Interfacial SiC formation in polysiloxane-derived Si–O–C ceramics

Poly(methylsilsesquioxane) (CH3SiO1.5)n (PMS) loaded with 40 vol.% Si-filler powder was pyrolyzed in inert atmosphere up to 1400 °C to fabricate Si–O–C composite ceramics. The evolution of the interface microstructure between the filler and the matrix was studied by high resolution electron microscopy (HREM), energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. While below pyrolysis temperatures of 1000 °C no filler reaction was observed (inert filler regime), a porous interface layer of nanosized ß-SiC was formed at reaction temperatures above 1200 °C. Due to a high fraction of open porosity of 13% (1000 °C) to 19% (1400 °C) in the polymer-derived Si–O–C matrix, gas-phase transport and reaction processes involving CO and SiO as the dominant species are likely to occur at the interface boundary layer.