highly flat cross-section of the sample has been prepared using an ultramicrotome and a diamond knife and subsequently analysed by EPMA line-scan analysis and AES spot analysis. It appeared that EPMA and AES do not have sufficient sensitivities to detect small amounts of the additive-derived carbon and sulphur impurities, although they have distinct advantages for micro-area analysis. Copyright (C) 2003 John Wiley Sons, Ltd.
  • HABAZAKI Hiroki, KONNO Hidetaka, SHIMIZU Ken-ichi  Jitsumu Hyomen Gijutsu  54-  (7)  456  -461  2003  [Not refereed][Not invited]
  • Shimizu, K., Habazaki, H., Skeldon, P. and Thompson, G.E.: "Impact of RF-GD-OES in practical surface analysis", Spectrochimica Acta Part B-Atomic Spectroscopy, 58: 1573-1583 (2003)*
    2003  [Not refereed][Not invited]
  • Mato, S., Alcala, G., Thompson, G.E., Skeldon, P., Shimizu, K., Habazaki, H., Quance, T., Graham, M.J. and Masheder, D.: "Anodic oxidation of Ta/Fe alloys", Corrosion Sci., 45: 2881-2892 (2003)*
    2003  [Not refereed][Not invited]
  • Teh, T.H., Berkani, A., Mato, S., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Initial stages of plasma electrolytic oxidation of titanium", Corrosion Sci., 45: 2757-2768 (2003)*
    2003  [Not refereed][Not invited]
  • Habazaki, H., Matsuo, T., Konno, H., Shimizu, K., Nagata, S., Matsumoto, K., Takayama, K., Oda, Y., Skeldon, P. and Thompson, G.E.: "Influence of silicon species on the electric properties of anodic niobia", Electrochim. Acta, 48: 3519-3526 (2003)*
    2003  [Not refereed][Not invited]
  • Iglesias-Rubianes, L., Skeldon, P., Thompson, G.E., Bailey, P., Noakes, T.C.Q., Habazaki, H. and Shimizu, K.: "Influence of oxidation rate and alloy composition on alloy enrichments of anodized Al-W alloys", Corrosion Sci., 45: 2915-2923 (2003)*
    2003  [Not refereed][Not invited]
  • Alcala, G., Mato, S., Skeldon, P., Thompson, G.E., Bailey, P., Noakes, T.C.Q., Habazaki, H. and Shimizu, K.: "Anodic film growth in the Al-Ta alloy system", Corrosion Sci., 45: 1803-1813 (2003)*
    2003  [Not refereed][Not invited]
  • Azumi, K., Yugiri, T., Kurihara, T., Seo, M., Habazaki, H. and Fujimoto, S.: "Direct plating of electroless Ni-P layers on sputter-deposited Al-Ni alloy films", J. Electrochem. Soc., 150: C461-C464 (2003)*
    2003  [Not refereed][Not invited]
  • Iglesias-Rubianes, L., Skeldon, P., Thompson, G.E., Kreissig, U., Grambole, D., Habazaki, H. and Shimizu, K.: "Behaviour of hydrogen impurity in aluminium alloys during anodizing", Thin Solid Films, 424: 201-207 (2003)*
    2003  [Not refereed][Not invited]
  • Iglesias-Rubianes, L., Skeldon, P., Thompson, G.E., Kreissig, U., Grambole, D., Habazaki, H. and Shimizu, K.: "Behavior of hydrogen impurity in aluminum alloys during anodizing", Thin Solid Films, 424: 201-207 (2003)*
    2003  [Not refereed][Not invited]
  • Liu, Y., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Chromate conversion coatings on aluminium: influences of alloying", Corrosion Sci., 46: 297-312 (2003)*
    2003  [Not refereed][Not invited]
  • Habazaki, H., Yokoyama, K. and Konno, H.: "The sulfidation and oxidation behavior of sputter-deposited Nb-Al-Cr alloys at high temperatures", Corrosion Science and Technology, 2: 141-147 (2003)*
    2003  [Not refereed][Not invited]
  • Liu, Y., Sultan, E.A., Koroleva, E.V., Skeldon, P., Thompson, G.E., Zhou, X., Shimizu, K. and Habazaki, H.: "Grain orientation effects on copper enrichment and oxygen generation during anodizing of an Al-lat.%Cu alloy", Corrosion Sci., 45: 789-797 (2003)*
    2003  [Not refereed][Not invited]
  • Mato, S., Alcala, G., Skeldon, P., Thompson, G.E., Quance, T., Graham, M.J., Habazaki, H., Shimizu, K. and Masheder, D.: "Oxygen generation in anodized Ta-Cu alloys", Philosophical Magazine, 83: 2733-2746 (2003)*
    2003  [Not refereed][Not invited]
  • Liu, Y., Colin, F., Skeldon, P., Thompson, G.E., Zhou, X., Habazaki, H. and Shimizu, K.: "Enrichment factors for copper in aluminium alloys following chemical and electrochemical surface treatments", Corrosion Sci., 45: 1539-1544 (2003)*
    2003  [Not refereed][Not invited]
  • Habazaki, H., Uozumi, M., Konno, H., Shimizu, K., Skeldon, P. and Thompson, G.E.: "Crystallization of anodic titania on titanium and its alloys", Corrosion Sci., 45: 2063-2073 (2003)*
    2003  [Not refereed][Not invited]
  • Y Aoki, H Habazaki, H Konno  CHEMISTRY OF MATERIALS  15-  (12)  2419  -2428  2003  [Not refereed][Not invited]
     
    Rare-earth metal(III) chromates(V), LaCrO(4), NdCrO(4), and Y(0.9)CrO(3.85), were found to show reversible structural changes by reduction with methanol and oxidation in air. This anomalous behavior was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared, in situ Raman spectroscopy, and other methods. After less than 30 min of reduction at 543 K, zircon-type NdCrO(4) in the bulk scale changed to the low-crystalline II-KDP-type phase, which has the same arrangement of metal atoms as zircon. The reduced phase was quickly reverted to the zircon-type phase by air oxidation at 543 K for a few minutes. NdCrO(4) was reduced by hydrogen from methanol by forming hydrogen bonds between CrO(4) units, which caused the oxygen displacement and the formation of pseudo-octahedral CrO(6-m)(OH)(m) units, leading to the distorted II-YDP-type structure. Defect zircon-type Y(0.9)CrO(3.85) changed more quickly to the low-crystalline II-KDP-type phase than NdCrO(4), and the structure was not completely restored by the oxidation at 543 K for 1 h, because of the formation of small amounts of YCrO(3) and Cr(2)O(3). Monazite-type LaCrO(4) changed to an amorphous phase with the formation of the Schottky defects of oxide ions because of the structural differences between the monazite-type and II-KDP-type phases and was restored by air oxidation at 723 K.
  • Alcala, G., Mato, S., Skeldon, P., Thompson, G.E., Mann, A.B., Habazaki, H. and Shimizu, K.: "Mechanical properties of barrier-type anodic alumina films using nanoindentation", Surface & Coatings Technology, 173: 293-298 (2003)*
    2003  [Not refereed][Not invited]
  • Habazaki, H., Uozumi, M., Konno, H., Nagata, S. and Shimizu, K.: "Formation of barrier-type amorphous anodic films on Ti-Mo alloys", Surface & Coatings Technology, 169: 151-154 (2003)*
    2003  [Not refereed][Not invited]
  • Takenaka, T., Habazaki, H. and Konno, H.: "Formation of black anodic films on aluminum in acid electrolytes containing titanium complex anion", Surface & Coatings Technology, 169: 155-159 (2003)*
    2003  [Not refereed][Not invited]
  • Mato, S., Alcala, G., Skeldon, P., Thompson, G.E., Mann, A.B., Masheder, D., Habazaki, H. and Shimizu, K.: "Dielectric and mechanical properties of anodic films in the Ta-Ti system", Surf. Interface Anal., 35: 477-482 (2003)*
    2003  [Not refereed][Not invited]
  • Habazaki, H., Matsuo, T., Konno, H., Shimizu, K., Nagata, S., Takayama, K., Oda, Y., Skeldon, P. and Thompson, G.E.: "Formation of N2O gas bubbles in anodic films on NbNx alloys", Thin Solid Films, 429: 159-166 (2003)*
    2003  [Not refereed][Not invited]
  • Garcia-Vergara, S., Skeldon, P., Thompson, G.E., Bailey, P., Noakes, T.C.Q., Habazaki, H. and Shimizu, K.: "Morphology of enriched alloy layers in an anodized Al-Cu alloy", Applied Surface Science, 205: 121-127 (2003)*
    2003  [Not refereed][Not invited]
  • Habazaki, H., Uozumi, M., Konno, H., Shimizu, K., Nagata, S., Asami, K., Matsumoto, K., Takayama, K., Oda, Y., Skeldon, P. and Thompson, G.E.: "Influences of structure and composition on growth of anodic oxide films on Ti-Zr alloys", Electrochim. Acta,・・・
    2003  [Not refereed][Not invited]
     
    Habazaki, H., Uozumi, M., Konno, H., Shimizu, K., Nagata, S., Asami, K., Matsumoto, K., Takayama, K., Oda, Y., Skeldon, P. and Thompson, G.E.: "Influences of structure and composition on growth of anodic oxide films on Ti-Zr alloys", Electrochim. Acta, 48: 3257-3266 (2003)*
  • Mato, S., Alcala, G., Skeldon, P., Thompson, G.E., Masheder, D., Habazaki, H. and Shimizu, K.: "Compositional self-organizing in the anodic film on a Mg-Ta alloy", J. Electrochem. Soc., 150: B439-B444 (2003)*
    2003  [Not refereed][Not invited]
  • Habazaki, H., Matsuo, T., Konno, H., Shimizu, K., Matsumoto, K., Takayama, K., Oda, Y., Skeldon, P. and Thompson, G.E.: "Analysis of anodic films on Nb and NbNx by glow discharge optical emission spectroscopy", Surf. Interface Anal., 35: 618-622 (2003)*
    2003  [Not refereed][Not invited]
  • KONNO Hidetaka, YONEDA Atsuo, HABAZAKI Hiroki, INAGAKI Michio  Tanso  2002-  (204)  159  -165  2002/10/07  [Not refereed][Not invited]
     
    Kapton-type polyimide films containing 0.1 at% Ni (PI-0.1Ni) and 0.5 at% Fe (PI-0.5Fe) were prepared from polyamic acid and each metallocene, and carbonized at a heat treatment temperature (HTT) of 400 -1600°C in flowing argon. Nickelocene was reduced to Ni metal particles of less than 20 nm in diameter at 450°C by 1h treatment. The PI-0.1Ni started to decompose by about 200K lower than the film without additives (PI), while with PI-0.5Fe such effect was not observed. Further, with PI-0.1Ni a sharp carbon 002 peak around 2θ=26° was developed markedly with raising HTT from 1000 to 1600°C. With PI-0.5Fe, the 002 peak became sharp at HTT =1050°C, but the peak intensity and profile changed only slightly in a range of 1100 1600°C. In the 1600°C treated PI-0.1 Ni, fairly large areas with oriented hexagonal carbon layers and those with entangled ribbon-like structure were observed in the lattice images by TEM. A small number of tunnel-like holes (1-2 μm in diameter) were observed by SEM in the cross-section of the film, which suggested the movement of Ni metal particles during the heat treatment. The 1000°C treated PI-0.1Ni was not graphitized by 1 h treatment at 3000°C, suggesting the formation of so-called "TS carbon." The present results showed that very small amounts of Ni are effective to the initial thermal decomposition of the polyimide and subsequent formation of turbostratic carbon, whereas Fe seemed to enhance the development of turbostratic carbon less effectively.
  • 幅崎 浩樹  日産科学振興財団研究報告書  25-  (0)  153  -516  2002  [Not refereed][Not invited]
  • Bonilla, F.A., Berkani, A., Liu, Y., Skeldon, P., Thompson, G.E., Habazaki, H., Shimizu, K., John, C. and Stevens, K.: "Formation of anodic films on magnesium alloys in an alkaline phosphate electrolyte", J. Electrochem. Soc., 149: B4-B13 (2002)*
    2002  [Not refereed][Not invited]
  • Lu, Q., Mato, S., Skeldon, P., Thompson, G.E., Masheder, D., Habazaki, H. and Shimizu, K.: "Anodic film growth on tantalum in dilute phosphoric acid solution at 20 and 85ーC", Electrochim. Acta, 47: 2761-2767 (2002)*
    2002  [Not refereed][Not invited]
  • K. Yoshimi, S. Nakatani, T. Suda, S. Hanada, H. Habazaki  Intermetallics  10-  (5)  407  -414  2002  [Not refereed][Not invited]
     
    A Mo5SiB2-based alloy having composition of Mo-12.3 mol% Si-24.9 mol% B was produced by arc-melting in an Ar atmosphere, and its oxidation behavior was investigated at temperature between 973 and 1673 K. At and above 1273 K, transient and steady state oxidation stages were clearly observed. The occurrence of the transient and steady state oxidation is interpreted in terms of rapid volatilization of MoO3 and B2O3 under ambient O2 pressure at the initial stage and the passive oxidation after completely sealing the substrate by silicate glass. Development of two layers onto the substrate, i.e. SiO2 glass scale and Mo solid solution interlayer including SiO2 dispersions, strongly supports the interpretation. Dissolution of B into the SiO2 scale was not confirmed because of low B concentration that was under a detectable limit of EPMA and TEM-EDS. It is suggested that the SiO2 glass scale formed on the Mo5SiB2-based alloy is more protective than as expected. © 2002 Elsevier Science Ltd. All rights reserved.
  • K. Shimizu, Y. Einaga, A. Fujishima, K. Ohnishi  Surface and Interface Analysis  33-  (1)  35  -40  2002  [Not refereed][Not invited]
     
    Analysis of a boron-doped diamond film, ∼13 μm thick, deposited onto a mirror-finished n-Si(100) substrate using microwave plasma chemical vapour deposition (CVD), demonstrates the suitability of radiofrequency glow discharge optical emission spectroscopy (rf-GDOES) for rapid depth profiling analysis. The distributions of boron and hydrogen are revealed clearly. Intrestingly, the sputtering of the diamond film is accompanied by smoothing of the initial rough, faceted surface, implying that the ridges sputter more rapidly than the valleys during analysis.
  • Shimizu, K., Habazaki, H., Skeldon, P., Thompson, G.E. and Wood, G.C.: "Role of metal ion impurities in generation of oxygen gas within anodic alumina", Electrochim. Acta, 47: 1225-1228 (2002)*
    2002  [Not refereed][Not invited]
  • Y Liu, P Skeldon, GE Thompson, H Habazaki, K Shimizu  CORROSION SCIENCE  44-  (5)  1133  -1142  2002  [Not refereed][Not invited]
     
    As a contribution towards the understanding of the electrochemical behaviour of magnesium-containing second phase particles in aluminium alloys, the formation of barrier-type anodic films on sputtering-deposited Al-21at.%Mg is examined by analytical transmission electron microscopy. Amorphous anodic films of uniform thickness develop on the alloy in ammonium pentaborate electrolyte of pH 8.3 at current densities between 0.1 and 100 mA cm(-2). The films contain incorporated magnesium species that reduce the electric field required for film growth. The magnesium species migrate through the film about three times faster than Al3+ ions and are lost to the electrolyte on reaching the surface of the film, leading to a reduced efficiency of growth of about 92%. Further, the growing films can detach from the alloy, particularly at relatively low current density. In strongly alkaline conditions, the comparatively rapid transport of magnesium species and the stability of the resulting magnesium-rich, surface regions of the film permits highly efficient film growth in sodium hydroxide solution of pH 13. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Iglesias-Rubianes, L., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Ionic transport in anodically oxidized Al/W layers", J. Electrochem. Soc., 149: B23-B26 (2002)*
    2002  [Not refereed][Not invited]
  • Bailey, P., Noakes, T.C.Q., Liu, Y., Alexander, M.R., Koroleva, E.V., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Damage of alumina films by medium energy hydrogen and helium ions", Nucl. Instru. Meth. B, 197: 265-270 (2002)*
    2002  [Not refereed][Not invited]
  • Ashitaka, Z., Skeldon, P., Thompson, G.E., Shimizu, K. and Habazaki, H.: "Enrichment behaviour of gallium in heat and surface treatments of Al-Ga foils", Corros. Sci., 44: 2725-2735 (2002)*
    2002  [Not refereed][Not invited]
  • Lu, Q., Skeldon, P., Thompson, G.E., Graham, M.J., Masheder, D., Habazaki, H. and Shimizu, K.: "Transmission electron microscopy of non-thickness-limited anodic films on tantalum", J. Electrochem. Soc., 149: B531-B533 (2002)*
    2002  [Not refereed][Not invited]
  • Alcala, G., Skeldon, P., Thompson, G.E., Mann, A.B., Habazaki, H. and Shimizu, K.: "Mechanical properties of amorphous anodic alumina and tantala films using nanoindentation", Nanotech., 13: 451-455 (2002)*
    2002  [Not refereed][Not invited]
  • Habazaki, H., Shimizu, K., Nagata, S., Skeldon, P., Thompson, G.E. and Wood, G.C.: "Ionic mobilities in amorphous anodic titania", J. Electrochem. Soc., 149: B70-B74 (2002)*
    2002  [Not refereed][Not invited]
  • Habazaki, H., Uozumi, M., Konno, H., Shimizu, K., Nagata, S., Asami, K., Skeldon, P. and Thompson, G.E.: "Influence of molybdenum species on growth of anodic titania", Electrochim. Acta, 47: 3837-3845 (2002)*
    2002  [Not refereed][Not invited]
  • Zhuravlyova, E., Iglesias-Rubianes, L., Pakes, A., Skeldon, P., Thompson, G.E., Zhou, X., Quance, T., Graham, M.J., Habazaki, H. and Shimizu, K.: "Oxygen evolution within barrier oxide films", Corros. Sci., 44: 2153-2159 (2002)*
    2002  [Not refereed][Not invited]
  • Hidetaka Konno, Akihiro Sudoh, Yoshitaka Aoki, Hiroki Habazaki  Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals  386-  (1)  15  -20  2002  [Not refereed][Not invited]
     
