Yoshio Murase

Thermal changes in texture of aggregates of ultra-fine crystallites in hydrolysed zirconia particles

Abstract Zirconia particles of about 1000 × 1000 × 300 A in size, which were aggregates of rectangular shaped and regularly oriented ultra-fine crystallites of about 30 × 100 A, were prepared by hydrolysis from 0.1 moll-1 ZrOCl2 solution. Changes in the texture of the particles on heating were studied by electron microscopy. The growth of the crystallites occurred predominantly at peripheries of the particles at 500°C and in the whole particles at 600°C, resulting in crystallites of 160–360 A in diameter at 800°C. The voids which were present initially among the crystallites, coalesced and increased in size at temperatures up to 600°C, but diminished above 800°C. Single crystals and (100) twins were formed at 1000°C.

Large surface area of SiO2-coated fibrous crystals of alumina after heating at > 1573 K

By coating with SiO2, fibrous crystals of alumina, prepared from ammonium aluminium carbonate dihydroxide [(NH4)AICO3(OH)2], are found to have large surface area ( >35 m2 g –1) even after heating at 1573 K.

Preparation of oxide superconductive composite by an electrostatic mixing process

Abstract This paper is concerned with the proposal of aerosol composite particles as raw powder for preparing superconductive composite. The composite particles were synthesized by using an electrostatic adhesion force acting between the electronegatively charged Ba2YCu3O7−x particle and the electropositively charged BaZrO3 particles. The amount of BaZrO3 coated on a Ba2YCu3O7−x particle was controlled by adjusting the ratio of the imparted charge. Superconductive composite bulk body was obtained, in which the fine BaZrO3 particles, less than 100 nm in diameter, were uniformly distributed. The improvement of Jc values of the composite sintered body was attributed to the contribution of charging to flux pinning enhancement caused by homogeneous distribution of pinning centers.

Crystalline products and their formation mechanism in thermal hydrolysis of ZrOSO4 solution

Solid products were prepared from mixtures of zirconyl carbonate and sulphuric acid solution under thermal hydrolysis at 240°C. These crystalline products and their formation mechanism were investigated by evaluating the amount of products, and by X-ray diffraction analysis and TEM observation. The solid products precipitated were zirconium oxide sulphates (ZOS, PZOS, ZrOSO4·H2O) and m-ZrO2. The area and thickness of the fine plate-like crystals of ZOS increased with increasing concentration of the solution and hydrothermal treatment time. For thin starting solutions, the precipitation velocity and the amount of PZOS increased. For thick starting solutions, those of ZOS increased. For 0.5 mol/l−1 ZrOSO4 solution (ZS0.5) from the thin solution, PZOS crystallized early and m-ZrO2 crystallized by releasing sulphuric acid ions in PZOS with treatment time. For ZS2.5 from the thick solution, ZrOSO4·H2O was crystallized by increasing the proportion of sulphuric acid ions to zirconium ions in the solution, which was caused by ZOS precipitation.

Preparation of acicular particles of α-alumina

Aluminum ammonium sulfate (AA) solution (0.1 mol/l) and ammonium hydrogen carbonate (AHC) solution (1.2 mol/l) were allowed to react at room temperature. The precipitates formed were kept with the mother liquor in a closed vessel and aged at 100 °C. Acicular-shaped crystalline particles of Al(NH 4 )CO 3 (OH) 2 , (AACH), were obtained after the elongated aging period. Acicular α-alumina particles were obtained through the thermal decomposition at 1300 °C out of the AACH particles which were previously treated with a small amount of tetraethoxysilane (about 1.6 wt. % of SiO 2 ).

Microstructure of binary silver borate glasses and estimation of electronic conductivity by the polarization method

Abstract Studies pertinent to the total electrical conductivity, ionic and electronic conductivities, microscopic observation and emf measurement were made for the glasses of the system x Ag 2 O·(100− x ) B 2 O 3 ( x = 22, 27 and 38 mol%). The temperature dependence of the total electrical conductivity for all glasses exhibited a linearity against 1/ T , indicating that the ionic conductivity prevails over electronic conductivity in the present glass system. Electronic conductivity was estimated by a polarization method and was found to be two to three orders of magnitude smaller than the total electrical conductivity. Crystalline diffraction rings were observed in the microstructure of glasses by electron diffraction measurement, which indicated the presence of metallic silver. The higher the Ag 2 O content in the glass, the larger the diameter of the silver particles. The electronic conduction of these glasses probably depends on the microstructure, which causes deposition of metallic silver particles.

Preparation of a microporous cell by dissolution of core particles within a core-shell-type composite powder-preparation of titania or silica microporous cells

Core-shell-type composite powders were prepared by hydrolysis of titanium tetraisopropoxide or tetraethyl orthosilicate in a dispersion of core particles adsorbed with water in hexane. Microporous cells could be made of the composite powder dissolved within the core particles in acetic acid solution. The content of titania in BaCO33-TiO2 composite powder was controlled by the amount of water adsorbed. The pore volume of the microporous cell changed with the content of titania. BaCO3-TiO2 composite powder was heated at 600°C for 10 h and barium ions in the core particles were diffused to titania. Thus, microporous cells composed of the BaTiO3 ultrafine particles were prepared.