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CONVERSION OF POLYCARBOSILANE (PCS) TO SiC-BASED CERAMIC. PT.2. PYROLYSIS AND CHARACTERISATION

The conversion to ceramic of a commercial polycarbosilane (PCS) under various pyrolysis conditions was investigated. The products of pyrolysis were characterised by solid state 29Si and 13C NMR spectroscopy and XRD. Some of the phases identified differed from those reported previously, particularly...

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Bibliographic Details
Published in:Journal of materials science 2001-01, Vol.36 (16), p.4045-4057
Main Authors: Ly, H Q, Taylor, R, Day, R J, Heatley, F
Format: Article
Language:English
Online Access:Get full text
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Summary:The conversion to ceramic of a commercial polycarbosilane (PCS) under various pyrolysis conditions was investigated. The products of pyrolysis were characterised by solid state 29Si and 13C NMR spectroscopy and XRD. Some of the phases identified differed from those reported previously, particularly in the earlier literature. Oxidation-cured PCS, when pyrolysed up to 1400 C in argon, generally produced silicon oxycarbide (SiOxCy) as the second major phase with beta-SiC as the major phase, and smaller amounts of free carbon. With increasing temperature above 1200 C, the silicon oxycarbide phase decomposed to give beta-SiC. SiO2 was also found to evolve from this silicon oxycarbide phase. Loss of some of the SiO2, probably by reaction with carbon, was found at 1400 C, possibly yielding SiO, CO and SiC. At 1500 C, crystalline alpha-cristobalite was found as a minor phase with beta-SiC as the major phase and a lower amount of free carbon. Pyrolysis in vacuum leads to production and crystallisation of beta-SiC at a lower temperature than required if pyrolysed in argon flow. After pyrolysis at 1600 C in vacuum, the cured PCS converted to almost stoichiometric beta-SiC. 57 refs.
ISSN:0022-2461