    B/C composites containing crystalline B4C particles were synthesized at 1400°C from the precursor composed of sugar-borate complexes. The precursors prepared from aqueous solutions of glucose and boric acid were found to be advantageous to the formation of B4C at low temperatures.
  • Lu, Q., Alcala, G., Skeldon, P., Thompson, G.E., Graham, M.J., Masheder, D., Shimizu, K. and Habazaki, H.: "Porous tantala and alumina films from non-thickness limited anodising in phosphate/glycerol electrolyte", Electrochim. Acta, 48: 37-42 (2002)*
    2002  [Not refereed][Not invited]
  • Konno Hidetaka, Yoneda Atsuo, Habazaki Hiroki  TANSO  2002-  (204)  171  -173  2002  [Not refereed][Not invited]
     
    Carbon and graphite films were prepared from the laboratory-made Kapton-type polyimide film, and the electric conductivities parallel, σ//, and perpendicular, σ⊥, to the surface were measured at room temperature. Anisotropy of electric conductivity was observed even for the 700°C treated film and the ratio, σ///σ⊥, increased with raising heat treatment temperature (HTT). The carbon films formed at HTT=1200-1600°C showed nearly the same conductivity, and σ///σ⊥ in this range was 450-550. The conductivities and sailla σ///σ⊥ ratio increased with further raising HTT up to 2800°C. The structural changes of the films were also investigated by using XRD and TEM.
  • Konno Hidetaka, Yoneda Atsuo, Habazaki Hiroki, Inagaki Michio  TANSO  2002-  (204)  159  -165  2002  [Not refereed][Not invited]
     
    Kapton-type polyimide films containing 0.1 at% Ni (PI-0.1Ni) and 0.5 at% Fe (PI-0.5Fe) were prepared from polyamic acid and each metallocene, and carbonized at a heat treatment temperature (HTT) of 400 -1600°C in flowing argon. Nickelocene was reduced to Ni metal particles of less than 20 nm in diameter at 450°C by 1h treatment. The PI-0.1Ni started to decompose by about 200K lower than the film without additives (PI), while with PI-0.5Fe such effect was not observed. Further, with PI-0.1Ni a sharp carbon 002 peak around 2θ=26° was developed markedly with raising HTT from 1000 to 1600°C. With PI-0.5Fe, the 002 peak became sharp at HTT =1050°C, but the peak intensity and profile changed only slightly in a range of 1100 1600°C. In the 1600°C treated PI-0.1 Ni, fairly large areas with oriented hexagonal carbon layers and those with entangled ribbon-like structure were observed in the lattice images by TEM. A small number of tunnel-like holes (1-2 μm in diameter) were observed by SEM in the cross-section of the film, which suggested the movement of Ni metal particles during the heat treatment. The 1000°C treated PI-0.1Ni was not graphitized by 1 h treatment at 3000°C, suggesting the formation of so-called "TS carbon." The present results showed that very small amounts of Ni are effective to the initial thermal decomposition of the polyimide and subsequent formation of turbostratic carbon, whereas Fe seemed to enhance the development of turbostratic carbon less effectively.
  • H Habazaki, Y Hayashi, H Konno  ELECTROCHIMICA ACTA  47-  (26)  4181  -4188  2002  [Not refereed][Not invited]
     
    WO3 films have been prepared on to IrO2-coated Ti substrate by cathodic deposition, and as-deposited and annealed films have been characterized using XRD, TEM, Raman and FT-IR spectroscopy. The as-deposited film consists of nanocrystalline, orthorhombic WO3.H2O and this phase transforms to amorphous WO3 by annealing at 250 degreesC and to monoclinic WO3 by annealing at and above 350 degreesC. The as-deposited and annealed films have been used as anodes for electrochemical decomposition of phenol in aqueous solutions with and without chloride ions. The monoclinic WO3 anodes prepared by annealing at 350 and 400 degreesC show relatively high electrochemical activity in the chloride-containing solution. In addition, the anodes possess high chemical and physical stabilities: very low dissolution rate of WO3 during the electrolysis and good adhesion to the substrate. Thus, WO3 anodes may be promising materials for anodic oxidation of bio-refractory organics in wastewater, although further improvement of electrochemical activity is needed for more effective decrease in total organic carbons in wastewater. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, RK Marcus  SPECTROSCOPY  17-  (10)  14  -+  2002  [Not refereed][Not invited]
     
    The need for reference materials that can be applied in, the area of thin (<10 mum) films analysis has long been realized but is still, in general, under-addressed. Alumina films of single-micrometer thickness, having either fine distributions of impurities or delta function impurity marker layers, can be prepared routinely by anodic oxidation of electropolished aluminum specimens in appropriate electrolytes. Selected films were examined by transmission electron microscopy (TEM) and analyzed by radio frequency glow discharge optical emission spectroscopy (rf-GD-OES), providing very rapid, yet high-resolution, depth-resolved analysis of these electrically insulating materials.
  • Konno, H., Matsuura, R., Yamasaki, M. and Habazaki, H.: "Microstructure of cobalt dispersed carbon sphere prepared from chelate resin", Syn. Met., 125: 167-170 (2002)*
    2002  [Not refereed][Not invited]
  • Bonilla, F.A., Berkani, A., Skeldon, P., Thompson, G.E., Habazaki, H., Shimizu, K., John, C. and Stevens, K.: "Enrichment of alloying elements in anodized magnesium alloys", Corros. Sci., 44: 1941-1948 (2002)*
    2002  [Not refereed][Not invited]
  • Caicedo-Martinez, C.E., Koroleva, E.V., Thompson, G.E., Skeldon, P., Shimizu, K., Habazaki, H. and Hoellrigl, G.: "Surface nanotextures on aluminium", Surf. Interface Anal., 34: 405-408 (2002)*
    2002  [Not refereed][Not invited]
  • Iglesias-Rubianes, L., Skeldon, P., Thompson, T.E., Habazaki, H. and Shimizu, K.: "Transient anodic oxidation of an Al-W alloy: effects of current ratio", Corros. Sci., 44: 751-760 (2002)*
    2002  [Not refereed][Not invited]
  • Caicedo-Martinez, C.E., Koroleva, E., Skeldon, P., Thompson, G.E., Hoellrigl, G., Bailey, P., Noakes, T.C.Q., Habazaki, H. and Shimizu, K.: "Behavior of impurity and minor alloying elements during surface treatments of aluminum", J. Electrochem. Soc., ・・・
    2002  [Not refereed][Not invited]
     
    Caicedo-Martinez, C.E., Koroleva, E., Skeldon, P., Thompson, G.E., Hoellrigl, G., Bailey, P., Noakes, T.C.Q., Habazaki, H. and Shimizu, K.: "Behavior of impurity and minor alloying elements during surface treatments of aluminum", J. Electrochem. Soc., 149: B139-B145 (2002)*
  • Liu, Y., Alexander, M., Koroleva, E., Skeldon, P., Thompson, G.E., Bailey, P., Noakes, T.C.Q., Shimizu, K. and Habazaki, H.: "Detachment of alumina films from aluminium by 100 keV H+ ions", Surf. Interface Anal., 33: 318-321 (2002)*
    2002  [Not refereed][Not invited]
  • Konno, H., Fujita, K., Habazaki, H. and Inagaki, M.: "Graphite formation at 1150-1200oC from hard carbon precursors and magnetite", Tanso, 203: 113-116 (2002)*
    2002  [Not refereed][Not invited]
  • H Konno, K Narumi, H Habazaki  CORROSION SCIENCE  44-  (8)  1889  -1900  2002  [Not refereed][Not invited]
     
    A molybdate(VI)-Al(III) chemical conversion process was developed as an alternative to the chromate processes. Steel and zine-plated steel specimens were treated in the solutions of 0.16 moll (1) ammonium alum (AlNH4(SO4)(2) . 12H(2)O) with small amounts of ammonium molybdate(VI) (0.002-0.016 mol l (1) (NH4)(6)Mo7O24 . 4H(2)O) at 60 degreesC for 10 30 min in an ultrasonic rinsing apparatus. The formed films were composed of oxyhydroxides containing Mo(V.VI). Al(III), Fe(II.III). and sulfate ions (and Zn(II) ions in the case of zinc-plated steel). and showed good corrosion resistance in an aerated 0.5 moll(-1) NaCl-0.15 moll (1) H3BO3, Solution (pH = 7). The films macerated during the corrosion test, but they did not detach and functioned as a protective layer, This process may be useful in forming undercoats for paints and polymer coatings on steel and zinc-plated steel. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Matsui, T., Habazaki, H., Kawashima, A., Asami, K., Kumagai, N. and Hashimoto, K.: "Anodically deposited manganese molybdenum tungsten oxide anodes for oxygen evolution in seawater electrolysis", J. Appl. Electrochem., 32: 993-1000 (2002)*
    2002  [Not refereed][Not invited]
  • Habazaki, H., Shimizu, K., Nagata, S., Skeldon, P., Thompson, G.E. and Wood, G.C.: "Ionic transport in amorphous anodic titania stabilised by incorporation of silicon species", Corros. Sci., 44: 1047-1055 (2002)*
    2002  [Not refereed][Not invited]
  • AOKI YOSHITAKA, HABAZAKI HIROKI, KONNO HIDETAKA  固体の反応性討論会講演予稿集  12th-  37  -39  2001/11/13  [Not refereed][Not invited]
  • HASHIMOTO Koji, MEGURO Shinsaku, SASAKI Teruhito, KATAGIRI Hiroshi, YAMASAKI Michiaki, IZUMIYA Koichi, KUMAGAI Naokazu, HABAZAKI Hiroki, KAWASHIMA Asahi, ASAMI Katsuhiko, AKIYAMA Eiji  Materia Japan  40-  (4)  372  -375  2001/04/20  [Not refereed][Not invited]
  • HASHIMOTO Koji, MEGURO Shinsaku, SASAKI Teruhito, KATAGIRI Hiroshi, YAMASAKI Michiaki, IZUMIYA Koichi, KUMAGAI Naokazu, HABAZAKI Hiroki, KAWASHIMA Asahi, ASAMI Katsuhiko, AKIYAMA Eiji  Materia Japan  40-  (4)  372  -375  2001/04/20  [Not refereed][Not invited]
  • AOKI YOSHIHISA, KONNO HIDETAKA, HABAZAKI HIROKI  電気化学会大会講演要旨集  68th-  171  2001/03/25  [Not refereed][Not invited]
  • HASHIMOTO Koji, YAMAZAKI Michiaki, MEGURO Shinsaku, SASAKI Teruhito, KATAGIRI Hiroshi, KUMAGAI Naokazu, IZUMIYA Koichi, HABAZAKI Hiroki, AKIYAMA Eiji, KAWASHIMA Asahi, ASAMI Katsuhiko  The Journal of the Surface Finishing Society of Japan  52-  (2)  195  -200  2001/02/01  [Not refereed][Not invited]
  • Ashitaka, Z., Thompson, G.E., Skeldon, P., Habazaki, H. and Shimizu, K.: "Behaviour of bismuth during simulated processing of model aluminium capacitor foils", J. Mater. Sci., 36: 2237-2243 (2001)*
    2001  [Not refereed][Not invited]
  • Habazaki, H., Shimizu, K., Skeldon, P., Thompson, G.E. and Wood, G.C.: "The behaviour of iron during anodic oxidation of sputtering- deposited Al-Fe alloys", Corrosion Sci., 43: 1393-1402 (2001)*
    2001  [Not refereed][Not invited]
  • Liu, Y., Skeldon, P., Thompson, G.E., Zhou, X., Habazaki, H. and Shimizu, K.: "Influence of surface treatment on detachment of anodic films from Al-Mg alloys", Corrosion Sci., 43: 2349-2357 (2001)*
    2001  [Not refereed][Not invited]
  • Katagiri, H., Meguro, S., Yamasaki, M., Habazaki, H., Sato, T., Kawashima, A., Asami, K. and Hashimoto, K.: "An attempt at preparation of corrosion-resistant bulk amorphous Ni-Cr-Ta-Mo-P-B alloys", Corros. Sci., 43: 183-191 (2001)*
    2001  [Not refereed][Not invited]
  • Iglesias-Rubianes, L., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "History effects in anodic oxidation of Al-W alloys", Philos. Mag. A-Phys. Condens. Matter Struct. Defect Mech. Prop., 81: 1579-1595 (2001)*
    2001  [Not refereed][Not invited]
  • Habazaki, H., Yokoyama, K. and Konno, H.: "The sulfidation and oxidation behavior of sputter-deposited Nb-Al-Cr alloys at high temperatures", Proc. 12th Asia-Pacific Corrosion Conference 2001, 785-794 (2001)
    2001  [Not refereed][Not invited]
  • Katagiri, H., Meguro, S., Yamasaki, M., Habazaki, H., Sato, T., Kawashima, A., Asami, K. and Hashimoto, K.: "An attempt at preparation of corrosion-resistant bulk amorphous Ni-Cr-Ta-Mo-P-B alloys", Corrosion Sci., 43: 183-191 (2001)*
    2001  [Not refereed][Not invited]
  • Shimizu, K., Habazaki, H., Skeldon, P., Thompson, G.E. and Wood, G.C.: "Migration of oxalate ions in anodic alumina", Electrochim. Acta, 46: 4379-4382 (2001)*
    2001  [Not refereed][Not invited]
  • Echeverria, F., Skeldon, P., Thompson, G.E., Habazaki, H. and Shimizu, K.: "Morphology and composition of layered anodic films on InP", J. Mater. Sci., 36: 1253-1259 (2001)*
    2001  [Not refereed][Not invited]
  • Kawashima, A., Habazaki, H. and Hashimoto, K.: "Highly corrosion-resistant Ni-based bulk amorphous alloys", Mater. Sci. Eng. A, 304: 753-757 (2001)*
    2001  [Not refereed][Not invited]
  • Habazaki, H., Sato, T., Kawashima, A., Asami, K. and Hashimoto, K.: "Preparation of corrosion-resistant amorphous Ni-Cr-P-B bulk alloys containing molybdenum and tantalum", Mater. Sci. Eng. A, 304: 696-700 (2001)*
    2001  [Not refereed][Not invited]
  • Habazaki, H., Mitsui, H., Lee, D.B., Hashimoto, K. and Mrowec, S.: "Sulfidation- and oxidation-resistant Nb-Al-Si alloy coatings prepared by sputter deposition", Mater. High Temp., 18: 95-100 (2001)*
    2001  [Not refereed][Not invited]
  • Habazaki, H., Sato, T., Kawashima, A. and Hashimoto, K.: "Preparation of corrosion-resistant amorphous Ni-Cr-P-B alloys containing molybdenum and tantalum", Mater. Sci. Eng. A, 304-306: 696-700 (2001)*
    2001  [Not refereed][Not invited]
  • Mato, S., Thompson, G.E., Skeldon, P., Shimizu, K., Habazaki, H. and Masheder, D.: "Enrichment of alloying elements beneath anodic oxides: investigation of Ta-1.5 at.% Cu alloy", Corrosion Sci., 43: 993-1002 (2001)*
    2001  [Not refereed][Not invited]
  • Shimizu, K., Habazaki, H., Skeldon, P., Thompson, G.E. and Marcus, R.K.: "Influence of interfacial depth on depth resolution during GDOES depth profiling analysis of thin alumina films", Surf. Interface Anal., 31: 869-873 (2001)*
    2001  [Not refereed][Not invited]
  • Pakes, A., Echeverria, F., Skeldon, P., Thompson, G.E., Fraser, J.W., McCaffrey, J.P., Moisa, S., Graham, M.J., Habazaki, H. and Shimizu, K.: "Role of oxygen bubble generation in anodic film growth on InP", Corrosion Sci., 43: 2173-2184 (2001)*
    2001  [Not refereed][Not invited]
  • Bailey, P., Skeldon, P., Noakes, T.C.Q., Thompson, G.E., Sakairi, M., Habazaki, H. and Shimizu, K.: "Composition and structure of enriched alloy layers in filmed Al alloys studied by medium-energy ion scattering", Surf. Interface Anal., 31: 480-483 (20・・・
    2001  [Not refereed][Not invited]
     
    Bailey, P., Skeldon, P., Noakes, T.C.Q., Thompson, G.E., Sakairi, M., Habazaki, H. and Shimizu, K.: "Composition and structure of enriched alloy layers in filmed Al alloys studied by medium-energy ion scattering", Surf. Interface Anal., 31: 480-483 (2001)*
  • Asami, K., Zhang, B.P., Mehmood, M., Habazaki, H. and Hashimoto, K.: "Effects of nanoscale heterogeneity on the corrosion behavior of non-equilibrium alloys", Scr. Mater., 44: 1655-1658 (2001)*
    2001  [Not refereed][Not invited]
  • Katagiri, H., Meguro, S., Yamasaki, M., Habazaki, H., Sato, T., Kawashima, A., Asami, K. and Hashimoto, K.: "Synergistic effect of three corrosion-resistant elements on corrosion resistance in concentrated hydrochloric acid", Corrosion Sci., 43: 171-18・・・
    2001  [Not refereed][Not invited]
     
    Katagiri, H., Meguro, S., Yamasaki, M., Habazaki, H., Sato, T., Kawashima, A., Asami, K. and Hashimoto, K.: "Synergistic effect of three corrosion-resistant elements on corrosion resistance in concentrated hydrochloric acid", Corrosion Sci., 43: 171-182 (2001)*
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood  CORROSION SCIENCE  43-  (2)  199  -205  2001  [Not refereed][Not invited]
     
