研究者データベース

研究者情報

マスター

アカウント(マスター)

  • 氏名

    幅﨑 浩樹(ハバザキ ヒロキ), ハバザキ ヒロキ

所属(マスター)

  • 工学研究院 応用化学部門 機能材料化学分野

所属(マスター)

  • 工学研究院 応用化学部門 機能材料化学分野

独自項目

syllabus

  • 2020, エネルギー材料特論, Materials for Energy Conversion and Storage, 修士課程, 総合化学院, エネルギー変換,エネルギー貯蔵,イオン伝導体,水素吸蔵材料,光エネルギー変換
  • 2020, 物理化学Ⅰ, Physical Chemistry Ⅰ, 学士課程, 工学部, 熱力学,気体の運動,物質の状態,エネルギー,自発反応
  • 2020, 電気化学, Electrochemistry, 学士課程, 工学部, 電位,電流密度,イオン伝導,電池,電気分解,物質創製,表面処理

timetable

  • 修士課程, 総合化学院, 2020, 応用化学特別講義

PositionHistory

  • 評価室室員, 2018年7月1日, 2020年6月30日
  • 評価室室員, 2020年7月1日, 2022年6月30日
  • 大学院工学研究院附属エネルギー・マテリアル融合領域研究センター長, 2016年4月1日, 2018年3月31日
  • 大学院工学研究院附属エネルギー・マテリアル融合領域研究センター長, 2018年4月1日, 2019年3月31日
  • 大学院工学研究院副研究院長, 2019年4月1日, 2021年3月31日
  • 教育研究評議会評議員, 2019年4月1日, 2021年3月31日

researchmap

プロフィール情報

学位

  • 理学博士(東北大学)

プロフィール情報

  • 幅崎, ハバザキ
  • 浩樹, ヒロキ
  • ID各種

    200901038068777831

対象リソース

業績リスト

研究キーワード

  • 界面電気化学   アノード酸化   ナノ薄膜   ナノポーラス材料   Nanoporous materials   

研究分野

  • ナノテク・材料 / 構造材料、機能材料
  • ナノテク・材料 / 材料加工、組織制御
  • ナノテク・材料 / ナノバイオサイエンス
  • ナノテク・材料 / ナノ材料科学

経歴

  • 2006年04月 - 2010年03月 北海道大学大学院工学研究科 教授
  • 2000年04月 - 2006年03月 北海道大学大学院工学研究科 助教授
  • 2000年10月 - 2005年09月 マンチェスター理工科大学腐食防食センター 客員研究員
  • 1988年04月 - 2000年03月 東北大学金属材料研究所 助手
  • 1993年11月 - 1995年10月 マンチェスター理工科大学腐食防食センター 博士研究員

委員歴

  • 2010年01月 - 現在   固体イオニクス学会   役員   固体イオニクス学会
  • 2009年01月 - 現在   電気化学会   キャパシタ技術委員会運営委員   電気化学会
  • 1997年01月 - 現在   表面技術協会,金属のアノード酸化皮膜の機能化部会   幹事
  • 2016年01月 - 2019年12月   表面技術協会 アノード酸化皮膜の機能化部会   代表幹事
  • 2018年03月 - 2019年02月   表面技術協会   編集委員長
  • 2017年01月 - 2018年12月   電気化学会   北海道支部長
  • 2015年01月 - 2016年12月   表面技術協会   北海道支部長
  • 2013年01月 - 2014年12月   腐食防食学会   北海道支部長
  • 2010年01月 - 2012年12月   腐食防食協会   北海道支部副支部長   腐食防食協会
  • 2010年 - 2011年   Internationa Society of Electrochemistry   シンポジウムオーガナイザー   Internationa Society of Electrochemistry
  • 2009年 - 2011年   電気化学会   編集委員   電気化学会
  • 2009年 - 2010年   International Society of Electrochemistry   シンポジウムオーガナイザー   Internationa Society of Electrochemistry
  • 2005年04月 - 2009年03月   表面技術協会   「表面技術」編集委員

論文

  • Nan Sheng, Jiahui Lu, Jingdong Hu, Ruijie Zhu, Laras Fadillah, Cheng Wang, Chunyu Zhu, Zhonghao Rao, Hiroki Habazaki
    Chemical Engineering Journal 420 2021年09月15日 [査読有り]
     
    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 O2 atmosphere is conducted to form a stable SnO2 shell. The Sn@SnO2 microcapsules exhibit a melting point of ~232 °C and latent heat of ~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.
  • Masahiro Nishimoto, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ACS Sustainable Chemistry and Engineering 9 28 9465 - 9473 2021年07月19日 [査読有り]
     
    Developing highly active and durable electrocatalysts, 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)F2 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.
  • Shinichi Hata, Keita Iwamoto, Sho Kitano, Hiroki Habazaki, Akari Hirakawa, Nanami Tani, Yukou Du, Yukihide Shiraishi, Naoki Toshima
    Colloids and Interface Science Communications 43 2021年07月 [査読有り]
     
    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.
  • Chunmei Tang, Katsuya Akimoto, Ning Wang, Laras Fadillah, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    Journal of Materials Chemistry A 9 24 14032 - 14042 2021年06月28日 [査読有り]
     
    Protonic solid oxide steam electrolysis cells (P-SOECs) based on BaZrxCe0.8−xYb0.1Y0.1O3−δproton 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−δ(BZCYYb6211), can be significantly improved by using a La0.5Sr0.5CoO3−δ(LSC) thin film (∼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 Ω cm2to 0.26 and 0.57 Ω cm2, respectively, with the LSC-AFL at 600 °C. In addition, the BZCYYb6211 cell achieved a high electrolysis current of 1.22 A cm−2at 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−δ(BZCYYb1711). BZCYYb6211 with LSC-AFL showed good durability at 500 °C under high steam conditions with an applied current of 1 A cm−2for 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 2021年06月14日 [査読有り]
     
    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−2to 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 2021年05月05日 [査読有り]
     
    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 O2 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 O2. 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 O2 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 2021年03月 [査読有り]
     
    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.
  • Ryota Yamamoto, Damian Kowalski, Ruijie Zhu, Keisuke Wada, Yuki Sato, Sho Kitano, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    Applied Surface Science 537 2021年01月30日 [査読有り]
     
    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.
  • 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 2021年01月25日 
    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-δ 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 °C and pH2O 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 °C. Impedance analysis confirmed that the polarization resistance of the La0.8Sr0.2Co0.7Ni0.3O3-δ cell was 0.09 ω cm2 under an open circuit potential at 600 °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 °C.
  • Takayoshi Yano, Shin Ishikawa, Hiroki Habazaki
    Materials Transactions 62 6 836 - 845 2021年 
    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 γ-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 γ-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.
  • Seong Woo Jeong, Ning Wang, Sho Kitano, Hiroki Habazaki, Yoshitaka Aoki
    Advanced Energy Materials 2021年 
    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 °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−δ electrolyte accumulates a large amount of oxide ions, thereby developing large concentration gradients. Thus, it achieves a cathode reaction resistance of 0.54 Ω cm2 at 400 °C with conventional cathode materials, La0.6Sr0.4Co0.2Fe0.8O3−δ. 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 2021年 
    The incorporation of mobile hydridic defects was demonstrated for low-crystalline zirconium nitride (Zr3N4-?) 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-? films exhibited n-type semiconductor behavior due to the presence of nitrogen vacancy donors with a carrier concentration of 1.4 × 1020 cm-3 and an electron mobility of 2.2 × 10-3 cm2 V-1 s-1 at room temperature. Electrochemical and spectroscopic measurements confirmed that Zr3N4-? was readily hydrogenated upon exposure to H2 gas at 300 °C to form hydridic defects via electron donation to hydrogen adatoms. Hence, the hydrogenated film exhibited H- ion/electron mixed conductor behavior in a H2 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 and Interfaces 2021年 
    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° 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 self-healing corrosion-resistant surfaces.
  • Naohito Yamada, Sho Kitano, Yuya Yato, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    ACS Applied Energy Materials 3 12 12316 - 12326 2020年12月28日 
    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.
  • Laras Fadillah, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    Electrochimica Acta 364 2020年12月20日 
    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.FeF2, whereas those formed on higher index number are composed of Fe3O4.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.
  • Yuki Sato, Sho Kitano, Damian Kowalski, Yoshitaka Aoki, Naoko Fujiwara, Tsutomu Ioroi, Hiroki Habazaki
    Denki Kagaku 88 6 566 - 573 2020年11月05日 
    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.
  • M. Sepúlveda, J. G. Castaño, F. Echeverría, Y. Aoki, D. Kowalski, H. Habazaki
    Electrochemistry Communications 120 2020年11月 
    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 quasi-spherical 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.
  • Ryoya Masuda, Damian Kowalski, Sho Kitano, Yoshitaka Aoki, Taisuke Nozawa, Hiroki Habazaki
    Coatings 10 11 1 - 12 2020年11月 
    In this study, zinc is anodized at different voltages in 0.1 mol·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.
  • Tomohiro Inoue, Akira Koyama, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 217 13 2020年07月 [査読有り][通常論文]
     
    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.
  • Ning Wang, Satoshi Hinokuma, Toshiaki Ina, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    JOURNAL OF MATERIALS CHEMISTRY A 8 21 11043 - 11055 2020年06月 [査読有り][通常論文]
     
    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.
  • Yuki Sato, Yoshitaka Aoki, Kentaro Takase, Hisao Kiuchi, Damian Kowalski, Hiroki Habazaki
    ACS APPLIED ENERGY MATERIALS 3 6 5269 - 5276 2020年06月 [査読有り][通常論文]
     
    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.
  • 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 2020年05月 [査読有り][通常論文]
     
    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.
  • Ruijie Zhu, Chunyu Zhu, Nan Sheng, Zhonghao Rao, Yoshitaka Aoki, Hiroki Habazaki
    CHEMICAL ENGINEERING JOURNAL 388 2020年05月 [査読有り][通常論文]
     
    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.
  • Yuki Sato, Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki
    APPLIED CATALYSIS A-GENERAL 597 117555 - 117555 2020年05月 [査読有り][通常論文]
     
    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.
  • Nan Sheng, Ruijie Zhu, Takahiro Nomura, Zhonghao Rao, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki, Tomohiro Akiyama
    SOLAR ENERGY MATERIALS AND SOLAR CELLS 206 2020年03月 [査読有り][通常論文]
     
    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 2020年02月 [査読有り][通常論文]
     
    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 2020年01月 [査読有り][通常論文]
     
    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.
  • Nan Sheng, Zhonghao Rao, Chunyu Zhu, Hiroki Habazaki
    APPLIED THERMAL ENGINEERING 164 2020年01月 [査読有り][通常論文]
     
    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 2019年12月 [査読有り][通常論文]
     
    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 2019年11月 [査読有り][通常論文]
     
    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 2019年10月 [査読有り][通常論文]
     
    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.
  • Damian Kowalski, Hisao Kiuchi, Teruki Motohashi, Yoshitaka Aoki, Hiroki Habazaki
    ACS APPLIED MATERIALS & INTERFACES 11 32 28823 - 28829 2019年08月 [査読有り][通常論文]
     
    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.
  • Cheong Kim, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHIMICA ACTA 314 173 - 187 2019年08月 [査読有り][通常論文]
     
    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.
  • M. Seo, H. Habazaki, M. Inaba, M. Yokomizo, T. Nakayama
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 23 7 2261 - 2275 2019年07月 [査読有り][通常論文]
     
    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 2019年06月 [査読有り][通常論文]
     
    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 2019年06月 [査読有り][通常論文]
     
    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 2019年04月 [査読有り][通常論文]
     
    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 2019年03月 [査読有り][通常論文]
     
    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.
  • A. Zaffora, F. Di Quarto, H. Habazaki, I. Valov, M. Santamaria
    FARADAY DISCUSSIONS 213 165 - 181 2019年02月 [査読有り][通常論文]
     
    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.
  • J. M. Torrescano-Alvarez, M. Curioni, H. Habazaki, T. Hashimoto, P. Skeldon, X. Zhou
    ELECTROCHIMICA ACTA 296 783 - 789 2019年02月 [査読有り][通常論文]
     
    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.
  • Cheong Kim, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH 58 8 3047 - 3059 2019年02月 [査読有り][通常論文]
     
    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.
  • Naohito Yamada, Damian Kowalski, Akira Koyama, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    RSC ADVANCES 9 7 3726 - 3733 2019年01月 [査読有り][通常論文]
     
    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.
  • Atsushi Kasuga, Akira Koyama, Katsutoshi Nakayama, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ISIJ INTERNATIONAL 59 2 345 - 350 2019年 [査読有り][通常論文]
     
    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.
  • Chunyu Zhu, Manami Takata, Yoshitaka Aoki, Hiroki Habazaki
    CHEMICAL ENGINEERING JOURNAL 350 278 - 289 2018年10月 [査読有り][通常論文]
     
    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.
  • Katsutoshi Nakayama, Akira Koyama, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ADVANCED MATERIALS INTERFACES 5 19 2018年10月 [査読有り][通常論文]
     
    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.
  • Yoshitaka Aoki, Etsushi Tsuji, Teruki Motohashi, Damian Kowalski, Hiroki Habazaki
    JOURNAL OF PHYSICAL CHEMISTRY C 122 39 22301 - 22308 2018年10月 [査読有り][通常論文]
     
    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.
  • A. Němcová, Y. Li, I. Kuběna, I. Vickridge, J. J. Ganem, A. Yerokhin, H. Habazaki, P. Skeldon
    Electrochimica Acta 280 300 - 307 2018年08月 [査読有り][通常論文]
     
    © 2018 Elsevier Ltd 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 nanocrystalline 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.%.
  • Jin-Hui Cao, Yuki Sato, Damian Kowalski, Chunyu Zhu, Yoshitaka Aoki, Yingliang Cheng, Hiroki Habazaki
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 22 7 2073 - 2081 2018年07月 [査読有り][通常論文]
     
    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.
  • Andrea Zaffora, Roberto Macaluso, Hiroki Habazaki, Ilia Valov, Monica Santamaria
    ELECTROCHIMICA ACTA 274 103 - 111 2018年06月 [査読有り][通常論文]
     
    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.
  • Jinhui Cao, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki
    ACS SUSTAINABLE CHEMISTRY & ENGINEERING 6 6 7292 - 7303 2018年06月 [査読有り][通常論文]
     
    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.
  • R. Elaish, M. Curioni, K. Gowers, A. Kasuga, H. Habazaki, T. Hashimoto, P. Skeldon
    SURFACE & COATINGS TECHNOLOGY 342 233 - 243 2018年05月 [査読有り][通常論文]
     
    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 2018年05月 [査読有り][通常論文]
     
    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 2018年04月 [査読有り][通常論文]
     
    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 4 610 - 618 2018年02月01日 [査読無し][通常論文]
     
    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.
  • 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 2018年02月 [査読有り][通常論文]
     
    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 2018年02月 [査読有り][通常論文]
     
