Residual carbon trapping effect of nano Si for stoichiometric SiC derived from polycarbosilane and its application in SiCf/SiC composites with largely improved thermal conductivity

Abstract

The inevitable residual carbon that normally appears in the polycarbosilane-derived SiC ceramics has notorious effects on the crystallinity and thermal conductivity of SiC ceramic. In this study, nano Si was employed to fully exhaust unwanted residual carbon in a liquid polycarbosilane. Through addition of 12 wt% theoretical nano Si and pyrolysis to 1600 °C, the ceramic yield of the liquid polycarbosilane increased from 72.0 wt% to 81.8 wt% and the C/Si ratio of ceramic product decreased from 1.14 to 0.99. Raman spectroscopy and transmission electron microscope also confirmed that the residual carbon almost completely disappeared. In addition, the crystallization ability of SiC also improved, and as a result dramatical improvement in the thermal conductivity of SiCf/SiC composite was achieved. The reaction mechanism was investigated in detail to understand the residual carbon trapping effect of nano Si during the precursor-to-ceramic conversion.