    The potential of glow discharge optical emission spectroscopy for the analysis of thin films on metals is examined using the example of electrodeposited NI-P, about 0.53 mum thick. The glow discharge optical emission spectroscopy depth profiles reveal layering of the deposited material with a good correlation between the sequence of layers in the composition profile and that observed by transmission electron microscopy. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • Iglesias-Rubianes, L., Skeldon, P., Thompson, G.E., Shimizu, K. and Habazaki, H.: "Influence of current density in anodizing of an Al-W alloy", Corrosion Sci., 43: 2217-2227 (2001)*
    2001  [Not refereed][Not invited]
  • Habazaki, H., Matsui, T., Kawashima, A., Asami, K., Kumagai, N. and Hashimoto, K.: "Nanocrystalline manganese-molybdenum-tungsten oxide anodes for oxygen evolution in seawater electrolysis", Scr. Mater., 44: 1659-1662 (2001)*
    2001  [Not refereed][Not invited]
  • IGLESIAS-RUBIANES L., SKELDON P., THOMPSON G. E., WOOD G. G., HABAZAKI H., SHIMIZU K.  軽金属  50-  (11)  538  -543  2000/11/30
  • F. Echeverria, P. Skeldon, G. E. Thompson, M. J. Graham, H. Habazaki, K. Shimizu  Corrosion Science  42-  (10)  1839  -1851  2000/10  [Not refereed][Not invited]
     
    The study examines the formation of amorphous anodic films on Al0.2Ga0.8As and Al0.8Ga0.2As substrates, using transmission electron and atomic force microscopies and Rutherford backscattering spectroscopy. The anodizing conditions consist of a constant current density, of 0.25 mA cm-2, with either 2 mM or 0.1 M aqueous sodium tungstate electrolyte, and a temperature of 293 K. The resultant films are of relatively uniform composition, except for the presence of about 1.5 at% tungsten species, which are derived from the electrolyte, in the outer ~36% of their thickness. The average compositions of the films are 0.24Al2O3·0.8Ga2O3·1.2As2O3 and 0.96Al2O3·0.2Ga2O3·1.2As2O3 for the films grown on Al0.2Ga0.8As and Al0.8Ga0.2As substrates, respectively. The reduced amounts of gallium in the film with respect to the substrate is due to fast outward migration of gallium ions relative to that of Al3+ and As3+ ions, and dissolution of gallium species at the film surface. The dissolution reduces the anodizing efficiency by about 10%. The formation ratios are approximately 1.92 and 1.44 for films grown on Al0.2Ga0.8As and Al0.8Ga0.2As substrates, respectively, consistent with an increased amount of Al3+ ions in the latter films. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • KAWASHIMA Asahi, Li X. -Y, HABAZAKI Hiroki, HASHIMOTO Koji  講演論文集  2000-  (35)  104  -105  2000/03/11  [Not refereed][Not invited]
  • 太陽エネルギーと海水電解を利用するグローバル二酸化炭素リサイクル
    橋本功二, 山崎倫昭, 泉屋宏一, 目黒眞作, 佐々木昭仁, 片桐洋, 秋山英二, 熊谷直和, 幅崎浩樹, 川嶋朝日, 浅見勝彦  海洋開発ニュース  28-  (6)  3  -8  2000/03  [Not refereed][Not invited]
  • 海水電解とグローバル二酸化炭素リサイクル二酸化炭素リサイクル
    橋本功二, 山崎倫昭, 松井徹郎, 泉屋宏一, 目黒眞作, 佐々木昭仁, 片桐洋, 秋山英二, 幅崎浩樹, 川嶋朝日, 浅見勝彦, 熊谷直和  水素エネルギーシステム  25-  (1)  55  -63  2000/01  [Not refereed][Not invited]
  • グローバル二酸化炭素リサイクル −地球温暖化防止と豊富なエネルギー供給のために−
    橋本功二, 山崎倫昭, 松井徹郎, 泉屋宏一, 目黒眞作, 佐々木昭仁, 片桐洋, 秋山英二, 熊谷直和, 幅崎浩樹, 川嶋朝日, 浅見勝彦  エレクトロヒート  111-  1  -9  2000/01  [Not refereed][Not invited]
  • Shimizu, K. Habazaki, H. Skeldon, P. and Thompson, G.E.: "GDOES depth profiling analysis and cross-sectional transmission electron microscopy of a hard disk", Surface Interface Analysis, 29: 887-890 (2000)*
    2000  [Not refereed][Not invited]
  • SHIMIZU Kenichi, HABAZAKI Hiroki, PETER Skeldon, GEORGE E. Thompson  Jitsumu Hyomen Gijutsu  51-  (5)  518  -523  2000  [Not refereed][Not invited]
     
    A Ni-P/Al hard disk substrate has been analyzed by Glow Discharge Optical Emission Spectroscopy (GDOES) and by cross-sectional transmission electron microscopy. With GDOES, all of the distributions of impurity species, as they related to disk fabrication processes, have been revealed successfully within the Ni-P layer, at the polished Ni-P surface, and at the Ni-P/Al interface with excellent sensitivity and depth resolution for the first time. Further, the structural details of the disk, such as the structure of Ni-P deposits, the Ni-P/Al interface, and the presence of alumina polishing particles on the surface, have been revealed clearly by cross-sectional transmission electron microscopy.
  • Shimizu, K. Habazaki, H. Skeldon, P. Thompson, G.E. and Wood, G.C.: ”Glow discharge optical emission spectroscopy (GDOES) and energy filtering transmission electron microscopy (FETEM) ; powerful techniques for the analysis of various surface films on a・・・
    2000  [Not refereed][Not invited]
     
    Shimizu, K. Habazaki, H. Skeldon, P. Thompson, G.E. and Wood, G.C.: ”Glow discharge optical emission spectroscopy (GDOES) and energy filtering transmission electron microscopy (FETEM) ; powerful techniques for the analysis of various surface films on aluminium and its alloys”, Proc. 2nd Int. Symp. Aluminium Surface Science and Technology, H. Terryn ed., ATB Metallurgie, pp.578-581 (2000)*
  • Zhou, X. Thompson, G.E. Habazaki, H. Paez, M.A. Shimizu, K. Skeldon, P. and Wood, G.C.: "Morphological development of oxygen bubbles in anodic alumina", Jour. Electrochemical Society, 147: 1747-1750 (2000)*
    2000  [Not refereed][Not invited]
  • Mato, S. Skeldon, P. Thompson, G.E. Masheder, D. Sproule, G.I. Graham, M.J. Habazaki, H. and Shimizu, K.: "Behaviour of copper and generation of oxygen during anodizing of Nb-Cu alloys", Surface and Interface Analysis, 29: 895-902 (2000)*
    2000  [Not refereed][Not invited]
  • Shimizu, K. Habazaki, H. Skeldon, P. Thompson, G.E. and Wood, G.C.: "Crystalline anodic barrier oxide growth on aluminium – a key feature linking anodizing, corrosion and high temperature oxidation of aluminium", Proc. 2nd Int. Symp. Aluminium Surface ・・・
    2000  [Not refereed][Not invited]
     
    Shimizu, K. Habazaki, H. Skeldon, P. Thompson, G.E. and Wood, G.C.: "Crystalline anodic barrier oxide growth on aluminium – a key feature linking anodizing, corrosion and high temperature oxidation of aluminium", Proc. 2nd Int. Symp. Aluminium Surface Science and Technology, H. Terryn ed., ATB Metallurgie, pp.119-126 (2000)*
  • Shimizu, K. Habazaki, H. Skeldon, P. Thompson, G.E. and Wood, G.C.: "Migration of sulphate ions in anodic alumina", Electrochimica Acta, 45: 1805-1809 (2000)*
    2000  [Not refereed][Not invited]
  • Echeverria, F. Skeldon, P. Thompson, G. E. Habazaki, H. and Shimizu, K.: "The formation of anodic oxides on InAs at high efficiency in sodium tungstate electrolyte", Thin Solid Films, 371: 303-309 (2000)*
    2000  [Not refereed][Not invited]
  • Habazaki, H. Shimizu, K. Skeldon, P. Thompson, G.E. and Wood, G.C.: "The behaviour of iron during anodic oxidation of sputter-deposited Al-Fe alloys", Proc. 2nd Int. Symp. Aluminium Surface Science and Technology, H. Terryn ed., ATB Metallurgie, pp.151・・・
    2000  [Not refereed][Not invited]
     
    Habazaki, H. Shimizu, K. Skeldon, P. Thompson, G.E. and Wood, G.C.: "The behaviour of iron during anodic oxidation of sputter-deposited Al-Fe alloys", Proc. 2nd Int. Symp. Aluminium Surface Science and Technology, H. Terryn ed., ATB Metallurgie, pp.151-157 (2000)*
  • Iglesias-Rubianes, L. Skeldon, P. Thompson, G.E. Habazaki, H. and Shimizu, K.: "Effects of current density on enrichment and oxidation of tungsten in an Al-W alloy", Proc. 2nd Int. Symp. Aluminium Surface Science and Technology, H. Terryn ed., ATB Meta・・・
    2000  [Not refereed][Not invited]
     
    Iglesias-Rubianes, L. Skeldon, P. Thompson, G.E. Habazaki, H. and Shimizu, K.: "Effects of current density on enrichment and oxidation of tungsten in an Al-W alloy", Proc. 2nd Int. Symp. Aluminium Surface Science and Technology, H. Terryn ed., ATB Metallurgie, pp.386-391 (2000)*
  • Ashitaka, Z. Thompson, G.E. Skeldon, P. Wood, G.C. Shimizu, K. and Habazaki, H.: "Effects of lead and copper during processing treatments of aluminium capacitor foils", Proc. 2nd Int. Symp. Aluminium Surface Science and Technology, H. Terryn ed., ATB M・・・
    2000  [Not refereed][Not invited]
     
    Ashitaka, Z. Thompson, G.E. Skeldon, P. Wood, G.C. Shimizu, K. and Habazaki, H.: "Effects of lead and copper during processing treatments of aluminium capacitor foils", Proc. 2nd Int. Symp. Aluminium Surface Science and Technology, H. Terryn ed., ATB Metallurgie, pp.443-448 (2000)*
  • Meguro, S. Sasaki, T. Katagiri, H. Habazaki, H. Kawashima, A. Sakaki, T. Asami, K. and Hashimoto, K.: "Electrodeposited Ni-Fe-C cathodes for hydrogen evolution", Jour. Electrochemical Society, 147: 3003-3009 (2000)*
    2000  [Not refereed][Not invited]
  • Shimizu, K. Habazaki, H. Skeldon, P. Thompson, G.E. and Wood, G.C.: "GDOES depth profiling analysis of the air-formed oxide film on a sputter-deposited Type 304 stainless steel", Surface and Interface Analysis, 29: 743-746 (2000)*
    2000  [Not refereed][Not invited]
  • H Habazaki, M Yamasaki, A Kawashima, K Hashimoto  APPLIED ORGANOMETALLIC CHEMISTRY  14-  (12)  803  -808  2000  [Not refereed][Not invited]
     
    Ni/ZrO2 and Ni/(Zr0.9Sm0.1)(0.95) catalysts were prepared by wet impregnation, and their catalytic activities for methanation of carbon dioxide were compared with the highly active catalysts prepared from amorphous nickel-zirconium-samarium alloys. The Ni(Zr0.9Sm0.1)O-1.95 catalyst showed higher activity for methanation of carbon dioxide than the samarium-free Ni/ZrO2 catalyst with the same nickel content. The higher activity of the samarium-containing catalyst is associated with the formation of the (Zr-Sm)O-x oxide with a tetragonal ZrO2 structure, similar to the Ni/(Zr-Sm)O-x catalysts prepared from the amorphous nickel-zirconium-samarium alloys. An increase in the nickel content from 30 to 60 mol% in cationic percentage results ina decrease in the activity, mainly because of a decrease in the surface area of the catalysts, although the activity of the catalysts prepared from amorphous nickel-zirconium-samarium alloys increases with the nickel content. Further, it was found that the activities of the Ni/(ZrSm)O-x catalysts prepared from the amorphous nickel-zirconium-samarium alloys are higher than those prepared by wet impregnation. Uniform dispersion of nickel in the catalysts prepared from amorphous single-phase alloys should be one of the reasons for the extremely high activity of the catalysts, Copyright (C) 2000 John Wiley & Sons, Ltd.
  • Yamasaki, M. Habazaki, H. Asami, K. and Hashimoto, K.: "Oxidation behavior of amorphous Ni-Zr and Ni-Zr-Sm alloys", Jour. Electrochemical Society, 147: 4502-4506 (2000)*
    2000  [Not refereed][Not invited]
  • Yamasaki, M. Habazaki, H. Asami, K. and Hashimoto, K.: "Oxidation behavior of amorphous Ni-Zr and Ni-Zr-Sm alloys", Jour. Electrochemical Society, 147: 4502-4506 (2000)*
    2000  [Not refereed][Not invited]
  • Herrera-Erazo, A.E. Habazaki, H. Shimizu, K. Skeldon, P. and Thompson, G.E.: "Anodic film growth on Al-Nd alloys", Corrosion Science, 42: 1823-1830 (2000)*
    2000  [Not refereed][Not invited]
  • Mehmood, M. Akiyama, E. Habazaki, H. Kawashima, A. Asami, K. and Hashimoto, K.: "Effects of nanocrystalline heterogeneity on the corrosion behavior of sputter-deposited chromium-niobium alloys", Corrosion Science, 42: 361-382 (2000)*
    2000  [Not refereed][Not invited]
  • Fujimura, K. Matsui, T. Habazaki, H. Kawashima, A. Kumagai, N. and Hashimoto, K.: "The durability of manganese-molybdenum oxide anodes for oxygen evolution in seawater electrolysis", Electrochimica Acta, 45: 2297-2303 (2000)*
    2000  [Not refereed][Not invited]
  • Shimizu, K. Brown, G.M. Habazaki, H. Kobayashi, K. Skeldon, P. Thompson, G.E. and Wood, G.C.: "Selective oxidation of aluminium and interfacial enrichment of iron during anodic oxide growth on an Al ↓6↓Fe phase", Corrosion Science, 42: 831-840 (2000)*
    2000  [Not refereed][Not invited]
  • Tzoganakou, K. Skeldon, P. Thompson, G.E. Zhou, X. Kreissig, U. Wieser, E. Habazaki, H. and Shimizu, K.: "Mobility of lithium ions in anodic alumina formed on an Al-Li alloy", Corrosion Science, 42: 1083-1091 (2000)*
    2000  [Not refereed][Not invited]
  • Lee, D. B. Habazaki, H. Kawashima, A. and Hashimoto, K.: "High temperature oxidation of a Nb-Al-Si coating sputter-deposited on titanium", Corrosion Science, 42: 721-729 (2000)*
    2000  [Not refereed][Not invited]
  • Kihn, Y. Thompson, G. E. Galaup, G. Skeldon, P. Zhou, X. Shimizu K. and Habazaki, H.: "Morphology, composition and structure of anodic films on Al-Cr alloys", Corrosion Science, 42: 533-544 (2000)*
    2000  [Not refereed][Not invited]
  • Margadant, N. Skeldon, P. Textor, M. Thompson, G.E. Wan, J. Habazaki, H. Shimizu, K. Spencer, N.D. and Wood, G.C.: "Gallium enrichment and film detachment during anodizing of an Al-Ga alloy", Corrosion Science, 42: 405-419 (2000)*
    2000  [Not refereed][Not invited]
  • Habazaki, H. Takahiro, K. Yamaguchi, S. Shimizu, K. Skeldon, P. Thompson, G.E. and Wood, G.C.: "Importance of amorphous-to-crystalline transitions for ionic transport and oxygen generation in anodic films", Philosophical Magazine A, 80: 1027-1042 (2000)*
    2000  [Not refereed][Not invited]
  • H Habazaki, K Hon-Yashiki, K Hashimoto, S Mrowec  DIFFUSION AND REACTIONS  72-  17  -21  2000  [Not refereed][Not invited]
     
    Novel Al-Nb-Mo alloys prepared by sputter deposition show two-stage parabolic behavior during sulfidation in a sulfur partial pressure of 1 x 10(3) Pa at 1073-1273 K. Their diffusion-controlled steady-state sulfidation rates, which are slower than the initial rates, are lower than the steady-state sulfidation rates of the Al-Nb, Al-Mo and Nb-Mo binary alloys. The sulfidation rate of the Nb-56Mo alloy is also lower than those of niobium and molybdenum. These results indicate the beneficial effect of the alloying of niobium and molybdenum on the sulfidation resistance. The scales formed on the Nb-Mo alloy are composed of two barrier layers, comprising an outer NbS2 layer and an inner MoS2 layer containing Nb3S4. Similarly, on the Al-Nb-Mo ternary alloys the two-layered refractory metal sulfide scale is formed beneath an outermost Al2S3 layer. The two-layer structure of the refractory metal sulfides results from the difference of diffusing matters and directions in these layers: the growth of the NbS2 and MoS2-Nb3S4 layers due to the outward diffusion of niobium and the inward diffusion of sulfur, respectively. Assuming that the predominant defects in the NbS2 and MoS2 are interstitial niobium and sulfide ions, respectively, it can be qualitatively explained that such two-layered structure decreases the growth rates of both the NbS2 and MoS2 layers. In addition, the lower sulfidation rates of the Al-Nb-Mo ternary alloys in comparison with the Al-free Nb-Mo alloy may be explained mainly in terms of doping effect, similarly to the AI-Nb and AI-Mo alloys.
  • Habazaki, H. Ito, K. Hon-yashiki, K. Kawashima, A. Hashimoto K. and Mrowec, S.: "The sulfidation and oxidation behavior of sputter-deposited Cr-Ta alloys at high temperatures", Proc. Per Kofstad Memorial Symposium, High Temperature Corrosion and Materi・・・
    2000  [Not refereed][Not invited]
     