    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.
  • Evaluation of thin film fuel cells with Zr-rich side BaZrxCe0.8-xY0.2O3- electrolytes fabricated by single step cofiring process
    S. W. Jeong, T. Kobayashi, K. Kuroda, H. Kwon, C. Zhu, H. Habazaki, Y. Aoki
    RSC Advances 8 7 26309 - 26317 2018年 [査読有り][通常論文]
  • Anode reaction analysis of solid oxide electrolyzer cells at BaZr0.4Ce0.4Y0.2O3-/Sm0.5Sr0.5CoO3- interfaces
    T. Kobayashi, K. Kuroda, S. W. Jeong, H. Kwon, C. Zhu, H. Habazaki, Y. Aoki
    Journal of the Electrochemical Society 165 5 F342 - F349 2018年 [査読有り][通常論文]
  • Hiroyuki Ogata, Hiroki Habazaki
    Zairyo to Kankyo/ Corrosion Engineering 67 41 - 49 2018年01月01日 [査読無し][通常論文]
     
    © 2018 Japan Society of Corrosion Engineering. All Rights Reserved. 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.
  • Etsushi Tsuji, Shiki Matsuura, Yoshitaka Aoki, Hiroki Habazaki
    ELECTROCHEMISTRY 86 4 184 - 189 2018年 [査読有り][通常論文]
     
    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.
  • V. A. Safonov, H. Habazaki, P. Glatzel, L. A. Fishgoit, O. A. Drozhzhin, S. Lafuerza, O. V. Safonova
    APPLIED SURFACE SCIENCE 427 566 - 572 2018年01月 [査読有り][通常論文]
     
    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.
  • Yoshitaka Aoki, Tomoyuki Yamaguchi, Shohei Kobayashi, Damian Kowalski, Chunyu Zhu, Hiroki Habazaki
    GLOBAL CHALLENGES 2 1 2018年01月 [査読有り][通常論文]
     
    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.
  • Taisei Kobayashi, Kosuke Kuroda, SeongWoo Jeong, Hyuna Kwon, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 165 5 F342 - F349 2018年 [査読有り][通常論文]
     
    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.
  • Seongwoo Jeong, Taisei Kobayashi, Kosuke Kuroda, Hyuna Kwon, Chunyu Zhu, Hiroki Habazaki, Yoshitaka Aoki
    RSC ADVANCES 8 46 26309 - 26317 2018年 [査読有り][通常論文]
     
    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.
  • Katsutoshi Nakayama, Takuya Hiraga, Chunyu Zhu, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    APPLIED SURFACE SCIENCE 423 968 - 976 2017年11月 [査読有り][通常論文]
     
    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 2017年11月 [査読有り][通常論文]
     
    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.
  • Cheng Gong Han, Chunyu Zhu, Yoshitaka Aoki, Hiroki Habazaki, Tomohiro Akiyama
    Green Energy and Environment 2 4 377 - 386 2017年10月 [査読有り][通常論文]
     
    © 2017 Institute of Process Engineering, Chinese Academy of Sciences 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 Li + -ion 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.
  • Chunyu Zhu, Cheong Kim, Yoshitaka Aoki, Hiroki Habazaki
    ADVANCED MATERIALS INTERFACES 4 19 2017年10月 [査読有り][通常論文]
     
    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.
  • H. Habazaki, K. Kobayashi, E. Tsuji, C. Zhu, Y. Aoki, S. Nagata
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 21 10 2807 - 2816 2017年10月 [査読有り][通常論文]
     
    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.
  • 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 2017年10月 [査読有り][通常論文]
     
    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.
  • R. Elaish, M. Curioni, K. Gowers, A. Kasuga, H. Habazaki, T. Hashimoto, P. Skeldon
    ELECTROCHIMICA ACTA 245 854 - 862 2017年08月 [査読有り][通常論文]
     
    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.
  • 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 2017年08月 [査読有り][通常論文]
     
    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.
  • 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 2017年07月 [査読有り][通常論文]
     
    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 2017年05月 [査読有り][通常論文]
     
    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.
  • M. Santamaria, A. Zaffora, F. Di Franco, G. Tranchida, H. Habazaki, F. Di Quarto
    ECS Transactions 75 38 1 - 15 2017年 [査読有り][通常論文]
     
    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. Impedance measurements were performed in a wide range of electrode potentials in order to study the response of the anodic oxides under anodic and cathodic polarization and to estimate their dielectric constants.
  • R. Elaish, M. Curioni, K. Gowers, A. Kasuga, H. Habazaki, T. Hashimoto, P. Skeldon
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 164 13 C831 - C839 2017年 [査読有り][通常論文]
     
    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.
  • Y. Aoki, T. Yamaguchi, S. Kobayashi, C. Zhu, H. Habazaki
    SOLID OXIDE FUEL CELLS 15 (SOFC-XV) 78 1 1511 - 1515 2017年 [査読有り][通常論文]
     
    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.
  • 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 2017年 [査読有り][通常論文]
     
    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.
  • Yoshitaka Aoki, Tomoyuki Yamaguchi, Shohei Kobayashi, Chunyu Zhu, Hiroki Habazaki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 164 6 F577 - F581 2017年 [査読有り][通常論文]
     
    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.
  • D. Quintero, M. A. Gomez, J. G. Castano, E. Tsuji, Y. Aoki, F. Echeverria, H. Habazaki
    SURFACE & COATINGS TECHNOLOGY 310 180 - 189 2017年01月 [査読有り][通常論文]
     
    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 2017年 [査読有り][通常論文]
     
    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.
  • Hiroyuki Ogata, Hiroki Habazaki
    ISIJ INTERNATIONAL 57 12 2207 - 2213 2017年 [査読有り][通常論文]
     
    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.
  • H. Takano, Y. Kirihata, K. Izumiya, N. Kumagai, H. Habazaki, K. Hashimoto
    APPLIED SURFACE SCIENCE 388 653 - 663 2016年12月 [査読有り][通常論文]
     
    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 2016年11月 [査読有り][通常論文]
     
    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 2016年11月 [査読有り][通常論文]
     
    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 2016年09月 [査読有り][通常論文]
     
    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.
  • Katsutoshi Nakayama, Etsushi Tsuji, Yoshitaka Aoki, Soo-Gil Park, Hiroki Habazaki
    JOURNAL OF PHYSICAL CHEMISTRY C 120 29 15684 - 15690 2016年07月 [査読有り][通常論文]
     
    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.
  • 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 2016年07月 [査読有り][通常論文]
     
    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.
  • Andrea Zaffora, Monica Santamari, Francesco Di Franco, Hiroki Habazaki, Francesco Di Quarto
    ELECTROCHIMICA ACTA 201 333 - 339 2016年05月 [査読有り][通常論文]
     
    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.
  • H. Habazaki, T. Kimura, Y. Aoki, E. Tsuji, T. Yano, K. Shimizu, A. W. Hassel
    ELECTROCHIMICA ACTA 201 311 - 319 2016年05月 [査読有り][通常論文]
     
    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.
  • A. Nemcova, I. Kubena, M. Smid, H. Habazaki, P. Skeldon, G. E. Thompson
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 20 4 1155 - 1165 2016年04月 [査読有り][通常論文]
     
    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 2016年02月 [査読有り][通常論文]
     
    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 2016年 [査読有り][通常論文]
     
    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.
  • Masato Onishi, Hisayoshi Matsushima, Mikito Ueda, Hiroki Habazaki, Kota Washio, Akira Kato
    MOLTEN SALTS AND IONIC LIQUIDS 20 75 15 297 - 304 2016年 [査読有り][通常論文]
     
    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.
  • A. Zaffora, M. Santamaria, F. Di Franco, H. Habazaki, F. Di Quarto
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 18 1 351 - 360 2016年01月 [査読有り][通常論文]
     
    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.
  • Chiharu Kura, Yoshitaka Aoki, Etsushi Tsuji, Hiroki Habazaki, Manfred Martin
    RSC ADVANCES 6 11 8964 - 8970 2016年 [査読有り][通常論文]
     
    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.
  • Khurram Shahzad, Chunyu Zhu, Etsushi Tsuji, Yoshitaka Aoki, Shinji Nagata, Hiroki Habazaki
    MATERIALS TRANSACTIONS 57 9 1552 - 1559 2016年 [査読有り][通常論文]
     
    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.
  • D. Quintero, O. Galvis, J. A. Calderon, M. A. Gomez, J. G. Castano, F. Echeverria, H. Habazaki
    SURFACE & COATINGS TECHNOLOGY 283 210 - 222 2015年12月 [査読有り][通常論文]
     
    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, Su-Il Pyun
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 19 12 3425 - 3426 2015年12月 [査読有り][通常論文]
  • Po-Chieh Li, Chi-Chang Hu, Hiroyuki Noda, Hiroki Habazaki
    JOURNAL OF POWER SOURCES 298 102 - 113 2015年12月 [査読有り][通常論文]
     
    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.
  • Hiroki Habazaki, Fumitaka Kataoka, Khurram Shahzad, Etsushi Tsuji, Yoshitaka Aoki, Shinji Nagata, Peter Skeldon, George E. Thompson
    ELECTROCHIMICA ACTA 179 402 - 410 2015年10月 [査読有り][通常論文]
     
    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 2015年10月 [査読有り][通常論文]
     
    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 2015年07月 [査読有り][通常論文]
     
    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 2015年06月 [査読有り][通常論文]
     
    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.
  • Y. Aoki, S. Kobayashi, T. Yamaguchi, E. Tsuji, H. Habazaki
    ECS Transactions 68 1 2735 - 2738 2015年 [査読有り][通常論文]
     
    Hydrogen membrane fuel cells, HMFC, were fabricated by RF sputtering deposition of BaCe< sup> 0.8< /sup> Y< sup> 0.2< /sup> O< sup> 3-δ< /sup> thin films on Pd solid anode. The HMFC can give OCV of 1.1 V and peak power density of 300 mW cm< sup> -2< /sup> at 600°C with H< inf> 2< /inf> fuels. On the other hand, the direct NH< inf> 3< /inf> fueled HMFC reveals OCV of 0.95 V and peak power density of 80 mW cm< sup> -2< /sup> at 600°C. The impedance spectroscopy reveals that anodic polarization is the main contribution to the loss in HMFC.
  • H. Habazaki, K. Shahzad, T. Hiraga, E. Tsuji, Y. Aoki
    ECS Transactions 69 211 - 223 2015年 [査読無し][通常論文]
  • H. Habazaki, M. Uemura, K. Fushimi, E. Tsuji, Y. Aoki, S. Nagata
    Journal of The Surface Finishing Society Japan 66 670 - 672 2015年 [査読有り][通常論文]
  • 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 2015年 [査読有り][通常論文]
     
    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 2015年01月 [査読有り][通常論文]
     
    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.
  • Yoshiki Konno, Etsushi Tsuji, Yoshitaka Aoki, Toshiaki Ohtsuka, Hiroki Habazaki
    FARADAY DISCUSSIONS 180 479 - 493 2015年 [査読有り][通常論文]
     
    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.
  • 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 2015年 [査読有り][通常論文]
  • 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 2015年 [査読有り][通常論文]
  • 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年12月 [査読有り][通常論文]
     
    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 2014年10月 [査読有り][通常論文]
     
    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.
  • 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 2014年09月 [査読有り][通常論文]
     
    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.
  • Hiroki Habazaki, Fumitaka Kataoka, Etsushi Tsuji, Yoshitaka Aoki, Shinji Nagata, Peter Skeldon, George E. Thompson
    ELECTROCHEMISTRY COMMUNICATIONS 46 30 - 32 2014年09月 [査読有り][通常論文]
     
    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.
  • Seong-Ki Ahn, Jeong-Jin Yang, Hong-Il Kim, Hiroki Habazaki, Soo-Gil Park
    CHEMISTRY LETTERS 43 6 898 - 900 2014年06月 [査読有り][通常論文]
     
    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 2014年05月 [査読有り][通常論文]
     
    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.
  • Tatsuya Kikuchi, Masumi Yoshida, Yoshiaki Taguchi, Hiroki Habazaki, Ryosuke O. Suzuki
    JOURNAL OF ALLOYS AND COMPOUNDS 586 148 - 154 2014年02月 [査読有り][通常論文]
     
    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.
  • 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 2014年02月 [査読有り][通常論文]
     
    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.
  • Alexander Mozalev, Masatoshi Sakairi, Hideaki Takahashi, Hiroki Habazaki, Jaromir Hubalek
    THIN SOLID FILMS 550 486 - 494 2014年01月 [査読有り][通常論文]
     
    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.
  • Hiroki Habazaki, Taiki Kimura, Yoshitaka Aoki, Etsushi Tsuji, Takayoshi Yano
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 161 1 C57 - C61 2014年 [査読有り][通常論文]
     
    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.
  • M. Seo, H. Habazaki, M. Inaba, M. Yokomizo, T. Wakabayashi, T. Nakayama
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 161 4 H195 - H202 2014年 [査読有り][通常論文]
     
    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.
  • Yoshitaka Aoki, Kazumasa Kikutani, Etsushi Tsuji, Hiroki Habazaki
    ECS ELECTROCHEMISTRY LETTERS 3 10 F61 - F64 2014年 [査読有り][通常論文]
     
    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.
  • 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 2014年 [査読有り][通常論文]
     
    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.
  • Masahiro Seo, Atsushi Hyono, Hiroki Habazaki, Takenori Nakayama
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 161 12 C550 - C556 2014年 [査読有り][通常論文]
     
    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.
  • Katsutoshi Nakayama, Etsushi Tsuji, Yoshitaka Aoki, Hiroki Habazaki
    RSC ADVANCES 4 58 30927 - 30933 2014年 [査読有り][通常論文]
     
    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.
  • 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 2013年12月 [査読有り][通常論文]
     
    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 2013年12月 [査読有り][通常論文]
     
    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 2013年11月 [査読有り][通常論文]
     
    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 2013年10月 [査読有り][通常論文]
     
    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 2013年10月 [査読有り][通常論文]
     
    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.
  • H. Habazaki, H. Sato, E. Tsuji, Y. Aoki, K. Shimizu
    ECS Transactions 58 41 75 - 83 2013年 [査読有り][通常論文]
     
    Organic layers of tetradecylphosphonic acid (TDP) and octadecyltrietoxysilane (OES) are formed on flat anodized aluminum surfaces by a simple immersion process. The organic layers are characterized by dynamic contact angle measurements for water, AFM, low-voltage SEM and angle-resolved XPS. The results indicate that a self-assembled monolayer is formed using TDP, but not for OES. Plasma surface treatment prior to the coating was found to significantly influence the formation of organic layers. © 2014 The Electrochemical Society.
  • H. Habazaki, T. Fujii, E. Tsuji, Y. Aoki
    PITS AND PORES 5: A SYMPOSIUM IN HONOR OF DAVID LOCKWOOD 50 37 217 - 224 2013年 [査読有り][通常論文]
     
    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.
  • 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 2013年 [査読有り][通常論文]
     
    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.
  • Ke Ye, Yoshitaka Aoki, Etsushi Tsuji, Shinji Nagata, Hiroki Habazaki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 160 9 F1096 - F1102 2013年 [査読有り][通常論文]
     
    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.
  • M. Ishizuka, E. Tsuji, Y. Aoki, A. Hyono, T. Ohtsuka, N. Sakaguchi, S. Nagata, H. Habazaki
    ELECTROCHEMICAL CAPACITORS 50 43 245 - 254 2013年 [査読有り][通常論文]
     
