Phase equilibria and thermal analysis of Si-C-N ceramics

The phase reactions, crystallization behaviour and thermal degradation of t wo Si-C-N ceramics derived from precursors VT50 and NCP200, respectively, w ere studied by means of CALPHAD type thermodynamic calculations and experim ental investigations by DTA/TG, XRD and SEM/EDX. The phase reaction Si3N4+3 C=3SiC+2N(2) proceeds during the thermal degradation of both ceramics. Addi tionally, the phase reaction Si3N4=3Si+2N(2) occurs during the thermal degr adation of the NCP200 ceramic. To explain quantitatively the high temperatu re behaviour of Si-C-N ceramics, thermodynamic functions, the reaction sche me, isothermal sections, isopleths, phase fraction diagrams and phase compo sition diagrams (for gas partial pressures) were calculated. The computer s imulations were confirmed by the experiments for both ceramics. (C) 2001 El sevier Science B.V. All rights reserved.