    Habazaki, H. Ito, K. Hon-yashiki, K. Kawashima, A. Hashimoto K. and Mrowec, S.: "The sulfidation and oxidation behavior of sputter-deposited Cr-Ta alloys at high temperatures", Proc. Per Kofstad Memorial Symposium, High Temperature Corrosion and Materials Chemistry, M. McNallan, E. Opola, T. Maruyama and T. Narita eds., The Electrochemical Society, Pennington, p.258-269 (2000).*
  • Yamasaki, M. Habazaki, H. Kawashima, A. Asami, K. Akiyama E. and Hashimoto K.:"Oxidation behavior of amorphous Ni-Zr and Ni-Zr-rare earth element alloys", Proc. Per Kofstad Memorial Symposium, High Temperature Corrosion and Materials Chemistry, M. McNa・・・
    2000  [Not refereed][Not invited]
     
    Yamasaki, M. Habazaki, H. Kawashima, A. Asami, K. Akiyama E. and Hashimoto K.:"Oxidation behavior of amorphous Ni-Zr and Ni-Zr-rare earth element alloys", Proc. Per Kofstad Memorial Symposium, High Temperature Corrosion and Materials Chemistry, M. McNallan, E. Opola, T. Maruyama and T. Narita eds., The Electrochemical Society, Pennington, p.180-191 (2000).*
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood  SURFACE AND INTERFACE ANALYSIS  27-  (12)  1046  -1049  1999/12  [Not refereed][Not invited]
     
    Through analysis of a porous anodic oxide film (10 mu m thick) with controlled distributions of colouring species (namely copper and nickel) deposited electrolytically within the innermost 1 mu m of the film, the effective depth resolutions of electron probe microanalysis (EPMA) line scan analysis across the him section and of glow discharge optical emission spectroscopy (GDOES) depth profiling have been compared, The excellent depth resolution of GDOES (similar to 100 nm Far the buried layers of the present specimen) is revealed by the relatively good agreement between the measured average thickness of copper and nickel layers and the average deposited thickness for the particular deposition conditions: similar to 700 and 500 nm, respectively, The difference in thickness is related to slight non-uniformity in sputtering and to variations in thickness of colouring material, with local thicknesses up to 1200 nm indicated by transmission electron microscopy, In contrast, owing to a more limited spatial resolution, EPMA line scan analysis revealed layers of increased thickness, namely similar to 3 mu m, Copyright (C) 1999 John Wiley & Sons, Ltd.
  • A. C. Crossland, G. E. Thompson, C. J E Smith, H. Habazaki, K. Shimizu, P. Skeldon  Corrosion Science  41-  (10)  2053  -2069  1999/10/15  [Not refereed][Not invited]
     
    The behaviour of manganese during formation of barrier-type anodic films on non-equilibrium Al-2.5 at.% Mn and Al-16 at.% Mn alloys in ammonium pentaborate electrolyte (pH 8.2), and, for the latter alloy, also in sodium hydroxide (pH 12.0) and sulphuric acid (pH 0.2) electrolytes, has been investigated by transmission electron microscopy, Rutherford backscattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS). For both alloys, a manganese-free, amorphous alumina film develops initially, as manganese is enriched in an alloy layer, of about 2 nm thickness, located immediately beneath the growing film. At a critical level of enrichment, oxidation of manganese commences and the alumina film thereafter contains manganese species, while the enrichment of the alloy remains approximately constant. For the Al-2.5 at.% Mn alloy, the critical enrichment corresponds to approximately 2.6 x 1019 Mn atoms m-2, equivalent to about 22 at.% Mn in the enriched alloy layer a similar level of enrichment is probably attained for the Al-16 at.% Mn alloy, although this could not be quantified by the RBS analyses. The manganese species migrate outward in the anodic films about three times faster than Al3+ ions and eventually reach the film surface where a thin manganese-rich layer forms during anodizing in pentaborate and hydroxide electrolytes, but not in sulphuric acid electrolyte due to enhanced loss of manganese species to the solution. At high pH, the manganese-rich surface layer and, at low pH, the underlying manganese-containing film material, are of significantly reduced reactivity compared with anodic alumina consequently, barrier-type anodic films can be grown in sodium hydroxide and sulphuric acid electrolytes under conditions that lead to porous films on aluminium. XPS reveals mainly Mn3+ species in the near surface regions of all films, although there is evidence of Mn2+ species in the underlying film material.
  • HASHIMOTO Koji, HABAZAKI Hiroki  触媒  41-  (7)  510  -515  1999/10/10  [Not refereed][Not invited]
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood  SURFACE AND INTERFACE ANALYSIS  27-  (10)  950  -+  1999/10  [Not refereed][Not invited]
     
    Degradation of depth resolution during glow discharge optical emission spectroscopy (GDOES) depth profiling analysis of thin films, formed on relatively rough substrates, has been investigated using preconditioned aluminium substrates of controlled surface roughness. The anodic alumina films, similar to 120 nm thick, were depth profiled partially and examined carefully by atomic force microscopy and by transmission electron microscopy of ultramicrotomed sections, It is revealed clearly that depth profiling sputters ridges, associated with the rough surface, more rapidly than valleys, thereby degrading depth resolution, Further, such observations show that him sputtering proceeds very smoothly, with relatively little damage to the remaining film material, The excellent depth resolution realized during GDOES depth profiling analysis of films grown on mirror-finished, microscopically flat substrates is clearly associated with the highly uniform sputtering of amorphous anodic alumina. Copyright (C) 1999 John Wiley & Sons, Ltd.
  • 瀬尾真浩, 上野馨, 伏見公志, 幅崎浩樹  材料と環境討論会講演集  46th-  43  -46  1999/09/01  [Not refereed][Not invited]
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood  CORROSION SCIENCE  41-  (9)  1783  -1790  1999/09  [Not refereed][Not invited]
     
    Interfacial enrichment of iron during anodic oxide growth on an Al6Fe phase has been confirmed by examination of the oxide/Al6Fe interface in a field-emission and energy-filtering transmission electron microscope, with images obtained using electrons which have suffered a particular loss of energy. The iron enrichment is confined to a thin layer, 1-2 nm thick, immediately beneath the anodic oxide. The composition of the iron-enriched layer, determined by EDX analysis, using an electron probe of diameter of about 1 nm, is Al80.5Fe19.5. The impact of energy-filtering transmission electron microscopy for corrosion studies is also considered. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • HABAZAKI Hiroki  材料と環境 : zairyo-to-kankyo  48-  (8)  491  -492  1999/08/15  [Not refereed][Not invited]
  • Zhou, X, GE Thompson, P Skeldon, GC Wood, K Shimizu, H Habazaki  CORROSION SCIENCE  41-  (8)  1599  -1613  1999/08  [Not refereed][Not invited]
     
    Anodic oxidation of binary A1-3 wt.% Mg and A1-5 wt.% Rig alloys has been undertaken in ammonium pentaborate electrolyte to develop barrier-type anodic films at relatively high current efficiency. During anodizing, aluminium and magnesium are oxidized at the alloy/film interface, entering the film as Al3+ and Mg2+ ions. Such behaviour is anticipated for an alloying element with a Gibbs free energy of oxide formation per equivalent less than that of alumina, further, the greater outward migration rate of Mg2+ ions relative to that of Al3+ ions in anodic alumina is expected from consideration of the respective single metal-oxygen bond energies. However, unexpectedly, with continued anodizing, the essentially alumina film detaches from the alloy surface, which is followed by growth of new film on the exposed substrate. The film detachment from the alloy is associated with void formation, considered to result from the significantly reduced Pilling-Bedworth ratio for formation of anodic MgO compared with that for anodic alumina. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • K Fujimura, T Matsui, K Izumiya, N Kumagai, H Habazaki, A Kawashima, K Asami, K Hashimoto  MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING  267-  (2)  254  -259  1999/07  [Refereed][Not invited]
     
    MnO2-type manganese-molybdenum oxide electrodes with extremely high oxygen evolution efficiency in chloride-containing solutions have been prepared by anodic deposition on IrO2-coated titanium substrates. The anodic activity and the durability of electrodes have been examined in a 0.5 hi NaCl solution at pH 12 and 30 degrees C. For all prepared compositions, the manganese-molybdenum oxide electrodes show an oxygen evolution efficiency of almost 100%, when adequately thick oxides are deposited on the substrate. The galvanostatic polarization reveals that an increase in molybdenum content results in an increase in overpotential at current densities lower than 100 Am-2. However, at a current density of 1000 Am-2, often used for practical electrolysis, the overpotential is almost independent of the molybdenum content. The manganese-molybdenum oxide electrodes have significantly higher durability than the manganese oxide electrodes. During electrolysis at 1000 Am-2, the manganese-molybdenum oxide electrodes show only a slight decrease in oxygen evolution efficiency. Surface observation indicates that the slight decrease in the oxygen evolution efficiency results from the fact that the oxide layer is partly peeled off after electrolysis, even though a thin manganese-molybdenum oxide layer remains in the peeled-off regions. (C) 1999 Elsevier Science S.A. All rights reserved.
  • H Habazaki, K Takahiro, S Yamaguchi, K Shimizu, P Skeldon, GE Thompson, GC Wood  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  146-  (7)  2502  -2507  1999/07  [Not refereed][Not invited]
     
    The role of iron during anodizing of a non-equilibrium Al-4 atom % Fe alloy at high faradaic efficiency has been examined using high resolution transmission electron microscopy, Rutherford backscattering spectroscopy, and X-ray photoelectron spectroscopy. Anodic oxidation proceeds with initial formation of an anodic alumina film, free from iron species, and subsequent formation of an iron-contaminated alumina film, which is eventually contaminated by iron species throughout its thickness. During the initial oxidation of aluminum, iron atoms are accumulated in a thin layer of alloy, about 2-3 nm thick, immediately beneath the anodic film. When the average composition of the enriched alloy layer reaches approximately Al-25 atom % Fe, both aluminum and iron are oxidized and are incorporated into the film in their approximate alloy proportions in the presence of the enriched alloy layer. The incorporated iron species are in the trivalent state, and migrate outward in the growing anodic film about 1.8 times faster than Al3+ ions. The iron species eventually reach the film/electrolyte interface, forming a thin, iron-rich, hydrated layer probably composed of gamma-FeOOH. (C) 1999 The Electrochemical Society. S0013-4651(98)11-076-5. All rights reserved.
  • K Takahiro, H Habazaki, S Nagata, M Kishimoto, S Yamaguchi, F Nishiyama, S Nimori  NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS  152-  (2-3)  301  -306  1999/05  [Not refereed][Not invited]
     
    We have studied the effects of Si-preimplantation on the formation of carbon nitride by N implantation into glassy carbon (GC). Structure, composition and chemical bonding of the Si-implanted carbon nitride layers are examined by using Backscattering spectroscopy (BS), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Raman spectroscopy reveals that the carbon nitride layer containing up to 8 at.% Si is amorphous and has an sp? bonded structure with a small amount of C=N bonds. XPS analysis suggests that local C=N-Si(CnN3-n) arrangements exist in the nitride layer. It was revealed from backscattering measurements that the Si-preimplantation increases the saturation concentration of the implanted N atoms; it increases from 26 at.% N for the nitride layer without Si-preimplantation to 35 at.% for the Si-preimplanted nitride. In addition, Si atoms in the nitride layer suppress oxygen incorporation during N implantation. (C) 1999 Elsevier Science B.V. All rights reserved.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood  SURFACE AND INTERFACE ANALYSIS  27-  (3)  153  -156  1999/03  [Not refereed][Not invited]
     
    Radio-frequency-powered glow discharge optical emission spectroscopy (GDOES) is an extremely powerful and reliable technique for depth profiling analysis of thin, insulating barrier anodic films formed on aluminium. It allows ready and rapid analysis of the films, with depth resolution and sensitivity comparable with, or better than, those of secondary ion mass spectrometry depth profiling. However, for successful application of the technique, surfaces of specimens should be microscopically flat; surface roughness of dimensions similar to the thickness of the films can lead to almost total degradation of the depth profiles. Copyright (C) 1999 John Wiley & Sons, Ltd.
  • 橋本功二, 山崎倫昭, 藤村和也, 松井徹郎, 泉屋宏一, 秋山英二, 幅崎浩樹, 川嶋朝日, 浅見勝彦, 熊谷直和  ソーダと塩素  50-  (6)  224  -232  1999  [Not refereed][Not invited]
     
    橋本功二, 山崎倫昭, 藤村和也, 松井徹郎, 泉屋宏一, 秋山英二, 幅崎浩樹, 川嶋朝日, 浅見勝彦, 熊谷直和
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto  CORROSION SCIENCE  41-  (6)  1095  -1118  1999  [Not refereed][Not invited]
     
    Amorphous Fe-Cr-Ni-Nb alloys containing 9-68 at.% niobium were successfully prepared by the D.C. magnetron sputtering method using targets consisting of a commercial Type 304 stainless steel disc and high purity niobium discs. The corrosion rate of the sputter-deposited Fe-Cr-Ni-Nb alloys containing more than 19 at.% niobium in 6 M HCl at 30 degrees C was more than four orders of magnitude lower than that of bulk Type 304 stainless steel and almost the same as that of sputter-deposited niobium metal, although the corrosion rate of the alloys was higher than that of the binary Cr-Nb alloys. The corrosion potential of the alloys was higher than that of niobium and all the Fe-Cr-Ni-Nb alloys were spontaneously passivated in 6 M HCl at 30 degrees C. XPS analysis revealed that the spontaneous passive films formed on the alloys after immersion in 6 M HCl for 48 h were rich in chromium and niobium cations and deficient in iron cation. The formation of the homogeneous double oxyhydroxide films containing chromium, niobium and iron cations is responsible for the high corrosion resistance of the alloys. (C) 1998 Elsevier Science Ltd. All rights reserved.
  • Corrosion-resistant Mn-Cr-Zr alloys in chloride-containing media, A. A. El-Moneim, E. Akiyama, H. Habazaki, A. Kawashima, A. Kawashima, K. Asami and K. Hashimoto, Mater. Sci. Eng. A267, 285-293 (1999).
    1999  [Not refereed][Not invited]
  • Sulfidation and oxidation behavior of sputter-deposited Al-Mo-Nb alloys, K. Hon-yashiki, H. Habazaki, E. Akiyama, A. Kawashima, K. Asami and K. Hashimoto, Mater. Sci. Eng. A267, 277-284 (1999).
    1999  [Not refereed][Not invited]
  • Ni-Mo-O cathodes for hydrogen evolution in electrolysis of hot concentrated sodium chloride solution, A. Kawashima, T. Sakaki, H. Habazaki and K. Hashimoto, Mater. Sci. Eng. A267, 246-253 (1999).
    1999  [Not refereed][Not invited]
  • CO2 methanation catalysts prepared from amorphous alloys, M. Yamasaki, M. Komori, E. Akiyama, H. Habazaki, A. Kawashima, K. Asami and K. Hashimoto, Mater. Sci. Eng. A267, 220-226 (1999).
    1999  [Not refereed][Not invited]
  • The critical size and nature of nanocrystalline heterogeneity for pitting corrosion, K. Hashimoto, M. Mehmood, X.-Y. Li, E. Akiyama, H. Habazaki, A. Kawashima and K. Asami, Proc. Symp. Critical Factors in Localized Corrosion, R. G. Kelly, G. S. Frankel・・・
    1999  [Not refereed][Not invited]
     
    The critical size and nature of nanocrystalline heterogeneity for pitting corrosion, K. Hashimoto, M. Mehmood, X.-Y. Li, E. Akiyama, H. Habazaki, A. Kawashima and K. Asami, Proc. Symp. Critical Factors in Localized Corrosion, R. G. Kelly, G. S. Frankel, P. M. Natishan and R. C. Newman eds., The Electrochemical Society, p.245-255 (1999).
  • K Fujimura, K Izumiya, A Kawashima, E Akiyama, H Habazaki, N Kumagai, K Hashimoto  JOURNAL OF APPLIED ELECTROCHEMISTRY  29-  (6)  765  -771  1999  [Not refereed][Not invited]
     
    Manganese-molybdenum oxide electrodes were prepared by anodic deposition on an IrO2-coated titanium substrate at a constant current density of 600 A m(-2) from baths containing 0.2 M MnSO4 and 0-0.1 M Na2MoO4 at 90 degrees C and pH 0.5. These electrodes were characterised for oxygen evolution in the electrolysis at 1,000 A m(-2) in 0.5 M NaCl solution at 30 degrees C and pH 8 or 12. The most active and stable oxygen evolving anode exhibited 100% efficiency for oxygen evolution, and an efficiency of 98.5% for over 1,500 h at pH 12 and of 96.5% for over 2,800 h at pH 8 of continuous electrolysis. X-ray diffraction measurement and XPS analysis indicated that the deposits consist of a nanocrystalline single gamma-MnO2 type phase, and manganese and molybdenum in the deposits are in the Mn4+ and Mo6+ states. The electrochemical studies showed that the manganese-molybdenum oxide electrodes drastically reduced the electrocatalytic activity for chlorine evolution to the undetectable level, resulting in 100% efficiency for oxygen evolution, although the addition of molybdenum slightly increased the oxygen overpotential.
  • Zhou, X, GE Thompson, P Skeldon, GC Wood, K Shimizu, H Habazaki  CORROSION SCIENCE  41-  (6)  1089  -1094  1999  [Refereed][Not invited]
     