    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.
  • Etsushi Tsuji, Naoto Hirata, Yoshitaka Aoki, Hiroki Habazaki
    MATERIALS LETTERS 91 39 - 41 2013年01月 [査読有り][通常論文]
     
    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.
  • 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 2013年 [査読有り][通常論文]
     
    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.
  • Y. Aoki, R. Nonaka, H. Habazaki
    SOLID OXIDE FUEL CELLS 13 (SOFC-XIII) 57 1 911 - 916 2013年 [査読有り][通常論文]
     
    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.
  • 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 2013年 [査読有り][通常論文]
     
    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.
  • Y. Konno, E. Tsuji, P. Skeldon, G. E. Thompson, H. Habazaki
    JOURNAL OF SOLID STATE ELECTROCHEMISTRY 16 12 3887 - 3896 2012年12月 [査読有り][通常論文]
     
    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 2012年11月 [査読有り][通常論文]
     
    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 2012年11月 [査読有り][通常論文]
     
    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 2012年10月 [査読有り][通常論文]
     
    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 2012年10月 [査読有り][通常論文]
     
    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 2012年07月 [査読有り][通常論文]
     
    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 2012年05月 [査読有り][通常論文]
     
    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 2012年04月 [査読有り][通常論文]
     
    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 2012年04月 [査読有り][通常論文]
     
    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 2012年02月 [査読有り][通常論文]
     
    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.
  • F. Di Franco, M. Santamaria, F. Di Quarto, E. Tsuji, H. Habazaki
    ELECTROCHIMICA ACTA 59 382 - 386 2012年01月 [査読有り][通常論文]
     
    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.
  • F. Di Franco, G. Zampardi, M. Santamaria, F. Di Quarto, H. Habazaki
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 159 1 C33 - C39 2012年 [査読有り][通常論文]
     
    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]
  • 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 2012年 [査読有り][通常論文]
     
    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.
  • 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年 [査読有り][通常論文]
     
    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.
  • Yoshitaka Aoki, Akihisa Harada, Aiko Nakao, Toyoki Kunitake, Hiroki Habazaki
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 14 8 2735 - 2742 2012年 [査読有り][通常論文]
     
    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.
  • F. Zhou, A. Baron-Wiechec, S. J. Garcia-Vergara, M. Curioni, H. Habazaki, P. Skeldon, G. E. Thompson
    ELECTROCHIMICA ACTA 59 186 - 195 2012年01月 [査読有り][通常論文]
     
    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.
  • 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 2012年 [査読有り][通常論文]
     
    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.
  • Hiroki Habazaki, Maria Janik Czachor, Pawel Kulesza
    APPLIED SURFACE SCIENCE 257 19 8139 - 8140 2011年07月 [査読有り][通常論文]
  • F. Di Franco, G. Zampardi, M. Santamaria, F. Di Quarto, H. Habazaki
    PHYSICS AND TECHNOLOGY OF HIGH-K MATERIALS 9 41 3 293 - 310 2011年 [査読有り][通常論文]
     
    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 2010年11月 [査読有り][通常論文]
     
    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.
  • H. Habazaki
    Shreir's Corrosion 2192 - 2204 2010年 [査読有り][通常論文]
     
    The very high corrosion resistance of amorphous alloys containing corrosion-resistant elements even in aggressive acid solutions is presented in this chapter. The high corrosion resistance of amorphous alloys is due to the high reactivity of the alloy surface, promoting the formation of passive films highly enriched in passivating elements, as well as the chemically homogeneous nature of the alloys. The corrosion behavior of nanocrystalline materials and bulk metallic glasses, both of which are potentially of practical importance, is outlined. © 2010 Copyright © 2010 Elsevier B.V. All rights reserved.
  • Hiroki Habazaki
    Corrosion Science 51 7 1481  2009年07月 [査読有り][通常論文]
  • Takatoshi Yamamoto, Koji Fushimi, Masahiro Seo, Shiro Tsuri, Tetsuo Adachi, Hiroki Habazaki
    CORROSION SCIENCE 51 7 1545 - 1553 2009年07月 [査読有り][通常論文]
     
    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.
  • Hiroki Habazaki
    CORROSION SCIENCE 51 7 1481 - 1481 2009年07月 [査読有り][通常論文]
  • Oikawa Y, Fushimi K, Aoki Y, Habazaki H
    ECS Transactions 16 3 345 - 351 2008年 [査読有り][通常論文]
  • S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, T. Hashimoto, H. Habazaki
    Journal of the Electrochemical Society 154 9 C540 - C545 2007年 [査読有り][通常論文]
     
    Using an Al-3.5 atom % W alloy, the formation of porosity in anodic alumina films is examined in phosphoric acid and borax electrolytes. During growth of major pores in phosphoric acid electrolyte, the film develops two main layers with respect to the cation species: an outer layer of tungsten-free alumina, located next to the electrolyte at the pore base and adjacent to the pore walls, and an inner layer of tungsten-containing anodic alumina, located next to the aluminum and the boundaries between the cells that contain individual pores. The W6+ ions in the inner layer do not reach the pore base regions, unlike expectations for pore generation by a dissolution mechanism. The porosity is attributed to electric-field-assisted flow of film material within the barrier layer region of the film toward the cell walls. In contrast, pore generation in anodic films grown in borax electrolyte occurs mainly due to field-assisted dissolution of film material. Accordingly, tungsten is present throughout the barrier layer and the cell wall regions of the major pores. The thickness of the anodic films formed in borax electrolyte is similar to that of the oxidized metal, whereas the thickness of anodic films formed in the phosphoric acid electrolyte exceeds that of the oxidized metal by a factor of about 1.42, consistent with flow of the film material in the latter electrolyte. © 2007 The Electrochemical Society.
  • Repassivation Current Transient from Iron Surface during Downward Micro-indentation in pH 8.4 Borate Solution
    K. Fushimi, T. Yamamoto, M. Seo, H. Habazaki
    Proceedings of EUROCORR 2007 (CD-ROM) 1227  2007年 [査読有り][通常論文]
  • H. Habazaki, T. Ogasawara, H. Konno, K. Shimizu, K. Asami, S. Nagata, P. Skeldon, G. E. Thompson
    Passivation of Metals and Semiconductors, and Properties of Thin Oxide Layers 211 - 216 2006年 [査読有り][通常論文]
     
    This chapter presents a study in which an amorphous-to crystalline transition of anodic niobia is examined by using magnetron-sputtered niobium and its alloy substrates, with particular attentions paid to the preexisting surface oxide layer as a nucleation site of crystalline oxide and incorporation of foreign species hindering its nucleation. Niobium and Nb-N films were prepared by magnetron sputtering on to glass, silicon and aluminum substrates. Aluminum substrates were electropolished and subsequently anodized in 0.1 mol dm-3 ammonium pentaborate electrolyte to 200 V to provide flat surfaces. The niobium and niobium alloy films prepared were anodized at a constant current density of generally 50 A m-2 to selected voltages with and without current decay in stirred 0.1 mol dm-3 ammonium pentaborate and 0.1 mol dm-3 phosphoric acid electrolytes at 60. o C. Platinum sheet was used as a counter electrode. Amorphous-to-crystalline transition of anodic niobia formed on the sputter-deposited niobium films, which are free from preferable sites, such as inclusions and surface roughness, of the transition, initiated at approximately outer 30% of the film thickness where air-formed oxide is located. The growth of the crystalline oxide to the metal/film interface is rapid and the phosphorus species incorporated from the phosphoric acid electrolyte suppress effectively the amorphous-to-crystalline transition. Similarly, the foreign species incorporated from the substrate, such as nitrogen, silicon, and tungsten species suppress the crystalline oxide formation. © 2006 Elsevier B.V. All rights reserved.
  • T Kuranishi, H Habazaki, H Konno
    SURFACE & COATINGS TECHNOLOGY 200 7 2438 - 2444 2005年12月 [査読有り][通常論文]
     
    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.
  • H Habazaki, T Ogasawara, H Konno, K Shimizu, K Asami, K Saito, S Nagata, P Skeldon, GE Thompson
    ELECTROCHIMICA ACTA 50 27 5334 - 5339 2005年09月 [査読有り][通常論文]
     
    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.
  • 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 2005年09月 [査読有り][通常論文]
     
    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.
  • Zhou, X, GE Thompson, P Skeldon, K Shimizu, H Habazaki, GC Wood
    CORROSION SCIENCE 47 5 1299 - 1306 2005年05月 [査読有り][通常論文]
     
    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.
  • H Habazaki, K Shimizu, S Nagata, K Asami, K Takayama, Y Oda, P Skeldon, GE Thompson
    THIN SOLID FILMS 479 1-2 144 - 151 2005年05月 [査読有り][通常論文]
     
    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 2005年04月 [査読有り][通常論文]
     
    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 2005年02月 [査読有り][通常論文]
     
    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.
  • H. Konno, T. Morishita, S. Sato, H. Habazaki, M. Inagaki
    ECS Transactions 1 4 509 - 514 2005年 [査読有り][通常論文]
     
    Two types of low molecular weight silicone compounds were impregnated into urethane foam pieces by sorption and cured in air. Formed block-type precursors were crushed and heat-treated at 1000-1600°C for 1 h in Ar. The Si-C-O compounds formed in a range of 1000-1300°C were glass-like by XRD and had nearly the same chemical composition, but the 1300°C product had less amounts of siloxane groups than the 1000°C product by MAS-NMR. The 1300°C product showed good cycle performance for Li+ ion insertion/extraction in 1 mol L-1 LiClO4 (EC:DEC=50:50 vol%) and no irreversible capacity except for the first cycle. The capacity was about 600 mA h g-1 at 50 mA g-1 and about 400 mA h g -1 at 200 mA g-1. In contrast, the product at lower temperature showed much higher initial capacity but it decreased steeply with number of cycles. copyright The Electrochemical Society.
  • Q Lu, T Hashimoto, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    ELECTROCHEMICAL AND SOLID STATE LETTERS 8 5 B17 - B20 2005年 [査読有り][通常論文]
     
    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.
  • H Konno, T Morishita, S Sato, H Habazaki, M Inagaki
    CARBON 43 5 1111 - 1114 2005年 [査読有り][通常論文]
  • Q Lu, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    THIN SOLID FILMS 471 1-2 118 - 122 2005年01月 [査読有り][通常論文]
     
    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.
  • Y Liu, AM Arenas, SG Garcia-Vergara, P Skeldon, GE Thompson, K Shimizu, H Habazaki
    CORROSION SCIENCE 47 1 145 - 150 2005年01月 [査読有り][通常論文]
     
    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.
  • F Monfort, A Berkani, E Matykina, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 152 6 C382 - C387 2005年 [査読有り][通常論文]
     
    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.
  • K Asami, H Habazaki, A Inoue, K Hashimoto
    NEW FRONTIERS OF PROCESSING AND ENGINEERING IN ADVANCED MATERIALS 502 225 - 230 2005年 [査読有り][通常論文]
     
    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 2005年 [査読有り][通常論文]
     
    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.
  • Q Lu, P Skeldon, GE Thompson, D Masheder, H Habazaki, K Shimizu
    CORROSION SCIENCE 46 11 2817 - 2824 2004年11月 [査読有り][通常論文]
     
    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, F. A. Bonilla, Y. Liu, M. A. Arenas, P. Skeleton, G. E. Thompson, P. Bailey, T. C.Q. Noakes, K. Shimizu, H. Habazaki
    Electrochimica Acta 49 26 4803  2004年10月15日 [査読有り][通常論文]
  • K Shimzu, H Fujitani, H Habazaki, P Skeldon, GE Thompson
    CORROSION SCIENCE 46 10 2549 - 2561 2004年10月 [査読有り][通常論文]
     
    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.
  • 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 2004年10月 [査読有り][通常論文]
  • Y Aoki, H Habazaki, H Konno
    CHEMISTRY LETTERS 33 8 992 - 993 2004年08月 [査読有り][通常論文]
     
    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 2004年08月 [査読有り][通常論文]
     
    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 2004年03月 [査読有り][通常論文]
     
    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 2004年02月 [査読有り][通常論文]
     
    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.
  • H Konno, S Sato, H Habazaki, M Inagaki
    CARBON 42 12-13 2756 - 2759 2004年 [査読有り][通常論文]
  • 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 2004年01月 [査読有り][通常論文]
     
    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, T Kinomura, H Habazaki, M Aramata
    CARBON 42 4 737 - 744 2004年 [査読有り][通常論文]
     
    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.
  • K Shimizu, R Payling, H Habazaki, P Skeldon, GE Thompson
    JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 19 5 692 - 695 2004年 [査読有り][通常論文]
     
    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.
  • S Mato, G Alcala, GE Thompson, P Skeldon, K Shimizu, H Habazaki, T Quance, MJ Graham, D Masheder
    CORROSION SCIENCE 45 12 2881 - 2892 2003年12月 [査読有り][通常論文]
     
    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 2003年12月 [査読有り][通常論文]
     
    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.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    CORROSION SCIENCE 45 12 2905 - 2913 2003年12月 [査読有り][通常論文]
     
    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.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, H Habazaki, K Shimizu
    CORROSION SCIENCE 45 12 2915 - 2923 2003年12月 [査読有り][通常論文]
     
    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.
  • 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 2003年10月 [査読有り][通常論文]
     
    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.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson
    SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY 58 9 1573 - 1583 2003年09月 [査読有り][通常論文]
     
    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.
  • S Mato, G Alcala, P Skeldon, GE Thompson, D Masheder, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 150 9 B439 - B444 2003年09月 [査読有り][通常論文]
     
    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.
  • 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 2003年09月 [査読有り][通常論文]
     
    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.
  • H Habazaki, M Uozumi, H Konno, K Shimizu, P Skeldon, GE Thompson
    CORROSION SCIENCE 45 9 2063 - 2073 2003年09月 [査読有り][通常論文]
     
    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.
  • S. Mato, G. Alcala, P. Skeldon, G. E. Thompson, T. Quance, M. J. Graham, H. Habazaki, K. Shimizu, D. Masheder
    Philosophical Magazine 83 23 2733 - 2746 2003年08月11日 [査読有り][通常論文]
     
    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-12at.% Cu and Ta-57at.% 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.
  • G Alcala, S Mato, P Skeldon, GE Thompson, AB Mann, H Habazaki, K Shimizu
    SURFACE & COATINGS TECHNOLOGY 173 2-3 293 - 298 2003年08月 [査読有り][通常論文]
     
    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 2003年08月 [査読有り][通常論文]
     
    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.
  • S Mato, G Alcala, P Skeldon, GE Thompson, D Masheder, H Habazaki, K Shimizu
    CORROSION SCIENCE 45 8 1779 - 1792 2003年08月 [査読有り][通常論文]
     
    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.
  • G Alcala, S Mato, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, H Habazaki, K Shimizu
    CORROSION SCIENCE 45 8 1803 - 1813 2003年08月 [査読有り][通常論文]
     
    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.
  • K Shimizu, N Kasahara, H Habazaki, P Skeldon, GE Thompson
    SURFACE AND INTERFACE ANALYSIS 35 7 611 - 617 2003年07月 [査読有り][通常論文]
     
    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.
  • 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 2003年07月 [査読有り][通常論文]
     
