Preparation and characterization of mesoporous silicon oxycarbide ceramics without free carbon from polysiloxane

Mesoporous silicon oxycarbide ceramics without free carbon were prepared by pyrolysis of cross-linked polysiloxane at different temperatures (1300–1450 °C) followed by post treatments. The post treatments comprised two steps (HF etching and oxidation at 650 °C in air). The sample pyrolyzed at 1300 °C after post treatments exhibits the largest specific surface area (SSA) reaching up to 204 m2/g and the biggest total pore volume (0.58 cm3/g) with an average pore size of 11.4 nm. Increasing pyrolysis temperature will lead a quick decline of SSA and total pore volume. The thermal stability of pore structure of the sample pyrolyzed at 1300 °C with post treatments was investigated in air. The SSA and total pore volume almost keeps the same up to 750 °C, and subsequently decreases with a high speed. The most possible reason is the pores are severely closed by viscous flow of SiO2 produced from SiC nanocrystallites.