Hiroshige Suzuki

A model of densification with simultaneous grain growth

A densification model in which grain growth and densification progress simultaneously in a powdered compact produced the relation between the relative density ρ and average particle/grain size R, logρ (1−ρ0)/ρ0(1−ρ) =k4KG log(R/R0), where R0 is the initial particle size, ρ0 is the green density, KG is the dimensionless parameter dependent on the spread of the distribution of particle/grain size in the compact, and k4=SS/(1−ρ) S (SS is the pore surface area of the compact and S is the total area of particles/grains). Sintering data of BaCl2‐ and halogen‐doped MgO compacts deviated slightly from the theoretically calculated relation. This discrepancy is interpreted in terms of the heterogeneously packed structure of particles/grains.

The thermal diffusivity of pyrolytic graphite at high temperatures

Abstract The thermal diffusivity of three pyrolytic graphites was measured using the modulating electron beam method over the temperature range from 1300°C to 1900°C. One of the specimens was as-deposited at 2500°C, and the others were the same heat-treated at 3000°C after deposition. The mean free path of phonons was estimated by analysis of the experimental data. The mean free path seems to be independent of temperature in the direction perpendicular to the deposition plane; being 4·8 A for the as-deposited specimen, 6·4 and 7·4 A for the two heat-treated ones, respectively. The temperature dependence of the mean free path parallel to the deposition plane cannot be expressed in analytical form. However, a monotonie decrease from 91 A at 1330°C to 56 A at 1980°C is indicated by a tentative approximate calculation.

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.

Irradiation effects of boron carbide used as control rod elements in fast breeder reactors

Abstract The paper describes radiation effects on 84C pellets used as control rod elements in the Enrico Fermi Fast Breeder Reactor. Pellet swelling (Δ V/V ) caused by irradiation was less than 1% in which crystal lattice swelling was less than 20%. Many microcracks, a main cause of pellet swelling, appeared in the irradiated pellets. The production of microcracks was related to graphite precipitation in the pellets before irradiation. Open pores which did not exist in the unirradiated pellets were formed in the irradiated ones. In a unit cell of B4C, the α-axis elongated by 0.025 A and the c- axis shrank by 0.07 A by irradiation. Moreover, we found three recovery stages which were from room temperature to 400°C, from 400 to 750°C and from 850 to 1100°C. The recovery mechanisms in the irradiated pellets are discussed in terms of the helium behavior.

Reactions between SiC and Pd or CeO2 at High Temperatures

Mixtures of SiC and Pd or CeO2 were heated in air and in vacuum, and the reaction products were determined by powder X-ray diffractometry. High temperature X-ray diffractometry was also conducted t...

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

Recent trends in the development of fine ceramics in Japan

Abstract In Japan, the 10 year programme initiated by the Ministry of International Trade and Industry (MITI) on the fine ceramics research and development project has been in progress since 1981. In the first phase of the project, bench-scale tests on the preparation of fine powders of Si 3 N 4 and SiC, and the forming and sintering of commercial powders on a test piece scale, were carried out. It is believed that the objectives in this phase have almost been accomplished successfully. In the second phase, work on larger-scale powder preparation, on processing full-sized samples of simple shape, on cutting and grinding, on property measurements, on non-destructive evaluation and on other tasks are ongoing. In addition to the MITI programme, many other research and development programmes are being conducted in Japan. The interesting results and the present status of these are reported. Research and development programmes are being conducted to modify the processing, to improve properties, to increase reliability in strength and to reduce production cost. These topics include improved injection moulding and ultrahigh pressure cold isostatic pressing. Special efforts have been made to increase the Weibull modulus and fracture toughness of these products and also to reveal relationships between these properties and the microstructure. Finally, the applications of fine ceramics in Japan are described in Appendix A.

Normal grain growth in porous and dense compacts

A rate equation of grain growth and a distribution function of grain radii were derived from the statistical viewpoint. The derived equation and function were successfully applied to the analysis of both the grain growth and grain radius distribution data in Cr-doped MgO. The diffusion coefficients of this sample were 103 times larger than the oxygen self-diffusion coefficients in pure MgO.

Effect of neutron irradiation on thermal conductivity, electric resistivity, and thermal expansion of boron carbide

Boron carbide possessing porosities of 91 and 77% theoretical density (T.D.) were irradiated at about 300 deg C to 6.0 x 10/sup 18/ ~ 3.3 x 10/sup 19/ n/cm/sup 2/ in helium atmosphere. The thermal conductivity, the electric resistivity and the linear thermal expansion were determined. Upon irradiation to 3.3 x 10/sup 19/ n/cm/sup 2/, cracking occurred in all of the 91% T.D. specimens and in two of the five 77% T.D. specimens. The thermal conductivity changed with irradiation more markedly in the case of the 77% T.D. specimen, which also increased its specific clectric resistivity by a factor of 10/sup 4/, while that of the 91% T.D. specimen increased by less than 10-fold. This significant difference in thermal and electric conductivity change by irradiation is attributed to the difference in microstructure. It was observed that the recovery of radiation damage began at about 300 deg C when the specimens were sub!ected to heating and the changes observed in respect of thermal conductivity, electric resistivity and linear thermal expansion. (auth)

Preparation of β-silicon carbide sintered ceramics

Current status of research and problems involving β-SiC ceramics in Japan is summarized, focusing on microstructural changes during sintering. SiC has been studied extensively for the past three decades for technical purposes, but generalized research such as on the detailed mechanism of the sintering process has not yet been fully discussed. This paper describes research on SiC for structural materials, and in addition, the issues related to activating SiC industries are discussed based on experimental results.