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Published online by Cambridge University Press: 25 February 2011
Analytical electron microscopy, X-ray diffractometry and secondary ion mass spectrometry (SIMS) have been used to characterize the intergranular microstructure of nitrided pressureless sintered (NPS) Si3N4 ceramics and the phase transformations which occur in the intergranular regions during oxidation. The phase transformations, which take place after crystallisation of the residual intergranular glass, are caused by an inward transport of oxygen and result in the development of sub-scalar phase gradients. Cubic Y2O3 stablized ZrO2 partitions from the oxynitride liquid phase sintering medium when a small amount of ZrO2(+ 3 mol% Y2O3) is added together with the Y2O3 and Al2O3 sintering additives. The latter material has a reduced oxidation resistance, presumeably due to the high oxygen conductivity of the cubic ZrO2 structure.