High temperature sintering of SiC with oxide additives: IV. Powder beds and the influence of vaporization on the behaviour of SiC compacts

The liquid phase sintering of SiC with Al2O3–Y2O3 additives is performed at high temperature and some loss of alumina is mainly observed. Powder beds made of SiC + Al2O3 coarse grains are used to counteract these losses. The present mass spectrometric study is aimed at the transfer of matter by the gas phase between the powder bed and the previously sintered pellet. Partial vapor pressures of Al(g), Al2O(g), SiO(g) and CO(g) are compared over the pellet alone, the beds alone and for the (pellet + bed) mixtures. Those of Al(g) and Al2O(g) are only slightly modified when the SiC powder is from different origins, meanwhile the CO(g)/SiO(g) ratio is very sensitive to the nature of the SiC powder. Thus, the main effect of the powder bed is not only to prevent or to limit the alumina losses, but also to impose carbon and oxygen activities for the sintering process.