Preparation of Silicon Oxycarbide Composites Toughened by Inorganic Fibers via Pyrolysis of Precursor Siloxane Composites

The optimization of silicon oxycarbide (SiOC) synthesis (sol-gel/pyrolysis) is described, starting from methyltriethoxysilane, dimethyldiethoxysilane, tetraethoxysilane, ethyltriethoxysilane and propyltriethoxysilane. Variation of final elemental composition was tested via change of monomer ratios and combinations. The main aim was to achieve low weight losses during cure and pyrolysis and high micromechanical properties. Gas chromatography and mass spectroscopy was used to analyse the by-products of cure and pyrolysis, indicating a prominent role of cyclosiloxane and polyhedral oligomeric silsesquioxane (POSS) oligomers. Best results were obtained with high contents of methyltriethoxysilane in the monomers mixture.