    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 2003年07月 [査読有り][通常論文]
     
    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.
  • K Azumi, T Yugiri, T Kurihara, M Seo, H Habazaki, S Fujimoto
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 150 7 C461 - C464 2003年07月 [査読有り][通常論文]
     
    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.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson
    SURFACE AND INTERFACE ANALYSIS 35 7 564 - 574 2003年07月 [査読有り][通常論文]
     
    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.
  • Y Aoki, H Habazaki, H Konno
    CHEMISTRY OF MATERIALS 15 12 2419 - 2428 2003年06月 [査読有り][通常論文]
     
    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.
  • H Habazaki, M Uozumi, H Konno, S Nagata, K Shimizu
    SURFACE & COATINGS TECHNOLOGY 169 151 - 154 2003年06月 [査読有り][通常論文]
     
    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 2003年06月 [査読有り][通常論文]
     
    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 2003年05月 [査読有り][通常論文]
     
    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 2003年04月 [査読有り][通常論文]
     
    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 2003年04月 [査読有り][通常論文]
     
    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.
  • S Garcia-Vergara, P Skeldon, GE Thompson, P Bailey, TCQ Noakes, H Habazaki, K Shimizu
    APPLIED SURFACE SCIENCE 205 1-4 121 - 127 2003年01月 [査読有り][通常論文]
     
    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.
  • GE Thompson, P Skeldon, Zhou, X, K Shimizu, H Habazaki, CFE Smith
    AIRCRAFT ENGINEERING AND AEROSPACE TECHNOLOGY 75 4 372 - 379 2003年 [査読有り][通常論文]
     
    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.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, U Kreissig, D Grambole, H Habazaki, K Shimizu
    THIN SOLID FILMS 424 2 201 - 207 2003年01月 [査読有り][通常論文]
     
    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.
  • Z Ashitaka, P Skeldon, GE Thompson, K Shimizu, H Habazaki
    CORROSION SCIENCE 44 12 2725 - 2735 2002年12月 [査読有り][通常論文]
     
    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 2002年12月 [査読有り][通常論文]
     
    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 2002年12月 [査読有り][通常論文]
     
    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 2002年11月 [査読有り][通常論文]
     
    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.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, RK Marcus
    SPECTROSCOPY 17 10 14 - + 2002年10月 [査読有り][通常論文]
     
    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.
  • H Habazaki, Y Hayashi, H Konno
    ELECTROCHIMICA ACTA 47 26 4181 - 4188 2002年10月 [査読有り][通常論文]
     
    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.
  • 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 2002年09月 [査読有り][通常論文]
     
    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.
  • H Habazaki, M Uozumi, H Konno, K Shimizu, S Nagata, K Asami, P Skeldon, GE Thompson
    ELECTROCHIMICA ACTA 47 24 3837 - 3845 2002年09月 [査読有り][通常論文]
     
    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 2002年09月 [査読有り][通常論文]
     
    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.
  • FA Bonilla, A Berkani, P Skeldon, GE Thompson, H Habazaki, K Shimizu, C John, K Stevens
    CORROSION SCIENCE 44 9 1941 - 1948 2002年09月 [査読有り][通常論文]
     
    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.
  • G Alcala, P Skeldon, GE Thompson, AB Mann, H Habazaki, K Shimizu
    NANOTECHNOLOGY 13 4 451 - 455 2002年08月 [査読有り][通常論文]
     
    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.
  • H Konno, K Narumi, H Habazaki
    CORROSION SCIENCE 44 8 1889 - 1900 2002年08月 [査読有り][通常論文]
     
    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.
  • CE Caicedo-Martinez, EV Koroleva, GE Thompson, P Skeldon, K Shimizu, H Habazaki, G Hoellrigl
    SURFACE AND INTERFACE ANALYSIS 34 1 405 - 408 2002年08月 [査読有り][通常論文]
     
    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 2002年07月 [査読有り][通常論文]
     
    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 2002年05月 [査読有り][通常論文]
     
    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.
  • K Yoshimi, S Nakatani, T Suda, S Hanada, H Habazaki
    INTERMETALLICS 10 5 407 - 414 2002年05月 [査読有り][通常論文]
     
    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 O-2 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. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Y Liu, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    CORROSION SCIENCE 44 5 1133 - 1142 2002年05月 [査読有り][通常論文]
     
    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.
  • 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 2002年04月 [査読有り][通常論文]
     
    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.
  • 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 2002年04月 [査読有り][通常論文]
     
    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 2002年04月 [査読有り][通常論文]
     
    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.
  • H Habazaki, K Shimizu, S Nagata, P Skeldon, GE Thompson, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 149 3 B70 - B74 2002年03月 [査読有り][通常論文]
     
    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.
  • 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 2002年02月 [査読有り][通常論文]
     
    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 2002年02月 [査読有り][通常論文]
     
    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.
  • H Habazaki, H Mitsui, K Ito, K Asami, K Hashimoto, S Mrowec
    CORROSION SCIENCE 44 2 285 - 301 2002年02月 [査読有り][通常論文]
     
    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 Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    ELECTROCHIMICA ACTA 47 8 1225 - 1228 2002年02月 [査読有り][通常論文]
     
    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.
  • H Konno, A Sudoh, Y Aoki, H Habazaki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 386 15 - 20 2002年 [査読有り][通常論文]
     
    B/C composites containing crystalline B4C particles were synthesized at 1400degreesC 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.
  • 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 2002年01月 [査読有り][通常論文]
     
    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.
  • K Shimizu, Y Einaga, K Ohnishi, A Fujishima, H Habazaki, P Skeldon, GE Thompson
    SURFACE AND INTERFACE ANALYSIS 33 1 35 - 40 2002年01月 [査読有り][通常論文]
     
    Analysis of a boron-doped diamond film, similar to13 mum 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. Interestingly, 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. Copyright (C) 2002 John Wiley Sons, Ltd.
  • K. Shimizu, H. Habazaki, P. Skeldon, G. E. Thompson
    Surface and Interface Analysis 31 12 1079 - 1084 2001年12月 [査読有り][通常論文]
     
    The properties of the interphase between Twaron® aramid fibres and polymer matrix systems can be optimized by a surface treatment process of the fibres. In this work, x-ray photoelectron spectroscopy and low-energy ion scattering have been used to analyse the surface layers, whereas the adhesion was measured by a bundle pull-out experiment. From the results, we succeeded in establishing a relation between the surface treatment, the resulting chemical/elemental surface composition and the adhesion to an epoxy matrix.
  • Y Liu, P Skeldon, GE Thompson, Zhou, X, H Habazaki, K Shimizu
    CORROSION SCIENCE 43 12 2349 - 2357 2001年12月 [査読有り][通常論文]
     
    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.
  • L Iglesias-Rubianes, P Skeldon, GE Thompson, K Shimizu, H Habazaki
    CORROSION SCIENCE 43 12 2217 - 2227 2001年12月 [査読有り][通常論文]
     
    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.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson
    SURFACE AND INTERFACE ANALYSIS 31 12 1085 - 1086 2001年12月 [査読有り][通常論文]
     
    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 2001年11月 [査読有り][通常論文]
     
    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.
  • 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 2001年11月 [査読有り][通常論文]
     
    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.
  • H Konno, R Matsuura, M Yamasaki, H Habazaki
    SYNTHETIC METALS 125 2 167 - 170 2001年11月 [査読有り][通常論文]
     
    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.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, RK Marcus
    SURFACE AND INTERFACE ANALYSIS 31 9 869 - + 2001年09月 [査読有り][通常論文]
     
    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 2001年08月 [査読有り][通常論文]
     
    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 2001年07月 [査読有り][通常論文]
     
    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.
  • 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 2001年06月 [査読有り][通常論文]
     
    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.
  • P Bailey, P Skeldon, TCQ Noakes, GE Thompson, M Sakairi, H Habazaki, K Shimizu
    SURFACE AND INTERFACE ANALYSIS 31 6 480 - 483 2001年06月 [査読有り][通常論文]
     
    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.
  • K Asami, BP Zhang, M Mehmood, H Habazaki, K Hashimoto
    SCRIPTA MATERIALIA 44 8-9 1655 - 1658 2001年05月 [査読有り][通常論文]
  • H Habazaki, T Sato, A Kawashima, K Asami, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 304 696 - 700 2001年05月 [査読有り][通常論文]
     
    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.
  • A Kawashima, H Habazaki, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 304 753 - 757 2001年05月 [査読有り][通常論文]
     
    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.
  • 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 2001年05月 [査読有り][通常論文]
     
    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.
  • H Habazaki, T Matsui, A Kawashima, K Asami, N Kumagai, K Hashimoto
    SCRIPTA MATERIALIA 44 8-9 1659 - 1662 2001年05月 [査読有り][通常論文]
  • S Mato, GE Thompson, P Skeldon, K Shimizu, H Habazaki, D Masheder
    CORROSION SCIENCE 43 5 993 - 1002 2001年05月 [査読有り][通常論文]
     
    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 2001年03月 [査読有り][通常論文]
     
    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.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 43 2 199 - 205 2001年02月 [査読有り][通常論文]
     
    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.
  • H Katagiri, S Meguro, M Yamasaki, H Habazaki, T Sato, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 43 1 171 - 182 2001年01月 [査読有り][通常論文]
     
    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.
  • E Akiyama, K Asami, H Habazaki, A Kawashima, K Hashimoto
    CORROSION AND CORROSION PROTECTION 2001 22 1 - 8 2001年 [査読有り][通常論文]
     
    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 2001年 [査読有り][通常論文]
     
    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 Katagiri, S Meguro, M Yamasaki, H Habazaki, T Sato, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 43 1 183 - 191 2001年01月 [査読有り][通常論文]
     
    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.
  • K Hashimoto, H Katagiri, H Habazaki, M Yamasaki, S Meguro, A Kawashima, K Asami
    CORROSION AND CORROSION PROTECTION 2001 22 18 - 25 2001年 [査読有り][通常論文]
     
    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 Habazaki, Y Naruse, H Konno, H Ukai, K Izumiya, K Hashimoto
    CORROSION AND CORROSION PROTECTION 2001 22 130 - 137 2001年 [査読有り][通常論文]
     
    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 2001年 [査読有り][通常論文]
     
    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.
  • H Habazaki, M Yamasaki, A Kawashima, K Hashimoto
    APPLIED ORGANOMETALLIC CHEMISTRY 14 12 803 - 808 2000年12月 [査読有り][通常論文]
     
    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.
  • M Yamasaki, H Habazaki, K Asami, K Hashimoto
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 147 12 4502 - 4506 2000年12月 [査読有り][通常論文]
     
    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
    SURFACE AND INTERFACE ANALYSIS 29 12 887 - 890 2000年12月 [査読有り][通常論文]
     
    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.
  • S Mato, P Skeldon, GE Thompson, D Masheder, GI Sproule, MJ Graham, H Habazaki, K Shimizu
    SURFACE AND INTERFACE ANALYSIS 29 12 895 - 902 2000年12月 [査読有り][通常論文]
     
    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, GC Wood
    SURFACE AND INTERFACE ANALYSIS 29 11 743 - 746 2000年11月 [査読有り][通常論文]
     
    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.
  • F Echeverria, P Skeldon, GE Thompson, MJ Graham, H Habazaki, K Shimizu
    CORROSION SCIENCE 42 10 1839 - 1851 2000年10月 [査読有り][通常論文]
     
    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 similar to 36% of their thickness, The average compositions of the films are 0.24Al(2)O(3). 0.8Ga(2)O(3). 1.2AS(2)O(3) and 0.96Al(2)O(3). 0.2Ga(2)O(3). 1.2As(2)O(3) 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.
  • AE Herrera-Erazo, H Habazaki, K Shimizu, P Skeldon, GE Thompson
    CORROSION SCIENCE 42 10 1823 - 1830 2000年10月 [査読有り][通常論文]
     
    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 2000年08月 [査読有り][通常論文]
     
    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 2000年08月 [査読有り][通常論文]
     
    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 2000年06月 [査読有り][通常論文]
     
    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.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 42 5 831 - 840 2000年05月 [査読有り][通常論文]
     
    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.
  • 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 2000年05月 [査読有り][通常論文]
     
    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.
  • Zhou, X, GE Thompson, H Habazaki, MA Paez, K Shimizu, P Skeldon, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 147 5 1747 - 1750 2000年05月 [査読有り][通常論文]
     
    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 2000年04月 [査読有り][通常論文]
     
    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.
  • N Margadant, P Skeldon, M Textor, GE Thompson, J Wan, H Habazaki, K Shimizu, ND Spencer, GC Wood
    CORROSION SCIENCE 42 3 405 - 419 2000年03月 [査読有り][通常論文]
     
    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.
  • Y Kihn, GE Thompson, G Galaup, P Skeldon, Zhou, X, K Shimizu, H Habazaki
    CORROSION SCIENCE 42 3 533 - 544 2000年03月 [査読有り][通常論文]
     
    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.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    SURFACE AND INTERFACE ANALYSIS 29 2 155 - 159 2000年02月 [査読有り][通常論文]
     
    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.
  • M Mehmood, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 42 2 361 - 382 2000年02月 [査読有り][通常論文]
     
    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 2000年02月 [査読有り][通常論文]
     
    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
    ELECTROCHIMICA ACTA 45 11 1805 - 1809 2000年 [査読有り][通常論文]
     
    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.
  • H Habazaki, K Ito, K Hon-yashiki, A Kawashima, K Hashimoto, S Mrowec
    HIGH TEMPERATURE CORROSION AND MATERIALS CHEMISTRY 99 38 258 - 269 2000年 [査読有り][通常論文]
     
    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.
  • M Yamasaki, H Habazaki, A Kawashima, K Asami, E Akiyama, K Hashimoto
    HIGH TEMPERATURE CORROSION AND MATERIALS CHEMISTRY 99 38 180 - 191 2000年 [査読有り][通常論文]
     
    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.
  • K Fujimura, T Matsui, H Habazaki, A Kawashima, N Kumagai, K Hashimoto
    ELECTROCHIMICA ACTA 45 14 2297 - 2303 2000年 [査読有り][通常論文]
     
    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 Hon-Yashiki, K Hashimoto, S Mrowec
    DIFFUSION AND REACTIONS 72 17 - 21 2000年 [査読有り][通常論文]
     
    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.
  • Z Ashitaka, GE Thompson, P Skeldon, GC Wood, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 147 1 132 - 139 2000年01月 [査読有り][通常論文]
     
    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.
  • 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 2000年 [査読有り][通常論文]
     
    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
    SURFACE AND INTERFACE ANALYSIS 27 12 1046 - 1049 1999年12月 [査読有り][通常論文]
     
    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.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    SURFACE AND INTERFACE ANALYSIS 27 11 998 - 1002 1999年11月 [査読有り][通常論文]
     
    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.
  • F Echeverria, P Skeldon, GE Thompson, H Habazaki, K Shimizu
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 146 10 3711 - 3715 1999年10月 [査読有り][通常論文]
     
    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.
  • AC Crossland, H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X, CJE Smith
    CORROSION SCIENCE 41 10 1945 - 1954 1999年10月 [査読有り][通常論文]
     
