Effect of pyrolysis temperature on the pore structure evolution of polysiloxane-derived ceramics

Homogeneous silicon oxycarbide (SiOC) ceramic powders were prepared by pyrolysis of cross-linked polysiloxane at different temperatures (1250–1500 °C) under vacuum. The effect of pyrolysis temperature on the pore structure evolution was investigated by means of N2 adsorption, SEM, XRD, IR and element analysis (EA). Studies showed that predominate mesoporous ceramics with the average pore size in the range of 2–13 nm were obtained after pyrolysis in this temperature range. The pore structure transformation is strongly correlated with the thermolytic decomposition process of the used precursor, such as phase separation and carbothermal reduction. At relatively lower temperature (1250–1350 °C), the ceramics had a relative small specific surface areas (35 m2/g) owing to the low degree of carbothermal reduction. However, as the carbothermal degree had an obvious augment at relative higher temperature (1400–1450 °C), the specific surface areas and total pore volume increased and reached to the maximum of 66 m2/g and 0.214 cm3/g, respectively, and subsequently decreased rapidly after 1500 °C for the reason of partial sintering of the nano-sized SiC derived from polysiloxane.