溶胶-凝胶法制备SiC前驱体

Synthesis of SiC Precursors by Sol-Gel Process

为了尽量减少硫、氯等有害元素的含量，本文用不含有害元素的草酸和六次甲基四胺（HMTA）为催化剂，正硅酸乙酯（TEOS）为硅源，酚醛树脂为碳源，成功探索出了制备SiC前驱体的两步法溶胶-凝胶工艺．第一步TEOS在草酸的催化下预水解，第二步用HMTA加速凝胶．实验得出了草酸含量、预水解时间、预水解温度等因素对凝胶形成的影响规律，进而讨论了水解和缩合的机理．所得SiC前驱体为黄色透明的玻璃态，由纳米级的颗粒组成，结构均匀而精细．

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.