    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.
  • AC Crossland, GE Thompson, CJE Smith, H Habazaki, K Shimizu, P Skeldon
    CORROSION SCIENCE 41 10 2053 - 2069 1999年10月 [査読有り][通常論文]
     
    The behaviour of manganese during formation of barrier-type anodic films on nonequilibrium 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 10(19) 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 RES 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, (C) 1999 Elsevier Science T-td. All rights reserved.
  • K Shimizu, H Habazaki, P Skeldon, GE Thompson, GC Wood
    SURFACE AND INTERFACE ANALYSIS 27 10 950 - + 1999年10月 [査読有り][通常論文]
     
    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.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 41 10 1971 - 1976 1999年10月 [査読有り][通常論文]
     
    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.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 41 9 1783 - 1790 1999年09月 [査読有り][通常論文]
     
    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.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 41 9 1849 - 1869 1999年09月 [査読有り][通常論文]
     
    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.
  • M Mehmood, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 41 9 1871 - 1890 1999年09月 [査読有り][通常論文]
     
    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.
  • Zhou, X, GE Thompson, P Skeldon, GC Wood, K Shimizu, H Habazaki
    CORROSION SCIENCE 41 8 1599 - 1613 1999年08月 [査読有り][通常論文]
     
    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.
  • 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 1999年07月 [査読有り][通常論文]
     
    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 1999年07月 [査読有り][通常論文]
     
    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 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 1999年07月 [査読有り][通常論文]
     
    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 1999年07月 [査読有り][通常論文]
     
    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.
  • 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 1999年07月 [査読有り][通常論文]
     
    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.
  • H Habazaki, K Takahiro, S Yamaguchi, K Shimizu, P Skeldon, GE Thompson, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 146 7 2502 - 2507 1999年07月 [査読有り][通常論文]
     
    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.
  • 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 1999年07月 [査読有り][通常論文]
     
    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.
  • K Fujimura, K Izumiya, A Kawashima, E Akiyama, H Habazaki, N Kumagai, K Hashimoto
    JOURNAL OF APPLIED ELECTROCHEMISTRY 29 6 765 - 771 1999年06月 [査読有り][通常論文]
     
    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年06月 [査読有り][通常論文]
     
    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.
  • P Skeldon, Zhou, X, GE Thompson, GC Wood, H Habazaki, K Shimizu
    CORROSION 55 6 561 - 565 1999年06月 [査読有り][通常論文]
     
    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).
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 41 6 1095 - 1118 1999年06月 [査読有り][通常論文]
     
    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.
  • AC Crossland, GE Thompson, P Skeldon, CJE Smith, H Habazaki, K Shimuzu
    TRANSACTIONS OF THE INSTITUTE OF METAL FINISHING 77 95 - 98 1999年05月 [査読有り][通常論文]
     
    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.
  • 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年05月 [査読有り][通常論文]
     
    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年03月 [査読有り][通常論文]
     
    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.
  • M Mehmood, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 41 3 477 - 499 1999年03月 [査読有り][通常論文]
     
    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.
  • 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 1999年02月 [査読有り][通常論文]
     
    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 1999年02月 [査読有り][通常論文]
     
    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 1999年02月 [査読有り][通常論文]
     
    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.
  • Fujimura, K, Matsui, T, Izumiya, K, Kumagai, N, Akiyama, E, Habazaki, H, Kawashima, A, Asami, K, Hashimoto, K
    Mater. Sci. Eng. A 267 2 254 - 259 1999年 [査読有り][通常論文]
  • Morlidge, JR, P Skeldon, GE Thompson, H Habazaki, K Shimizu, GC Wood
    ELECTROCHIMICA ACTA 44 14 2423 - 2435 1999年 [査読有り][通常論文]
     
    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.
  • GE Thompson, P Skeldon, GC Wood, Zhou, X, U Kreissig, E Wieser, H Habazaki, K Shimizu
    SURFACE AND INTERFACE ANALYSIS 27 1 57 - 62 1999年01月 [査読有り][通常論文]
     
    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.
  • GE Thompson, H Habazaki, K Shimizu, M Sakairi, P Skeldon, Zhou, X, GC Wood
    AIRCRAFT ENGINEERING AND AEROSPACE TECHNOLOGY 71 3 228 - 238 1999年 [査読有り][通常論文]
     
    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.
  • 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年 [査読有り][通常論文]
     
    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.
  • K Shimizu, GM Brown, H Habazaki, G Kobayashi, P Skeldon, GE Thompson, GC Wood
    SURFACE AND INTERFACE ANALYSIS 27 1 24 - 28 1999年01月 [査読有り][通常論文]
     
    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 1999年 [査読有り][通常論文]
     
    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.
  • Felhosi, I, H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    CORROSION SCIENCE 40 12 2125 - 2139 1998年12月 [査読有り][通常論文]
     
    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 1998年11月 [査読有り][通常論文]
     
    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 1998年09月 [査読有り][通常論文]
     
    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.
  • 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 1998年09月 [査読有り][通常論文]
     
    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 1998年09月 [査読有り][通常論文]
     
    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.
  • AA El-Moneim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 9 1491 - 1512 1998年09月 [査読有り][通常論文]
     
    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 1998年09月 [査読有り][通常論文]
     
    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.
  • H Habazaki, M Yamasaki, BP Zhang, A Kawashima, S Kohno, T Takai, K Hashimoto
    APPLIED CATALYSIS A-GENERAL 172 1 131 - 140 1998年08月 [査読有り][通常論文]
     
    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.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 40 7 1229 - 1238 1998年07月 [査読有り][通常論文]
     
    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
  • 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 1998年07月 [査読有り][通常論文]
     
    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.
  • F Echeverria, P Skeldon, GE Thompson, Walton, JR, H Habazaki, K Shimizu
    ELECTROCHEMICAL AND SOLID STATE LETTERS 1 1 24 - 26 1998年07月 [査読有り][通常論文]
     
    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.
  • K Shimizu, GM Brown, H Habazaki, K Kobayashi, P Skeldon, GE Thompson, GC Wood
    CORROSION SCIENCE 40 6 963 - 973 1998年06月 [査読有り][通常論文]
     
    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.
  • AC Crossland, GE Thompson, P Skeldon, GC Wood, CJE Smith, H Habazaki, K Shimizu
    CORROSION SCIENCE 40 6 871 - 885 1998年06月 [査読有り][通常論文]
     
    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.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 4-5 821 - 838 1998年04月 [査読有り][通常論文]
     
    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 4-5 757 - 779 1998年04月 [査読有り][通常論文]
     
    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.
  • J Bhattarai, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 2-3 155 - 175 1998年02月 [査読有り][通常論文]
     
    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.
  • K Izumiya, E Akiyama, H Habazaki, N Kumagai, A Kawashima, K Hashimoto
    MATERIALS TRANSACTIONS JIM 39 2 308 - 313 1998年02月 [査読有り][通常論文]
     
    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.
  • AA El-Moneim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 2-3 235 - 250 1998年02月 [査読有り][通常論文]
     
    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.
  • P Sheldon, GE Thompson, GC Wood, Xhou, X, H Habazaki, K Shimizu
    DIELECTRIC MATERIAL INTEGRATION FOR MICROELECTRONICS 98 3 350 - 361 1998年 [査読有り][通常論文]
     
    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.
  • J Bhattarai, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 40 1 19 - 42 1998年01月 [査読有り][通常論文]
     
    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 1998年01月 [査読有り][通常論文]
     
    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.
  • 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年 [査読有り][通常論文]
     
    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 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年 [査読有り][通常論文]
     
    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.
  • 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 1998年 [査読有り][通常論文]
     
    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.
  • 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 1998年 [査読有り][通常論文]
     
    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.
  • 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 1998年 [査読有り][通常論文]
     
    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 Izumiya, E Akiyama, H Habazaki, N Kumagai, A Kawashima, K Hashimoto
    ELECTROCHIMICA ACTA 43 21-22 3303 - 3312 1998年 [査読有り][通常論文]
     
    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.
  • 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 1997年12月 [査読有り][通常論文]
     
    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 1997年12月 [査読有り][通常論文]
     
    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 1997年12月 [査読有り][通常論文]
     
    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.
  • 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 1997年10月 [査読有り][通常論文]
     
    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.
  • K Izumiya, E Akiyama, H Habazaki, N Kumagai, A Kawashima, K Hashimoto
    MATERIALS TRANSACTIONS JIM 38 10 899 - 905 1997年10月 [査読有り][通常論文]
     
    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.
  • AA El-Moneim, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 10-11 1965 - 1979 1997年10月 [査読有り][通常論文]
     
    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 1997年10月 [査読有り][通常論文]
     
    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.
  • BP Zhang, A Kawashima, H Habazaki, K Asami, K Hashimoto
    CORROSION SCIENCE 39 10-11 2005 - 2018 1997年10月 [査読有り][通常論文]
     
    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 1997年09月 [査読有り][通常論文]
     
    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.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 8 1365 - 1380 1997年08月 [査読有り][通常論文]
     
    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
    PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 453 1963 1593 - 1609 1997年08月 [査読有り][通常論文]
     
    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.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 30 13 1833 - 1841 1997年07月 [査読有り][通常論文]
     
    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 1997年07月 [査読有り][通常論文]
     
    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.
  • A Kawashima, E Akiyama, H Habazaki, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 226 905 - 909 1997年06月 [査読有り][通常論文]
     
    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.
  • E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 226 920 - 924 1997年06月 [査読有り][通常論文]
     
    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 1997年06月 [査読有り][通常論文]
     
    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, WP Yu, BP Zhang, H Habazaki, K Asami, K Hashimoto
    MATERIALS TRANSACTIONS JIM 38 5 443 - 450 1997年05月 [査読有り][通常論文]
     
    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.
  • H Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    THIN SOLID FILMS 300 1-2 131 - 137 1997年05月 [査読有り][通常論文]
     
    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.
  • XY Li, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 5 935 - 948 1997年05月 [査読有り][通常論文]
     
    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, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    CORROSION SCIENCE 39 4 731 - 737 1997年04月 [査読有り][通常論文]
     
    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.
  • H Habazaki, P Skeldon, GE Thompson, Zhou, X, J DeLaet, GC Wood
    CORROSION SCIENCE 39 4 719 - 730 1997年04月 [査読有り][通常論文]
     
    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.
  • M Komori, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    APPLIED CATALYSIS B-ENVIRONMENTAL 11 3-4 243 - 255 1997年03月 [査読有り][通常論文]
     
    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.
  • AC Crossland, GE Thompson, J Wan, H Habazaki, K Shimizu, P Skeldon, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 144 3 847 - 855 1997年03月 [査読有り][通常論文]
     
    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.
  • HW Wang, R DuranRomero, H Habazaki, P Skeldon, GE Thompson, GC Wood, K Shimizu
    SURFACE & COATINGS TECHNOLOGY 89 3 262 - 269 1997年03月 [査読有り][通常論文]
     
    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.
  • 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 1997年03月 [査読有り][通常論文]
     
    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.
  • 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 1997年03月 [査読有り][通常論文]
     
    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.
  • MW Tan, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 3 589 - 603 1997年03月 [査読有り][通常論文]
     
    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.
  • J Bhattarai, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 39 2 355 - 375 1997年02月 [査読有り][通常論文]
     
    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 1997年02月 [査読有り][通常論文]
     
    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 1997年02月 [査読有り][通常論文]
     
    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, K Shimizu, P Skeldon, GE Thompson, GC Wood, Zhou, X
    TRANSACTIONS OF THE INSTITUTE OF METAL FINISHING 75 18 - 23 1997年01月 [査読有り][通常論文]
     
    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 59 - 76 1997年01月 [査読有り][通常論文]
     
    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
  • H Habazaki, Zhou, X, K Shimizu, P Skeldon, GE Thompson, GC Wood
    ELECTROCHIMICA ACTA 42 17 2627 - 2635 1997年 [査読有り][通常論文]
     
    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 1997年01月 [査読有り][通常論文]
     
    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.
  • Zhou, X, GE Thompson, H Habazaki, K Shimizu, P Skeldon, GC Wood
    THIN SOLID FILMS 293 1-2 327 - 332 1997年01月 [査読有り][通常論文]
     
    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.
  • H Mitsui, H Habazaki, K Hashimoto, S Mrowec
    CORROSION SCIENCE 39 1 9 - 26 1997年01月 [査読有り][通常論文]
     
    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
  • MW Tan, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 12 2137 - 2151 1996年12月 [査読有り][通常論文]
     
    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 1996年11月 [査読有り][通常論文]
     
    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
  • PY Park, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 10 1649 - 1667 1996年10月 [査読有り][通常論文]
     
    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
  • CA NunezLopez, H Habazaki, P Skeldon, GE Thompson, H Karimzadeh, P Lyons, TE Wilks
    CORROSION SCIENCE 38 10 1721 - 1729 1996年10月 [査読有り][通常論文]
     
    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
  • H Habazaki, P Skeldon, D Ghidaoui, SB Lyon, K Shimizu, GE Thompson, GC Wood
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 29 10 2545 - 2553 1996年10月 [査読有り][通常論文]
     
    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.
  • PY Park, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 10 1731 - 1750 1996年10月 [査読有り][通常論文]
     
    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
  • H Mitsui, H Habazaki, K Asami, K Hashimoto, S Mrowec
    CORROSION SCIENCE 38 9 1431 - 1447 1996年09月 [査読有り][通常論文]
     
    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 1996年09月 [査読有り][通常論文]
     
    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
  • M Komori, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    APPLIED CATALYSIS B-ENVIRONMENTAL 9 1-4 93 - 106 1996年09月 [査読有り][通常論文]
     
    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 Habazaki, K Shimizu, P Skeldon, GE Thompson, GC Wood
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 143 8 2465 - 2470 1996年08月 [査読有り][通常論文]
     
    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 1996年08月 [査読有り][通常論文]
     
    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 1996年07月 [査読有り][通常論文]
     
    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.
  • HJ Lee, E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    CORROSION SCIENCE 38 3 469 - 485 1996年03月 [査読有り][通常論文]
     
    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 1996年03月 [査読有り][通常論文]
     
    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, 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 1996年03月 [査読有り][通常論文]
     
    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 1996年03月 [査読有り][通常論文]
     
    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 1996年03月 [査読有り][通常論文]
     
    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.
  • 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 1996年02月 [査読有り][通常論文]
     
    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.
  • H. Habazaki, K. Shimizu, P. Skeldon, G. E. Thompson, G. C. Woodj
    Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties 73 3 445 - 460 1996年 [査読有り][通常論文]
     
    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 ∼ 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 A12O3, 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 ∼ 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 23V, the outer ∼30% of the film thickness is composed of relatively pure alumina, while the inner ∼ 70% of the film is composed of a mixture of units of A12O3 and WO3. © 1996 Taylor & Francis Group, LLC.
  • H. Habazaki, P. Skeldon, G. E. Thompson, G. C. Wood, K. Shimizu
    Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties 73 2 297 - 308 1996年 [査読有り][通常論文]
     
    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 film 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 film growth. However, near to the alloy film/anodic film 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 film 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. © 1996 Taylor & Francis Group, LLC.
  • MA Paez, TM Foong, CT Ni, GE Thompson, K Shimizu, H Habazaki, P Skeldon, GC Wood
    CORROSION SCIENCE 38 1 59 - 72 1996年01月 [査読有り][通常論文]
     
