INSITU SYNTHESIS OF SILICON-CARBIDE WHISKERS FROM SILICON-NITRIDE POWDERS

Silicon carbide whiskers were synthesized in situ by direct carbothermal reduction of silicon nitride with graphite in an argon atmosphere. Phase evolution study reveals that the formation of beta-SiC was initiated at 1400-degrees to 1450-degrees-C; above 1650-degrees-C silicon was formed when carbon was deficient. Nevertheless, Si3N4 could be completely converted to SiC with molar ratio Si3N4: C = 1:3 at 1650-degrees-C. The morphology of the SiC whiskers is needlelike, with lengths and diameters changing with temperature. SiC fibers were produced on the surface of the sample fired at 1550-degrees-C with an average diameter of 0.3-mu-m. No catalyst was used in the syntheses, which minimizes the amount of impurities in the final products. A reaction mechanism involving the decomposition of silicon nitride has been proposed.