    Anodic film growth on an electropolished Al-2wt% Cu alloy is associated with copper enrichment in the alloy immediately below the alumina film, oxidation of copper and incorporation of outwardly mobile Cu2+ ions within the thickening alumina film. Oxygen gas generation is also evident within the alumina which, through bubble formation, film cracking and healing, results in highly roughened anodized surfaces. Interestingly, gas generation is dependent upon alloy grain orientation, suggesting that the shape, size, arrangement and persistence of the individual copper-rich clusters in the enriched layer influence the anodizing behaviour. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • Adhesion of anodic films on aluminum-lithium alloys, P. Skeldon, X. Zhou, G.E. Thompson, G.C. Wood, H. Habazaki and K. Shimizu, Corrosion, 55, 561-565 (1999).
    1999  [Not refereed][Not invited]
  • Acid- and alkali-resistant film generation on an Al-Mn-Ce alloy, A.C. Crossland, G.E. Thompson, P. Skeldon, C.J.E. Smith, H. Habazaki and K. Shimizu, Trans. Inst. Metal Finish., 77, 95-98 (1999).
    1999  [Not refereed][Not invited]
  • M Mehmood, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto  CORROSION SCIENCE  41-  (9)  1871  -1890  1999  [Not refereed][Not invited]
     
    The effect of heat treatment, inducing the formation of nanocrystalline two phase alloys on the corrosion resistance of sputter-deposited Cr-Ti alloys containing 22, 48, 60, and 72 at.% titanium has been studied in 6M HCl. The as-deposited homogeneous Cr-Ti alloys are spontaneously passive in 6M HCl, except Cr-72Ti alloy, although both chromium and titanium metals undergo active dissolution in this environment. The air-formed surface films on the alloys containing sufficient amounts of both chromium and titanium are highly protective, being responsible for spontaneous passivation. The heat treatment of the alloys leading to the formation of hcp titanium or bcc chromium with a grain size of 20-25 nm as well as CT2Ti is detrimental for the high corrosion resistance of these alloys. However, when Cr2Ti and bcc solid solution of titanium containing similar to 14 at.% chromium are formed, the high corrosion resistance of the as-deposited alloys is sustained. The high corrosion resistance of the sputter-deposited Cr-Ti alloys is largely reduced by the formation of less corrosion-resistant hcp titanium or bce chromium phases, but is maintained when only the phases containing certain amounts of both elements are formed by heat treatment. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • Spontaneously passive amorphous Fe-Cr-Ni-Ta alloys in 12M HCl, K. Hashimoto, X.-Y. Li, E. Akiyama, H. Habazaki, A. Kawashima and K. Hashimoto, 14th Int. Cong. Corrosion, paper No.400, pp.1-10 (1999).
    1999  [Not refereed][Not invited]
  • Behaviour of copper during electropolishing and anodizing of Al-0.9 at% Cu alloy, X. Zhou, G.E. Thompson, P. Skeldon, H. Habazaki, K. Shimizu, G.C. Wood, M.A. Paez and G. Scamans, 14th Int. Cong. Corrosion, paper No.365, pp.1-11 (1999).
    1999  [Not refereed][Not invited]
  • Residual flaws due to formation of oxygen bubbles in anodic alumina, A.C.Crossland, H. Habazaki, K. Shimizu, P. Skeldon, G.E. Thompson, G.C. Wood, X. Zhou and C.J.E Smith, Corros. Sci., 41, 1945-1954 (1999).
    1999  [Not refereed][Not invited]
  • F Echeverria, P Skeldon, GE Thompson, H Habazaki, K Shimizu  JOURNAL OF THE ELECTROCHEMICAL SOCIETY  146-  (10)  3711  -3715  1999  [Not refereed][Not invited]
     
    Procedures are described for the examination in cross section of thin films by atomic force microscopy (AFM), with reference to anodic films on III-V semiconductors and aluminium as examples of possible applications. It is shown that by preparing cross-sectional surfaces with a diamond knife, the thickness and morphology of anodic films can be disclosed by AFM at a resolution approaching that of transmission electron microscopy, with features such as local nonuniformity of film thickness and layering of the film being revealed. (C) 1999 The Electrochemical Society. S0013-4651(99)05-051-X. All rights reserved.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood  SURFACE AND INTERFACE ANALYSIS  27-  (11)  998  -1002  1999  [Not refereed][Not invited]
     
    Analysis of a surface film similar to 4 ram thick formed on electropolished, high-purity aluminium given a post-electropolishing treatment in a hot CrO3-H3PO4 solution demonstrates the suitability of glow discharge optical emission spectroscopy for in-depth analysis of very thin films. Thus, the distributions of impurity species, namely chromium, hydrogen and phosphorus species, in the film are revealed, with excellent depth resolution, Further, copper enrichment in a thin layer a few nanometres thick in the metal immediately beneath the surface film, resulting from initial oxidation of aluminium during electropolishing, is revealed, Copyright (C) 1999 John Wiley & Sons, Ltd.
  • 清水健一  表面技術  50-  (1)  2  -9  1999  [Not refereed][Not invited]
  • Anodizing of aluminium alloys, G.E. Thompson, H. Habazaki, K. Shimizu, M. Sakairi, P. Skeldon, X. Zhou and G.C. Wood, Aircraft Eng. Aerospace Tech., 71, 228-238 (1999).
    1999  [Not refereed][Not invited]
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood  CORROSION SCIENCE  41-  (10)  1971  -1976  1999  [Not refereed][Not invited]
     
    Through the use of a thin layer covering an aluminium surface, obtained by electropolishing and subsequent dipping in a hot CrO3-H3PO4 solution, as a source for incorporation of Cr3+ and PO43- species, the migrations of the respective species in growing anodic alumina have been examined successfully. It was found that the Cr3+ species migrate outward and the PO43- species migrate inward. The rates of migration of Cr3+ species relative to that of Al3+ ions and PO43- ions relative to that of O2- ions are 0.74 and 0.51, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • M Mehmood, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto  CORROSION SCIENCE  41-  (3)  477  -499  1999  [Not refereed][Not invited]
     
    The effect of heat treatment on the corrosion resistance of sputter-deposited aluminum-chromium alloys containing 16-51 at% chromium has been studied in 0.1 and 0.5 M HCl. Structural relaxation decreases the corrosion rate of Al-16Cr alloy on which the passive film cannot be formed, since the corrosion rate is controlled by the reactivity of the alloy surface. The corrosion rate of spontaneously passive Al-35Cr alloy increases by crystallization. The chromium enrichment of the matrix, as a result of precipitation of a nanocrystalline aluminum-rich phase, results in enhancement of the corrosion resistance. However, if the size of the less corrosion-resistant aluminum-rich grains exceeds a critical limit of similar to 20 nm, the corrosion resistance decreases. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • Gel formation and the efficiency of anodic film growth on aluminum, J. R. Morlidge, P. Skeldon, G. E. Thompson, H. Habazaki, K. Shimizu and G. C. Wood, Electrochim. Acta, 44, 2423-2435 (1999).
    1999  [Not refereed][Not invited]
  • HABAZAKI Hiroki, SHIMIZU Kenichi, SKELDON Peter, THOMPSON George e, WOOD Graham c  Journal of the Surface Science Society of Japan  19-  (12)  772  -780  1998/12/10  [Not refereed][Not invited]
     
    The growth of barrier-type anodic films on aluminium and its alloys is reviewed, with particular consideration of ionic transport processes in the growing anodic films. The films formed are generally amorphous, and grow both at the film/electrolyte interface by outwards migration of cations and at the metal/film interface by inwards migration of ani-ons. Various types of foreign species are incorporated into the anodic films from electrolytes or alloy substrates. The in-corporated species are mobile inwards, or outwards or immobile under the high electric field of 106-107 V cm-2. This provides us with some important information on the complex ionic transport processes in amorphous anodic films. The anodic films formed on uniform Al-valve metal alloys are generally of two layers, due to the different migration rates of A13+ ions and valve metal ions. The properties and growth behavior of the films vary almost linearly with film composi-tion.
  • SHIMIZU Kenichi, HABAZAKI Hiroki, SKELDON Peter, THOMPSON George e, WOOD Graham c  Journal of the Surface Science Society of Japan  19-  (12)  805  -811  1998/12/10  [Not refereed][Not invited]
     
    Based on the literatures published over the past fifty years, a brief review is given of the studies on anodic oxide growth on tantalum. It has been demonstrated clearly that the oxide growth involves highly complex and unprecedented processes of ionic transport to which no satisfactory theory has yet been presented. Thus, in amorphous oxide and in the presence of a high electric field of 106-107 V cm-1 range, both Ta5+ and O2- ions migrate in a highly correlated manner, with new oxide formation proceeding simultaneously at the oxide/electrolyte and metal/oxide interfaces. Further small amounts of electrolyte anions are incorporated into the oxide which, depending on their nature, may be immobile or mobile inwardly or outwardly. To date, such complex processes of ionic transport may be best explained, though only qualitatively, by a "liquid droplet" model presented recently by Mott. However, further insights into the nature of liquid droplets, whose formation is thought to be an elemental process of ionic transport, are apparently required in the eventual development of an integrated theory of ionic transport. It is emphasized that the tracer experiments, in which migrations or non-migrations of various foreign cationic or anionic tracers are studied and interpreted in terms of the role of high electric fields, acting either generally or locally, on the dissociation or non-dissociation of various structural units in the oxides, provide an important and effective rote towards the required understanding.
  • T Aihara, A Kawashima, E Akiyama, H Habazaki, K Asami, K Hashimoto  MATERIALS TRANSACTIONS JIM  39-  (10)  1017  -1023  1998/10  [Refereed][Not invited]
     
    Binary Co-Mo and Co-Al, and ternary Co-Mo-Al alloy electrodes for hydrogen evolution were prepared by using sputter deposition on a nickel substrate with good adhesion. The hydrogen evolution reaction (HER) of these alloy electrodes in the deaerated 1 kmol.m(-3) NaOH at 303 K is enhanced significantly compared with pure cobalt electrode. The effective surface area of these alloy electrodes estimated from ac impedance technique is largely increased by leaching of aluminum into alkaline solution. The electrocatalytic activity sequence is Co-Mo-Al > Co-Mo > Co-Al. The maximum activity is obtained for Co-10Mo-58Al alloy with a hydrogen overpotential as low as 110 mV at 10(3) A.m(-2). The enhancement of HER is attributed to both the synergistic effect of alloy constituents and the large effective surface area.
  • D Huerta, PY Park, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto  PROCEEDINGS OF THE SYMPOSIUM ON PASSIVITY AND ITS BREAKDOWN  97-  (26)  770  -780  1998  [Refereed][Not invited]
     
    Sputter-deposited Mo-Nb alloys are spontaneously passive in 12 M HCl and show significantly higher corrosion resistance than molybdenum and niobium. The air-formed film is slightly rich in niobium. Immediately after immersion, the molybdenum content in the film begins to increase and finally the molybdenum-enriched film is formed on the alloys except the alloys with 75 at% or higher niobium. After immersion for 50 min no concentration gradient in depth is observed, while immersion for 168 h leads to a niobium enrichment in the exterior of the film mostly due to transpassive dissolution of molybdenum. Nevertheless, the Mo content significantly increases in the interior of the film, indicating an increase in the protectiveness of the passive film. Synergistic effect of molybdenum and niobium is responsible for the high corrosion resistance. The niobium enrichment in the exterior of the film prevents transpassive dissolution of molybdenum and the increase in the Mo4+ content in the interior of the film increases the protectiveness of the passive film.
  • M Mehmood, BP Zhang, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto  CORROSION SCIENCE  40-  (1)  1  -17  1998/01  [Refereed][Not invited]
     
    Sputter-deposited amorphous Cr-60Zr and Cr-67Zr alloys are spontaneously passive in 6 M HCl but suffer pitting by anodic polarization. The change in pitting susceptibility by the introduction of heterogeneity to the homogeneous amorphous alloys by crystallization heat treatment is studied. Heat treatment results in two-stage crystallization: (i) precipitation of hcp zirconium ranging in average size from 8 to 20 nm and (ii) massive transformation from amorphous phase to intermetallic compound, Cr2Zr. The heat treatment gives rise to the ennoblement of pitting potential in spite of the formation of nanocrystalline phases. This is due to the fact that the formation of the hcp zirconium phase leads to an increase in the chromium content of the matrix phase which is able to form thin, protective chromium-rich passive films covering the entire heterogenous alloy surface. When the average size of the less corrosion-resistant hcp zirconium precipitates exceeds a critical size, 20 nm, the protective chromium-rich passive films cannot completely cover the precipitates and the pitting resistance decreases. (C) 1997 Elsevier Science Ltd.
  • K Funayama, H Habazaki, E Akiyama, A Kawashima, K Asami, K Hashimoto, M Komori  MATERIALS TRANSACTIONS JIM  38-  (7)  643  -649  1997/07  [Refereed][Not invited]
     
    Sputter deposition technique has been applied to the preparation of amorphous alloy precursors of catalysts on a fine oxide powder, in order to overcome the low surface area of the catalysts prepared from melt-spun amorphous alloy precursors. Amorphous Ni-Ta-Pd alloys have been sputter-deposited onto the gamma-alumina powder with a high surface area, and then pre-oxidized al 1023 K in a 0.5% NO atmosphere. During the preoxidation, the amorphous alloys have been converted to palladium catalysts supported on the NiTa2O6 double oxide. The BET areas of the catalysts thus prepared (sputter-deposited catalysts) are approximately 50 times higher than those prepared from a melt-spun Ni-40Ta-1Pd alloy precursor (melt-spun catalyst). The catalytic activity of the sputter-deposited catalysts for NO decomposition becomes about twice as high as that of the melt-spun catalyst. Furthermore, the selectivity of nitrogen formation is also improved compared with the melt-spun catalyst. Accordingly, the application of sputtering technique is quite suited for preparing amorphous alloy catalyst precursors with a high surface area.
  • HJ Lee, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto  CORROSION SCIENCE  39-  (2)  321  -332  1997/02  [Refereed][Not invited]
     
    The corrosion behavior of Ni-10Ta-20P, Ni-10Ta and Ni-20P alloys in 12 M HCl solution open to air at 30 degrees C was investigated in order to clarify the roles of tantalum and phosphorus. Additions of 10 at% tantalum and 20 at% phosphorus to the nickel alloy result in excellent corrosion resistance and in the accumulation of tantalum and phosphorus in the surface film on this alloy owing to dissolution of the nickel from just after immersion, the highly protective passive film formed being stable during prolonged immersion. By contrast, the binary nickel alloy with only a tantalum addition is not passivated and dissolves actively, forming a thick corrosion product film. The nickel alloy containing only phosphorus is not corrosion-resistant, forming a nickel phosphate him, although the film is more stable than that formed on the nickel alloy containing only tantalum. (C) 1997 Elsevier Science Ltd.
  • BP Zhang, K Funayama, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto  MATERIALS TRANSACTIONS JIM  38-  (2)  123  -132  1997/02  [Refereed][Not invited]
     
    Amorphous Ni-40Ta-Pd alloys are known as the precursor of the catalysts for the decomposition of nitrogen monoxide. Since the catalytic activity appears after oxidation, the relationship between the activity and structure was investigated after oxidation in air al 750 degrees C for different periods of time. The structure developed by oxidation was characterized with special interest in the dispersion state of palladium phase in the matrix oxides by means of SEM/EDX, EPMA and TEM/EDX. At the early stage of the oxidation, NiO, Ta2O5 and PdO are first formed. The oxides consist of two layers; comprising an outer NiO layer and an inner layer containing Ni, Ta and Pd ions. The outer NiO is developed by the outward diffusion of nickel ion during oxidation. Prolonged oxidation leads to the development of porosity of the specimen and to the formation of double NiTa2O6 oxide by the reaction of NiO with Ta2O5 in the inner layer. The inner layer formed after the complete oxidation for the amorphous Ni-40Ta-Pd alloy has sponge-like morphology, and consists of PdO, NiO and NiTa2O6. The addition of palladium prevents the diffusion of nickel to the surface, leading to the decrease in the thickness of the surface NiO layer and to the decrease in the grain size of matrix oxides. No change in the supporting oxides was observed but PdO is decomposed to Pd after the decomposition of NO gas. Palladium particles of 50-100 nm in diameter were dispersed homogeneously in the matrix oxide. The high catalytic activity for the decomposition of NO gas is attributable to the palladium dispersed on the matrix oxides with fine grain size and porous structure developed by the oxidation of amorphous Ni-Ta-Pd alloys.
  • 橋本 功二, 秋山 英二, 幅崎 浩樹  月刊エコインダストリ-  2-  (2)  5  -14  1997/02  [Not refereed][Not invited]
  • HASHIMOTO Koji, AKIYAMA Eiji, HABAZAKI Hiroki, KAWASHIMA Asahi, SHIMAMURA Kazuo, KOMORI Mitsuru, KUMAGAI Naokazu  Corrosion engineering  45-  (10)  614  -620  1996/10/15  [Not refereed][Not invited]
     
    Effective electrodes for electrolysis of seawater for production of hydrogen (H2) ~without releasing chlorine into atmosphere and catalysts for production of methane (CH4~) by the reaction of carbon dioxide (CO2) with H2 have been tailored. Using these novel materials a CO2 recycling plant for substantiation of our proposal has been built on the roof of Institute for Materials Research, Tohoku University. The CO2 recycling plant consists of a desert, a coast close to the desert and an energy consuming district. At the desert electricity is generated by solar cell operation and transmitted to the coast close to the desert. At the coast H2 is produced by electrolysis of seawater using the electricity, and then CH4 is formed by the reaction of H2 and CO2. CH4 is transported to the energy consuming district. At the energy consuming district combustion of CH4 is carried out not by air but by O2 and CO2 is recovered after removing H2O from the exhaust gas composed only of CO2 and H2O. The recovered CO2 is sent again to the coast close to the desert for reproduction of CH4. The CO2 recycling plant has substantiated that the solar energy at the desert can be used by energy consumers in the form of CH4 without emitting CO2 into atmosphere.
  • HJ Lee, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto  MATERIALS TRANSACTIONS JIM  37-  (3)  383  -388  1996/03  [Refereed][Not invited]
     
