2006 Volume 114 Issue 1335 Pages 950-957
Thermodynamic modelling has been used to explain structural transformations during crystallization of amorphous Si-C-N polymer derived ceramics. Nanocrystalline SiC and nanocrystalline Si3N4 identified in ceramic microstructure have been regarded as metastable NASIC and NASIN phases of the Si-C-N system. Gibbs energies G(NASIC) and G(NASIN) have been derived considering an excess energy coupled with interfaces of nanocrystallites. The metastable phase equilibria including the nanocrystalline phases and the amorphous am-SICN phase have been analysed. Formation of NASIC and NASIN phases by eutectoid transformation of am-SICN phase and continuous growth of nanocrystallites have been ascertain as a possible way of crystallization. The resistance of Si3N4 against disintegration by reaction with carbon has been explained as a thermodynamic effect of nanocrystalline structure.
