研究者データベース

王 永明(ワン ヨンミン)
創成研究機構 ナノテクノロジー連携研究推進室
特任助教

基本情報

所属

  • 創成研究機構 ナノテクノロジー連携研究推進室

職名

  • 特任助教

学位

  • 工学博士(北海道大学)

J-Global ID

研究キーワード

  • 水素貯蔵材料   電子顕微鏡   材料科学   

研究分野

  • ナノテク・材料 / 構造材料、機能材料

所属学協会

  • 日本顕微鏡学会   

研究活動情報

論文

  • Tengfei Zhang, Shigehito Isobe, Ankur Jain, Yongming Wang, Shotaro Yamaguchi, Hiroki Miyaoka, Takayuki Ichikawa, Yoshitsugu Kojima, Naoyuki Hashimoto
    JOURNAL OF ALLOYS AND COMPOUNDS 711 400 - 405 2017年07月 [査読有り][通常論文]
     
    Lithium metatitanate (Li2TiO3) doped magnesium hydride (MgH2) has been investigated in this paper. Desorption properties of the sample with catalyst are compared to the pure MgH2. Particularly, MgH2 doped with 5 mol % Li2TiO3 started to desorb hydrogen at 170 degrees C with a peak temperature at 211 degrees C, which is 100 degrees C and 80 degrees C lower than that of the as-milled MgH2. The reversibility and cyclability of sample with catalyst have also been investigated. Compared with the raw material, the desorption activation energy was reduced from 113 kJ/mol to 84 kJ/mol. Furthermore, the catalytic mechanism was discussed according to the experimental results. (C) 2017 Elsevier B.V. All rights reserved.
  • Shotaro Yamaguchi, Takayuki Ichikawa, Yongming Wang, Yuki Nakagawa, Shigehito Isobe, Yoshitsugu Kojima, Hiroki Miyaoka
    ACS Omega 2 3 1081 - 1088 2017年03月31日 [査読有り][通常論文]
     
    Lithium alloys are synthesized by reactions between lithium metal and group 14 elements, such as carbon, silicon, germanium, and tin. The nitrogenation and denitrogenation properties are investigated by thermal and structural analyses. All alloys dissociate the nitrogen triple bond of gaseous molecules to form atomic state as nitrides below 500 °C, which is lower than those required for conventional thermochemical and catalytic processes on nitride syntheses. For all alloys except for germanium, it is indicated that nanosized lithium nitride is formed as the product. The denitrogenation (nitrogen desorption) reaction by lithium nitride and metals, which is an ideal opposite reaction of nitrogenation, occurs by heating up to 600 °C to form lithium alloys. Among them, the lithium-tin alloy is a potential material to control the dissociation and recombination of nitrogen below 500 °C by the reversible reaction with the largest amount of utilizable lithium in the alloy phase. The nitrogenation and denitrogenation reactions of the lithium alloys at lower temperature are realized by the high reactivity with nitrogen and mobility of lithium. The above reactions based on lithium alloys are adapted to the ammonia synthesis. As a result, ammonia can be synthesized below 500 °C under 0.5 MPa of pressure. Therefore, the reaction using lithium alloys is recognized as a pseudocatalyst for the ammonia synthesis.
  • Synthesis, Crystal Structure, and Physical Properties of New Layered Oxychalcogenide La2O2Bi3AgS6
    Yudai Hijikata, Tomohiro Abe, Chikako Moriyoshi, Yoshihiro Kuroiwa, Yosuke Goto, Akira Miura, Kiyoharu Tadanaga, Yongming Wang, Osuke Miura, Yoshikazu Mizuguchi
    Journal of the Physical Society of Japan 86 124802/1 - 4 2017年 [査読有り][通常論文]
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Chaomei Liu, Naoyuki Hashimoto, Keisuke Takahashi
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 18 39 27623 - 27629 2016年10月 [査読有り][通常論文]
     
    High efficiency catalysts are needed to improve the kinetics of complex hydrides for practical applications. In this study, lithium metatitanate (Li2TiO3) is introduced in lithium alanate (LiAlH4), and the catalytic effect for notable complex/metal hydrides, such as LiAlH4, is investigated. Experiment results indicate that Li2TiO3 improves the kinetics of LiAlH4. In particular, Li2TiO3 dramatically improves the onset temperature of LiAlH4, which decreases to 75 degrees C and is within the temperature range for use in proton exchange membrane fuel cells. Transmission electron microscopy (TEM) observations help understand the catalytic effect of Li2TiO3 in the nanoscale. First principles calculations also show the improvement of H- and Li+ mobility by doping Li2TiO3, where calculations indicate that the physical origin of the catalytic effect is due to two factors: charge transfer and minor surface relaxation. Thus, experimental and theoretical evidence reveals the catalytic mechanism of Li2TiO3 in LiAlH4.
  • David Cempel, Mai Thanh Nguyen, Yohei Ishida, Hiroki Tsukamoto, Hiroaki Shirai, Yongming Wang, Kevin C. -W. Wu, Tetsu Yonezwa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 16 9 9257 - 9262 2016年09月 [査読有り][通常論文]
     
    Plasma-in-liquid process (PLP) has become a hot topic in green synthesis of metal nanoparticles (NPs). In order to overcome one of the current challenges associated with the impurity produced from metal electrodes, this study utilized a ceramic-coated electrode to prepare pure Au NPs stabilized by L-arginine. Using this electrode, the reduction of Au ions during the plasma irradiation, the formation of Au NPs, their size and size distribution as a function of the pH were investigated. Our results show that a bimodal NP size distribution was obtained at pH 3.5-12.0. The fraction of small sized Au NPs becomes significant at pH 6.0 and 12.0 while that of big sized Au NPs is dominant at pH 3.5. The results in the present study suggested that this change in the size distribution of Au NPs was governed by the reduction rate of gold ion at different pH under plasma generated in water.
  • Tengfei Zhang, Yuki Nakagawa, Takenobu Wakasugi, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    ACS APPLIED MATERIALS & INTERFACES 8 23 14548 - 14551 2016年06月 [査読有り][通常論文]
     
    A window type of the environmental cell system for a high-voltage electron microscope was developed and applied to in situ observation of a palladium (Pd) thin film. For in situ hydrogenation of Pd thin films, the distances of the lattice fringes were 0.20 and 0.23 nm, which correspond to the lattice d spacings of beta-phase (200) and (111) planes. Expansion of the Pd lattice happened as a result of phase transformation from the alpha phase to the beta phase. In particular, the lattice fringes were clearly distinguished, and the dislocation behavior during Pd hydrogenation was easily recognized according to the corresponding inverse fast fourier transform images. Furthermore, significant growth in the number of dislocations was observed at the grain boundary during increasing hydrogen pressure in the cell.
  • Keisuke Nakamura, Tomoya Oshikiri, Kosei Ueno, Yongming Wang, Yoshiomi Kamata, Yuki Kotake, Hiroaki Misawa
    The Journal of Physical Chemistry Letters 7 6 1004 - 1009 2016年03月 [査読有り][通常論文]
     
