Oxidation Resistance Improvement of Carbon Aerogel Composites by Pyrolyzed SiOC Ceramic Inner Coating

To modify the oxidation resistance of carbon fiber-reinforced carbon aerogel composites for thermal insulators, SiOC precursor sol was prepared using dimethyldiethoxylsilane (DMDES) and methyltrimethoxysilane (MTMS) as raw materials; then the carbon aerogel composites were impregnated with the SiOC precursor sol, after gelation, aging, solvent exchanging, ambient drying, and pyrolysis, SiOC ceramic inner coating was deposited in the carbon aerogel composites. Anti-oxidation composites were obtained by repeating this procedure for several cycles. Results show that, for the composite deposited with three cycle SiOC coatings, the density is 0.77 g/cm(3) (0.20 g/cm(3) for the aerogel composite without SiOC coating) and the thermal conductivity at 25 degrees C is 0.33 W/m.K (0.11 W/m.K without SiOC coating). The mass loss after 1600 degrees C, 20 min heat treatment in air decreases with increasing the depositing cycles. For the composite with three cycle SiOC coatings, the mass loss is 10.33% and the linear shrinkage is 1.16%. It evidently indicates that infiltrating organic-inorganic silica sol and then carbonizing to form SiOC coatings on the inside and outside surface of the nano-porous carbon aerogel composites can improve their oxidation resistance properties.