Synthesis of Silicon Carbide Powders from Methyl-Modified Silica Aerogels

beta-silicon carbide (SiC) powders were synthesized by the carbothermal reduction of methyl-modified silica aerogel/carbon mixtures. The correlations between the phase evolution and morphologies of the SiC powders and the C/SiO(2)ratio were investigated. At a C/SiO(2)ratio of 3, beta-SiC formed at 1425 degrees C and single-phase SiC powders were obtained at 1525 degrees C. The methyl groups (-CH3) on the silica aerogel surfaces played important roles in the formation of SiC during the carbothermal reduction. SiC could be synthesized from the silica aerogel/carbon mixtures under lower temperature and C/SiO(2)ratios than those needed for quartz or hydrophilic silica. The morphology of the SiC powder depended on the C/SiO(2)ratio. A low C/SiO(2)ratio resulted in beta-SiC powder with spherical morphology, while agglomerates consisting of fine SiC particles were obtained at the C/SiO(2)ratio of 3. High-purity SiC powder (99.95%) could be obtained with C/SiO2= 0.5 and 3 at 1525 degrees C for 5 h.