Tadao Sato

Microstructural development with crystallization of hexagonal boron nitride

Abstracts are not published in this journal

Influence of plasma modification of titanium carbide powder on its sintering properties

The object of the present investigation is to study the effect of in-flight particle compositional modification, induced by plasma treatment, on the sintering properties of titanium carbide powders. Special attention is given to the role played by carbon-site vacancies and oxygen adsorption on the surface of the powder in the sintering process.

Measurement of Young’s modulus of oxides at high temperature related to the oxidation study

Abstract α-Al2O3, Cr2O3, and α-Fe2O3 specimens were prepared by a sintering process. A 400 – 1000-Hz sine wave was applied to the specimen at 290 – 1273 K. The applied and respond waves were monitored by using force and acceleration sensors. The intensity ratio and phase shift between the applied and respond waves were analysed, and the anti-resonance frequency was obtained. Young’s moduli of α-Al2O3, Cr2O3, and α-Fe2O3 are estimated to be 386, 286, and 220 GPa at 298 K, respectively. The temperature dependence values of these oxides are estimated to be 54.3, 46.9, and 42.0 MPa K-1, respectively. The temperature dependence of Young’s modulus can be classified on the basis of the crystal structure of solids. The estimation of Young’s modulus at 1273K is possible with an error range of 10 – 30 GPa for a crystalline solid if the crystal structure of the solid is known. It is found that the temperature dependence of Young’s modulus depends on the density of the oxides, and an experiment in which well-characterized crystalline solids are used must be conducted to minimize the error range.

High-Temperature Oxidation of Low-Carbon Steel Coated by Solution-Spraying with Cerium and Aluminum Ions

Solutions containing cerium and aluminum ions were sprayed on a low-carbon steel, and high-temperature oxidation of the coated steels was examined. It is found that the oxidation rate was low, and removal of oxide scales was easy for the coated steels. These features were thought to be caused by the suppression of wüstite formation when the coating was applied.

Preparation and Property of Tantalum Fine Powder by Arc-Plasma CVD Method.

Tantalum fine powder has been prepared by means of arc-plasma CVD method. Tantalum chloride was used as raw materials for the formation of the powder. The prepared amount of the powder increased with the reaction time, and a constant mean particle-sized powder was formed without relation to reaction time. On the other hand, the mean particle size decreased with an increase in the ratio of H2/TaCl5 in the reactant gases. From the SEM observation, the powder was found to have a complicated shape. According to the distribution measurement of particle size, the mean particle size of the powder was found to be in the range of 0.08 to 0.3μm and its distribution curve showed normal one. The bulk density, particle density and specific surface area of the powder having the mean particle size of 0.15μm were 1.4×103 kg/m3, 7.0×103kg/m3 and 15.8×103 m2/kg respectively.The mean particle size of tantalum fine powder was found to be controlled by changing the concentration ratio of tantalum chloride and hydrogen in reactant gases.

Fundamental studies on the elimination of impurity elements in aluminum using segregation phenomena.

The purification behavior in liquid aluminum alloys containing impurities of Mn, Fe and Si was investigated by the segregation process of impurity elements. The distribution of impurity was examined as a function of the solidified length after liquid aluminum alloys were unidirectionally solidified. For an aluminum containing Mn the concentration was the same as the initial one and no segregation of Mn was observed. Thus, the purification of an aluminum containing Mn was difficult by this method. For an aluminum containing Fe the distribution of Fe depended on the initial concentration. This behavior was explained by the shape change in the solid-liquid interface. For an aluminum containing Si the concentration was lower than the initial one. This indicated that the segregation process was effective to remove Si from the liquid aluminum. The purification degree for the aluminum alloys depended on the solidification condition. This was explained in terms of the equilibrium distribution coefficient and solid-liquid interface shape. The purification of an aluminum containing 0.014 wt%Fe or 0.107 wt%Si proceeded in accordance with the theoretical solidification curve when unidirectionally solidified with mechanical stirring.