Phase equilibria of precursor‐derived Si–(B–)C–N ceramics

Phase equilibria and phase reactions of precursor‐derived ceramics of the Si–C–N and the Si–B–C–N systems at temperatures higher than 1700 K are described. CALPHAD (CALculation of PHAse Diagrams) results confirm quantitatively the data from thermogravimetry and differential thermal analysis of precursor‐derived Si–C–N ceramics. A model for explanation of the thermal stability of specific Si–B–C–N precursor ceramics was developed. Phase reactions of polymeric precursors of the Si–C–N–H system were calculated and compared with analyses concerning the composition of the solid ceramic and gaseous products from thermolysis at a temperature of 1323 K. The results­show that a semi‐quantitative description of­the thermolysis process is possible. Copyright­© 2001 John Wiley & Sons, Ltd.