Hideo Okuyama

Electrophoretic deposition of α-alumina particles in a strong magnetic field

The electrophoretic deposition of single-crystalline α-alumina particles dispersed in aqueous media was performed in a strong magnetic field of 10 T. The α-alumina particles in the stable suspension were aligned due to their anisotropic diamagnetic susceptibility and then deposited on a cathodic substrate. The orientation of the α-alumina crystallites was confirmed by x-ray diffraction of the sintered specimen.

Synthesis and characterization of Fe and composite Fe–TiN nanoparticles by dc arc-plasma

Abstract Fe and composite Fe–TiN nanoparticles were prepared by an active plasma–metal reaction method. The structure and morphology were examined by X-ray diffraction, transmission electron microscopic observation and Mossbauer experiment. The morphology of Fe is spherical and that of the composite Fe–TiN nanoparticle is dumbbell-like. The surface oxide of the nanoparticles exposed to air was characterized and the reduction characteristics in a hydrogen atmosphere were examined. The thermal stability of the nanocomposite particle is vastly superior to that of the metal particle. The hydrogen sorption–desorption characteristics of the nanoparticles were examined by temperature-programmed desorption measurements. Hydrogen desorption at above 450 K was observed for the composite Fe–TiN nanoparticles. The effect of CO coadsorption on the hydrogen desorption was also examined and a large amount of hydrogen desorption was observed.

Hydrogen generation from water using Mg nanopowder produced by arc plasma method

Abstract We report that hydrogen gas can be easily produced from water at room temperature using a Mg nanopowder (30–1000 nm particles, average diameter 265 nm). The Mg nanopowder was produced by dc arc melting of a Mg ingot in a chamber with mixed-gas atmosphere (20% N2–80% Ar) at 0.1 MPa using custom-built nanopowder production equipment. The Mg nanopowder was passivated with a gas mixture of 1% O2 in Ar for 12 h in the final step of the synthesis, after which the nanopowder could be safely handled in ambient air. The nanopowder vigorously reacted with water at room temperature, producing 110 ml of hydrogen gas per 1 g of powder in 600 s. This amount corresponds to 11% of the hydrogen that could be generated by the stoichiometric reaction between Mg and water. Mg(OH)2 flakes formed on the surface of the Mg particles as a result of this reaction. They easily peeled off, and the generation of hydrogen continued until all the Mg was consumed.

Control of crystalline texture in polycrystalline alumina ceramics by electrophoretic deposition in a strong magnetic field

Highly crystalline-textured pure dense alumina ceramics were fabricated from spherical alumina powder without any seed particles and sintering additives by electrophoretic deposition (EPD) in a strong magnetic field of 10 T. The crystalline texture was confirmed by x-ray diffraction (XRD) for alumina ceramics deposited at 10 T followed by sintering at 1873 K. The angle between the directions of the magnetic and electric fields (φ B-E ) was altered to control the dominant crystal faces of the α-alumina monoliths. The average orientation angles estimated from the XRD diagram of the samples prepared at φ B-E = 0°, 45°, and 90° were 16.52°, 45.15°, and 84.90°, respectively. Alumina/alumina laminar composites with different crystalline-oriented layers were also fabricated by alternately changing the φ B-E layer by layer during EPD in a 10 T magnetic field. It was demonstrated that by using this technique, it is possible to control the crystalline orientation by changing the angle of E versus B during the EPD.

Fabrication and characterization of TiN–Ag nano-dice

TiN-Ag nanocomposite was synthesized by dc arc-plasma method. Microstructures of TiN-Ag nanocomposite were carefully characterized by powder X-ray diffraction method and transmission electron microscopy, and nano-morphologies by three-dimensional electron tomography. It was found that the surface of nanocrystalline TiN matrix was densely covered by finely dispersed Ag nanoparticles, and it was found that they were physically attached but not chemically bonded from their orientation relationships.