    We have successfully fabricated all-solid-state plasmonic photoelectric conversion devices composed of titanium dioxide (TiO2)/nickel oxide (NiO) p-n junctions with gold nanoparticles (Au-NPs) as prototype devices for a plasmonic solar cell. The characteristics of the crystal structures and the photoelectric properties of the all-solid-state devices were demonstrated. We observed that the crystalline structure of the NiO thin film and the interfacial structure of TiO2/Au-NPs/NiO changed significantly during an annealing treatment. Furthermore, the photoelectric conversion devices exhibited plasmon-induced photocurrent generation in the visible-wavelength region. The photo current may result from plasmon-induced charge separation. The photoelectric conversion properties via plasmon-induced charge separation were strongly correlated with the morphology of the TiO2/Au-NPs/NiO interface. The long-term stability of the plasmonic photoelectric conversion device was found to be very high because a stable photocurrent was observed even after irradiation for 3 days.
  • Akira Miura, Yoshikazu Mizuguchi, Tsuyoshi Sugawara, Yongming Wang, Takahiro Takei, Nobuhiro Kumada, Eisuke Magome, Chikako Moriyoshi, Yoshihiro Kuroiwa, Osuke Miura, Kiyoharu Tadanaga
    INORGANIC CHEMISTRY 54 21 10462 - 10467 2015年11月 [査読有り][通常論文]
     
    The relationship between the structure and superconductivity of Bi4O4S3 powders synthesized by heating under ambient and high pressures was investigated using synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM) observation. The Bi4O4S3 powders synthesized under ambient pressure exhibited a strong superconductivity (diamagnetic) signal and zero resistivity below similar to 4.5 K, while the Bi4O4S3 powder synthesized by the high-pressure method exhibited a low-intensity signal down to 2 K. Further annealing of the latter Bi4O4S3 powder under ambient pressure led to the development of a strong signal and zero resistivity. The crystal structures of all Bi4O4S3 phases consisted of Bi4O4Bi2S4 blocks including a Bi-S layer and anion(s) sandwiched between Bi4O4Bi2S4 blocks, but minor structural differences were detected. A comparison of the structures of the superconductive and nonsuperconductive Bi4O4S3 samples suggested that the superconductive Bi4O4S3 phases had slightly smaller lattice parameters. The average structures of the superconductive Bi4O4S3 phases were characterized by a slightly shorter and less bent BiS plane. Raman spectroscopy detected vibration of the S-O bonds, which can be attributed to sandwiched anion(s) such as SO42-. TEM observation showed stacking faults in the superconductive Bi4O4S3 phases, which indicated local fluctuation of the average structures. The observed superconductivity of Bi4O4S3 was discussed based on impurity phases, enhanced hybridization of the px and py orbitals of the Bi-S plane within Bi4O4Bi2S4 blocks, local fluctuation of the average structures, compositional deviation related to suspicious anion(s) sandwiched between Bi4O4Bi2S4 blocks, and the possibility of suppression of the charge-density-wave state by enriched carrier concentrations.
  • P. P. Liu, Q. Zhan, Z. Y. Fu, Y. P. Wei, Y. M. Wang, F. M. Wang, S. Ohnuki, F. R. Wan
    JOURNAL OF ALLOYS AND COMPOUNDS 649 859 - 864 2015年11月 [査読有り][通常論文]
     
    Good understanding of blistering and embrittlement mechanism depends on good investigation of surface and internal microstructure damage of gas-ion-irradiated materials. Internal and surface microstructure of He+ ion irradiated CLAM steel were examined by cross-sectional transmission electron microscopy combining focused ion beam. Variation of helium bubble density and size distribution versus depth in CLAM steel after high dose helium irradiation at room temperature was investigated. The average size of helium bubble increased within 100-400 nm but decreased near the non-irradiated matrix with the increase of depth, while the density followed a reverse trend. The formation and growth mechanism of helium bubble is different at different irradiation depth. The formation of a zone of large bubbles under the surface is the main reason of surface blistering and flaking. Helium induced irradiation swelling and surface blistering at low temperature were also discussed. (C) 2015 Elsevier B.V. All rights reserved.
  • Wei Xie, Aiko Kawahito, Takuya Miura, Takashi Endo, Yongming Wang, Takashi Yanase, Taro Nagahama, Yukitoshi Otani, Toshihiro Shimada
    CHEMISTRY LETTERS 44 9 1205 - 1207 2015年09月 [査読有り][通常論文]
     
    We report the synthesis of a new carbon material diamondlike carbon film codeposited with 1% C-60 molecules by plasma-assisted chemical vapor deposition. The synthesized films exhibited strong iridescent colors after being exposed to an atmosphere containing water vapor. An electron microscopy examination revealed that the film expanded by a factor of more than two, while forming 10-100-nm-sized grain-like structures after its exposure to water vapor. This work demonstrates a new concept of incorporating reaction centers in carbon solids to make carbon-based nanostructures.
  • Hiroki Miyaoka, Yongming Wang, Satoshi Hino, Shigehito Isobe, Kazuhiko Tokoyoda, Takayuki Ichikawa, Yoshitsugu Kojima
    MATERIALS 8 7 3896 - 3909 2015年07月 [査読有り][通常論文]
     
    Various synthesis and rehydrogenation processes of lithium hydride (LiH) and magnesium amide (Mg(NH2)(2)) system with 8:3 molar ratio are investigated to understand the kinetic factors and effectively utilize the essential hydrogen desorption properties. For the hydrogen desorption with a solid-solid reaction, it is expected that the kinetic properties become worse by the sintering and phase separation. In fact, it is experimentally found that the low crystalline size and the close contact of LiH and Mg(NH2)(2) lead to the fast hydrogen desorption. To preserve the potential hydrogen desorption properties, thermochemical and mechanochemical rehydrogenation processes are investigated. Although the only thermochemical process results in slowing the reaction rate due to the crystallization, the ball-milling can recover the original hydrogen desorption properties. Furthermore, the mechanochemical process at 150 degrees C is useful as the rehydrogenation technique to preserve the suitable crystalline size and mixing state of the reactants. As a result, it is demonstrated that the 8LiH and 3Mg(NH2)(2) system is recognized as the potential hydrogen storage material to desorb more than 5.5 mass% of H-2 at 150 degrees C.
  • P.P. Liu, Y.M. Zhu, M.Z. Zhao, S.N. Jiang, C.X. Liu, Y.M. Wang, F.R. Wan, S.Ohnuki
    Fusion Engineering and Design 95 20 - 26 2015年06月 [査読有り][通常論文]
     
