SYNTHESIS AND CHARACTERIZATION OF SIC-SI3N4 COMPOSITES BY DUAL IRRADIATION OF CO2 AND EXCIMER LASERS

Ultrafine SiC and Si/C/N powders were prepared by photochemical reacti ons of SiH4, C2H4 and NH3 under dual irradiation of CO2 and excimer la ser beams, Effects of process variables on the characteristics of thes e powders wen studied. Enhanced crystallization and size reduction of SiC particles were observed by irradiation of excimer laser, Growth of the particles proceeded by CO2 laser irradiation, whereas refinement of the particles occurred by ablation of the initially formed particle s under excimer laser irradiation. Uniformly mixed state of silicon, c arbon and nitrogen atoms in the Si/C/N composite particles was confirm ed by TEM and XPS analyses. Aerosol particles of SiC-Si3N4 with yttriu m and aluminum compounds were directly transferred and impinged on a s ubstrate to form green compacts in a closed apparatus. It was found ch at the vapor-phase reaction using dual-type CO2 and excimer lasers off ered a feasible method for controlling composition, crystallinity and particle size in the preparation of ultrafine single- and multi-compon ent powders.