    The addition of 30 at% or more tantalum to Ni-5P alloy greatly enhances the corrosion resistance in 12 M HCl at 30 degrees C. The corrosion rate of amorphous Ni-40Ta-5P alloy is about three orders of magnitude lower than that of Ni-5P alloy. The addition of sufficient amounts of tantalum to Ni-5P alloys leads to an ennoblement of the open circuit potential and to spontaneous passivation. The addition of a large amount of tantalum to the Ni-Ta alloy contained a small amount of phosphorus, such as 5 at%, enhances the formation of the tantalum enriched passive film which prevents oxidation of phosphorus.
  • Hashimoto, K, Habazaki, H, Akiyama, E  Zairyo  45-  (9)  1067  -1068  1996  [Refereed][Not invited]
  • Hiroki Habazaki, Koji Hashimoto  Zairyo-to-Kankyo  44-  (3)  174  -182  1995  [Not refereed][Not invited]
     
    A review is given of our work on the development of new, novel alloys with high resistance to high temperature corrosion in sulfidizing and oxydizing environments. The corrosion behavior of sputter-deposited amorphous Al-(34-46)Mo and Al-(31-33)Mo-(6-16)Si alloys has been studied as a function of temperature of 973–1273 K in sulfur vapor of 103 Pa as well as in oxygen of 105 Pa and in air. The sulfidation process has been found to follow parabolic kinetics, being thus diffusion controlled. Marker experiments have shown that the slowest step, determining the overall reaction rate, is the inward diffusion of sulfur through the inner barrier layer of the scale. Over the whole temperature range studied these binary and ternary alloys have shown excellent resistance to sulfide corrosion, their sulfidation rates being comparable to or even lower than the oxidation rates of chromia-forming materials. No influence of silicon on the sulfidation rate of Al-Mo alloys has been observed. The oxidation resistance of binary Al-Mo alloys has been found to be satisfactory, but only at temperatures below 1073 K. Above the melting point of Mo03 (1069 K), the scale, consisting mainly of A1203 with about 5% of Mo03 becomes unprotective because of evaporation of molybdenum oxide. On the other hand, ternary Al-Mo-Si alloys show excellent resistance to oxidizing environments, up to about 1200 K, their oxidation rates being comparable to those of alumina formers. No traces of molybdenum have been found in alumina scales on these alloys. © 1995, Japan Society of Corrosion Engineering. All rights reserved.
  • H HABAZAKI, K TAKAHIRO, S YAMAGUCHI, K HASHIMOTO, J DABEK, S MROWEC, M DANIELEWSKI  CORROSION SCIENCE  36-  (1)  199  -202  1994/01  [Not refereed][Not invited]
     
    The growth mechanism of the sulphide scale on amorphous Al-Mo alloys has been studied using a marker technique. A very thin (5 nm) gold marker film was deposited onto the surface of the Al-46Mo alloy and after sulphidation for 5 hours at 1073 K the gold marker distribution in the scale has been determined by RBS. It has been found that the main part of the marker remained at the scale surface indicating that the double-layer sulphide scale on the discussed alloy is growing by the inward diffusion of sulphur.
  • PARK P Y, AKIYAMA E, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  36-  (8)  1395  -1410  1994  [Not refereed][Not invited]
  • TAKAMURA K, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Mater. Sci. Eng.  181/182-  1137  -1140  1994  [Not refereed][Not invited]
  • TADA T, HABAZAKI H, AKIYAMA E, KAWASHIMA A, ASAMI K, HASHIMOTO K  Mater. Sci. Eng.  181/182-  1133  -1136  1994  [Not refereed][Not invited]
  • AKIYAMA E, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Mater. Sci. Eng.  181/182-  1128  -1132  1994  [Not refereed][Not invited]
  • KOMORI M, HABAZAKI H, AKIYAMA E, KAWASHIMA A, ASAMI K, HASHIMOTO K  Mater. Sci. Eng.  181/182-  1123  -1127  1994  [Not refereed][Not invited]
  • IM B‐M, AKIYAMA E, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  ┣DBMater. Sci. Engng. (/)-┫DB  181/182-  1119  -1122  1994  [Not refereed][Not invited]
  • B. P. Zhang, E. Akiyama, H. Habazaki, A. Kawashima, K. Asami, K. Hashimoto  Materials Science and Engineering A  181/182-  (C)  1114  -1118  1994  [Not refereed][Not invited]
     
    To prepare highly corrosion-resistant amorphous CrNiP alloys, the amorphizable composition range was determined and the corrosion resistance was assessed from the weight loss in concentrated HCl and HF solutions. All the amorphous CrNiP alloys showed extremely high corrosion resistance in both concentrated HCl and HF solutions. The effects of crystallinity and the chromium content on the corrosion resistance were clearly observed in the concentrated HCl solution. In the concentrated HF solution, all the CrNiP alloys were extremely corrosion resistant, while the binary CrNi alloys had low corrosion resistance. The amorphous CrNi19P alloys also exhibited the low corrosion rate of about 0.004 mm per year in the mixture of aggressive 12 M HCl and 47% HF solution. The effects of crystallinity and alloying with phosphorus and chromium on the corrosion resistance in HCl and HF solutions were explained in terms of the homogeneity of alloys, the formation of an elemental phosphorus layer during the initial dissolution, and the formation of the highly protective, passive chromium oxyhydroxide. © 1994.
  • KAWASHIMA A, HABAZAKI H, ASAMI K, HASHIMOTO K, MURATA H, ICHIKAWA K, FUJII S, SHINOHARA T  Mater. Sci. Eng.  181/182-  1109  -1113  1994  [Not refereed][Not invited]
  • K. Ebidzuka, H. Habazaki, E. Akiyama, A. Kawashima, K. Asami, K. Hashimoto  Materials Science and Engineering A  181/182-  (C)  1091  -1094  1994  [Not refereed][Not invited]
     
    Catalytic decomposition by hydrolysis of CCl2F2 (CFC-12) to HF, HCl and CO2 was studied for the amorphous binary NiZr and ternary NiZrCr alloy catalysts. The activity and durability for each catalyst were measured and compared. The amorphous Ni40at.%Zr alloy maintained its high activity for 70 h at 723 K, after which it decreased drastically. The amorphous NiZrCr alloy, activated at 823 K for several hours, showed a high activity and gave much longer durability at 723 K. The increase in the alloy chromium content enhanced the activity and elongated the life time. Among the NiZr15at.%Cr alloys, the specimen containing 40 at.% Zr showed the highest activity for the decomposition of CFC-12 but the specimen with 70 at.% Zr could not even be activated. The characterization of the reacted specimens was carried out using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy. Their structures were significantly changed by the reaction, because they were exposed to corrosive HCl and HF, formed by the decomposition reaction of CFC-12. © 1994.
  • Toshiyuki Mori, Eiji Akiyama, Hiroki Habazaki, Asahi Kawashima, Katsuhiko Asami, Koji Hashimoto  Materials Science and Engineering A  181/182-  (C)  1081  -1084  1994  [Not refereed][Not invited]
     
    Amorphous Ni-valve metal alloys containing a few atomic per cent of platinum group elements were prepared by rapid quenching and were employed for electrochemical oxidation of sulfite in 0.075 M Na2B4O7 + 0.3 M H3BO3 + 1 M Na2SO3 at 30°C. Of the amorphous alloy electrodes containing ruthenium, rhodium, iridium or platinum, the platinum-containing electrodes showed the highest activity, which was almost the same as or even higher than that of the platinized platinum black electrode. Furthermore, the combined addition of platinum and ruthenium enhanced the catalytic activity. When ruthenium was substituted for part of the platinum, the maximum activity for amorphous Ni40NbxPt(1 - x)Ru alloys was observed at about 0.8 at.% Pt. © 1994.
  • KIM J H, AKIYAMA E, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  36-  (3)  511  -523  1994  [Not refereed][Not invited]
  • M KOMORI, H HABAZAKI, E AKIYAMA, A KAWASHIMA, K ASAMI, K HASHIMOTO  MATERIALS TRANSACTIONS JIM  34-  (8)  725  -731  1993/08  [Not refereed][Not invited]
     
    Surface-activated amorphous Co-Zr alloys containing platinum group elements were used for decomposition of nitrogen monoxide. The alloys were immersed in hydrofluoric acid for activation. The HF-treated amorphous alloys were initially inactive for decomposition of nitrogen monoxide at 773 K, but became active after oxidation by exposure to nitrogen monoxide at 773 K. XRD and XPS analyses revealed that the active catalysts were composed of platinum group elements, Co3O4 and ZrO2. Platinum group elements in both metallic and oxidized states were supported on the oxides. The catalytic activity depended on platinum group elements. The palladium-containing alloy showed the highest activity and even higher activity than that of a palladium-black. The high activity of the palladium-containing catalyst was attributed to the synergistic effect of palladium and oxides of cobalt and zirconium.
  • E HIROTA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO  SCIENCE REPORTS OF THE RESEARCH INSTITUTES TOHOKU UNIVERSITY SERIES A-PHYSICS CHEMISTRY AND METALLURGY  38-  (1)  53  -62  1993/03  [Not refereed][Not invited]
     
    An attempt was made for preparation of magnesium alloys with valve metals, such as titanium, zirconium, niobium and tantalum whose melting points far exceed the boiling point of magnesium. These alloys became single phase solid solutions in wide composition ranges, but were crystalline in contrast to the fact that other alloys with valve metals such as nickel-, copper-and aluminum-base alloys were amorphous in wide composition ranges. The alloys containing sufficient amounts of valve metals showed high corrosion resistance due to spontaneous passivation in 1 M HCl at 30-degrees-C. The high corrosion resistance was attributed to the formation of passive oxyhydroxide films in which valve metal cations were remarkably concentrated. However, because of crystalline alloys and because of the presence of active magnesium, their corrosion resistance is lower than that of valve metals.
  • T SHIMADA, A KAWASHIMA, H HABAZAKI, K ASAMI, K HASHIMOTO  SCIENCE REPORTS OF THE RESEARCH INSTITUTES TOHOKU UNIVERSITY SERIES A-PHYSICS CHEMISTRY AND METALLURGY  38-  (1)  63  -75  1993/03  [Not refereed][Not invited]
     
    Exploratory work has been done on the performance of electrocatalytic reduction of oxygen and anodic oxidation of ethylene and methane on the gas-diffusion electrodes prepared from amorphous alloys containing one atomic percent platinum group elements. Gas-diffusion electrodes were made by coating the mixture of catalysts prepared by immersion in 46% HF from melt-spun ribbon shaped amorphous alloys, carbon black, polytetrafluoroethylene and sugar, and subsequent baking in nitrogen gas. The electrode made of catalyst prepared from amorphous nickel-niobium alloy containing platinum and ruthenium was the most active for electrocatalytic reduction of oxygen. For electro-oxidation of ethylene and methane, amorphous nickel-valve metal alloy containing only platinum possesses higher activity in comparison to the electrode made of platinum black powder.
  • K WAKUDA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO  SCIENCE REPORTS OF THE RESEARCH INSTITUTES TOHOKU UNIVERSITY SERIES A-PHYSICS CHEMISTRY AND METALLURGY  38-  (1)  76  -87  1993/03  [Not refereed][Not invited]
     
    The amorphous Ni-valve metal (Ti, Zr, Nb and Ta) alloys containing a few at% of platinum group elements were activated by immersion into hydrofluoric acid and used for hydrogenation of carbon dioxide at 100-300-degrees-C. This surface activation led to formation of nanocrystalline surface alloys with high surface area, and to surface enrichment of platinum group elements on the titanium-, niobium- and tantalum-containing alloys, but not on the zirconium-containing alloys. The surface of the latter alloys was mainly composed of nickel. The activity and selectivity for methane formation on the titanium-, niobium- and tantalum-containing alloys were significantly affected by the difference in the platinum group elements; the ruthenium- and rhodium-containing alloys showed higher activity and selectivity for methane formation while the platinum-containing alloys exhibited the lowest activity for methane formation and produced mainly carbon monoxide. The zirconium-containing alloys showed the one order of magnitude higher activity for methanation of carbon dioxide in comparison with the titanium-, niobium- and tantalum-containing alloys and produced exclusively methane independent of platinum group elements contained. The alloying with zirconium seems very important to prepare the alloy catalysts having the extremely high activity.
  • HABAZAKI H.  The Electrochemical Society Proceedings Series, Pennington, NJ, 1993  393  -404  1993
  • KIM J H, AKIYAMA E, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  34-  (12)  1947  -1955  1993  [Not refereed][Not invited]
  • Byung Mo Im, Eiji Akiyama, Hiroki Habazaki, Asahi Kawashima, Katsuhiko Asami, Koji Hashimoto  Corrosion Science  34-  (11)  1829  -1839  1993  [Not refereed][Not invited]
     
    The corrosion behaviour of amorphous Fe-Cr-13P-7C, Fe-Cr-13P-7B and Fe-Cr-20B alloys in 9M H2SO4 solution at 30°C was investigated. An increase in the alloy chromium content improved the corrosion resistance of the amorphous Fe-Cr-13P-7C and Fe-Cr-13P-7B alloys. When only B is contained as a metalloid, alloying with chromium up to 15 at% is ineffective in increasing the corrosion resistance. The addition of phosphorous accelerates the cathodic reaction of hydrogen evolution on the amorphous Fe-Cr alloys.This leads to sharp ennoblement in the corrosion potential of amorphous Fe-8Cr-13P-7M (M = C,B) alloys from the active state to the passive state with immersion time, while the corrosion potential of Fe-8Cr-20B alloy is unchanged. Chromium is concentrated in the passive film on the amorphous Fe-8Cr-7M (M = C,B) alloys formed by immersion in 9M H2SO4 solution, and is further concentrated by prolonged immersion. In particular, the concentration of chromic ions in the passive film on the Fe-8Cr-13P-7C alloy is higher than in the film on the Fe-8Cr-13P-7B alloy.
  • KIM J H, AKIYAMA E, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  34-  (11)  1817  -1827  1993  [Not refereed][Not invited]
  • KIM J H, AKIYAMA E, YOSHIOKA H, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  34-  (6)  975  -987  1993  [Not refereed][Not invited]
  • ASAMI K, HABAZAKI H, KAWASHIMA K, HASHIMOTO K  Corros. Sci.  34-  (3)  445  -459  1993  [Not refereed][Not invited]
  • ZHANG B‐P, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  34-  (2)  201  -215  1993  [Not refereed][Not invited]
  • AKIYAMA E, YOSHIOKA H, KIM J H, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  34-  (1)  27  -40  1993  [Not refereed][Not invited]
  • TERUUCHI K, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Applied Catalysis  76-  (1)  79  -93  1991  [Not refereed][Not invited]
  • HABAZAKI H, LU Y‐P, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  32-  (11)  1227  -1235  1991  [Not refereed][Not invited]
  • HIROTA E, YOSHIOKA H, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  32-  (11)  1213  -1225  1991  [Not refereed][Not invited]
  • YOSHIOKA H, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Electrochim. Acta  36-  (7)  1227  -1233  1991  [Not refereed][Not invited]
  • ZHANG B‐P, HABAZAKI H, KAWASHIMA A, ASAMI K, HIRAGA K, HASHIMOTO K  Corros. Sci.  32-  (4)  433  -442  1991  [Not refereed][Not invited]
  • YAN Q, YOSHIOKA H, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  32-  (3)  327  -335  1991  [Not refereed][Not invited]
  • YOSHIOKA H, HABAZAKI H, KAWASHIMA A, ASAMI K, HASHIMOTO K  Corros. Sci.  32-  (3)  313  -325  1991  [Not refereed][Not invited]
  • HABAZAKI H.  J. Electrochem. Soc  138-  (1)  76  -81  1991  [Not refereed][Not invited]
  • Q YAN, H YOSHIOKA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO  JOURNAL OF NON-CRYSTALLINE SOLIDS  125-  (1-2)  25  -31  1990/11  [Not refereed][Not invited]
  • Q YAN, H YOSHIOKA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO  CORROSION SCIENCE  31-  401  -406  1990  [Not refereed][Not invited]
  • K ASAMI, SC CHEN, H HABAZAKI, A KAWASHIMA, K HASHIMOTO  CORROSION SCIENCE  31-  727  -732  1990  [Not refereed][Not invited]
  • A KAWASHIMA, BP ZHANG, H HABAZAKI, K ASAMI, K HASHIMOTO  CORROSION SCIENCE  31-  355  -360  1990  [Not refereed][Not invited]
  • H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO  CORROSION SCIENCE  31-  343  -348  1990  [Not refereed][Not invited]
  • Habazaki H, Ding S.Q, Kawashima A, Asami K, Hashimoto K, Inoue A, Masumoto T  Corrosion Science  29-  (1112)  1319  -1328  1989  [Not refereed][Not invited]

Books etc

  • Shreir's Corrosion
    Elsevier 2009

Association Memberships

  • 固体イオニクス学会   表面技術協会   腐食防食学会   日本金属学会   日本化学会   電気化学会   炭素材料学会   The Electrochemical Society   Internationa Society of Electrochemistry   日本鉄鋼協会   

