Papers by Author: Masahiko Demura

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Authors: Kyosuke Kishida, Masahiko Demura, Toshiyuki Hirano
Abstract: Texture and microstructure evolution during cold rolling of binary Ni3Al single crystals were studied as a function of the initial crystal orientations. Cold rolling behavior of the single crystals is strongly dependent on the initial crystal orientations, especially on the initial rolling direction (RD). Macroscopic texture evolutions for binary Ni3Al single crystals with the initial RD close to <001> are characterized as development of dual {110}<¯112> texture above 90% cold reduction and the banded structure formation. Microstructure observations reveal the extensive formation and accumulation of the planar defects including the stacking faults and the planes where the localized shear deformations occurs, which must be responsible for the observed anisotropic cold rolling behavior of Ni3Al single crystals.
Authors: Ya Xu, Dong Hyun Chun, Jun Hyuk Jang, Masahiko Demura, Dang Moon Wee, Toshiyuki Hirano
Abstract: The catalytic activity of oxidation-reduction pre-treated Ni3Al powder for methane steam reforming was examined. The oxidation-reduction pre-treatment consisted of two steps: oxidation in air at various temperatures from 973 to 1373 K, and then followed by reduction in H2 at 873 K. It was found that the oxidation-reduction treatments significantly reduced the onset temperature of activity, i.e., improved the activity of Ni3Al powder at low temperatures. The characterization of Ni3Al surface showed that an outer surface layer of fine NiO particles were formed on the surface of Ni3Al after oxidation. These NiO particles were reduced to metallic Ni by the subsequent reduction treatment, resulting in the high activity for methane steam reforming. These results indicate that the Ni3Al can form highly active surface structure with oxidation-reduction treatment, having excellent heat resistance.
Authors: Ya Xu, Satoshi Kameoka, Kyosuke Kishida, Masahiko Demura, An Pong Tsai, Toshiyuki Hirano
Abstract: Ni3Al has attractive high temperature properties, such as high strength and good oxidation/corrosion resistance, and is possible to be used for high temperature chemical processing and manufacture. Until now, the catalytic properties of Ni3Al were rarely investigated since the leaching of aluminum from Ni3Al is difficult to obtain a porous Raney-Ni compared to NiAl3 and Ni2Al3. In the present work, the catalytic properties of Ni3Al were examined for hydrogen production reactions from methanol. It was found that alkali-leached Ni3Al showed high activity for methanol decomposition (CH3OH→ 2H2+CO). Furthermore, Ni3Al catalysts suppress the formation of methane, i.e. they show higher selectivity for the methanol decomposition reaction than Ni catalyst. These results indicate a possibility for Ni3Al used as a catalyst for hydrogen production reaction.
Authors: Y. Xu, Jun You Yang, Masahiko Demura, Toshiyuki Hirano, Yoshitaka Matsushita, Masahiko Tanaka, Yoshio Katsuya
Abstract: The catalytic activity of Ni-Al (Ni25Al) nanoparticles fabricated by thermal plasma evaporation was examined for methanol decomposition and CO oxidation. The nanoparticles exhibited high activity for both reactions. Characterization of the nanoparticles revealed that the fabricated nanoparticles were mainly comprised of Ni and Ni3Al phases. During CO oxidation, the Ni phase was oxidized to NiO, while the Ni3Al phase remained unchanged. The NiO phase is supposed to serve as the active sites for CO oxidation. In contrast, during methanol decomposition, no obvious oxidation was observed for both Ni and Ni3Al phases. The Ni and Ni3Al phases are supposed to contribute to the high activity for methanol decomposition.
Authors: Junya Sakurai, Ya Xu, Masahiko Demura, Toshiyuki Hirano, Ryuji Tamura
Abstract: The catalytic properties of the cold-rolled foils of intermetallic compound TiNi were studied for hydrogen production from methanol in a temperature range of 513-793 K. The catalytic activity for methanol decomposition increased with a reaction temperature, especially above 673 K. The SEM and EDS analyses revealed the formation of numerous Ni-enriched particles dispersed in the layer of carbon fibers during the reaction. The catalytic activity of TiNi foils is attributed to those Ni-enriched particles.
Authors: Hye Youn Lee, Masahiko Demura, Y. Xu, Dang Moon Wee, Toshiyuki Hirano
Abstract: Evolution of surface morphology in Ni(γ)/Ni3Al(γ´) two-phase foil of binary Ni-18 at.%Al was examined during the electrochemically selective etching in the electrolyte of distilled water including 1 wt.% (NH4)2SO4 and 1 wt.% citric acid. In the early stage (0.5 h), only the γ matrix was etched and the outmost γ´ particles were protected by a preexisting surface product. As the γ matrix was etched more, the side surfaces of the outmost γ´ particles and the γ´ particles that were located inside were exposed in the electrolyte. They were dissolved, and had a high density of fine dimples. However, the dissolution rate of the γ´ particles was slower than that of the γ matrix and thus the selective etching was retained in this stage. Finally, at 5h, more γ´ particles were exposed and the flat and smooth surfaces of the outmost γ´ particles were completely eliminated by the dissolution on the side surfaces. From these observations plus the saturation of the current density observed in the electrochemical test, we concluded that the change in the surface morphology was finished at this stage. Thus, the surface became more rough and irregular, which resulted from the original two-phase microstructure and the fine dimple structure by transpassivation.
Authors: Ya Xu, Masahiko Demura, Toshiyuki Hirano
Abstract: The effect of acid and alkali leaching on catalytic activity of an atomized Ni3Al powder for methanol decomposition was investigated. It was found that a two-step process, an acid leaching followed by an alkali leaching, was most effective for improving the activity. The optimal conditions of acid and alkali leaching were examined. The effect of the acid and alkali leaching was attributed to the formation of fine Ni species and a porous surface structure.
Authors: Toshiyuki Hirano, Masahiko Demura, Kyosuke Kishida, Satoru Kobayashi, Yozo Suga
Authors: Kyosuke Kishida, Masahiko Demura, Satoru Kobayashi, Ya Xu, Toshiyuki Hirano
Abstract: We have studied the texture and microstructure evolution during cold rolling of Ni3Al single crystals as a function of the initial crystal orientations and revealed that the cold rolling behavior of the single crystals are strongly dependent on the initial crystal orientations, especially on the initial rolling direction (RD). An optimum condition for thin foil fabrication is determined that the initial RD is close to <001>. According to the conditions we have successfully fabricated the wide and thin foils of binary Ni3Al by cold rolling the single crystalline ingots. The thinnest foils obtained so far are about 20µm in thickness and 50mm in width. This document reviews the current status of our research on the thin foils of intermetallic compound Ni3Al.
Authors: Masahiko Demura, Ya Xu, Kyosuke Kishida, Toshiyuki Hirano
Abstract: Primary recrystallization textures were examined in the 84% and 95% cold-rolled boron-free Ni3Al single crystals with a Goss texture using the electron backscatter diffraction method. It was found that the main components of the textures in the specimens heat-treated at 873K/0.5h had a 40° rotation relationship about <111> to the original, Goss texture. All the eight variants of 40°<111> rotated grains existed. However, the number density is not even but dependent on whether the rotation axis is identical to the normal of slip planes activated during the prior cold rolling. The ratio of the number density among the variants was same in both the 84% and 95% cold-rolled foils. Based on these results, the formation of these 40°<111> rotated grains was explained assuming the modified multiple twinning mechanism where the annealing twinning occurred at the activated slip planes, followed by the subsequent twinning.
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