Papers by Author: Hideo Okuyama

Abstract: Composite nanoparticles of Ni-TiC and Ni-TiN were prepared by an active plasma-metal reaction method. The structure and morphology were evaluated by X-ray diffraction and transmission electron microscopy observations. The morphology of the composite particles is dice-like or dumbbell-like, where the outer sides are metallic and the inner part of the rod (or dice)-like structure is TiC or TiN. The formation mechanism of the composite particles is considered by analogy to the VSL mechanism. The thermal stability of the nanocomposite particles is vastly superior to that of the metal particle. The excellent catalytic property of the Ni-TiN composite particle was confirmed when compared to the well-known Raney Ni particle and mixed particles of Ni and TiC.

Abstract: The disintegration of 6 different Nb-Zr-Fe alloys and their hydrogen storage properties due to hydrogenation have been investigated. The hydrogenation was performed in a 0.1MPa hydrogen pressure held at room temperature in arc melting chamber without exposure to air atmosphere. The thermal stability of hydrogen dissolved in disintegrated powder was measured in the temperature range from room temperature to 600°C by using the thermal analysis equipment. Hydrogen contents in alloys were evaluated from the mass difference of TG curve and chemical determinations for hydrogen gas analysis. The values of hydrogen content are in accordance with both chemical and mass difference methods. The hydrogen contents of disintegrated alloys synthesized were in the range of 1.2-2.0 wt% which depend on the composition of alloys.

Abstract: Highly crystalline-textured alumina ceramics were fabricated by electrophoretic deposition (EPD) in a strong magnetic field of 12 T. Preferred orientation of the bulk was controlled by changing the direction of the applied electric field E relative to the magnetic field B during the EPD. Average orientation angle of the prepared monoliths as a function of the angle between the vectors E and B, ϕ B-E was estimated from the X-ray diffraction analysis. Alumina/alumina laminar composites with crystalline- oriented layers were also fabricated by alternately changing the ϕ B-E layer by layer during EPD in a magnetic field of 12 T.