Facile synthesis of resorcinol-formaldehyde/silica composite aerogels and their transformation to monolithic carbon/silica and carbon/silicon carbide composite aerogels

Resorcinol-formaldehyde/silica composite (RF/SiO ₂) gels were synthesized in one pot by simply mixing the monomers and dried under supercritical carbon dioxide to form RF/SiO ₂ aerogels. Carbon/silica composite (C/SiO ₂) and carbon/silicon carbide composite (C/SiC) aerogels were formed from the RF/SiO ₂ aerogels after carbonization and carbothermal reduction. The as-prepared C/SiC products exhibited a preserved monolithic morphology similar to the original templates and were composed of carbon particles and α-SiC nanocrystals. The C/SiC specimen possessed a BET surface area of 892 m ²/g and a porosity of 94.8%, both of which were significantly higher than the BET surface area and porosity of C/SiO ₂ and RF/SiO ₂ aerogels. The resulting C/SiC monolith was stable up to temperatures near 550 °C, which is almost 150 °C higher than what C/SiO ₂ aerogels can tolerate.