Synthesis of high purity Si3N4 and SiC powders by CVD method

Fine, sub-micrometer, amorphous powders of SiC and Si3N4 have been prepared from SiH4 - NH3 and C2H2 - SiH4 gaseous systems respectively, in tubular flow reactor. The Si3N4 powder prepared at 1373 K and NH3/SiH4 molar ratio of 11.5 is near stoichiometric in composition, isometric in morphology and the particle size is in range of 50 - 150 nm. The particle size of SiC powder prepared at 1373 K and SiH4/C2H2 molar ratio of 2:1 was from the interval 10 to 100 nm. Recrystallization of these powders at 1853 K did not change substantially the particle size distribution and confirmed the Si3N4 and SiC as major compounds respectively. The content of metal impurities as Al, Cr, Cu and Fe in the presented powders is one order of magnitude lower compared to the commercially available powders prepared by other methods.