    The dynamic behavior of individual loops of the both interstitial and vacancy types is believed to be strongly connected to the degradation processes that affect radiation-resistant materials used in nuclear-fission and fusion devices. Meanwhile, the isotopic effect of hydrogen on irradiation damage has attracted wide interest. In situ transmission electron microscopy investigation of the dynamic behavior of dislocation loops under high-energy electron irradiation was carried out in pure Fe with deuterium implantation at room temperature and aged at different temperatures. Shrinkage of dislocation loop was observed in implanted sample annealed at 753 K, except the popular growth of dislocation loop. The loop shrinkage was also observed in H implanted sample annealed at relatively lower temperature. The shrinking loop is identified to be < 100 > vacancy-type loop by acknowledged "inside-outside" method. Origin for the dynamic behavior of both type loops and the isotopic effect on the behavior were discussed. (C) 2015 Elsevier B.V. All rights reserved.
  • Eni Sugiarti, Kemas A. Zaini, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Shigenari Hayashi
    OXIDATION OF METALS 83 5-6 453 - 464 2015年06月 [査読有り][通常論文]
     
    Metastable Al2O3 scale formation on NiCoCrAl coated layers was investigated during initial-stage reaction for up to 100 h exposure at 800 A degrees C in air. NiCoCrAl was diffusion-coated onto low carbon steel by electroplating a NiCo layer followed by pack-cementation deposition of Cr and Al. The microstructural characterization of as-coated and oxidized samples was carried out at the micro- and nano-scales. The XRD and diffraction pattern in TEM analysis revealed the presence of metastable Al2O3, spinel NiAl2O4 and cubic (Cr,Al)(2)O-3 in the oxide. The phase identification using XRD and electron diffraction analysis associated with the coating composition was plotted on an isothermal oxidation map.
  • Eni Sugiarti, Fredina Destyorini, Kemas A. Zaini, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Shigenari Hayashi
    SURFACE & COATINGS TECHNOLOGY 265 68 - 77 2015年03月 [査読有り][通常論文]
     
    Coatings formed from NiCoCrAl were deposited by a combination of electroplating and pack cementation on a carbon steel substrate. The effect of Co concentration and temperature on the oxidation and hardness properties of the carbon steel was studied. The microstructure and morphology of the coatings were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microhardness of the coated samples was evaluated by a Vickers microhardness tester. FeNi(5%)CoCrAl coated sample exhibited better oxidation and hardness properties than that of FeNi(1%)CoCrAl coated sample. The microstructure and phase constitution of these coatings developed at 800 degrees C were similar. Samples coated at 800 degrees C and 1000 degrees C consisted of three and two layers, respectively. The formation of an intermetallic layer in all the coatings was confirmed. The gamma-(Ni,Fe), beta-(Ni,Al) and zeta exagonal structures were identified in the coated layers of all samples, while orthorhombic Al3Ni was only identified in the samples coated at 800 degrees C An analysis of the correlations between the structure, hardness properties, oxidation behaviors, and phase formation is also discussed. (C) 2015 Elsevier B.V. All rights reserved.
  • Tengfei Zhang, Shigehito Isobe, Motoaki Matsuo, Shin-ichi Orimo, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    ACS Catalysis 5 3 1552 - 1555 2015年03月 [査読有り][通常論文]
     
    This paper presents a relationship between ionic mobility and reaction kinetics for the Li-N-H system after doping LiTi2O4. The structural characteristic of this fast ionic conductor was introduced to the complex-hydride system. On one hand, the properties of the dehydrogenation process were improved significantly. On the other hand, the relationship between lithium ionic conductivity and the catalytic effect on the dehydrogenation was investigated according to the alternating current (AC) impedance results. The lithium ionic conductivity of samples with catalyst was higher than the samples without catalyst. Especially, the conductivity of LiNH2 and LiH mixtures with LiTi2O4 was almost 1.5 times higher than that of LiNH2 and LiH. The mobility of the Li+ ions between LiH and LiNH2 solid phases was enhanced by adding LiTi2O4.
  • Development of High Pressure Gas Environmental Cell and its Application to Hydrogen Reaction
    H. Nagakura, T. Wakasugi, K. Ohkubo, T. Tanioka, T. Endo, S. Isobe, Y. Wang, N. Hashimoto, S. Ohnuki
    Microscopy 64 i29 - i29 2015年 [査読有り][通常論文]
  • An In-Situ Environmental Cell-Holder of Conventional Transmission Electron Microscope and Its Applications
    Yongming Wang, Takenobu Wakasugi, Hiroki Nagakura, Shigehito Isobe, Naoyuki Hashimoto, Somei Ohnuki
    Microscopy 64 i91 - i91 2015年 [査読有り][通常論文]
  • Multi-layer Method combined with Nano-indentation, FIB and XTEM for Nano-hardness Measurement
    Ryoko Kurishiba, T. Endo, N. Miyazaki, Y. Wang, H. Oka, Y. Sato, A. Sawa, N. Hashimoto, S. Ohnuki
    Microscopy 64 i119 - i119 2015年 [査読有り][通常論文]
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    RSC Advances 5 24 18375 - 18378 2015年 [査読有り][通常論文]
     
    We have decreased the end temperature of the Li-N-H system, a hydrogen storage material developed in 2002, to below 260 degrees C, and obtained a lowest peak temperature of 223 degrees C.
  • Yongming Wang, Takenobu Wakasugi, Shigehito Isobe, Naoyuki Hashimoto, Somei Ohnuki
    MICROSCOPY 63 6 437 - 447 2014年12月 [査読有り][通常論文]
     
    Transmission electron microscope (TEM) observation of light metal hydrides is complicated by the instability of these materials under electron irradiation. In this study, the electron kinetic energy dependences of the interactions of incident electrons with lithium, sodium and magnesium hydrides, as well as the constituting element effect on the interactions, were theoretically discussed, and electron irradiation damage to these hydrides was examined using in situ TEM. The results indicate that high incident electron kinetic energy helps alleviate the irradiation damage resulting from inelastic or elastic scattering of the incident electrons in the TEM. Therefore, observations and characterizations of these materials would benefit from increased, instead decreased, TEM operating voltage.
  • Shigehito Isobe, Yudai Ikarashi, Hao Yao, Satoshi Hino, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 55 8 1138 - 1140 2014年08月 [査読有り][通常論文]
     
