EFFECT OF HEAT TREATMENT ON THE STRUCTURE OF SiC−Si3N4 COMPOSITE ULTRAFINE POWDER

Abstract

Effect of heat treatment on the structure of SiC−Si3N4 composite ultrafine powder was studied. SiC-Si3N4 composite ultrafine powder synthesized by laser-induced gas-phase reaction was heat-treated at various temperatures below 1773 K in 99% Ar +1% H2 gas mixture. The change of the structure was studied by chemical analysis, x-ray diffraction (XRD), and transmission electron microscope (TEM). The structure of the powder did not change significantly in lattice constant, particle size, and composition by the treatment up to 1573 K . The structure of the powder changed drastically by the treatment above 1673 K . The broad XRD pattern due to β- Si for the original powder changed to the four phases of β- SiC , Si and α, β- Si 3N4 by the treatment at 1773 K , accompanied by large increases in particle size and lattice parameter, and decreases in nitrogen content and specific surface area.