    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, K Shimizu, MA Paez, P Skeldon, GE Thompson, GC Wood, Xhou, X
    SURFACE AND INTERFACE ANALYSIS 23 13 892 - 898 1995年12月 [査読有り][通常論文]
     
    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.
  • H Habazaki, P Skeldon, K Shimizu, GE Thompson, GC Wood
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 28 12 2612 - 2618 1995年12月 [査読有り][通常論文]
     
    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.
  • T MORI, A KAWASHIMA, E AKIYAMA, H HABAZAKI, K ASAMI, K HASHIMOTO
    JOURNAL OF APPLIED ELECTROCHEMISTRY 25 10 953 - 961 1995年10月 [査読有り][通常論文]
     
    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.
  • 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 1995年09月 [査読有り][通常論文]
     
    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.
  • H HABAZAKI, P SKELDON, K SHIMIZU, GE THOMPSON, GC WOOD
    CORROSION SCIENCE 37 9 1497 - 1509 1995年09月 [査読有り][通常論文]
     
    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.
  • HJ LEE, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 37 8 1313 - 1324 1995年08月 [査読有り][通常論文]
     
    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 1995年07月 [査読有り][通常論文]
     
    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 1995年05月 [査読有り][通常論文]
     
    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.
  • PY PARK, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 37 2 307 - 320 1995年02月 [査読有り][通常論文]
     
    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.
  • HJ LEE, E AKIYAMA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 37 2 321 - 330 1995年02月 [査読有り][通常論文]
     
    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.
  • H. Habazaki, P. Skeldon, G. E. Thompson, G. C. Wood, K. Shimizu
    Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties 71 1 81 - 90 1995年 [査読有り][通常論文]
     
    The formation of barrier-type anodic films on sputter-deposited amorphous A1-30W (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 Am-2to 150 V in aqueous 0-01 M ammonium pentabor-ate 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 A12O3and 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. © 1995 Taylor & Francis Group, LLC.
  • E Akiyama, H Habazaki, A Kawashima, K Asami, K Hashimoto
    PASSIVATION OF METALS AND SEMICONDUCTORS 185- 809 - 818 1995年 [査読有り][通常論文]
  • K Hashimoto, PY Park, JH Kim, E Akiyama, H Habazaki, A Kawashima, K Asami
    PASSIVATION OF METALS AND SEMICONDUCTORS 185- 779 - 788 1995年 [査読有り][通常論文]
  • 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 1995年01月 [査読有り][通常論文]
     
    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.
  • Z GRZESIK, H HABAZAKI, K HASHIMOTO, S MROWEC
    CORROSION SCIENCE 36 9 1499 - 1511 1994年09月 [査読有り][通常論文]
     
    The beneficial effect of alloying with aluminum to enhance the sulphidation resistance of molybdenum using sputter-deposited amorphous Mo-Al alloys has been studied as a function of temperature (1073-1273 K), aluminum content (1.7, 6.2 and 10.7 at% Al) and sulphur vapor pressure (20-4000 Pa) in He-S2 gas mixtures. It has been shown that the sulphidation process follows parabolic kinetics, being diffusion controlled. The reaction rate of Mo-Al alloys with low aluminum contents is lower than that of pure molybdenum and decreases with increasing aluminum content in the alloy. Because sulphide scales formed on Mo-Al alloys containing small amounts of aluminum are homogeneous and composed only of MoS2, the lower sulphidation rate of those alloys is explained in terms of the aluminum doping effect in the MoS2 scale. It is believed that the better protective properties of the sulphide scale on Mo-Al alloys in comparison with those of the MoS2 scale on pure molybdenum result from a lower defect concentration in aluminum-doped MoS2 phase. The experimentally obtained dependence of the sulphidation rate of Mo-1.7 Al alloy on the sulphur pressure at 1173 K is in accordance with that predicted from theoretical considerations.
  • H HABAZAKI, K TAKAHIRO, S YAMAGUCHI, K HASHIMOTO, J DABEK, S MROWEC, M DANIELEWSKI
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 181 1099 - 1103 1994年05月 [査読有り][通常論文]
     
    High temperature corrosion of sputter-deposited amorphous Al-(34-46)Mo and Al-31Mo-(6-16)Si alloys has been studied as a function of temperature (973-1273 K) in sulfur vapor (10(3) 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 Al-Mo 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 Al-Mo-Si 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.
  • Kawashima, Asahi, Wang, Ying, Akiyama, Eiji, Habazaki, Hiroki, Asami, Katsuhiko, Hashimoto, Koji
    Zairyo Kankyo 43 11 654 - 659 1994年 [査読有り][通常論文]
  • Im, B.-M, Akiyama, E, Habazaki, H, Kawashima, A, Asami, K, Hashimoto, K
    Corros. Sci. 36 9 1537 - 1541,1543-1550 1994年 [査読有り][通常論文]
  • H HABAZAKI, H MITSUI, K ASAMI, S MROWEC, K HASHIMOTO
    ADVANCED MATERIALS '93, I - A & B 14 A & B 309 - 312 1994年 [査読有り][通常論文]
  • H MITSUI, H HABAZAKI, K ASAMI, K HASHIMOTO, S MROWEC
    ADVANCED MATERIALS '93, I - A & B 14 A & B 243 - 246 1994年 [査読有り][通常論文]
  • BP ZHANG, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 34 4 599 - & 1993年04月 [査読有り][通常論文]
     
    The corrosion resistance of the Cr-P alloys containing 0-5 at% phosphorus prepared by arc-melting was investigated by corrosion tests, electrochemical measurements and SEM/EDX analyses. Chromium and low phosphorus alloys suffer serious intergranular corrosion in 47% HF solution at 30-degrees-C. The alloys containing 0.8 at% or more phosphorus are corrosion-resistant, showing about four orders of magnitude lower corrosion rates than that of low phosphorus alloys. Phosphorus added to chromium segregated at grain boundaries in the form of Cr3P regardless of the amount of the addition. The Cr3P phase has high activities for both hydrogen evolution and oxygen reduction, and accordingly the addition of a small amount of phosphorus accelerates active dissolution of phosphorus-free phase under open circuit conditions, while the addition of sufficient amounts of phosphorus gives rise to spontaneous passivation due to enhancement of oxygen reduction.
  • 王頴, 秋山英二, 幅崎浩樹, 川嶋朝日, 浅見勝彦, 橋本功二
    材料と環境 42 3 158 - 165 1993年03月 [査読有り][通常論文]
  • H HABAZAKI, J DABEK, K HASHIMOTO, S MROWEC, M DANIELEWSKI
    CORROSION SCIENCE 34 2 183 - & 1993年02月 [査読有り][通常論文]
     
    The sulphidation behaviour of sputter-deposited amorphous Al-Mo alloys has been studied as a function of temperature (973-1273 K) and alloy composition (34-46 at%Mo) in pure sulphur vapour at 10(3) Pa pressure. It has been shown that under these conditions the sulphidation process follows parabolic kinetics, being diffusion controlled. No influence of the alloy composition on the reaction rate has been observed. The scales were heterogeneous and composed of two layers. The outer scale layer was built of aluminium sulphide, while the inner layer was heterogeneous and composed of a mixture of Al0.5-Mo2S4, Al2S3 and MoS2 phases, the latter being the major component. It is believed that the slowest step, determining the overall reaction rate, is the inward diffusion of sulphur through the inner barrier layer of the scale. Over the whole temperature range studied the alloys showed excellent resistance to sulphide corrosion, their sulphidation rates being comparable with, or even lower than the oxidation rates of chromia forming materials. The better protective properties of the sulphide scale on Al-Mo alloys in comparison with those of the MoS2 scale on pure molybdenum result probably from lower defect concentration in aluminium-doped MoS2 phase, constituting the major part of the inner barrier layer. Preliminary results indicate that the alloys under investigation show satisfactory oxidation resistance in the temperature range not exceeding about 1123 K. Under these conditions a protective oxide scale is formed composed virtually only of Al2O3 and the oxidation rates are lower than those of chromia formers. At higher temperatures aluminium activity in the alloy is too low to suppress the formation and evaporation of molybdenum oxides.
  • 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 1993年 [査読有り][通常論文]
     
    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, K HASHIMOTO
    CORROSION SCIENCE 35 1-4 43 - 49 1993年 [査読有り][通常論文]
     
    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.
  • Y HAYAKAWA, A KAWASHIMA, H HABAZAKI, K ASAMI, K HASHIMOTO
    JOURNAL OF APPLIED ELECTROCHEMISTRY 22 11 1017 - 1024 1992年11月 [査読有り][通常論文]
     
    Powder catalysts were prepared by immersion of amorphous Ni-40Zr and Ni-40Ti alloys containing a few at % of platinum group elements in HF solution. This treatment led to preferential dissolution of the valve metal and nickel with a consequent formation of microcrystalline alloy powders consisting of concentrated platinum group elements and some nickel and valve metal. Porous gas-diffusion electrodes prepared by using these alloy catalyst powders were employed for electrochemical reduction of oxygen and oxidation of hydrogen in 1 M H2SO4 at 25-degrees-C. The activity of the electrodes prepared from the amorphous alloys containing Pt-Ru, Pt-Rh, Pt and Pd for oxygen reduction was considerably higher than that of the platinum black electrode. Oxidation of hydrogen occurred readily close to the equilibrium potential. Amorphous alloy electrodes containing Pt-Ru, Pt-Rh and Pt were more active than the platinum black electrode for the hydrogen oxidation.
  • JH KIM, H YOSHIOKA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 33 10 1507 - 1518 1992年10月 [査読有り][通常論文]
     
    Cu-Ta alloys containing 44-91 at% tantalum are amorphous and are spontaneously passive showing almost the same low corrosion rate as that of tantalum metal. Formation of a single fcc Cu phase alloy supersaturated with tantalum of up to 21 at% of tantalum is not effective in enhancing the corrosion resistance in aggressive 12 M HCI. The passive films on the amorphous alloys and tantalum metal consist only of Ta2O5. The passive films on Cu-28Ta and Cu-36Ta alloys consisting of a mixture of microcrystalline fcc Cu phases in the amorphous matrix are composed of TaO2OH and are thicker and less protective in comparison with the Ta2O5 film. Polarization at potentials higher than potentials for oxygen and chlorine evolution prevents the formation of the tantalum-enriched passive film on the amorphous Cu-Ta alloys and results in sharp increase in the anodic current.
  • BP ZHANG, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 33 10 1519 - 1528 1992年10月 [査読有り][通常論文]
     
    In order to develop alloys resistant to aggressive hydrofluoric acids, the corrosion behavior of the amorphous Ni-Cr-19P alloys in 47% HF solution was examined by corrosion tests, electrochemical measurements and XPS analyses. The corrosion rate for the Ni-19P alloy is 0.7 mm y-1 at 30-degrees-C, which is about 20% of that for Ni. This high corrosion resistance is based on the formation of an elemental phosphorus layer on the alloy surface which acts as a diffusion barrier against alloy dissolution, as has been found in HCI solutions. The addition of Cr enhances the corrosion resistance due to spontaneous passivation. The corrosion rate of amorphous Ni-Cr-19P alloys containing greater-than-or-equal-to 15 at% Cr is 2-7 x 10(-3) mm y-1. The passive film on the chromium-containing alloys consists mainly of hydrated chromium and nickel oxyhydroxide.
  • JH KIM, H YOSHIOKA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 156 2 211 - 216 1992年08月 [査読有り][通常論文]
     
    Binary Cu-Ta alloys were prepared by magnetron sputtering using tantalum-covered copper targets. The alloys containing 44-91 at.% Ta are amorphous. When a single-phase solid solution is formed, the position of the most intense reflection in X-ray diffraction changes continuously with alloy composition, regardless of the crystallinity. A deviation from a continuous change in the position of the most intense reflection indicates the formation of two phases. The alloys containing up to 21 at.% Ta consist of an f.c.c. phase supersaturated with tantalum. The alloys Cu-28Ta and Cu-36Ta are composed of an f.c.c. copper phase supersaturated with tantalum and an amorphous phase with a fairly high concentration of tantalum. The latter amorphous phase was identified after preferential dissolution of the crystalline phase in 12 M HCl.
  • BP ZHANG, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 33 5 667 - 679 1992年05月 [査読有り][通常論文]
     
    The corrosion behavior of the amorphous Ni-Cr-19P alloys in 1, 6 and 12 M HCl solutions at 30-degrees-C was investigated. The amorphous Ni-19P alloy shows an almost constant corrosion rate of about 0.05 mm y-1 regardless of the concentration of hydrochloric acid. This is attributed to the formation of an elemental phosphorus layer acting as a diffusion barrier against active dissolution of the alloy. The corrosion rate of the amorphous Ni-Cr-19P alloys decreases with increase in alloy chromium content, but increases in 12 M HCl when 15 at% or more chromium is added. The formation of the elemental phosphorus layer on Ni-P and low chromium alloys is effective in decreasing the corrosion rate and in ennobling the corrosion potential with a consequent passivation. By contrast, when the content of active chromium is very high such as 15 at% or more, active dissolution of chromium in 12 M HCl solution prevents the formation of an elemental phosphorus layer, and hence no passivation by the formation of chromium enriched passive film occurs. Pitting corrosion occurred only in 12 M HCl but the pitting corrosion resistance can be improved effectively by the addition of chromium.
  • H YOSHIOKA, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 33 3 425 - 436 1992年03月 [査読有り][通常論文]
     
    Using electrochemical measurements and XPS analysis, the corrosion behavior of sputter-deposited Al-Zr alloys in 1 M HCl solution at 30-degrees-C was investigated. Their open circuit corrosion resistance, pitting corrosion resistance and passivating ability were enhanced with increasing zirconium. Alloying of aluminum with zirconium extends the time to reach the steady passive state by potentiostatic polarization and decreases the steady state current density. XPS analysis revealed that when potentiostatic polarization was continued in the passive region, Zr4+ cations in the surface film was slightly concentrated simultaneously with the concentration of zirconium in the underlying alloy surface, due to preferential dissolution of aluminum. The cationic fraction of the surface film finally consisted of Al3+ and Zr4+ according to the bulk alloy composition, although the Zr4+ content was apt to be higher than the alloy zirconium content. Therefore, the higher the alloy zirconium content, the higher the corrosion resistance of the sputter-deposited Al-Zr alloys.
  • H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 33 2 225 - 236 1992年02月 [査読有り][通常論文]
     
    Polarization measurement shows that the additions of molybdenum and tungsten to amorphous Fe-8Cr-13P-7C and Fe-15Cr-13P-7C alloys significantly decrease the active dissolution current and passivation potential in 6 M HCl solution. XPS and electrochemical investigations reveal that molybdenum and tungsten prevent dissolution of chromium from the air-formed films during potentiostatic passivation, although small amounts of iron dissolve from the air-formed films and alloys. The tungsten addition is more effective than the molybdenum addition. This difference seems to result from the fact that molybdenum dissolves actively at low potentials in the active region of the alloys, while tungsten does not dissolve at potentials lower than 100 mV(SCE). When an excess amount of molybdenum or tungsten is added. the passivity becomes unstable and the passive film is less enriched in chromic ions, because of transpassive dissolution of molybdenum and tungsten.
  • BP ZHANG, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 33 1 103 - 112 1992年 [査読有り][通常論文]
     
    The relationship between the corrosion behavior and structure of a rapidly quenched Cr-27at% Ni-15at% P alloy composed of some microcrystallites in the amorphous matrix has been studied in 6 M HCl solution at 30-degrees-C. The cathodically pre-polarized Cr-27Ni-15P alloy shows a high current density in the active region. Both the passive films formed on the specimens with and without cathodic prepolarization consist exclusively of hydrated chromium oxyhydroxide. Even if the air-formed film is the same as the hydrated chromium oxyhydroxide film, the presence of microheterogeneity of the alloy leads to depassivation in the aggressive solution. The corrosion resistance is not only related to the nature of the passive film but is also strongly dependent on the structure of the alloy.
  • H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 134 1033 - 1036 1991年03月 [査読有り][通常論文]
     
    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 ASAMI, SC CHEN, H HABAZAKI, A KAWASHIMA, K HASHIMOTO
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 134 1025 - 1028 1991年03月 [査読有り][通常論文]
     
    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.
  • 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 1991年03月 [査読有り][通常論文]
     
    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 1991年03月 [査読有り][通常論文]
     
    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.
  • H YOSHIOKA, O YAN, H HABAZAKI, A KAWASHIMA, K ASAMI, K HASHIMOTO
    CORROSION SCIENCE 31 349 - 354 1990年 [査読有り][通常論文]
  • Hiroshi Ogino, Hiromi Tobita, Hiroki Habazaki, Mamoru Shimoi
    Journal of the Chemical Society, Chemical Communications 13 828 - 829 1989年 [査読有り][通常論文]
     
    The permethylferrocenophane [(pdmcp)Fe] [pdmcp = η< sup> 5< /sup> , η< sup> 5< /sup> -C< inf> 5< /inf> Me< inf> 4< /inf> (CH< inf> 2< /inf> )< inf> 3< /inf> C < inf> 5< /inf> Me< inf> 4< /inf> ] and its oxidised species, monocation and dication salts, were synthesised, in which the latter, [(pdmcp)Fe(NCMe)](PF < inf> 6< /inf> )< inf> 2< /inf> , has a substantially bent bis(cyclopentadienyl) moiety to accommodate one molecule of MeCN.

