Satoru Ohno

Oxidation and Degradation of Titanium Nitride Ultrafine Powders Exposed to Air

Titanium nitride ultrafine powders were synthesized by an active plasma-metal reaction method. Gas desorption measurements were conducted to estimate the surface chemistry of the powders after exposure to air and storage at room temperature. H2O, H2, CO2, CO, and NH3 gases were mainly evolved. These gases were considered to be formed by the surface reaction of adsorbed gases on surface oxide of the powders and decomposition of hydroxide-like or ammonialike compounds, which might be produced during a slow oxidation treatment and storage.

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.

Electrical Properties of Liquid Ge–Se Alloys

The conductivities of liquid Ge 1- c Se c alloys on the Ge-rich side decrease monotonically with increasing Se composition. The composition dependence of conductivity at 1023 K exhibits a broad minimum at the composition c =0.72. The composition dependence of thermopower exhibits a maximum and a minimum with positive values at the compositions c =0.55 and 0.6, respectively. The addition of Se to liquid GeSe 2 gives rise to an abrupt increase in thermopower. The electrical behaviour of liquid Ge 1- c Se c alloys with c ≦0.3 was understood from the decrease in the conduction electrons due to the formation of chemical bonds. The conductivity and thermopower near the stoichiometric GeSe and GeSe 2 were analyzed by assuming an energy-dependent conductivity. The conductivity gap at 1023 K varies widely from about 0 eV for liquid GeSe to about 1.4 eV for liquid GeSe 2 .

Hydrogen desorption characteristics of composite Co-TiN nanoparticles

Abstract A new type of nanocomposite particles are produced by an active plasma-metal reaction method. Co-TiN nanocomposite particle with dumbbell-like morphology shows good thermal stability. Hydrogen desorption characteristics are examined by temperature-programmed desorption experiments. Hydrogen desorption is observed at 380–600 K. The effect of CO coadsorption on the hydrogen desorption is examined and no significant effect is observed for the Co-TiN nanocomposite particle. The results are compared with those of Ni-TiN nanocomposite particle.

Preparation of YBaCu oxide precursor by the citrate gel process

Abstract The citrate gel process was developed to prepare YBa2Cu3 oxide superconductor. A citrate-nitrate solution was dehydrated to yield the precursor gel. The thermal decomposition phenomena were studied using thermogravimetric, evolved gas, X-ray diffraction and infrared analyses. The gel was pulverized in air by thermal decomposition at around 200°C. At this stage, the weight loss was 52%. Gradually the loss reached 68% at around 500°C to yield mixed Y2O3, CuO and BaCO3 powders. It was proved that the heat process includes elimination of water, and thermal decomposition of metal carboxylate and other organic species. Violent reaction during pyrolysis at about 200°C was assumed to be mainly the result of an abrupt oxidation of carboxyl groups attached to copper and yttrium ions. Two-step decomposition, first in an inert gas and subsequently in an oxidizing gas atmosphere, has been proposed to depress the violent oxidation.

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.

Electrical Properties of Liquid Pb–Se Alloys

The conductivity of liquid Pb 1- c Se c alloys decreases rapidly with increasing Se composition, and shows a broad minimum and a broad maximum at the composition c =0.55 and 0.75, respectively. The dependence of the thermopower on concentration exhibits a sharp minimum and a broad maximum at the composition c =0.5 and 0.7, respectively. The electronic behaviour of liquid Pb 1- c Se c alloys with c ≤0.35 was studied by the nearly free electron model. The conductivity and thermopower near the stoichiometry PbSe were analyzed by using the equations derived from the Kubo-Greenwood formula. The conductivity gap almost closed for liquid Pb–Se alloys near the stoichiometry.

Comparison of Magnetic and Electrical Properties of Liquid Ag–Te and Ag–Se Alloys

Measurements of the magnetic susceptibility, electrical conductivity and thermo-electric power of liquid Ag–Te and Ag–Se alloys have been extended to the whole composition range. The susceptibility data of liquid Ag–Se alloys near the stoichiometry are very similar to those of liquid Ag–Te alloys. However, the composition dependence of conductivity for liquid Ag–Se and Ag–Te systems exhibits a sharp peak and a deep minimum at the stoichiometry, respectively. The thermopower data of liquid Ag–Te and Ag–Se alloys show a p - n transition at c =0.315 and 0.360, respectively. The conductivity and thermopower of liquid Ag–Se and Ag–Te alloys near the stoichiometry were analyzed by using the equations derived from the Kubo-Greenwood formula.

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.

Electrical properties of liquid Ni–Se and Cu–Se alloys

Abstract The electrical conductivities, σ, of liquid Cu–Se and Ni–Se alloys on the Se-rich side increase on the addition of Cu and Ni, respectively. The σs obtained at 1373 K are 1400, 5000, 4130 and 1920 Ω−1 cm−1 for liquid CuSe, NiSe, CoSe and FeSe, respectively. The thermoelectric power, S, of liquid Cu–Se alloys shows a p–n transition near the stoichiometric composition Cu2Se. The Ss obtained at 1373 K are 70 and 4 μV/K for liquid CuSe and NiSe, respectively. The large values of σ for liquid transition metal–Se alloys are related to the density of d-like states at the Fermi level due to the p–d hybridization.