Characterization of the pyrolytic conversion of polysilsesquioxanes to silicon oxycarbides

A series of silsesquioxane copolymers synthesised by hydrolysis and condensation of phenyl- and methyltrimethoxysilanes were studied as preceramic polymers. The ratio of phenyl to methyl groups in the copolymer was found to control polymer structure and rheology, as well as ceramic composition and c...

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Bibliographic Details
Published in:Journal of materials science 1993-01, Vol.28 (24), p.6622-6630
Main Authors: HURWITZ, F. I, HEIMANN, P, FARMER, S. C, HEMBREE, D. M
Format: Article
Language:English
Subjects:
Applied sciences
Building materials. Ceramics. Glasses
Ceramic industries
Chemical industry and chemicals
Exact sciences and technology
Miscellaneous
Technical ceramics
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Summary:A series of silsesquioxane copolymers synthesised by hydrolysis and condensation of phenyl- and methyltrimethoxysilanes were studied as preceramic polymers. The ratio of phenyl to methyl groups in the copolymer was found to control polymer structure and rheology, as well as ceramic composition and char yield. On pyrolysis to 1000 C under inert conditions, silicon oxycarbides were formed, along with glassy carbon. On heating from 1200 C to 1400 C, the oxycarbide structure diminished, and the materials were comprised primarily of amorphous silica, amorphous Si-C, some small crystallite SiC and graphitic carbon. The carbon content increased and char yield decreased, with increasing concentration of phenyl groups in the copolymer. The presence of free carbon appears to inhibit the crystallisation of silica. Significant carbothermal reduction was observed only above 1500 C. Oxidation studies of the pyrolysed materials indicated the presence of at least two forms of carbon. 30 refs.
ISSN:0022-2461
1573-4803
DOI:10.1007/bf00356406