    Recently, LiAlH4 has attracted attention as one of the most promising hydrogen storage materials, because LiAlH4 is able to release large amount of hydrogen (7.9 mass%H-2) below 250 degrees C. However, the kinetics of the dehydrogenation reaction of LiAlH4 is too slow for applications to fuel cell vehicles. To improve the dehydrogenation kinetics, the dopant effect of TiCl3 has been investigated in this research. Here, LiAlH4 doped with various ratios (0, 0.1, 0.2, 0.5, 1.0, and 2.0 mol%) of TiCl3 were prepared by ball milling for 30 min under a 1.0 MPa H-2 atmosphere. The decomposition of LiAlH4 proceeds via a two-step reaction and the dehydrogenation kinetics of each step were compared to determine the optimum amount of TiCl3 that would assist the process. With increasing of TiCl3 amount, the dehydrogenation temperature for both of the reactions decreased. Activation energies decreased with increasing TiCl3 amount, however the amount of desorbed hydrogen decreased. Considering the kinetics and hydrogen capacity in the both steps, the results suggest that the optimum amount of doped TiCl3 for the dehydrogenation of LiAlH4 is around 0.2 mol%.
  • Keisuke Takahashi, Yongming Wang, Shotaro Chiba, Yuki Nakagawa, Shigehito Isobe, Somei Ohnuki
    SCIENTIFIC REPORTS 4 4598/1 - 4 2014年04月 [査読有り][通常論文]
     
    Hydrogenation of iron nanoparticles was performed both computationally and experimentally where previously chemically-bonded iron hydride is considered to be unachievable under ordinary conditions. Density functional theory (DFT) calculations predict that hydrogenated iron nanoparticles are stabilized on a single-layer graphene/Cu substrate. Experimentally, iron nanoparticles were deposited onto a graphene/Cu substrate by vacuum deposition. Hydrogenation was done at 1atm of hydrogen gas and under liquid nitrogen. Mass spectrometry peak confirmed the hydrogen release from hydrogenated iron nanoparticles while a scanning transmission electron microscopy is used in order to link a geometrical shape of iron hydride nanoparticles between experimental and theoretical treatments. The hydrogenated iron nanoparticles were successfully synthesized where hydrogenated iron nanoparticles are stable under ordinary conditions.
  • Siwei Chen, Kohei Tadaki, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 55 3 443 - 446 2014年03月 [査読有り][通常論文]
     
    In-situ observations of ferritic/martensitic steels by electron irradiation with a 1.25 MeV high voltage microscope at 573 K were carried out to study damage evolution in the steels. The development of interstitial type loops and cavities in both of the two steels, F82H-IEA and F82H-ODS, showed smaller and more numerous defects in the ODS steel. The cavities were formed preferentially at the interface between oxide particles and matrix. The results suggest that ODS particles may function to suppress the nucleation and growth of loops and cavities arising from irradiation. The effect of pre-implanted helium was also studied. The pre-implanted helium led to a homogenous distribution of black dots and cavities in the steels, and these may act as sinks for point defects arising from irradiation, causing a suppression of the subsequent growth of loops and cavities. The hardening corresponding to the microstructural evolution was estimated by assuming parameters extracted from the ion irradiation.
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    ChemCatChem 6 3 724 - 727 2014年03月 [査読有り][通常論文]
     
    In this study, LiTi2O4 was synthesized as a possible catalyst in the Li-N-H system. The properties of hydrogen desorption in the Li-N-H system with a homogeneous catalyst have been investigated. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that the single phase of LiTi2O4 was successfully synthesized and it was stable in the sample after high energy ball-milling and heat treatment. LiTi2O4 exhibited a catalytic effect in the Li-N-H system according to the thermogravimetry differential thermal analysis results. During dehydrogenation, a storage capacity of 5.7wt% was obtained under moderate temperature. A sharp peak of thermal gas desorption mass spectrometry curve occurred at 227 degrees C. Furthermore, the catalytic mechanism of LiTi2O4 in the Li-N-H system was discussed in accordance with the experimental results.
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Hiroshi Oka, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF MATERIALS CHEMISTRY A 2 12 4361 - 4365 2014年 [査読有り][通常論文]
     
    In this study, LiTi2O4 was synthesized as a possible catalyst for complex metal hydrides. LiTi2O4 was stable in the sample after high-energy ball milling and heat treatment. LiTi2O4 exhibited a catalytic effect among the samples of MgH2, LiAlH4 and LiNH2. The desorption kinetics and the purity of the desorbed hydrogen gas have been improved by doping LiTi2O4. Furthermore, the catalytic mechanism of LiTi2O4 was discussed in accordance with the experimental results.
  • T. Yanase, A. Kawahito, Y. Hashimoto, T. Endo, Y. Wang, T. Nagahama, T. Shimada
    RSC Advances 4 52 27620 - 27624 2014年 [査読有り][通常論文]
     
    We re-examined the growth of single crystalline Fe whiskers by chemical vapour deposition with regard to modern nanowire (NW) growth techniques. Single Fe NWs (100-300 nm diameter) with a high aspect ratio and unique [021] orientation were grown by optimizing the flow of raw materials (FeCl2 and H-2) and using a Au nanoparticle catalyst and single crystalline substrate. The growth mechanism was investigated by transmission electron microscopy and electron diffraction analysis of the NW-catalyst interface.
  • S. Eni, K. Zaini, Y. Wang, N. Hashimoto, S. Hayashi, S. Ohnuki
    Advanced Materials Research 896 586 - 590 2014年 [査読有り][通常論文]
     
    The corrosion of carbon steel is major infrastructure degradation problem in most industries, including chemical materials, mineral, and petrochemical industries. Coating on carbon steel is one of the techniques to improve corrosion resistance in extreme environments. In present work, NiCoCrAl was diffusion-coated onto low carbon steel by electrodeposition for NiCo and pack cementation for Cr and Al. The cross section of coated specimen was observed and analyzed using SEM and TEM. Two types of coating processes were conducted to promote the formation of bond-coat layer on carbon steel substrate with different temperature coating process. SEM and EDS results show that the coating comprises three layers on the substrate: intermetallics zone of Ni(Al) and Al(Cr) and interdiffusion zone of Ni(Co). By XTEM observation, it was found that γ(Ni,Fe) and ζ hexagonal structure were identified in all specimens. Orthorhombic structure with the Al3Ni was identified in specimen developed at temperature of 800°C. Further, the top surface of a 1000°C specimen has two phases of β-NiAl and ζ hexagonal structure. In order to understand the performance of two types coating system with different temperature process, oxidation test at temperature of 800°C for 100 hours has been carried out and the result shows that coating system which was developed at 800°C has better oxidation resistance than the system developed at 1000°C. © (2014) Trans Tech Publications, Switzerland.
  • Siwei Chen, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    PHILOSOPHICAL MAGAZINE LETTERS 94 7 433 - 438 2014年 [査読有り][通常論文]
     
