Pressureless fabrication of dense monolithic SiC ceramics from a polycarbosilane

This paper presents the pressureless preparation of dense and crack-free near stoichiometric SiC monoliths via cross-linking and pyrolysis of a polycarbosilane, followed by polymer-infiltration-pyrolysis cycles. The composition and the porosity of the samples strongly depend on the processing temperature. Thus, at 1050-1100 degrees C, the SiC monoliths are X-ray amorphous and exhibit low amounts of oxygen and excess Carbon; their porosity was rather high (>10%). Higher processing temperatures induced the crystallization of beta-SiC. The removal of oxygen and excess carbon due to CO release allowed for obtaining near-stoichiometric compositions at 1700 degrees C. However, the residual porosity of the samples increased. The use of the PIP technique led already after six cycles to dense monoliths (residual porosity ca. 0.5%). The present study emphasizes the potential of the polymer processing technique for the fabrication of near stoichiometric and dense SiC monoliths, which might be used for structural applications in harsh conditions. (C) 2014 Elsevier Ltd. All rights reserved.