Phase formation in porous liquid phase sintered silicon carbide: Part III: Interaction between Al2O3–Y2O3 and SiC

The structure and phase formation of porous liquid phase sintered silicon carbide (porous LPS-SiC), containing yttria and alumina additives have been studied. The present paper is focused on the system Y–Al–Si–C–O. The systems Al–Si–C–O and Y–Si–C–O have been studied in previous papers [J. Eur. Ceram. Soc. (in press) parts I and II]. action products of the interaction of Al2O3/Y2O3 with SiC and resulting microstructures were analysed by model experiments. The influences of different sintering atmospheres, namely argon and Ar/CO and different temperatures have been investigated. Thermodynamic calculations and sintering experiments reveal that silicides or carbides can be formed in addition to stable oxides. The main parameters controlling the formation of the different reaction products are the free carbon content, the oxygen activity and the temperature. CO containing atmospheres, the decomposition of the oxide additives can be effectively suppressed and stable porous LPS-SiC can be produced.