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2027/03 
    Author : 幅崎 浩樹, 北野 翔
  • 高性能・小次世代高電力密度パワエレ機器に向けた高性能コンデンサの研究開発
    文部科学省：革新的パワーエレクトロニクス創出基盤技術研究開発事業
    Date (from‐to) : 2021 -2025
  • 科学技術振興機構：産学が連携した研究開発成果の展開 研究成果展開事業 研究成果最適展開支援プログラム(A-STEP) トライアウト トライアウト
    Date (from‐to) : 2022 -2023 
    Author : 幅崎 浩樹
     
    本研究開発では高効率な水素製造を可能とするために、集電体ともなりうる各種FeNiおよびFeNiCo実用合金のアノード酸化によって、アルカリ水電解による酸素発生反応および水素発生反応を活性化し、0.6Acm-2の電流において0.35V以下の過電圧を1か月保持できるか検証し、ライフサイクルコストの低い実用的水素製造用電極の開発を目指す。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)
    Date (from‐to) : 2020/07 -2022/03 
    Author : Habazaki Hiroki
     
    In this study, to clarify the possibility of a magnesium cathode current collector in environments containing fluoride ions for lithium-ion batteries, the stability of magnesium in various electrolyte solutions for lithium-ion batteries at high potentials was investigated. As a result, in the LiPF6-based electrolyte, magnesium can be passivated up to about 4 V vs Li+/Li, and is deactivated at higher potentials. Surface analysis suggests that this is due to the inability to form a stable passivation film composed of MgF2 in this environment. On the other hand, when the stability was evaluated using the electrolyte for the fluoride shuttle battery, it was found that no de-passivation occurred up to 10 V.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2019/04 -2022/03 
    Author : Habazaki Hiroki
     
    Highly efficient hydrogen production by alkaline water electrolysis is an important process for achieving carbon neutrality. In this study, we found that the overpotential of the oxygen evolution reaction in KOH solution can be significantly reduced by simple anodic oxidation of commercially available FeNiCo and FeNi alloys, and that the electrode has excellent durability. It was also found that the porous fluoride layer formed by anodic oxidation is an excellent precursor that is quickly converted to highly active oxyhydroxides in KOH.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2016/04 -2019/03 
    Author : Habazaki Hiroki, Kowalski Damian, Aoki Yoshitaka, Zhu Chunyu, Yamada Naohito, Sakashita Ryosuke, Sato Yuki
     
    In this study, platelet-type carbon nanofibers (pCNF) were prepared using porous anodic alumina template with many cylindrical nanopore channels and Co3O4 nanoparticles were deposited on pCNF for tailoring highly active and durable oxygen reduction and oxygen evolution reactions that would be required to develop next-generation fuel cells and metal-air batteries. We found that Co3O4 nanoparticles were uniformly dispersed on pCNF that has exposed carbon edge plane at the side wall of pCNF, and the Co3O4/pCNF exhibited a good oxygen reduction reaction activity. In contrast, poor dispersion of Co3O4 was found on multi-walled carbon nanotubes, in which basal planes of carbon were exposed on the side wall. Through this study, we found the importance of carbon surface structure on the dispersion of oxide nanoparticles and electrocatalytic activities.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Date (from‐to) : 2015/04 -2017/03 
    Author : Habazaki Hiroki, TSUJI Etsushi
     
    Fabrication of anti-fouling and ice-phobic surfaces on practical metallic materials, such as stainless steels, is of importance in daily life and for industrial applications. In this study, we successfully fabricated superhydrophobic and superoleophobic surfaces on stainless steel. The surfaces were obtained by preparing the hierarchical micro-/nano-scale rough surfaces, and the roughness was introduced by single chemical or electrochemical etching of stainless steel and following novel anodizing technique.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2012/04 -2015/03 
    Author : HABAZAKI HIROKI, AOKI Yoshitaka, TSUJI Etsushi
     
    IIn this study, we investigated the fabrication of membrane-electrode assembly using proton conductive anodic ZrO2-WO3 or ZrO2-WO3-SiO2 nanofilms, which were developed by us, for intermediate temperature fuel cells operating below ~300 degre C. Hydrogen permeable anode foils have been utilized as a support of the proton conducting nanofilms and several fabrication processes have been proposed and examined. We succeeded to generate power. Further, by modifying the anodizing process to form the proton conducting anodic films, we have increased the proton conductivity by nearly one order of magnitude.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Date (from‐to) : 2011 -2012 
    Author : HABAZAKI Hiroki, AOKI Yoshitaka, TSUJI Etsushi
     
    Nobel proton-conducting oxide thin films were fabricated by simple anodizing technique for possible application as an solid electrolyte for intermediate-temperature fuel cells. The amorphous ZrO2-WO3-SiO2 films formed by anodizing revealed the proton conductivity sufficient for the fuel cell application at ~200oC. In addition, the oxide films showed unique thickness-dependent conductivity with theconductivity highly enhanced by reducing the film thickness less than 300 nm.
  • 日本学術振興会：科学研究費助成事業 挑戦的萌芽研究
    Date (from‐to) : 2009 -2010 
    Author : 幅崎 浩樹
     
    本研究では,アルミニウムやチタンなどの軽金属表面にアノード酸化をいう簡便な手法により,表面形態を制御した多孔質酸化皮膜を形成し,超撥水・超撥油性表面を創製することを目的とした。超撥水および超撥油表面を創製するには,表面エネルギーが小さくなるように表面組成を制御するとともに,表面粗さを導入する必要がある。特に階層構造をもった多孔質表面が表面を超撥水化するのに必要となる。 階層構造表面を形成するために,まず,斜入射マグネトロンスパッタ法(OAD)とアノード酸化法を組み合わせた。アルミニウム上にOADによりサブミクロンサイズのAl-Nb合金カラム構造を得,さらにアノード酸化によりナノボアを導入した。酸化物表面は親水性であるので,現在知られている物質で最も表面エネルギーを小さくできるCF_3基を末端に持つフルオロアルキルリン酸単分子層で表面をコーティングした。その結果,超撥水のみならず,超撥油性までも発現することができた。この研究を通して,超撥油性を達成するには,階層構造を精密に制御する必要があることがわかり,特にサブミクロンカラム間のギャップサイズの制御が重要であることを明らかにした。 一方,アノード酸化のみにより,階層構造を形成する手法の開拓として,ニオブのアノード酸化を行った。高温のリン酸塩含有グリセリン溶液中におけるアノード酸化により,マイクロコーン上の表面形態をしたナノポーラス皮膜が得られる。このコーンサイズやナノ構造をアノード酸化電圧や電解液中の水分量で制御でき,サイズが大きく,コーンの先端角が小さいほど,水の接触角が大きくなることがわかった。その結果,175°という極めて大きな接触角を持つ超撥水表面を得ることができた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2007 -2010 
    Author : HABAZAKI Hiroki, FUSHIMI Koji, AOKI Yoshitaka
     
    Plasma electrolytic oxidation (PEO) is an attractive process to form ceramics coatings on light metals, including magnesium, aluminum and titanium, in aqueous electrolytes at ambient temperature. The present study discloses the excellent healing properties of discharge channels in alkaline silicate electrolyte. Further, novel two-step PEO process is developed to form wear-resistant and highly adherent ceramics coating on β-Ti alloy with high mechanical strength and cold workability.
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    Date (from‐to) : 2007 -2008 
    Author : 幅崎 浩樹, 伏見 公志
     
    グロー放電発光分光法(GDOES)がナノ薄膜の迅速分析法として有効であることを示し, 高分解能デプスプロファイルを得るための手法を確立する研究を推進した。まず, 耐海水ステンレス鋼であるSUS312L鋼を用いて, 異なる粒径のアルミナ研磨液を用いて試料を鏡面研磨した。その表面粗さを原子間力顕微鏡(AFM)を用いて計測し, GDOES分析における深さ分解能との相関関係を調べた。研磨条件によりステンレス鋼上に生成する大気酸化皮膜の厚さや組成が変化する可能性があるので, 深さ分解能の評価としてその皮膜直下に存在する銅濃縮層を指標として用いた。GDOESプロファイル上の界面濃縮層の銅のピークの半値幅は表面粗さの対数に対して直線的に変化し, 表面粗さの分解能の影響がきわめて大きいことを明らかにした。同じ鏡面研磨でも表面粗さをできるだけ低減することがナノ薄膜の分析において, 高い深さ分解能を得る上で重要であることを示した。 また, 従来のX線光電子分光法やオージェ電子分光法などの表面分析法では, 感度が低く, 塩化物イオン含有水溶液中で生成した不動態皮膜中の塩化物イオンをGDOESを用いることで検出できた。塩化物イオンは不動態皮膜中の鉄リッチな皮膜外層にのみ存在しており, クロムリッチな皮膜内層には達していないことを示すことができた。 以上のように, ステンレス鋼の不動態皮膜や大気酸化皮膜のような厚さ2-3nm程度の表面酸化皮膜でも, 十分に表面を平滑にした試料を用いることで, 高分解能, 高感度で分析できる手法を確立できた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2004 -2006 
    Author : HABAZAKI Hiroki, FUSHIMI Koji, KONNO Hidetaka
     
    1.Formation of self-organized porous anodic oxide We have successfully developed self-organized porous anodic oxide films on Ti-Si alloys in hot glycerol solution containing dibasic phosphate. The key issue for the formation of the porous films is suppression of the crystallization of anodic oxide, which induces gas evolution during anodic film growth. The similar porous films are also developed on niobium and aluminum substrates. The cell size of the porous films on aluminum is dependent upon the formation voltage, similar to those formed in acid aqueous solutions. 2.Formation of barrier-type anodic oxide with excellent dielectric properties Incorporation of foreign species from substrate suppresses effectively the development of crystalline anodic oxide on titanium. By increasing alloying element content, the structure of the air-formed film present before anodizing is modified, such that growth of amorphous oxide continues to higher formation voltages. The compositional dependence of the dielectric properties of anodic oxides formed on a range of titanium alloys has been examined systematically. 3.Hard coating of titanium alloys by spark anodizing Spark anodizing of titanium, Ti-6Al-4V and Ti-15V-3Al-3Cr-3Sn has been performed in alkarine electrolyte containing aluminate and phosphate. Highly crystalline Al2TiO5-based oxide coatings,〜20μm thick, have been developed by dc-biased ac anodizing to high voltages. Regardless of the materials used, the coatings with hardnes of 〜6GPa have been obtained. The coatings have porosity, associated with discharge channel. From optical measurements during spark anodizing, the temperature at the discharge region has been estimated to be 4500〜5000℃. Such high temperature allows us to develop the highly crystalline coatings with high concentration of electrolyte species even in an aqueous solution at ambient temperature.
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    Date (from‐to) : 2004 -2005 
    Author : 幅崎 浩樹, 金野 英隆
     
    ポリ塩化ビニル(PVC)と多孔質アノード酸化アルミナテンプレートから液相鋳型炭素化で得られるカーボンナノファイバーの構造について,詳細な検討を行った。まず,600℃の低温熱処理の段階でファイバー軸方向への炭素の層の積層が確認され,PVCがピッチ状になった段階で生成している多環芳香族化合物がface-onの配向を持ってアルミナと相互作用することがこのような配向の生成原因であることが示唆された。 また,2800℃〜3000℃の熱処理によりカーボンナノファイバーの側面に炭素の層5層程度からなるループの形成が確認され,TEMによる試料の傾斜観察からファイバーの螺旋構造の可能性もあることが示された。 このような熱処理による構造の変化およびファイバー径のリチウムイオン二次電池の負極特性との関連を検討した。1000℃熱処理した試料の可逆容量が大きく,1500および2800℃熱処理した試料の可逆容量は200mAhg^<-1>程度しかなかった。黒鉛化している2800℃熱処理試料の容量が通常の黒鉛材料(理論容量372mAhg^<-1>)よりもかなり小さいのは,ループの生成が関係している可能性が大である。1000℃熱処理試料では,充放電電流密度を増大させても容量の低下は小さく,特にファイバー径が小さいときに容量の低下が小さくなる傾向が見られた。これは,径を小さくすることでインターカレーションしたリチウムイオンの炭素内での拡散距離が短くなることと対応しているものと考えられる。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2001 -2003 
    Author : KONNO Hidetaka, HABAZAKI Hiroki
     
    Exfoliated graphite has very large sorption capacity for oils. Utilizing this property, various metal complexes, silicone compounds, metal alkoxides and others were impregnated into exfoliated graphite, and pretreated, mainly by heat treatment in air or hydrolysis in water vapor, to form precursors. By heating these precursors in an inert atmosphere, the following multi-functional carbonaceous materials were synthesized. (1) Ni/graphite composite, Fe/graphite composite, Fe_3O_4/graphite composite (potential applications : magnetic materials, absorber for electromagnetic radiation, catalyst, and so on) (2) Graphite coated with ultra thin Si-C-O composites (oxidation resistant carbon material, conductive materials at high temperatures) (3) Mn2O3 or MnO2/graphite composite (electrode materials for super capacitors) (4) Nano-particles of single or multi-component metal carbides, such as β-SiC, TiC, ZrC, (Ti,Zr)C and others. The developed method to synthesize (4) is promising as an industrial process because it is simple and low cost.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2001 -2002 
    Author : HABAZAKI Hiroki
     
    Sputter-deposited Nb alloys containing both aluminum and chromium reveal high oxidation resistance above 1073 K, in contrast to less oxidation-resistant Nb-Al and Nb-Cr binary alloys. The oxidation of the ternary alloys generally follows the parabolic rate law, indicating that diffusional transport of matter is the rate-determining step. However, the high oxidation resistance of the ternary alloys containing about 40 at% niobium is not due to the formation of an alumina scale, but due to an outer chromia layer with the inner layer consisting of a mixture of alumina, chromium-niobium and/or aluminum-niobium double oxides. When the ternary alloys containing about 40 at% niobium were oxidized in O_2-SO_2 atmospheres, preferential oxidation of aluminum occurs as a consequence of a transient sulfidation of aluminum at the alloy/scale interface. However, the preferential oxidation results in internal oxidation of the alloys, not in the formation of continuous external alumina scale. Further increase in aluminum content by reducing niobium content, finally results in the formation of highly protective α-alumina scales above 1073 K. Coating of this aluminum-rich niobium alloy to niobium-base alloys with high mechanical properties at high temperatures may induce interdiffusion between the coating and substrate, leading to degradation of the oxidation resistance. The authors have successfully demonstrated that introduction of an anodic alumina layer between the coating and substrate as a diffusion barrier layer suppresses effectively the interdiffusion, thus high oxidation resistance of the coating is sustained at high temperatures.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 1998 -2001 
    Author : ASAMI Katsuhiko, SHIMAMURA Kazuo, KIKUCHI Michio, KAWASHIMA Asahi, KUMAGAI Naokazu
     
    We are proposing a CO_2 recycling system for preventing global warming caused by CO_2 emissions in conjunctions with development of human activities. The system consists of methanation of CO_2 which are recovered at fuel consumers sites such as power plants. Methanation needs highly active catalysts and hydrogen which can be obtained from seawater electrolysis using solar energy. To substantiate this system in global scale, we need to develop low cost catalysts and electrode with high efficiency for hydrogen evolution and oxygen evolution reactions at seawater electrolysis. The objectives of this investigation are to develop such new catalysts and electrode substances. Comparison between Ni-Mo and Ni-Mo-O alloy electrodes fabricated on Ni substrate showed existence of small amount of O imparts both higher activity for hydrogen evolution reaction and higher durability. Another electrode candidate was Ni-Fe-C alloy system. It showed almost no increase in hydrogen overpotential even after accelerating test for two years at a high current density of 50,000 A/m^2. It was also stable and suffered no corrosion even after repeated stoppage of electrolysis in a concentrated NaOH solution at high temperature. For the first time in the world, we have succeeded in preparation of electrodes with 100 % oxygen evolution efficiency for seawater electrolysis using MnO_2 type oxide electrode installed on titanium substrate. It was also found combined addition of Mo and W was more effective for selective oxygen evolution at seawater electrolysis and we were able to reduce electrolysis voltage successfully. Moreover, we found methanation catalysts prepared from amorphous Ni-Zr alloys had high activity sfpr methanation. We have also succeeded in develop more active catalyst using amorphous Ni-Zr-Sm alloys as precursors of the catalysts. It was clarified that samarium stabilize tetragonal phase of zirconia on which dispersion of Ni particles were also enhanced.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 1999 -2000 
    Author : HABAZAKI Hiroki
     
    Corrosion-resistant bulk Ni-Cr-Nb-P-B, Ni-Cr-Ta-P-B and Ni-Cr-Me-P-B alloys with cylindrical shape of 1 and 2 mm diameter are prepared by a copper mold casting method. A good correlation between the glass forming ability and stability of super-cooled liquid state has been found for these alloy systems except the molybdenum-containing alloy system. The bulk amorphous alloys thus prepared are spontaneously passive even in very aggressive 6M and 12M HCl solutions open to air at 303 K.The bulk amorphous alloys reveal the same anodic and cathodic polarization curves as the corresponding melt-spun alloy ribbons, as far as amorphous single phase alloys are obtained. Precipitation of fcc Ni phase in the bulk amorphous alloys is detrimental to the corrosion resistance of the alloys. The influence of the precipitation is, however, strongly dependent upon the size of the precipitates. When fcc Ni with size of 20〜nm is formed in the amorphous matrix, the alloys show about two orders of magnitude higher passive current density in comparison with the amorphous single phase alloys. In contrast, precipitation of fcc Ni with only 2-3 nm size results in the increase only twice in the passive current density. Bulk amorphous Ni-10Cr-5Nb-16P-4B alloy plates of 2 mm thickness are also prepared by consolidation of gas-atomized amorphous alloy powders by sheath rolling at a super-cooled liquid state, that is, 708 K.The bulk alloy thus prepared is found to reveal similar extremely low corrosion rate in 6M HCl at 303 K to the corresponding melt-spun alloy. However, in 12M HCl solution, the sheath-rolled alloy shows preferential corrosion attack at boundaries of the gas-atomized powders, possibly due to the influence of the oxidation of the particle surface during heating for consolidation. Thus, further improvement of the preparation processes to obtain highly corrosion-resistant bulk amorphous alloys using this method.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B).
    Date (from‐to) : 1998 -2000 
    Author : ASAMI Katsuhiko, KIKUCHI Michio, KAWASHIMA Asahi
     
