Synthesis of SiC Precursors by Sol-Gel Process

To minimize the contamination of detrimental elements such as sulfur and chlorine,a two-step sol-gel process was successfully developed to synthesize SiC precursors with oxalic acid and hexamethylenetetramine(HMTA) as the catalysts,which are free of sulfur and chlorine. Tetraethoxysilane(TEOS) and phenolic resin were used as the silicon source .and carbon source,respectively. At the first step TEOS was prehydrolyzed under the catalysis of oxalic acid.At the second step HMTA was added to accelerate gelation.The dependence of products on oxalic acid content, prehydrolysis time,and prehydrolysis temperature was concluded. The mechanisms of hydrolysis and condensation were discussed.The SiC precursors obtained were transparent yellowish glassy solids,with homogeneous microstructure composed of nanometer sized particles.