SILSESQUIOXANE-DERIVED CERAMIC FIBERS

Fibres formed from blends of silsesquioxane polymers were characterized to study the pyrolytic conversion of these precursors to ceramics. The morphology of fibres pyrolysed to 1400-degrees-C revealed primarily amorphous glasses whose conversion to beta-SiC is a function of both blend composition and pyrolysis conditions. Formation of beta-SiC crystallites within the glassy phase is favoured by higher than stoichiometric C/Si ratios, while carbothermal reduction of Si-O bonds to form SiC with loss of SiO and CO occurs at higher methyl/phenylpropyl silsesquioxane (lower C/Si) ratios. As the carbothermal reduction is assumed to be diffusion controlled, the fibres can serve as model systems to gain understanding of the silsesquioxane pyrolysis behaviour, and therefore are useful in the development of polysilsequioxane-derived ceramic matrices and coatings as well.