Thermal redistribution reactions of Blackglas™ ceramic

Abstract

Abstract Silicon oxycarbides undergo SiO and SiC bond redistribution when heated in an inert atmosphere above 900°C. This redistribution has a great influence on the mechanical, thermal, and oxidative stability properties of Blackglas™ ceramic. Based on a statistical method, three independent thermal redistribution reactions were chosen to describe the redistribution reactions between 900 and 1350°C. Over this temperature range, only SiO and SiC bond redistribution is involved, and the char yield is constant. The equilibrium constants of each independent reaction and their temperature dependence are calculated directly by using 29 Si‐NMR experimental data for temperatures of 900, 1000, and 1100°C and fitted to a cubic polynomial. A redistribution reaction model (RRM) is proposed to describe how the microcompositions of silicon oxycarbide change with respect to temperature. The model is based on 29 Si‐NMR data from 900 to 1100°C. It enables one to extrapolate results to 1400°C and indicates that the silicon oxycarbide can survive above 1400°C and that the microcomposition is very sensitive to the ratio O/Si in the polymer precursor. This prediction is in a good agreement with the experimental results observed by Belot et al., Corriu et al., Bois et al., and F. Babonneau et al. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 143–152, 2001