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年 [査読無し][通常論文]
  • 青木芳尚, 青木芳尚, 幅崎浩樹 セラミックス 52 (2) 82‐86 2017年02月01日 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • Marcin Pisarek, Hiroki Habazaki, Aleksander Krupski, Pawel Kulesza, Maria Janik-Czachor APPLIED SURFACE SCIENCE 388 605 -607 2016年12月 [査読有り][通常論文]
  • 幅崎 浩樹 表面技術 67 (10) 508 -514 2016年 [査読無し][通常論文]
  • 野田裕之, 辻悦司, 本橋輝樹, 青木芳尚, 小山幸典, 森正弘, 内本喜晴, 荒井創, 幅崎浩樹 電池討論会講演要旨集 56th 472 2015年11月10日 [査読無し][通常論文]
  • 辻悦司, 野田裕之, 本橋輝樹, 青木芳尚, 谷田肇, 小山幸典, 森正弘, 内本喜晴, 荒井創, 幅崎浩樹 電池討論会講演要旨集 56th 473 2015年11月10日 [査読無し][通常論文]
  • 小林昌平, 青木芳尚, 青木芳尚, 辻悦司, 幅崎浩樹 電池討論会講演要旨集 56th 159 2015年11月10日 [査読無し][通常論文]
  • 片岡文崇, 辻悦司, 青木芳尚, 幅崎浩樹, 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 2014 72 -73 2015年06月 [査読無し][通常論文]
  • 小林昌平, 青木芳尚, 辻悦司, 幅崎浩樹 電気化学会大会講演要旨集(CD-ROM) 82nd ROMBUNNO.1C24 2015年03月09日 [査読無し][通常論文]
  • 野田裕之, 辻悦司, 本橋輝樹, 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集(CD-ROM) 82nd ROMBUNNO.3K20 2015年03月09日 [査読無し][通常論文]
  • 倉千晴, 青木芳尚, 辻悦司, 幅崎浩樹 電気化学会大会講演要旨集(CD-ROM) 82nd ROMBUNNO.3H28 2015年03月09日 [査読無し][通常論文]
  • 岡崎有杜, 辻悦司, 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集(CD-ROM) 82nd ROMBUNNO.PS84 2015年03月09日 [査読無し][通常論文]
  • 小林泰星, 青木芳尚, 國貞雄治, 辻悦司, 幅崎浩樹 電気化学会大会講演要旨集(CD-ROM) 82nd ROMBUNNO.PS73 2015年03月09日 [査読無し][通常論文]
  • 黒田孝亮, 青木芳尚, 辻悦司, 幅崎浩樹 電気化学会大会講演要旨集(CD-ROM) 82nd ROMBUNNO.PFC22 2015年03月09日 [査読無し][通常論文]
  • 中山勝利, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 131st 267 2015年02月20日 [査読無し][通常論文]
  • 片岡文崇, SHAHZAD Khurram, 辻悦司, 青木芳尚, 永田晋二, 幅崎浩樹 表面技術協会講演大会講演要旨集 131st 265 2015年02月20日 [査読無し][通常論文]
  • 平賀拓也, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 131st 51 2015年02月20日 [査読無し][通常論文]
  • 辻悦司, 野田裕之, 本橋輝樹, 青木芳尚, 幅崎浩樹 電池討論会講演要旨集 55th 466 2014年11月19日 [査読無し][通常論文]
  • 青木芳尚, 小林昌平, 辻悦司, 幅崎浩樹, 八代圭司, 川田達也 固体イオニクス討論会講演要旨集 40th 187 -188 2014年11月16日 [査読無し][通常論文]
  • 中山勝利, 辻悦司, 青木芳尚, 幅崎浩樹 日本学術会議材料工学連合講演会講演論文集 58th 460 -461 2014年10月27日 [査読無し][通常論文]
  • 小林康平, 辻悦司, 青木芳尚, 永田晋二, 幅崎浩樹 電気化学秋季大会講演要旨集 2014 90 2014年09月27日 [査読無し][通常論文]
  • 松浦志紀, 辻悦司, 青木芳尚, 幅崎浩樹 電気化学秋季大会講演要旨集 2014 13 2014年09月27日 [査読無し][通常論文]
  • 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年09月27日 [査読無し][通常論文]
  • 辻悦司, 衡田直人, 青木芳尚, 永田晋二, 幅崎浩樹 表面技術協会講演大会講演要旨集 130th 212 2014年09月10日 [査読無し][通常論文]
  • 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年09月01日 [査読無し][通常論文]
  • 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年06月 [査読無し][通常論文]
  • 紺野祥岐, 辻悦司, 青木芳尚, 大塚俊明, 幅崎浩樹 電気化学会大会講演要旨集 81st 136 2014年03月29日 [査読無し][通常論文]
  • 野田裕之, 辻悦司, 本橋輝樹, 青木芳尚, 竹口竜弥, 幅崎浩樹 電気化学会大会講演要旨集 81st 449 2014年03月29日 [査読無し][通常論文]
  • 小林康平, 辻悦司, 青木芳尚, 永田晋二, 幅崎浩樹 電気化学会大会講演要旨集 81st 93 2014年03月29日 [査読無し][通常論文]
  • 菊谷和正, 青木芳尚, 辻悦司, 幅崎浩樹 電気化学会大会講演要旨集 81st 43 2014年03月29日 [査読無し][通常論文]
  • 小林昌平, 青木芳尚, 辻悦司, 幅崎浩樹 日本化学会講演予稿集 94th (2) 636 2014年03月12日 [査読無し][通常論文]
  • 倉千晴, 青木芳尚, 辻悦司, 永田晋二, 幅崎浩樹 日本化学会講演予稿集 94th (3) 1000 2014年03月12日 [査読無し][通常論文]
  • 木村大樹, 辻悦司, 青木芳尚, 矢野孝宜, HASSEL A. W, 幅崎浩樹 表面技術協会講演大会講演要旨集 129th 145 2014年03月03日 [査読無し][通常論文]
  • 中山雄貴, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 129th 236 2014年03月03日 [査読無し][通常論文]
  • 中山勝利, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 129th 239 2014年03月03日 [査読無し][通常論文]
  • 山崎壮矩, 辻悦司, 青木芳尚, PARK Soo‐Gil, 幅崎浩樹 表面技術協会講演大会講演要旨集 129th 211 2014年03月03日 [査読無し][通常論文]
  • 片岡文崇, 辻悦司, 青木芳尚, 永田晋二, 幅崎浩樹 表面技術協会講演大会講演要旨集 129th 250 2014年03月03日 [査読無し][通常論文]
  • 小林康平, 辻悦司, 青木芳尚, 永田晋二, 幅崎浩樹 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年01月28日 [査読無し][通常論文]
  • 衡田直人, 辻悦司, 青木芳尚, 幅崎浩樹 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年01月28日 [査読無し][通常論文]
  • 佐藤妃奈, 辻悦司, 青木芳尚, 幅崎浩樹 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年01月28日 [査読無し][通常論文]
  • 小林昌平, 青木芳尚, 辻悦司, 幅崎浩樹 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年01月28日 [査読無し][通常論文]
  • 大庭博司, 青木芳尚, 辻悦司, 幅崎浩樹 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年01月28日 [査読無し][通常論文]
  • 呉冠文, 辻悦司, 青木芳尚, 幅崎浩樹 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年01月28日 [査読無し][通常論文]
  • 松浦志紀, 辻悦司, 青木芳尚, 幅崎浩樹 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年01月28日 [査読無し][通常論文]
  • 野田裕之, 辻悦司, 本橋輝樹, 青木芳尚, 幅崎浩樹 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年01月28日 [査読無し][通常論文]
  • 幅崎 浩樹, 藤井 隆志, 中山 勝利, 辻 悦司, 青木 芳尚 表面技術 65 (9) 426 -431 2014年 [査読無し][通常論文]
  • 幅崎浩樹, 中山勝利, 辻悦司, 青木芳尚 日本学術会議材料工学連合講演会講演論文集 57th 215 2013年11月25日 [査読無し][通常論文]
  • 呉冠文, 辻悦司, 青木芳尚, 幅崎浩樹 電気化学秋季大会講演要旨集 2013 64 2013年09月27日 [査読無し][通常論文]
  • 辻悦司, 掛田興, 桐生雅彦, 青木芳尚, 幅崎浩樹 電気化学秋季大会講演要旨集 2013 243 2013年09月27日 [査読無し][通常論文]
  • 木村大樹, 辻悦司, 青木芳尚, 幅崎浩樹, 矢野孝宜 表面技術協会講演大会講演要旨集 128th 158 2013年09月10日 [査読無し][通常論文]
  • 中山勝利, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 128th 162 -163 2013年09月10日 [査読無し][通常論文]
  • 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年09月03日 [査読無し][通常論文]
  • 幅崎 浩樹 電気化学および工業物理化学 : denki kagaku 81 (7) 2013年07月05日 [査読無し][通常論文]
  • 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年06月 [査読無し][通常論文]
  • 水素を経て使える燃料の形での再生可能エネルギーの利用
    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年05月 [査読無し][通常論文]
  • 紺野祥岐, 辻悦司, 青木芳尚, 幅崎浩樹 材料と環境講演集 2013 275 -276 2013年04月30日 [査読無し][通常論文]
  • 幅崎 浩樹 表面 51 (4) 170 -181 2013年04月 [査読無し][通常論文]
  • 辻悦司, 田口宜瑛, 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集 80th 359 2013年03月29日 [査読無し][通常論文]
  • 幅崎浩樹, 石塚雅敏, 辻悦司, 青木芳尚, 坂口紀史, 永田晋二 電気化学会大会講演要旨集 80th 147 2013年03月29日 [査読無し][通常論文]
  • 呉冠文, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 127th 192 2013年03月06日 [査読無し][通常論文]
  • 衡田直人, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 127th 200 -201 2013年03月06日 [査読無し][通常論文]
  • 佐藤妃奈, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 127th 189 -190 2013年03月06日 [査読無し][通常論文]
  • 幅崎 浩樹 旭硝子財団助成研究成果報告 1 -4 2013年 [査読無し][通常論文]
  • 野中亮, 青木芳尚, 辻悦司, 幅崎浩樹 電池討論会講演要旨集 53rd 438 2012年11月13日 [査読無し][通常論文]
  • 田口宜瑛, 衡田直人, 辻悦司, 青木芳尚, 幅崎浩樹 日本学術会議材料工学連合講演会講演論文集 56th 369 2012年10月29日 [査読無し][通常論文]
  • 石塚雅敏, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 126th 69 2012年09月12日 [査読無し][通常論文]
  • 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年09月10日 [査読無し][通常論文]
  • 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 2011 12 -13 2012年06月 [査読無し][通常論文]
  • 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年04月11日 [査読無し][通常論文]
  • 藤井隆志, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 125th 188 2012年03月01日 [査読無し][通常論文]
  • S. Ono, H. Habazaki CORROSION SCIENCE 53 (11) 3521 -3525 2011年11月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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.
  • 田口宜瑛, YANG Shu, 紺野祥岐, 辻悦司, 青木芳尚, 幅崎浩樹 材料と環境討論会講演集 58th 181 -182 2011年09月16日 [査読無し][通常論文]
  • 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年09月09日 [査読無し][通常論文]
  • 恒川聡, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 124th 106 2011年09月09日 [査読無し][通常論文]
  • 田口宜瑛, 辻悦司, 青木芳尚, 川喜多仁, 幅崎浩樹 表面技術協会講演大会講演要旨集 124th 105 2011年09月09日 [査読無し][通常論文]
  • 紺野祥岐, 辻悦司, 青木芳尚, 幅崎浩樹 電気化学秋季大会講演要旨集 2011 229 2011年09月09日 [査読無し][通常論文]
  • 藤井隆志, 辻悦司, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 124th 103 2011年09月09日 [査読無し][通常論文]
  • 三澤貴浩, 幅崎浩樹, 青木芳尚, 辻悦司, 小野昭二 電気化学秋季大会講演要旨集 2011 197 2011年09月09日 [査読無し][通常論文]
  • 小山瞬, 青木芳尚, 永田晋二, 幅崎浩樹 電気化学秋季大会講演要旨集 2011 198 2011年09月09日 [査読無し][通常論文]
  • Shu Yang, Hiroki Habazaki, Takashi Fujii, Yoshitaka Aoki, Peter Skeldon, George E. Thompson ELECTROCHIMICA ACTA 56 (22) 7446 -7453 2011年09月 [査読有り][通常論文]
     
    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年07月01日 [査読無し][通常論文]
  • 野中亮, 青木芳尚, 辻悦司, 幅崎浩樹 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年07月01日 [査読無し][通常論文]
  • Takashi Fujii, Yoshitaka Aoki, Hiroki Habazaki APPLIED SURFACE SCIENCE 257 (19) 8282 -8288 2011年07月 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
     
    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年06月 [査読無し][通常論文]
  • Yoshitaka Aoki, Hiroki Habazaki, Toyoki Kunitake SOLID STATE IONICS 192 (1) 93 -96 2011年06月 [査読有り][通常論文]
     
