In this study, ultra-fine SiC-Si3N4 composite powders were synthesized by a vapor phase reaction using TMS (Tetramethylsilane: Si(CH3)4, NH3, and H2 gases at reaction temperatures 1000~1200oC and with input ratios (NH3/Si(CH3)4) 1~3. XRD and TEM were used to analyze the crystalline phases and the average particle sizes of the synthesized composite powders. It was found that the powders obtained under the conditions choosen were all amorphous and spherical with a particle size of about 70~130 nm. The particle size was kept constant regardless of the input ratio, but it decreased with increasing reaction temperature. From the results of FT-IR and EA analysis, it was found that the synthesized powders had been formed from compounds composed of Si, N, C and H. After the synthesized composite powders of different input ratios were heat-treated for 2 hours at 1550oC in a N2 atmosphere, crystalline b-SiC, a-Si3N4 and b-Si3N4 phases coexisted in the case of a low input ratio, while only the crystalline a-Si3N4 phase appeared in the case of a high input ratio.

Keywords: Ultra-fine composite, a-SiC, b-Si3N4, a-Si3N4, Chemical Vapor Deposition (CVD)