High temperature sintering of SiC with oxide additives: I. Analysis in the SiC–Al2O3 and SiC–Al2O3–Y2O3 systems

The vaporization behaviour of pure Al2O3, Y2O3 and SiC as well as SiC–Al2O3 and SiC–Al2O3/Y2O3 mixtures has been analysed by thermodynamic calculations in an open system. Pure Al2O3 and Y2O3 evaporate congruently in the 1200–2300 K temperature range. Pure SiC vaporizes in a non-congruent manner leading to graphite formation as by-product. A SiC–Al2O3 mixture evaporates congruently according to the main vaporization reaction, 2 SiC(s) + Al2O3(s) +Al2O(g) ⇆ 2 SiO(g) + 2 CO(g) +4 Al(g), but the overall composition changes: for SiC rich samples, the mixture tends towards pure SiC in time, and for Al2O3 rich samples towards pure Al2O3. A SiC–Al2O3/Y2O3 mixture shows similar behaviour.