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Reaction sintering of silicon
282
NEWS SILICON
REACTION NITRIDE
According to recent studies by S. Dutta and B. Buzek (NASA Lewis Res. Ctr.) the inclusion of 10 wt.-% yttria-stabilized zirconia to silicon nitride shows a great improvement over MgO-doped Si,N,, in such properties as hot strength (very little strength degradation at 1400 o C) and creep resistance. Oxidation resistance at 1370 o C was similar to that of SIC.
TRICHROMIUM
CARBIDE
Three Japanese firms (Nippon Tungsten Co., Nippon Steel Co. and Kubota Ltd.) have started production of trichromium carbide, which could replace SIC in some refractory applications. It has oxidation resistance of up to 12OO’C with 20-45 kg/mm2 bend strength at the same temperature. The material is said to be produced using a special sintering additive and hot isostatic pressing.
A STUDY OF CERAMIC PREPARATION IN JAPAN
POWDER
Akio Kato [Am. Ceram. Sot. Bull., 66 (4) (1987) 647-6501 reviews the current status of ceramic powder preparation studies in Japanese universities, with special attention to the sintering properties of fine powders (CVD MgO, Si,N,, SIC) and discussion of their relation with preparation methods. He also considers the commercial production of ceramic powders in Japan (Al,O,, ZrO,, Si,N,, Sic). The author emphasizes that studies on powder preparation have tended to increase in number every year over the last seven years, providing new and non-conventional techniques, and that the current high cost of fine powders is the main thing holding back their wide application, rather than the technological difficulties encountered during their preparation. Reactivity
of Solids,
News
SINTERING
OF SILICON
The consolidation, sintering and nitridation of very fine silicon particles (0.1-0.2 pm) is studied by O.J. Gregory and SangBoek Lee [J. Am. Ceram. Sot., 70 (3) (1987) C52-CSS]. Because of its small particle size, Si compacts were nitrided at higher rates and lower temperatures than those usually employed. The authors propose an optimal temperature progression and the employment of lower temperatures and higher nitrogen pressures to achieve full densification. During sintering, the intra-agglomerate pores tended to shrink, whereas the interagglomerate pores grew. The a to p ratio in the resulting SijN, compacts was independent of the nitriding parameters.
EFFECT DURES SODIUM PHATES
OF SYNTHESIS PROCEON THE STRUCTURE OF ZIRCONIUM SILICOPHOS-
High-temperature solid-state reaction, hydrothermal synthesis, the aqueous silica gel technique and sol-gel synthesis are the four methods used for preparing Nasicon (Na Super Ionic Conductor) which are compared by A. Moini and A. Clearfield [Advanced Ceramic Materials, 2 (2) (1987) 1731. Both the structural differences and the stoichiometry are evaluated.
ULTRAFINE
FERRITES
By combustion/decomposition of solid solution precursors (hydrazinium metal hydrazinecarboxylate hydrates), P. Ravindranathan and K.C. Pate1 [Am. Ceram. Sot. Bull., 66 (4) (1987) 6881 prepared ultrafine ferrites having particle sizes of 6-22 nm and a surface area of loo-140 m2/g. In this way the sintering of the powder was achieved at lower temperatures than usual.
Brief, Vol. 4, No. 3, December
1987
NEWS SILICON
REACTION NITRIDE
According to recent studies by S. Dutta and B. Buzek (NASA Lewis Res. Ctr.) the inclusion of 10 wt.-% yttria-stabilized zirconia to silicon nitride shows a great improvement over MgO-doped Si,N,, in such properties as hot strength (very little strength degradation at 1400 o C) and creep resistance. Oxidation resistance at 1370 o C was similar to that of SIC.
TRICHROMIUM
CARBIDE
Three Japanese firms (Nippon Tungsten Co., Nippon Steel Co. and Kubota Ltd.) have started production of trichromium carbide, which could replace SIC in some refractory applications. It has oxidation resistance of up to 12OO’C with 20-45 kg/mm2 bend strength at the same temperature. The material is said to be produced using a special sintering additive and hot isostatic pressing.
A STUDY OF CERAMIC PREPARATION IN JAPAN
POWDER
Akio Kato [Am. Ceram. Sot. Bull., 66 (4) (1987) 647-6501 reviews the current status of ceramic powder preparation studies in Japanese universities, with special attention to the sintering properties of fine powders (CVD MgO, Si,N,, SIC) and discussion of their relation with preparation methods. He also considers the commercial production of ceramic powders in Japan (Al,O,, ZrO,, Si,N,, Sic). The author emphasizes that studies on powder preparation have tended to increase in number every year over the last seven years, providing new and non-conventional techniques, and that the current high cost of fine powders is the main thing holding back their wide application, rather than the technological difficulties encountered during their preparation. Reactivity
of Solids,
News
SINTERING
OF SILICON
The consolidation, sintering and nitridation of very fine silicon particles (0.1-0.2 pm) is studied by O.J. Gregory and SangBoek Lee [J. Am. Ceram. Sot., 70 (3) (1987) C52-CSS]. Because of its small particle size, Si compacts were nitrided at higher rates and lower temperatures than those usually employed. The authors propose an optimal temperature progression and the employment of lower temperatures and higher nitrogen pressures to achieve full densification. During sintering, the intra-agglomerate pores tended to shrink, whereas the interagglomerate pores grew. The a to p ratio in the resulting SijN, compacts was independent of the nitriding parameters.
EFFECT DURES SODIUM PHATES
OF SYNTHESIS PROCEON THE STRUCTURE OF ZIRCONIUM SILICOPHOS-
High-temperature solid-state reaction, hydrothermal synthesis, the aqueous silica gel technique and sol-gel synthesis are the four methods used for preparing Nasicon (Na Super Ionic Conductor) which are compared by A. Moini and A. Clearfield [Advanced Ceramic Materials, 2 (2) (1987) 1731. Both the structural differences and the stoichiometry are evaluated.
ULTRAFINE
FERRITES
By combustion/decomposition of solid solution precursors (hydrazinium metal hydrazinecarboxylate hydrates), P. Ravindranathan and K.C. Pate1 [Am. Ceram. Sot. Bull., 66 (4) (1987) 6881 prepared ultrafine ferrites having particle sizes of 6-22 nm and a surface area of loo-140 m2/g. In this way the sintering of the powder was achieved at lower temperatures than usual.
Brief, Vol. 4, No. 3, December
1987