Finely divided Si{sub}3N{sub}4-SiC powders and materials on their basis

摘要

The aim of the present work was to investigate the preparation of homogeneous ultrafine composite powders of Si{sub}3N{sub}4-SiC in one stage plasma process and characteristics of ceramics, produced from these powders. The chemical and phasecomposition of produced powders depend on particle size distribution of raw powder, feeding rate of silicon, flow rate of ammonia and hydrogencarbon, their ratio. The specific surface area particle size and crystallinity of produced compounds depend onconcentration of particles in the gas flow and the cooling rate of products. Variation of above mentioned parameters allows to produce Si{sub}3N{sub}4 and Si{sub}3N{sub}4-SiC powders with the specific surface area from 24 up to 80 m{sup}2/g and content of free silicon or free carbon less than 0,5 mass. %. The content of SiC in the composite powders is from some percents up to 90 mass. %. The main phases of produced powders areα-Si{sub}3N{sub}4, β-Si{sub}3N{sub}4, β-SiC and X-ray amorphousSi{sub}3N{sub}4. Thr dense Si{sub}3N{sub}4- and Si{sub}3N{sub}-SiC-based materials were prepared both by hot pressing at 1800℃ and loading pressure of 30 MPa and gas pressure sintering at temperatures of l60-1900℃ and 0,5 MPa nitrogen pressure. Theplasma composites have smaller pore channel diameter and the higher densification rate, the microstructure of produced materials is more fine-grained than for materials sintered from commercial powders.