Teizo Hase

Formation process of β-SiC during reaction-sintering

Abstract Reaction-sintered bodies of β-SiC were prepared from various carbon powders, such as non-graphitizable carbon, petroleum coke, artificial graphite and kish graphite. The maximum particle size of carbon powder that can be completely siliconized was estimated from the difference of particle size distribution between carbon raw materials and unreacted carbon observed in the reaction-sintered bodies. The lattice strain of β-SiC formed in situ was measured by an X-ray line broadening method. It was suggested from these data that the formation process of β-SiC during the reaction-sintering was influenced by the microstructure of carbon raw materials; the crystallite size and the degree of preferred orientation of crystallite.

Shrinkage ofβ-SiC powder treated with a mixed acid of HF and HNO3

Le traitement par un melange 1:1 de HF et HNO 3 provoque un leger retrait (inferieur a 3%) de compacts de poudre de β-SiC entre 1400° et 1600°C. On propose deux mecanismes possibles pour expliquer ce phenomene

Initial-Stage Sintering of Sol-Gel Urania

The initial-stage sintering mechanism of hyperstoichiometric urania prepared by sol-gel process was determined in relation to temperature during constant rate heating (CRH). The urania powder used in this experiment was prepared by crushing in Ar atmosphere the micro- spheric gel of UO2 obtained by sol-gel process, and reducing the resulting powder by heating in H2 for 1 hr at 500°C. The results obtained from densification measurements indicated that the initial-stage sintering proceeded in two phases governed by different shrinkage mechanisms, as follows. 1. The sintering up to 675°C would be due to a mechanism such as rearrangement of grains and/or plastic flow. 2. Sintering from 750° to 800°C was interpreted as being controlled by uranium volume diffusion. The estimated diffusion coefficient D = 1.42×10−6 exp(-52,500/RT) cm2/sec. This value agreed in order of magnitude with the uranium diffusion coefficients measured by other workers for hyperstoichiometric urania.

A New Aspect of Grain Growth of Sol-Gel Urania

Grain growth in sol-gel urania compacts was determined as a function of temperature by observing with scanning electron microscope the fractured surface of compacts heated up to predetermined temperatures at a constant rate of heating. Rapid grain growth, unexplainable by currently accepted square or cubic growth kinetics, was observed to occur in the sintered compact when the density reached 70 to 75%T.D., which was attained at about 1,000°C in the case of heating rate of 5°C/min. It was considered that this rapid grain growth proceeded by plastic flow of which driving force was the surface tension of the grains, when a large number of primary grains were closely packed against each other, i.e., arranged in quite high coordination number. A rough estimation showed that the rate of coalescence of grains was dependent on the temperature and the grain size or the surface tension of the material, and that the multi-grain-coalescence model, which was previously reported for the case of sintering of BeO, could...

DEPOSITION RATE OF PYROCARBON IN A FLUIDIZED BED.

For the development of coated particle fuels for use in high temperature gas-cooled reactors, the relation between the conditions of deposition of pyrocarbon (PyC) and the inherent characteristics of this material has been widely studied by many workers. The results have revealed that the nature of coating gas, the temperature, the total gas flow rate and the initial bed surface area strongly influenced the coating rate, the efficiency and the