    The onset of plasticity during nanoindentation is a new method to investigate the irradiation damage of structural materials in fission and fusion reactors. In this paper, nanoindentation experiment was carried out to helium implanted F82H-IEA and nano-sized oxide dispersion strengthened F82H-ODS steels for studying the elastic-plastic transition at a constant loading rate. The onset of plasticity shifted after helium implantation. By a statistical thermal activation model, activation volume was extracted to discuss the strength of barrier for dislocation motion. The results reveal an increase in the pinning force and number density of effective obstacles for dislocation motion in He-implanted F82H-IEA, and a decrease in the local pinning force without changing the density of effective obstacles in He-implanted F82H-ODS.
  • Yuki Nakagawa, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Liang Zeng, Shusheng Liu, Takayuki Ichikawa, Yoshitsugu Kojima
    JOURNAL OF ALLOYS AND COMPOUNDS 580 S1 S163 - S166 2013年12月 [査読有り][通常論文]
     
    Dehydrogenation processes of alpha- and gamma-AlH3 were investigated by in situ transmission electron microscopy observations. The relationship between Al2O3 thickness and dehydrogenation kinetics was also clarified. The initial shape of alpha-AlH3 particle was cubic and that of gamma-AlH3 particle was rod-shaped. The process of gamma-AlH3 was quite similar with alpha-AlH3. The precipitation and growth of Al was observed in both processes. The dehydrogenation kinetics did not depend on Al2O3 thickness. It was found that milling effect on the dehydrogenation kinetics was larger than doping effect. The dehydrogenation process was discussed in terms of both microscopic and kinetic studies. (C) 2013 Elsevier B.V. All rights reserved.
  • Takenobu Wakasugi, Shigehito Isobe, Ayaka Umeda, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF ALLOYS AND COMPOUNDS 580 S1 S127 - S130 2013年12月 [査読有り][通常論文]
     
    A close type of an environmental cell was developed for a high voltage electron microscope. Using this cell allowed an in situ observation of hydrogenation in Pd particles under H-2 gas of 0.05 MPa at RT. Two types of window films, Tri-Acetyl-Cellulose (TAC) and Silicon Nitride (SiN), were used for testing the contamination on the sample, as well as the strength for pressure. We confirmed the hydrogenation in diffraction patterns and images, and additionally the image resolution of 0.19 urn was obtained by using a SiN film with a thickness of 17 nm. (C) 2013 Elsevier B.V. All rights reserved.
  • Shigehito Isobe, Sumito Yamada, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Hiroki Miyaoka, Takayuki Ichikawa, Yoshitsugu Kojima
    JOURNAL OF APPLIED PHYSICS 114 9 093509/1 - 093509/7 2013年09月 [査読有り][通常論文]
     
    Li-C-H system, which can store about 5.0 mass% of rechargeable H-2, has been reported as a promising hydrogen storage system by Ichikawa et al. [Appl. Phys. Lett. 86, 241914 (2005); Mater. Trans. 46, 1757 (2005)]. This system was investigated from the thermodynamic and structural viewpoints. However, hydrogen absorption/desorption mechanism and the state of hydrogen atoms absorbed in the composite have not been clarified yet. In order to find new or better hydrogen storage system, graphite powder and nano-structural graphite ball-milled under H-2 and Ar atmosphere were prepared and milled with Li and Mg under Ar atmosphere in this study. Microstructural analysis for those samples by transmission electron microscope revealed that LiC6 and/or LiC12 were formed in Li-C-H system. On the other hand, MgC2 was found in Mg-C-H system ball-milled under H-2 atmosphere, but not in the system ball-milled under Ar atmosphere. These results indicated that nano-structure in composites of nano-structural graphite is different from that of alkali (-earth) metal. For these reasons, metal-C-H system can be recognized to be a new family of hydrogen storage materials. (C) 2013 AIP Publishing LLC.
  • Shuai Wang, Naoyuki Hashimoto, Yongming Wang, Somei Ohnuki
    ACTA MATERIALIA 61 13 4734 - 4742 2013年08月 [査読有り][通常論文]
     
    In order to monitor the influence of hydrogen on the coupled evolution of dislocation velocity and mobile dislocation density, we applied repeated transients to pure iron under simultaneous hydrogen cathodic charging conditions. The effective activation volume and the thermal stress were determined at different hydrogen concentrations. The effective activation volume decreases immediately with cathodic charging. At high hydrogen concentrations, the activation volume decreases and the thermal stress increases rapidly. The density of mobile dislocations in the hydrogen-charged iron has a lower rate of exhaustion than the hydrogen-free one. The thermal activation energy decreases and the average dislocation velocity increases as a function of hydrogen concentration. Transmission electron microscopy reveals hydrogen-induced tangled dislocations, which indicates a weakening of the repulsive stress field between dislocations. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • Tao Ma, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF PHYSICAL CHEMISTRY C 117 20 10302 - 10307 2013年05月 [査読有り][通常論文]
     
    The state of Nb-contained catalysts in MgH2 nanocomposites was investigated during the full cycle. X-ray diffraction (XRD) results showed that Nb2O5 and Nb reacted with MgH2 during ball-milling, forming NbH2 and NbH, respectively. In the following dehydrogenation, the (di)hydride decomposed, and Nb was produced. Then NbH was generated in both samples after rehydrogenation. Similar composition in both samples suggests that the catalytic effect follows the same mechanism, the Nb-gateway model, in which Nb facilitates the hydrogen transportation from MgH2 to the outside. By contrast, NbO remained during the full cycle. Scanning and transmission electron microscopy (SEM and TEM) observations revealed that the Nb2O5-doped sample tended to be refined in size, compared to the Nb-doped and NbO-doped ones. Nb crystals in the Nb2O5-doped sample were observed to be highly dispersed in the sample, with 10-20 nm in size. Given all that, tiny Nb crystals distributed in the composites worked as the gateway facilitating hydrogen transportation and improving dehydrogenation properties.
  • Hao Yao, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 38 9 3689 - 3694 2013年03月 [査読有り][通常論文]
     
    The thermal decomposition process of lithium alanate (LiAlH4) was investigated by TEM, TG-DTA and XRD. It was shown that LiAlH4 decomposes through a two-step reaction: a liquid-to-solid phase transition in the first step of the decomposition and a solid-to-solid reaction in the second step of the decomposition, both steps accompanied by hydrogen release. The particle size of the aluminum (Al), which formed in the first decomposition step, was much larger than that in the second decomposition step. In addition, Al particles formed in the liquid phase of LiAlH4 in the first decomposition step, while, they form in solid phase of Li3AlH6 in the second decomposition step, resulting in the kinetics of the first decomposition step being faster than that of the second decomposition step. The investigation clearly demonstrated the reaction model of the decomposition of LiAlH4 in the nano-scale, showing different diffusion processes of Al in each of the decomposition steps. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
  • Shigehito Isobe, Miki Dohkoshi, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Satoshi Hino, Takayuki Ichikawa, Yoshitsugu Kojima
    JOURNAL OF THE JAPAN INSTITUTE OF METALS 77 12 571 - 574 2013年 [査読有り][通常論文]
     