    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年06月 [査読有り][通常論文]
     
    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年05月20日 [査読無し][通常論文]
  • 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年05月 [査読有り][通常論文]
     
    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年05月 [査読有り][通常論文]
     
    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.
  • YANG S, AOKI Y, SKELDON P, THOMPSON G. E, HABAZAKI H Journal of Solid State Electrochemistry 15 (4) 689 -696 2011年04月 [査読有り][通常論文]
     
    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.
  • 田口宜瑛, 青木芳尚, 幅崎浩樹, 川喜多仁 電気化学会大会講演要旨集 78th(CD-ROM) ROMBUNNO.1H29 2011年03月29日 [査読無し][通常論文]
  • 小山瞬, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 123rd 125 -126 2011年03月07日 [査読無し][通常論文]
  • 恒川聡, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 123rd 95 2011年03月07日 [査読無し][通常論文]
  • 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年03月07日 [査読無し][通常論文]
  • Yoshitaka Aoki, Hiroki Habazaki, Shinji Nagata, Aiko Nakao, Toyoki Kunitake, Shu Yamaguchi JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 (10) 3471 -3479 2011年03月 [査読有り][通常論文]
     
    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.
  • 小宮山正造, 青木芳尚, 幅崎浩樹 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年02月01日 [査読無し][通常論文]
  • 田口宜瑛, 青木芳尚, 幅崎浩樹 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年02月01日 [査読無し][通常論文]
  • 福永悠希, 青木芳尚, 幅崎浩樹 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年02月01日 [査読無し][通常論文]
  • Y. Aoki, Y. Fukunaga, H. Habazaki, T. Kunitake JOURNAL OF THE ELECTROCHEMICAL SOCIETY 158 (8) B866 -B870 2011年 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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年01月 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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.
  • 福永悠希, 青木芳尚, 幅崎浩樹 電池討論会講演要旨集 51st 315 2010年11月08日 [査読無し][通常論文]
  • Hiroki Habazaki, Yoshiki Konno, Yoshitaka Aoki, Peter Skeldon, George E. Thompson JOURNAL OF PHYSICAL CHEMISTRY C 114 (44) 18853 -18859 2010年11月 [査読有り][通常論文]
     
    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.
  • 藤井隆志, 青木芳尚, 幅崎浩樹 日本学術会議材料工学連合講演会講演論文集 54th 364 2010年10月25日 [査読無し][通常論文]
  • 幅崎浩樹, TANVIR M.T, 青木芳尚 日本学術会議材料工学連合講演会講演論文集 54th 363 2010年10月25日 [査読無し][通常論文]
  • Takashi Fujii, Yoshitaka Aoki, Koji Fushimi, Takeshi Makino, Shoji Ono, Hiroki Habazaki NANOTECHNOLOGY 21 (39) 395302 2010年10月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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.
  • 青木芳尚, 原田明寿, 幅崎浩樹 電気化学秋季大会講演要旨集 2010 75 2010年09月02日 [査読無し][通常論文]
  • 青木芳尚, 三澤貴浩, 幅崎浩樹 電気化学秋季大会講演要旨集 2010 183 2010年09月02日 [査読無し][通常論文]
  • 恒川聡, 青木芳尚, 幅崎浩樹 電気化学秋季大会講演要旨集 2010 67 2010年09月02日 [査読無し][通常論文]
  • 寺岡匡伸, 青木芳尚, PARK Soo‐Gil, 幅崎浩樹 表面技術協会講演大会講演要旨集 122nd 110 -111 2010年08月20日 [査読無し][通常論文]
  • 紺野祥岐, 青木芳尚, 永田晋二, 幅崎浩樹 表面技術協会講演大会講演要旨集 122nd 112 2010年08月20日 [査読無し][通常論文]
  • 三澤貴浩, 青木芳尚, 幅崎浩樹 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年06月25日 [査読無し][通常論文]
  • 小山瞬, 青木芳尚, 幅崎浩樹, 永田晋二, 木村久道 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年06月 [査読無し][通常論文]
  • S. Ono, H. Habazaki CORROSION SCIENCE 52 (6) 2164 -2171 2010年06月 [査読有り][通常論文]
     
    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.
  • 紺野祥岐, 青木芳尚, 永田晋二, 木村久道, 幅崎浩樹 材料と環境講演集 2010 357 -358 2010年04月26日 [査読無し][通常論文]
  • 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年04月26日 [査読無し][通常論文]
  • 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年04月 [査読有り][通常論文]
     
    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年04月 [査読有り][通常論文]
     
    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年04月 [査読有り][通常論文]
     
    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.
  • 原田明寿, 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集 77th 457 2010年03月26日 [査読無し][通常論文]
  • 小川幸太, 青木芳尚, 幅崎浩樹, 山口周 電気化学会大会講演要旨集 77th 310 2010年03月26日 [査読無し][通常論文]
  • 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集 77th 311 2010年03月26日 [査読無し][通常論文]
  • 恒川聡, 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集 77th 453 2010年03月26日 [査読無し][通常論文]
  • 小山瞬, 青木芳尚, 永田晋二, 木村久道, 幅崎浩樹 電気化学会大会講演要旨集 77th 277 2010年03月26日 [査読無し][通常論文]
  • 福永悠希, 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集 77th 483 2010年03月26日 [査読無し][通常論文]
  • S. Koyama, Y. Aoki, S. Nagata, H. Kimura, H. Habazaki ELECTROCHIMICA ACTA 55 (9) 3144 -3151 2010年03月 [査読有り][通常論文]
     
    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年03月 [査読有り][通常論文]
     
    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.
  • 小宮山正造, 青木芳尚, 永田晋二, 木村久道, 幅崎浩樹 表面技術協会講演大会講演要旨集 121st 238 -239 2010年02月26日 [査読無し][通常論文]
  • 藤井隆志, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 121st 236 -237 2010年02月26日 [査読無し][通常論文]
  • 立野靖博, SAH S. P, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 121st 252 2010年02月26日 [査読無し][通常論文]
  • 小山瞬, 青木芳尚, 永田晋二, 木村久道, 幅崎浩樹 表面技術協会講演大会講演要旨集 121st 240 -241 2010年02月26日 [査読無し][通常論文]
  • 幅崎 浩樹 表面技術 = The journal of the Surface Finishing Society of Japan 61 (2) 159 -160 2010年02月01日 [査読無し][通常論文]
  • 清水 健一, 幅崎 浩樹 表面技術 = The journal of the Surface Finishing Society of Japan 61 (2) 157 -158 2010年02月01日 [査読無し][通常論文]
  • 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年02月 [査読有り][通常論文]
     
    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年02月 [査読有り][通常論文]
     
    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.
  • 堀口匠, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 原田明寿, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 平田周平, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 福永悠希, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 立野靖博, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 紺野祥岐, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 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年 [査読有り][通常論文]
     
    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年01月 [査読有り][通常論文]
     
    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年01月 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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.
  • 青木芳尚, 幅崎浩樹 固体イオニクス討論会講演要旨集 35th 168 -169 2009年12月07日 [査読無し][通常論文]
  • S. J. Garcia-Vergara, D. Le Clere, T. Hashimoto, H. Habazaki, R. Skeldon, G. E. Thompson ELECTROCHIMICA ACTA 54 (26) 6403 -6411 2009年11月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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年09月11日 [査読無し][通常論文]
  • 小宮山正造, 青木芳尚, 泉知夫, 幅崎浩樹 電気化学秋季大会講演要旨集 2009 254 2009年09月10日 [査読無し][通常論文]
  • 寺岡匡伸, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 120th 60 2009年09月07日 [査読無し][通常論文]
  • KOWALSKI Damian, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 120th 68 2009年09月07日 [査読無し][通常論文]
  • 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年08月 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
     
    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年07月 [査読有り][通常論文]
     
    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年05月08日 [査読無し][通常論文]
  • S. J. Garcia-Vergara, T. Hashimoto, P. Skeldon, G. E. Thompson, H. Habazaki ELECTROCHIMICA ACTA 54 (13) 3662 -3670 2009年05月 [査読有り][通常論文]
     
    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.
  • 小川幸太, 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集 76th 298 2009年03月29日 [査読無し][通常論文]
  • 寺岡匡伸, 青木芳尚, 幅崎浩樹 電気化学会大会講演要旨集 76th 461 2009年03月29日 [査読無し][通常論文]
  • 青木芳尚, 幅崎浩樹, 国武豊喜 電気化学会大会講演要旨集 76th 298 2009年03月29日 [査読無し][通常論文]
  • 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年03月29日 [査読無し][通常論文]
  • 小宮山正造, 青木芳尚, 泉知夫, 幅崎浩樹 表面技術協会講演大会講演要旨集 119th 40 -41 2009年03月02日 [査読無し][通常論文]
  • 小山瞬, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 119th 105 -106 2009年03月02日 [査読無し][通常論文]
  • 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年03月02日 [査読無し][通常論文]
  • Koji Fushimi, Shunsuke Yamamoto, Hidetaka Konno, Hiroki Habazaki CHEMPHYSCHEM 10 (2) 420 -426 2009年02月 [査読有り][通常論文]
     
    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.
  • 藤井隆志, 青木芳尚, 牧野猛, 小野昭二, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 小川幸太, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 小山瞬, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 寺岡匡伸, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 三浦吉幸, 青木芳尚, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • 小宮山正造, 青木芳尚, 泉知夫, 幅崎浩樹 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年01月26日 [査読無し][通常論文]
  • F. La Mantia, M. Santamaria, H. Habazaki, F. Di Quarto ECS Transactions 19 (3) 411 -422 2009年 [査読無し][通常論文]
     
    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年 [査読無し][通常論文]
  • Damian Kowalski, Yoshitaka Aoki, Hiroki Habazaki ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 48 (41) 7582 -7585 2009年 [査読有り][通常論文]
  • H. Habazaki, Y. Oikawa, K. Fushimi, Y. Aoki, K. Shimizu, R. Skeldon, G. E. Thompson ELECTROCHIMICA ACTA 54 (3) 946 -951 2009年01月 [査読有り][通常論文]
     
    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年01月 [査読有り][通常論文]
     
    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.
  • 青木芳尚, 幅崎浩樹, 国武豊喜 固体イオニクス討論会講演要旨集 34th 57 -58 2008年12月03日 [査読無し][通常論文]
  • Masahiro Seo, Koji Fushimi, Hiroki Habazaki, Takenori Nakayama CORROSION SCIENCE 50 (11) 3139 -3146 2008年11月 [査読有り][通常論文]
     
    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年11月 [査読有り][通常論文]
     
    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年11月 [査読有り][通常論文]
     
    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.
  • 小山瞬, 青木芳尚, 幅崎浩樹 表面技術協会講演大会講演要旨集 118th 215 2008年08月20日 [査読無し][通常論文]
  • 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年08月20日 [査読無し][通常論文]
  • 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年08月20日 [査読無し][通常論文]
  • 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年07月19日 [査読無し][通常論文]
  • 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年07月19日 [査読無し][通常論文]
  • M. Santamaria, F. Di Quarto, H. Habazaki CORROSION SCIENCE 50 (7) 2012 -2020 2008年07月 [査読有り][通常論文]
     
    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年06月 [査読有り][通常論文]
     
    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年05月 [査読有り][通常論文]
     
    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年05月 [査読有り][通常論文]
     
    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年04月25日 [査読無し][通常論文]
  • 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年04月25日 [査読無し][通常論文]
  • 青木芳尚, 幅崎浩樹, 国武豊喜 電気化学会大会講演要旨集 75th 235 2008年03月29日 [査読無し][通常論文]
  • Masahiko Kiriu, Koji Fushmi, Hidetaka Konno, Hiroki Habazak ELECTROCHEMISTRY 76 (3) 197 -202 2008年03月 [査読無し][通常論文]
     
    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年03月 [査読有り][通常論文]
     
    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年02月29日 [査読無し][通常論文]
  • 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年02月29日 [査読無し][通常論文]
  • 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年02月29日 [査読無し][通常論文]
  • 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年02月29日 [査読無し][通常論文]
  • 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年02月29日 [査読無し][通常論文]
  • 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年02月29日 [査読無し][通常論文]
  • 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年02月29日 [査読無し][通常論文]
  • E. Matykina, R. Arrabal, P. Skeldon, G. E. Thompson, H. Habazaki THIN SOLID FILMS 516 (8) 2296 -2305 2008年02月 [査読有り][通常論文]
     
    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年02月 [査読有り][通常論文]
     
    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年01月21日 [査読無し][通常論文]
  • 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年01月21日 [査読無し][通常論文]
  • 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年01月21日 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • T. Yamamoto, K. Fushimi, H. Habazaki, H. Konno, S. Miura ECS Transactions 16 (52) 133 -140 2008年 [査読無し][通常論文]
     
    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年 [査読無し][通常論文]
     
    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年 [査読無し][通常論文]
     
    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年 [査読無し][通常論文]
     
    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年 [査読無し][通常論文]
     
    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.
  • 表面技術 59 863 -868 2008年 [査読無し][通常論文]
  • M. Santamaria, F. Di Quarto, H. Habazaki ELECTROCHIMICA ACTA 53 (5) 2272 -2280 2008年01月 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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年01月 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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年01月 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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年 [査読有り][通常論文]
     
    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.
  • H. Habazaki, Y. Oikawa, K. Fushimi, K. Shimizu, S. Nagata, P. Skeldon, G. E. Thompson ELECTROCHIMICA ACTA 53 (4) 1775 -1781 2007年12月 [査読有り][通常論文]
     
    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年11月28日 [査読無し][通常論文]
  • S. J. Garcia-Vergara, P. Skeldon, G. E. Thompson, H. Habazaki SURFACE AND INTERFACE ANALYSIS 39 (11) 860 -864 2007年11月 [査読有り][通常論文]
     
    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年10月15日 [査読無し][通常論文]
  • H. Habazaki, M. Kiriu, M. Hayashi, H. Konno MATERIALS CHEMISTRY AND PHYSICS 105 (2-3) 367 -372 2007年10月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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年10月 [査読有り][通常論文]
     
    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年09月11日 [査読無し][通常論文]
  • 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年09月11日 [査読無し][通常論文]
  • 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年09月11日 [査読無し][通常論文]
  • 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年09月11日 [査読無し][通常論文]
  • 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年09月11日 [査読無し][通常論文]
  • M. Tauseef Tanvir, K. Fushimi, K. Shimizu, S. Nagatac, P. Skeldon, G. E. Thompson, H. Habazaki ELECTROCHIMICA ACTA 52 (24) 6834 -6840 2007年08月 [査読有り][通常論文]
     
    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年08月 [査読有り][通常論文]
     
    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年08月 [査読有り][通常論文]
     
    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年08月 [査読有り][通常論文]
     
    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年07月21日 [査読無し][通常論文]
  • 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年07月21日 [査読無し][通常論文]
  • Takatoshi Yamamoto, Koji Fushimi, Masahiro Seo, Shiro Tsuri, Tetsuo Adachi, Hiroki Habazaki ELECTROCHEMISTRY COMMUNICATIONS 9 (7) 1672 -1676 2007年07月 [査読有り][通常論文]
     
    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