Stable highly porous silicon oxycarbide glasses from pre-ceramic hybrids

Abstract

The introduction of Si–H bonds into the structure of a sol–gel derived ceramic material leads to a hybrid that generates a highly porous silicon oxycarbide material stable up to pyrolysis temperatures above 1200 °C. The fractal analysis reveals an increase in the pore anisotropy in the first stages of ceramisation of the pre-ceramic hybrid material indicating the creation of a narrow interconnected porous (<4 nm) network stable with temperature. The formation of C-enriched units during pyrolysis supports the porous structure throughout the thermal treatment strengthening against collapse. The presence of highly reactive bonds gives rise to huge differences in the pre-ceramic hybrid which radically influence the characteristics of the derived silicon oxycarbide materials. The hybrid material without Si–H bonds displays an open macroporous microstructure and during the thermal treatment the gaseous species generated inside can easily escape generating micropores, which tend to disappear as the temperature increases. However the presence of highly reactive Si–H bonds produces a fully dense material and during pyrolysis the different paths followed by the redistribution reactions favour the creation of a micro–mesoporous structure which is preserved up to 1200 °C.