Thermodynamic analysis of structural transformations induced by annealing of amorphous Si–C–N ceramics derived from polymer precursors

Abstract

Abstract Thermodynamic modeling has been used to explain structural transformations induced by heat treatment of amorphous Si –C–N ceramics derived from polymers. Nanocrystalline silicon carbide and nanocrystalline silicon nitride identified in the ceramic microstructure have been regarded as metastable NASIC and NASIN phases in the Si–C–N system. The Gibbs energies G(NASIC) and G(NASIN) have been derived and used together with the previously modeled Gibbs energy of the amorphous am-SICN to compute metastable phase diagrams. Computational results allow explanation of the crystallization process of amorphous Si –C–N ceramics. According to this model, the temperature of invariant reaction between carbon and silicon nitride changes with the growth of nanocrystallites, which explains the dependence of the thermal stability on the ceramic microstructure.