    In order to clarify the reaction mechanism of the hydrogenation process in the Li(2)NHsystem, we have observed the partially hydrogenated samples by transmission electron microscopy (TEM). From the TEM images of partially hydrogenated samples, it was shown that the LiNH2 phase was located between Li2NH phase, which was almost at the center of the particle, and LiH particles with the size of 100 nm. This result indicated that LiH was generated and grew up at the outside of the complex particle of Li2NH and LiNH2 with Li moving from the center to the surface of the particle.
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    RSC ADVANCES 3 18 6311 - 6314 2013年 [査読有り][通常論文]
     
    The reaction mechanism of the (de) hydrogenation of a LiNH2 + LiH mixture with a nanoscale catalyst has been investigated. In this research, the position of each solid phase was examined by transmission electron microscopy (TEM). The observation showed that LiH particles, around 100 nm in size, formed around LiNH2 in the hydrogenation process. According to in situ TEM observation of the dehydrogenation process, the LiH particles became smaller as they reacted with LiNH2. Fine particles of Li2NH with crystallites of size 30-40 nm formed on the surface of the LiNH2. It indicated that H+ from the LiNH2 moved to the interface and combined with H- from the LiH in the dehydrogenation process, consequently H-2 was released. At the same time, Li+ ions diffused from the LiH to the LiNH2 through the interface and Li2NH formed. On the other hand, it was confirmed that the catalyst was located at the interface between the LiH and LiNH2. It was found that the catalyst had the effect of improving the migration of Li+ from LiH to LiNH2.
  • Tao Ma, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    CATALYSTS 2 3 344 - 351 2012年09月 [査読有り][通常論文]
     
    We report a study on the desorption properties, crystallography and chemical state of MgH2 and 1 mol% Nb2O5 ball-milled composites. Desorption temperatures of the composites decreased with increase of ball-milling time. Size of MgH2 crystallites decreased during ball-milling. Reduction of Nb2O5 after ball-milling was confirmed by tracing the chemical state of Nb and was further supported by TEM observation. The reduced phases may act as more effective catalysts improving the desorption properties.
  • Tao Ma, Shigehito Isobe, Keisuke Takahashi, Yongming Wang, Shuai Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF PHYSICAL CHEMISTRY C 116 32 17089 - 17093 2012年08月 [査読有り][通常論文]
     
    Mg-Nb2O5 evaporated composites, which were prepared by evaporating Mg thermally on single crystals of Nb2O5, were investigated in this work. We attempted to hydrogenate the sample under 5 bar H-2 atmosphere at 250 degrees C for 2 h. The electron microscope was used to observe the microstructure of the as-prepared and hydrogenated samples. It was found that the phase transition occurred along the particular orientation where Mg(002) is parallel to MgH2(101) or MgO(200). Density functional theory calculations were carried out on MgH2 and MgO slabs, showing that MgH2(101) and MgO(200) have the lowest surface-formation energy. On the basis of the observation and calculation, the phase-transition process of Mg during hydrogenation and oxidation was discussed. Finally, a structural model including Mg-Mg distance adjustment and layer shift was proposed to demonstrate the phase-transition process.
  • P. P. Liu, J. W. Bai, D. Ke, F. R. Wan, Y. B. Wang, Y. M. Wang, S. Ohnuki, Q. Zhan
    JOURNAL OF NUCLEAR MATERIALS 423 1-3 47 - 52 2012年04月 [査読有り][通常論文]
     
    The interactions between deuterium atoms and irradiation defects in materials are important for designing materials in fusion reactors due to the fact that deuterium widely exists in nuclear reactions, and that the interactions provide a means to study the dynamic behavior of the isotopes of hydrogen in the material based on the isotope effects. In the current paper, the effects of deuterium implantation and the subsequent electron irradiation on the microstructure of Fe-10 wt%Cr model alloy have been investigated using ultra-high voltage transmission electron microscopy (TEM). The in situ observation showed that the size of dislocation loops increases with increasing electron irradiation dose and irradiation temperature. No distinct voids were observed at irradiation temperature up to 823 K. The migration energy (E-m) of deuterium-vacancy complex was calculated from the growth speed of dislocation loops at 623-773 K. A high-resolution TEM image of dislocation loops because of deuterium ion implantation was also achieved. (C) 2012 Elsevier B.V. All rights reserved.
  • Hao Yao, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF ELECTRON MICROSCOPY 60 6 375 - 378 2011年12月 [査読有り][通常論文]
     
    A plastic bag method was developed to observe air-sensitive samples on microstructure and phase distribution without exposure to air during the holder transfer process into the transmission electron microscope (TEM). As an example, a type of lithium aluminum hydride (Li(3)AlH(6)) was observed in the TEM to demonstrate the effectiveness of this method. Results show that the plastic bag method is a simple and practical TEM transfer method utilized to reduce air contact for a series of air-sensitive materials.
  • Y. Wu, Y. M. Wang, G. M. Song, X. W. Li
    Oxidation of Metals 76 5-6 419 - 431 2011年12月 [査読有り][通常論文]
     
    Oxidation behavior of a Re-based diffusion barrier/Ni-Al coated single-crystal (SC) Ni-based TMS-82+ superalloy was studied to compare with those of the base and Ni-Al coated superalloys under cyclic air at 1150 degrees C for 200 h. The base superalloy showed a negative mass gain due to extensive oxide spallation, and the Ni-Al coated superalloy without the diffusion barrier started to spall slightly after about 90 h. The oxidation resistance of the Ni-Al coated superalloy with the Re-based diffusion barrier was greatly improved due to the formation of a dense alpha-Al2O3 layer in the scale. The Re-based alloy was an effective diffusion barrier layer against inward diffusion of Al and outward diffusion of alloying elements in the alloy substrate due to the reduced thickness of interdiffusion zone with small amount of detrimental precipitates and higher content of Al in the Ni-Al coating that supplied enough Al for formation of the alpha-Al2O3 layer.
  • Tao Ma, Shigehito Isobe, Eri Morita, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Toru Kimura, Takayuki Ichikawa, Yoshitsugu Kojima
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 19 12319 - 12323 2011年09月 [査読有り][通常論文]
     
