Fabrication and microstructure evolution of monolithic bridged polysilsesquioxane-derived SiC ceramic aerogels

SiC aerogels are representative high-temperature ceramic aerogels that have demonstrated extensive potential utility in the thermal insulation field under extreme conditions. Although the efficient fabrication of monolithic and highly crystalline SiC aerogels is crucial, it remains highly challenging. Herein, a one-step pyrolysis strategy of a bridged polysilsesquioxane (BPSi) aerogel precursor is reported. The preceramic BP aerogel was prepared via a sol-gel method followed by vacuum drying, and the subsequent pyrolysis process conveniently converted the BPSi aerogel precursor into a SiC aerogel. This circumvents the need for harsh synthetic conditions, high-cost noble metal catalysts, special drying, and additional calcination processes. Furthermore, a competitive mechanism between the "gas-escape" caused by the volatilization of low molecular compounds and carbothermal reduction reaction, and the "volume-shrinkage" resulting from high-temperature sintering was proposed to explain the evolution of phase composition and pore hierarchy of BPSi-derived ceramic aerogels.