Removal of Aerosol by Magnetic Separation

We concluded high gradient magnetic separation experiments of iron (ferromagnetic) nano-particles with a nominal diameter of 50 nm by using a superconducting magnet. In the experiment, we fabricated fine iron particles using a thermal reactive plasma method in argon and hydrogen mixed gas and sent them directly to the magnetic separator. We present the experimental results, functions of the capture ratio on the magnetic flux density, and velocity of flow. We conclude that high gradient magnetic separation can separate nano-particles and is useful for nano-technology

Morphology and hydrogen desorption characteristic of Ni-TiN nanocomposite particle prepared by RF plasma

Abstract Ni-TiN nanocomposite particles are prepared by RF plasma. Dumbbell-like and dice-like morphologies are seen. Hydrogen sorption-desorption characteristics of the nanocomposite particles were examined by temperature-programmed desorption measurements. Hydrogen desorption at 500–700 K is observed, which implies that a new adsorption state of hydrogen exists. Hydrogen desorption characteristics are not so influenced by coadsorption of CO. The results are compared with the previously reported ones that were produced by a DC plasma reaction method.

Characterization of degraded surfaces of Al and AlN ultrafine powders

Abstract Aluminum (Al) and aluminum nitride (AlN) ultrafine powders (UFPs) were synthesized by an active plasma-metal reaction method. Temperature-programmed gas Desorption (TPD) measurements were conducted for the Al and/or AlN UFPs after exposure to air. H 2 O gas for AlN UFP, and H 2 O and H 2 gases for (Al + AlN) UFPs were mainly detected. The surface chemistry of the powders after exposure to air is estimated in comparison of the desorption characteristics with infrared spectrometry spectra. The evolved H 2 around 420 °C from the (Al + AlN) UFPs is due to the reaction of H 2 O with inner Al. The evolved H 2 O is considered to be formed by the reaction of adsorbed H 2 O on surface oxide of the powders and decomposition of hydroxide-like compounds.

Adsorption of hydrogen on Ni and NiTiO2 composite ultrafine particles

Abstract The adsorption of hydrogen on Ni and NiTiO2 composite ultrafine particles (UFPs) was studied by temperature-programmed desorption (TPD) experiments. The desorption characteristics of hydrogen on Ni and NiTiO2 composite UFPs were similar to those of a Ni single crystal or polycrystal. The amount of adsorption of hydrogen on NiTiO2 composite UFPs was dependent upon the temperature of exposure, and the phenomenon attributed to the spillover of hydrogen from Ni onto TiO2. The CO hydrogenation reaction on NiTiO2 composite UFPs proceeded above 373 K. TPD spectra showed new desorption peaks after the catalytic reaction above 373 K and suggested the formation of new adsorption states.

Preparation of ultrafine powders of AlN and (AlN + Al) by nitrogen plasma-Al reaction

Ultrafine powders of AlN and (AlN+Al) with particle sizes of less than 0.5μm were produced by arc melting of Al in atmospheres of N2+Ar, N2+H2, N2+NH3 at 0.1MPa pressure. The size, surface area, chemical composition, and crystal structure of obtained powders were determined by electron microscope, BET method, chemical analysis and X-ray diffraction analysis respectively. The following results were obtained.(1) AlN ratio in (AlN+Al) powders obtained in (N2+Ar) atmospheres decreases from 0.3 to zero with decreasing nitrogen partial pressure.(2) AlN ratio in (AlN+Al) powders obtained in (N2+NH3) atmospheres increases from 0.3 to 0.95 with increasing NH3 partial pressure.(3) Projections were formed on molten Al surface by evolved nitrogen gas from the melt and by reaction between nitrogen and molten Al.The reaction between nitrogen plasma and molten Al plays an important role in the formation of ultrafine particles. The driving force for the formation of ultrafine particles can be explained as follows; In arc melting of Al in a nitrogen atmosphere, molten Al simultaneously contacts with two gas phases, one is atomic nitrogen in the arc gas phase and another is the molecular nitrogen in the non-arc gas phase. The extent of dissolution of atomic nitrogen in the molten Al is much larger than that of molecular one. Then, the dissolved nitrogen through the arc gives higher nitrogen content for the non-arc gas phase. That is, super-saturated nitrogen will evolve in non-arc gas phase carrying with Al vapor. A kind of enhanced evaporation of Al is induced. This Al vapor reacts with surrounding gas species near the arc such as N2, N, NH3, NH2, NH in high temperature ranges (above 1600K) to form AlN or (AlN+Al) vapor which condense to ultrafine particles.