    We reported on the hydrogen desorption properties, microstructure, kinetics, and chemical bonding state of catalyst surface for composites of MgH(2) and 1 mol% Nb(2)O(5) ball-milled for 0.02 h, 0.2 h, 2 h, 20 h under 1 MPa H(2) atmosphere, as well as hand-mixed (HM) one. Hydrogen desorption properties were significantly improved by ball-milling with Nb(2)O(5). Then, we estimated by Kissinger Method the activation energy (E(a)) of hydrogen desorption reaction that decreased with the increase of ball-milling time. Especially, E(a) of the sample ball-milled for 0.2 h was drastically decreased, compared with that of the sample ball-milled for 0.02 h. TEM observations revealed that the distribution of Nb(2)O(5) in MgH(2) was gradually improved during ball-milling. On the other hand, we confirmed by XPS that in the sample ball-milled for 0.2 h, Nb(2)O(5-x) phase(s) existed at least on the surface. It can be suggested that these deoxidized Nb(2)O(5-x) phases eventually decrease E(a) as substantial catalyst rather than Nb(2)O(5) itself. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
  • Yohei Kawai, Motohiro Uo, Yongming Wang, Sayaka Kono, Somei Ohnuki, Fumio Watari
    DENTAL MATERIALS JOURNAL 30 3 286 - 292 2011年05月 [査読有り][通常論文]
     
    Zirconia has found wide application in dentistry because of its high mechanical strength and superior esthetic properties. However, zirconia degradation caused by phase transformation occurring in a hydrothermal environment is of concern. in the present study, phase transformation and microstructure of tetragonal zirconia polycrystal partially stabilized with yttrium oxide (Y-TZP) and alumina-toughened zirconia (ATZ) sintered at different temperatures were estimated. On grazing angle X-ray diffraction analysis, ATZ showed less phase transformation to the monoclinic phase during hydrothermal treatment and this transformation appeared to occur within a few micrometers below the surface. At a higher sintering temperature the monoclinic phase content of ATZ was found to be lesser than that of Y-TZP, indicating that the alumina in ATZ was effective in suppressing hydrothermal degradation. Examination by transmission electron microscopy and studying of electron backscatter diffraction patterns indicated that grain growth in ATZ was slightly suppressed compared with that in Y-TZP at higher sintering temperatures. The present study demonstrated the effect of adding alumina to zirconia for suppressing hydrothermal degradation and studied the effect of this addition on grain growth in zirconia.
  • Eni Sugiarti, Youngmin Wang, Naoyuki Hashimoto, Somei Ohnuki, Toshio Narita
    MATERIALS TRANSACTIONS 52 3 319 - 323 2011年03月 [査読有り][通常論文]
     
    An electron microscopy phase characterization was carried out for a Re-based diffusion barrier layer, which was deposited on the Nb substrate used as an ultra high temperature material. The coating process produced three layers; an outer Cr(Re) layer, an intermediate Cr-Nb-Re layer, and an inner Nb(Re) layer. The Cr-Nb-Re layer is considered to act as a diffusion barrier layer between the substrate and the outer Cr(Re) reservoir layer. The Cr(Re) and Nb(Re) layers are in single phase with a similar bcc structures, but they are different in structure from the intermediate layer, which is composed of a dual phase of Re63Cr25Nb17 with a cubic structure and Nb42Re33Cr25 with a hexagonal structure determined by transmission electron microscopy (TEM) in this study. [doi:10.2320/matertrans.MB201022]
  • Y. Wu, X. W. Li, G. M. Song, Y. M. Wang, T. Narita
    Oxidation of Metals 74 5-6 287 - 303 2010年12月 [査読有り][通常論文]
     
    Oxidation behavior of the uncoated base, Ni-Al coated and Re-Cr-Ni plus Ni-Al coated single-crystal (SC) Ni-based TMS-82+ superalloy is studied under cyclic air at 900 degrees C for 200 h to assess the oxidation resistance. Regardless of the coating processing, Ni-Al coating is effective in improving the oxidation resistance due to the formation of a continuous alpha-Al(2)O(3) a layer in the scale. For the uncoated base superalloy, the mass-gain curves are fitted by a subparabolic relationship, and complex oxide products including predominately NiO, some CrTaO(4), alpha-Al(2)O(3), Cr(2)O(3), a minor of spinels of (Ni, Co)Al(2)O(4), AlTaO(4) and theta-Al(2)O(3) are detected. Time-dependence of the oxide growth rate for both coated superalloy with/without the diffusion barrier is explained by the parabolic relationship. The oxide scales consist predominately of alpha-Al(2)O(3) and a minor of theta-Al(2)O(3). The diffusion barrier of sigma-phase plays a negligible effect on the oxidation resistance during
  • Qingxin Tang, Takeshi Hoshino, Shigeharu Ukai, Bin Leng, Shigenari Hayashi, Yongming Wang
    MATERIALS TRANSACTIONS 51 11 2019 - 2024 2010年11月 [査読有り][通常論文]
     
    The effect of adding minor elements, such as Ti, Mg, Zr, Ca or Hf, on the size of oxide particles was investigated in Ni-based ODS alloy, Ni-0.5 mass%Al-1 mass%Y2O3. Among these elements, Hf is the most effective at refining the oxide particles, particularly at a concentration of 0.8 mass% Hf, as verified by TEM observation and hardness measurement. X-ray diffraction measurements indicate that the formation of Y2Hf2O7 is responsible for the refinement of oxide particles. The Hf is also effective for a commercial superalloy of PM1000. [doi:10.2320/matertrans.M2010163]
  • Shigehito Isobe, Hao Yao, Yongming Wang, Hiroshi Kawasaki, Naoyuki Hashimoto, Somei Ohnuki
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 35 14 7563 - 7567 2010年07月 [査読有り][通常論文]
     
    In-situ transmission electron microscopy (TEM) has been performed to observe decomposition process of sodium alanate (NaAlH4) in this work. NaAlH4 was ground in a glove box under inert gas, and then it was transferred into microscope without exposed to air by Plastic Bag Method. The results of in-situ electron beam diffraction showed that NaAlH4 decomposed to Na3AlH6 + Al, and NaH + Al during heated up to 150 and 200 degrees C, respectively. Moreover, we obtained the result of high-resolution (HR) TEM images about the decomposition of NaAlH4 by high voltage electron microscopy (HVEM) of 1250 key. It showed that the porous structures appeared with increase of temperature. This should be from structural defects and/or cavities due to volume change of the phases. It was also shown that Na3AlH6 and Al particles with the grain size of several 10 nm were irregularly distributed near the pores. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
  • Shigehito Isobe, Akifumi Ono, Hao Yao, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    APPLIED PHYSICS LETTERS 96 22 223109/1 - 3 2010年05月 [査読有り][通常論文]
     