    We are proposing a CO_2 recycling system for preventing global warming caused by CO_2 emissions in conjunctions with development of human activities. The system contsists of methanation of CO_2 which are recovered at fuel consumers sites such as power plants. Methanation needs highly active catalysts and hydrogen which can be obtained from seawater electrolysis using solar energy. To substantiate this system global scale, we need to develop low cost catalysts and electrode with high efficiency for hydrogen evolution and oxygen evolution reactions at seawater electrolysis. The objectives of this investigation are to develop such new catalysts and electrode substances. We have found methanation catalysts prepared from amorphous Ni-Zr alloys have high activity for methanation. We have also succeeded in develop more active catalyst using amorphous Ni-Zr-Sm alloys as precursors of the catalysts. It was clarified that samarium stabilize tetragonal phase of zirconia on which dispersion of Ni particles are also enhanced. Catalysts prepared from gas-atomized Ni-Zr-Sm alloys also had high activity. Ni-Mo and Co-Al-Mo alloy electrode fabricated by sputter-deposition showed high activity for hydrogen evolution reaction. By using arc-ion-plating method, not only adhesiveness to the substrate but also hydrogen evolution efficiency of Ni-Mo alloy electrode was improved ; the most effective composition was Ni-(10-20)at%Mo-(5-10)at%O with the overpotential for hydrogen evolution lower than 100 mV at the cuurent density of 4×10^3A/m^2. It was succeeded to prepare an electrode with 100% oxygen evolution efficiency for seawater electrolysis using MnO_2 type oxide electrode installed on titanium stubstrate. The structure of the prepared electrode consisted of chemically homogeneous nanocrystalline manganese oxide with γ-MnO_2 structure containing solid-solved hexavalent tungsten. It was also found combined addition of Mo and W is more effective for selective oxygen evolution at seawater electrolysis and we were able to reduce electrolysis voltage successfully.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1997 -1999 
    Author : ASAMI Katsuhiko, HABAZAKI Hiroki, KIKUCHI Michio
     
    1. Ni catalysts supported by zirconia, which have high activity for the reaction for methanation of carbon dioxide with hydrogen, were prepared from amorphous Ni-Zr alloys, and evaluated their activity in relation with alloy composition, reaction temperature. It was found that their activity was highest when they have prepared from Ni-Zr alloys containing Zr from 40 to 50at%Zr. The origin of the alloy composition dependence was explained by the alloy composition dependence of dispersion of metallic Ni on the catalyst surface, turnover number, and the relative concentration of tetragonal zirconia in the support. On the base of the above results, catalysts with higher activity were prepared by addition of a certain amount of Sm which caused stabilization of tetragonal phase of zirconia and increase of Ni dispersion on zirconia. 2. Non-equilibrium Nb-W and Nb-Mn alloys were prepared by sputtering method. They showed amorphous structure within the composition range of 20-50at%W and 26-75at%Mn, respectively. Their corrosion resistance and surface compositions were evaluated by electrochemical measurements and photoelectron spectroscopy. 3. Co-20at%Al alloy prepared by sputtering method was a non-equilibrium metallic compound with CsCl-type structure. When alloy films were prepared by reactive sputtering in NィイD22ィエD2 and OィイD22ィエD2 containing atmosphere, they showed ferromagnetic property with high performance even at high frequency region. It was clarified that they were composed of nano-particles of Co surrounded by insulating AlN and AlィイD22ィエD2OィイD23ィエD2, respectively. 4. Sr-Bi-Ta oxides prepared by sol-gel method followed by annealing at low temperatures showed no ferroelectric properties. But they become ferroelectric substance at high temperature annealing. Their performance was, however, dependent on annealing temperature and atmosphere during annealing. It was made clear that deviation of surface composition from stoichiometry and existence of metallic Bi were harmful to ferroelectric performance.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 1997 -1998 
    Author : KAWASHIMA Asahi, HABAZAKI Hiroki
     
    First of all, we have compared the steady state conventional potentiostatic method with pulsed method in the electrochemical reduction of CO_2. It was found that the faradaic efficiencies for the pulsed electroreduction ofCO_2 to methane and ethylene using copper electrode are higher than those for the potentiostatic reduction and more stable in a long-term electrolysis. In the next study, we have made various electrolysis from copper-based alloys and examined the faradaic efficiencies for methane and ethylene production from CO_2 reduction using pulsed electrolysis in CO_2 saturated 0.1 M KHCO_3 solution at room temperature. Amorphous Cu-Zr and Cu-Tialloy electrodes were prepared using a single-roller melt-spinning method. The sputtering method was applied to prepare Cu-Ag alloys. The amorphous Cu-(30, 40, 60)Zr and Cu-30Ti alloys showed considerably low faradaic efficiencies for methane and ethylene production and both efficiencies were less than 3 %. The sputter-deposited crystalline Cu-Ag alloy electrodes, when the alloys contain small amount of Ag (5-7at%), have a higher faradaic efficiency of methane in comparison with pure Cu electrode. However, excess amount of Ag was detrimental. Although methane and ethylene were not detected on pure Ag electrode, the efficiency of methane increased with the addition of a small amount of Cu but the efficiency was lower than that on pure Cu electrode. Next, gas-diffusion electrodes have been employed as the cathode. The gas-diffusion electrodes have been prepared from sputter-deposited Cu-Ag alloyed powder, carbon black powder and polytetrafluoroethylene dispersion. Thegas-diffusion electrode only made up of carbon black powder produced exclusively hydrogen gas. However, the Cu-Ag alloy powder-loaded gas-diffusion electrodes produced methane and ethylene and the total reduction current density was remarkably high, but their faradaic efficiencies were lower than those on the plate-type alloyelectrodes.
  • 日本学術振興会：科学研究費助成事業 奨励研究(A)
    Date (from‐to) : 1997 -1998 
    Author : 幅崎 浩樹
     
    スパッタ法を用いてアモルファスAl-Nb-Mo三元合金を石英基板上に作製し,その高温硫化および酸化環境における耐食性を評価するとともに,その耐食機構について検討した.まず,Al-Nb-Mo合金の高温硫化は二段階の放物線則に従う硫化挙動を示し,保護性の硫化物スケールが生成し,その中の拡散が律速となることがわかった.定常状態における硫化速度は初期よりも小さく,より保護性の高いスケールが定常状態では生成している.その定常状態の硫化速度はニオブやモリブデン単体よりも小さく,さらにAl-MoやAl-Nb二元合金よりも小さいことが明らかとなった.また,その硫化速度はアルミニウム量がほぼ同じ場合,モリブデンよりもニオブの割合が多いほうが小さくなることも判明した.生成した硫化物スケールの解析を行ったところ,3層からなるスケールが生成していることがわかった.最外層にはAl_2S_3があり,その下に少量のアルミニウムを含むNbS_2,そして最内層は少量のアルミニウムを含んだMoS_2とNb_3S_4からなる.初期の比較的速い硫化はアルミニウムが優先的に硫化し,より保護性の高い高融点金属の硫化物が生成する前にAl_2S_3スケールが生成し,この中の拡散が反応を律速するためである.Nb-Mo二元合金を硫化した場合もNbS_2MoS_2-Nb_3S_4の2層スケールが形成したが,この合金よりもAl-Nb-Mo三元合金の方が高い耐高温硫化性を示したことから,Al^<3+>イオンがドープされたNbS_2/MoS_2-Nb_3S_4スケールはAl^<3+>イオンを含まない同じスケールよりも保護性が高いことが明らかとなった.Al-Nb-Mo三元合金の耐高温酸化性は合金中のアルミニウム量が多くなるほど向上し,直線則から放物線則に従う酸化挙動に変化した.放物線則を示した合金ではスケール表面に保護性の高いAl_2O_3層が生成することで耐酸化性が向上し,Al-21Nb-14Mo合金ではクロミアスケールを生成する耐熱合金に匹敵する耐高温酸化性を示すした.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1995 -1998 
    Author : HASHIMOTO Koji, AKIYAMA Eiji, HABAZAKI Hiroki, KAWASHIMA Asahi, ASAMI Katsuhiko
     
    Since non-equilibrium alloys become a single phase supersaturated solid solution by additions of large amounts of various elements, tailoring of catalysts for conservation of environments by combination of elements necessary for high reactivity and selectivity was aimed. 1. Catalysts for decomposition of nitrogen oxides : For direct decomposition of nitrogen oxide to nitrogen and oxygen, Pd/NiTaO_6 catalyst formed from amorphous Ni-Ta-Pd alloys showed the most stable high reactivity in a wide temperature range up to 900ﾟC.When this was used as a catalyst for reduction of nitrogen monoxide by propane in oxygen containing atmosphere, a high conversion was observed at low temperatures such as 300ﾟC 2. Catalysts for decomposition of chlorofluorocarbon : Amorphous Ni-Zr alloys possess high reactivity and durability for hydrolytic decomposition of CFC-12 into CO_2, HC1 and HF.The durability increased remarkably by the addition of phosphorus. Active species formed from the alloys were ZrF2, (F,O)_<2,706> and Zr(F,O)_<3.80ﾟ> 3. Catalysts for methanation of carbon dioxide : Amorphous Ni-Zr alloys have the highest activity and 100% selectivity for methane formation by the reaction of CO_2 with H_2 in comparison with conventional Ni-impregnated ZrO_2, crystalline Ni-Zr and precious metal catalysts. Because nickel supported on tetragonal ZrO_2, which is an essentially metastable phase and formed during the reaction, showed a selectively high activity and because the addition of rare earth elements stabilizes the tetragonal ZrO_2 phase, the most active catalysts were obtained from amorphous Ni-Zr-rare earth element alloys. 4. Hydrogen evolution cathodes for seawater electrolysis : Tailoring of highly active electrodes for production of hydrogen necessary for methanation of CO_2 was carried out by preparing amorphous alloys. Modification of the electronic structure of nickel by the addition of molybdenum resulted in the cathodes whose activities are competitive to that of platinum.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1993 -1995 
    Author : HASHIMOTO Koji, KUMAGAI Naokazu, YOSHIOKA Hideaki, HABAZAKI Hiroki, KAWASHIMA Asahi, ASAMI Katsuhiko
     
    One of the objectives of this work is to tailor amorphous surface alloys on conventional metals by sputter deposition in order to protect the underlying conventional metals against sulfidation and oxidation at high temperatures. Tailoring active catalysis from amorphous alloy precursors for hydrolytic decomposition of cholorofluorocarbon is another aim of this work. We succeeded to prepare amorphous Al-Mo, Al-Nb and Al-Ta alloys with high resistance against both sulfidation and oxidation. In addition, the above-mentioned alloys with small additions of silicon have been obtained for further enhancement of oxidation resisitance. It is the first time on the history of corrosion science that the alloys with low sulfidation rates which are comparable to the oxidation rates of oxidation-resistant conventional alloys are obtained. Sulfide scales formed on these alloys consist of an outer aluminum sulfide layr and an inner refractory metal sulfide layr, the latter of which has high protectiveness against sulfidation. The amorphous alloys are converted to intermetallics at high temperatures where sulfidation and oxidation take place, but the formation of fine grained intermatallics is responsible for better adhesion of the alloys to the substrate metals. Silicone contained in the alloys form silicides with refractory elements in the alloys at high temperatures, and because the silicides are stable against oxidation, the presence of silicon suppresses oxidation of refractory elements. Amorphous surface alloys have been successfully prepared on 304 stainless steel and show high protectiveness against both sulfidation and oxidation at high temperatures. In the catalytic decomposition of a cholorofluorocarbon CCl_2F_2 by hydrolysis into CO_2, HCl and HF the catalyst should be exposed to very aggressive decomposition products. The active and durable catalysts have been obtained as a result of the catalystic reaction from amorphous Ni-Zr alloy precursors containing small amounts of chromium, molybdenum or tungsten.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1993 -1994 
    Author : HASHIMOTO Koji, J-CZACHOR M., MROWEC S., AKIYAMA Eiji, KAWASHIMA Asahi, ASAMI Katsuhiko
     
    High temperature corrosion of sputter-deposited amorphous Al- (34-46) Mo and Al-31Mo- (6-16) Si alloys has been studies as a function of temperature in sulfur vapor, as well as in oxygen and air. The sulfidation process follows parabolic kinetics. The alloys showed excellent resistance to sulfide corrosion, their sulfidation rates being comparable with oxidation rates of chromia-forming materials. The oxidation resistance of binary Al-Mo alloys has been found to be satisfactory, but only at temperatures not exceeding 1073K.Above the melting point of MoO_3 (1069K), the scale, consisting mainly of Al_2O_3 with 5% MoO_3, becomes unprotectable because of evaporation of MoO_3. However, ternary Al-Mo-Si alloys show excellent resistance to oxidizing environment up to about 1200K,their oxidation rates being comparable with those of Al_2O_3 formers. This resulted from the fact that during heating of the ternary alloys, Mo_5Si_3 scale was formed instead of AlMo_3 formed. The beneficial effect of alloying with aluminum enhancing the sulfidation resistance of molybdenum has been studied as a function of aluminum content. The reaction rate of Mo-Al alloys with low aluminum contents is lower than that of pure molybdenum and decreases with increasing aluminum content. The lower sulfidation rate is explained in terms of the aluminum doping effect in the MoS_2 scale. Sputter-deposited Al-Nb alloys have excellent sulfidation resistance, their sulfidation rates being lower than that of niobium. Although their initial sulfidation rate is high due to the preferential sulfidation of aluminum, which leads to the enrichment of niobium at metal/scale interface, and consequently, the protective NbS_2 scale formed on the Al-Nb alloys. The resistance of these alloys to high temperature oxidation is higher than that of niobium. The oxide scale is composed of a double aluminum-niobium oxide and alumina, which lead to high oxidation resistance.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1991 -1994 
    Author : HASHIMOTO Koji, AKIYAMA Eiji, HABAZAKI Hiroki, KAWASHIMA Asahi, ASAMI Katsuhiko
     
    X-ray photoelectron spectroscopy is an effective method for nondestructive determination of valence and composition in the specimen surface. In-situ determination of the surface is particularly necessary for a better understanding of chemical species contributing to the reaction on the electrode surface exposed to relatively low oxidizing power. In-situ characterization in XPS is to determine the surface without oxidation of the surface species as a result of exposure to air before being exposed to high vacuum of the X-ray photoelectron spectrometer. In the present work an electrode in an electrolytic cell is rinsed with deaerated distillled water, transferred without air exposure into a globe box and is mounted on an air-tight transfer vessel for X-ray photoelectron spectrometer under nitrogen atmosphere in the globe box. Useful information has been obtained for the electrode surface without the detrimental effect of air oxidation. These include fuel cell electrodes for hydrogen, methane, ethane and propane as fuels, electrodes for evolution of hydrogen, chlorine and oxygen in electrolysis of seawater and electrodes for electrochemical oxidation of sulfite. In the study of amorphous alloy electrodes for fuel cells additions of platinum group elements and tin are effective in enhancing the electrocatalytic activity. The presence of a redox system of Sn^<2+>/Sn^<4+> which accelerates oxidation of fuels is confirmed. When the electrode is exposed to air after electrolysis, even platinum group elements are readily covered with oxides and hence the specification of the effective species for the electrode reactions is difficult. In fact platinum group elements directly act in the metallic state for oxidation of fuels and sulfite. These could not be obtained so far by ex-situ surface characterization.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1993 -1993 
    Author : 幅崎 浩樹, 秋山 英二
     
    耐高温硫化性と耐高温酸化性を兼ね備えた材料を見出すことを目的として,スパッター法によりアモルファスアルミニウム-高融点合金を作製し,その耐高温硫化性を10^3Paの硫黄蒸気中,耐高温酸化性を空気中で調べた。アモルファスAl-Mo合金の硫化は,放物線則に従い,その耐高温硫化性は金属モリブデンよりも高く,これまで知られている金属材料の中でも最も高いことがわかった。生成したスケールは二層からなり,外層はAl_2S_3,内層はMoS_2が主体であった。また,スケールは硫黄の内方拡散により成長することがマーカー試験により明らかになった。このアモルファスAl-Mo合金が高い耐高温硫化性を示す理由は,内層の主体であるMoS_2へのアルミニウムのドーピング効果によると考えられる。実際,モリブデンへ少量のアルミニウムを添加した場合,その添加量に応じて硫化速度が低下することからも,このことは支持された。 Al-Mo合金の高温酸化速度は,1123Kまでは,クロミアスケールを形成する合金に匹敵するが,それ以上の温度では,酸化モリブデンの蒸発のため,重量減少が起こり,耐酸化性は充分ではない。このAl-Mo合金にケイ素を添加すると,耐酸化性は1223Kまで典型的なアルミナスケールを形成する合金に匹敵するほどまで向上した。ただし,過剰のケイ素の添加は耐高温硫化性を低下させた。ケイ素の添加のより耐酸化性が向上するのは,Al-Mo二元合金の場合には,高温でAl_8Mo_3とAlMo_3が生成するのに対し,ケイ素を添加した合金ではモリブデンリッチの金属間化合物に代わって,シリコンリッチで,耐酸化性に優れたMo_5Si_3が生成することが最も大きな要因であり,これによりモリブデンの酸化が抑制されたと考えられる。Al-Nb合金は耐酸化性は低いものの,耐高温硫化性はニオブを上回ることがわかった。
  • 機能性材料表面の創製
  • Tailoring of novel materials with surface functions

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