High temperature structure evolution of macroporous SiOC ceramics prepared by a sol–gel method

Macroporous SiOC ceramics have been prepared by the pyrolysis of the preceramic precursor obtained from methyltrimethoxysilane and dimethyldimethoxysilane. The structural evolution of the sol–gel derived SiOC ceramics at high temperatures was investigated using SEM, TG, FTIR, XRD and Raman spectra. The SiOC xerogel exhibited a porous structure consisting of cross-linked spherical gel particles. The structural rearrangement appeared and the SiOC ceramic particles changed from spherical to irregular shape after thermal pyrolysis. The ceramic yield was found to be approximately 70% until 1400 °C, and decreased to 38% at 1600 °C owing to carbothermal reduction. The SiC nanorods were in situ formed from macroporous SiOC ceramic wall at 1600 °C. The β-SiC nanocrystals precipitated from the SiOC matrix at 1400 °C and grew up to 4.6 nm at 1600 °C. The graphitization degree of free carbon increased with the increase of pyrolysis temperature.