Thermal redistribution reactions of Blackglas (TM) ceramic

Silicon oxycarbides undergo Si-O and Si-C bond redistribution when heated i n an inert atmosphere above 900 degreesC. This redistribution has a great i nfluence on the mechanical, thermal, and oxidative stability properties of Blackglas (TM) ceramic. Based on a statistical method, three independent th ermal redistribution reactions were chosen to describe the redistribution r eactions between 900 and 1350 degreesC. Over this temperature range, only S i-O and Si-C bond redistribution is involved, and the char yield is constan t. The equilibrium constants of each independent reaction and their tempera ture dependence are calculated directly by using Si-29-NMR experimental dat a for temperatures of 900, 1000, and 1100 degreesC and fitted to a cubic po lynomial. A redistribution reaction model (RRM) is proposed to describe how the microcompositions of silicon oxycarbide change with respect to tempera ture. The model is based on Si-29-NMR data from 900 to 1100 degreesC. It en ables one to extrapolate results to 1400 degreesC and indicates that the si licon oxycarbide can survive above 1400 degreesC and that the microcomposit ion is very sensitive to the ratio O/Si in the polymer precursor. This pred iction is in a good agreement with the experimental results observed by Bel ot et al., Corriu at al., Bois et al., and F. Babonneau et al. (C) 2001 Joh n Wiley & Sons, Inc. J Appl Polym Sci 81: 143-152, 2001.