    In situ observation on dehydrogenation of MgH2 was performed by using transmission electron microscope (TEM). The dehydrogenation of MgH2 with 1 mol % Nb2O5 and formation of nanosized Mg particles were observed at 150 degrees C. Nb2O5 was not confirmed in diffraction patterns and TEM images probably due to wide dispersion. On MgH2 with 10 mol % Nb2O5, the high resolution TEM could recognize the dehydrogenation at the interface between MgH2 and Nb2O5, proceeding with increasing temperature. This suggests that hydrogen atoms could diffuse from MgH2 phase to the interface between Mg and Nb2O5, resulting in formation of hydrogen molecules at the interface. (C) 2010 American Institute of Physics. [doi:10.1063/1.3442910]
  • Hao Yao, Hiroshi Kawasaki, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 51 5 1016 - 1019 2010年05月 [査読有り][通常論文]
     
    Sodium alanate (NaAlH4) was ground in a dove box in inert gas and transferred to a microscope without exposing the samples to air, using a plastic bag method. The results of in-situ electron beam diffraction showed that NaAlH4 decomposed to Na3AlH6 and Al, and then to NaH and Al when heated to 150 degrees C and then 200 degrees C. The decomposition of NaAlH4 was observed by ex-situ transmission electron microscopy (TEM) at 1250 keV. Porous structures appeared when the samples were heated and dehydrogenated. These are likely due to structural defects or are cavities due to volume changes between phases. The Na3AlH6 and Al particles were found to distribute around the pores. [doi:10.2320/matertrans.MBW200902]
  • Akifumi Ono, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF THE JAPAN INSTITUTE OF METALS 74 3 205 - 208 2010年03月 [査読有り][通常論文]
     
    In situ observation of the catalytic action of MgH2-1 mol%Nb2O5 and MgH2-10 mol%Nb2O5 was carried out by using transmission electron microscopy (TEM). In case of MgH2-1 mol%Nb2O5, TEM analysis indicated that MgH2 started to decompose at 150 degrees C and nano size particle of Mg formed. However, Nb2O5 was not observed in the diffraction pattern and images. In case of MgH2-10 mol%Nb2O5, high resolution images, FFT and IFFT, revealed that the decomposition of MgH2 started with the contact region in Nb2O5 and Mg formed. The result suggested that the reaction of dehydration could proceed due to hydrogen diffusion to the Mg-Nb2O5 interface.
  • In-situ TEM Observation with Environmental Cell for Hydrogen Storage Materials
    Shigehito Isobe, Yongming Wang, Koya Okudera, Hiroko Hirasawa, Naoyuki Hashimoto, Somei Ohnuki
    Materia Japan 48 12 616  2009年 [査読有り][招待有り]
  • Yongming Wang, Somei Ohnuki, Shigenari Hayashi, Toshio Narita
    MATERIALS TRANSACTIONS 48 3 526 - 530 2007年03月 [査読有り][通常論文]
     
    Cross sectional structure of a Re-based diffusion barrier layer coated on a Ni-based single-crystal superalloy has been investigated in submicron scale. The barrier layer was prepared by electroplating of a Ni-73 at%Re film onto the alloy substrate, followed by a Cr-pack cementation in a mixture of Ni-30Cr and Al2O3 powders at 1573 K for 36 ks in vacuum. The diffusion barrier containing 38 at%Re, 35 at%Cr, 16 at%Ni and few amount of Al was identified to be topologically close-packed alpha-phase using electron backscattered diffraction method. Voids formed with precipitates in the diffusion barrier layer. Poly-crystallization and gamma-phase coarsening occurred in the superalloy substrate close to the Re-based alloy layer.
  • Yongming Wang, Somel Ohnuki, Shigenari Hayashi, Takayuki Yoshioka, Motoi Hara, Toshio Narita
    MATERIALS TRANSACTIONS 48 2 127 - 132 2007年02月 [査読有り][通常論文]
     
    The thermal stability of coatings containing a Re-based diffusion barrier layer was investigated by surface and cross-sectional analysis methods. A Re-bascd barrier layer accompanied by in outer Ni-O-Al layer was prepared by electrolytic plating onto a Ni-based superalloy, followed by Cr-pack cementation in vacuum at 1523 K. Vacuum annealing was carried out at 1423 K for 25 h. Another type of coating specimen, with an additional Al reservoir layer on the Re-based barrier layer, was oxidized in air for 25 one-hour cycles at 1423 K. EDXRF, XRD, SEM, EDS and EPMA were used for analysis to evaluate the effects of the heat treatments. It was found that the barrier layer decomposed at high temperature when it was coated with a low-Al Ni-Cr-Al phase. but had good stability when it was adjacent to a high-M Ni-Cr-Al phase.
  • Y Wang, M Kanedome, T Yasuda, T Suda, S Watanabe, S Ohnuki, T Nagasaka, T Muroga
    JOURNAL OF NUCLEAR MATERIALS 329 477 - 480 2004年08月 [査読有り][通常論文]
     
    To clarify hydrogen effects on mechanical properties of pure vanadium, two kinds of tensile tests were performed using hydrogen charged miniature specimens at room temperature. One is with hydrogen charging prior to testing, and the other is with hydrogen charging during testing with continuous or intermittent methods. The cathodic hydrogen charging was carried out electrolytically in various concentrations of H2SO4 with different current densities. The hydrogen charged specimens were tested to obtain stress-strain curves. The fractography was performed by SEM, and hydride formation and microstructural change were examined by TEM. Hydrogen-induced softening and hardening in vanadium resulted from hydrogen charging. The variations in mechanical property of specimens depended on the amount of dissolved hydrogen, that was determined by hydrogen diffusion and hydrogen desorption. Dislocation motion also plays a role in the variation of flow stress. (C) 2004 Elsevier B.V. All rights reserved.
  • Advanced Coal Power Cycle with a Stand-alone Magneto-hydrodynamic Generator
    N. Kayukawa, Y. Wang
    J. Propulsion and Power 20 3 566 - 571 2004年 [査読有り][通常論文]
  • N. Kayukawa, Y. Wang
    J. Propulsion and Power 19 5 972 - 975 2003年 [査読有り][通常論文]

特許

  • 特開P2009-196863A:水素貯蔵材料の製造方法  2009年09月03日
    小島 由継, 市川 貴之, 王 永明, 常世田 和彦, 窪川 豊之
  • RU2004101734 (A):Stand-alone high efficiency magnetohydrodynamic power generation method & system  2004年01月20日
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  • 特開P2004-229374A:MHD単独高効率発電方法およびシステム  2004年08月12日
    粥川尚之, 王永明
  • AU2004200239 (A1):Stand-alone MHD high efficiency power generation method and system  2004年01月21日
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  • KR20040067952 (A):POWER GENERATING METHOD AND POWER GENERATING SYSTEM OF MHD USING COMBUSTION PLASMA AS OPERATING FLUID  2004年01月19日
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  • EP1441434 (A2):Stand-alone high efficiency magnetohydrodynamic power generation method and system  2004年01月21日
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  • CN1518196 (A):High-efficient generating method and generating system of independent using magnetohydrodynamics  2004年01月20日
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