Sol-gel synthesis of preceramic polyphenylsilsesquioxane aerogels and their application toward monolithic porous SiOC ceramics

A facile route toward monolithic porous SiOC ceramics from preceramic polyphenylsilsesquioxane (PSQ) aerogels was reported herein. The supercritical drying derived aerogels were synthesized through a sol-gel process wherein Span-20 was used to suppress the phase separation that caused by the oligomers of hydrolysed precursors. It was found that the amount of Span-20 had a significant effect on the microstructure of PSQ aerogels. At an optimized condition, as-synthesized aerogel showed a narrow pore size distribution (~12 nm) and a high specific surface area (632.27 m2/g). Moreover, the structure evolution as well as the phase transformation of the aerogel at different sintering temperatures were simultaneously investigated. Porous amorphous SiOC monoliths with specific surface areas up to 247.06 m2/g were synthesized under 1200 ℃. While for aerogels pyrolyzed over 1400 ℃, the microstructure collapsed and only bulk SiC ceramics were obtained.