The Microstructure and the Oxidation Behaviour of Si2N2O/Zro2 Composites
The microstructure and oxidation behaviour of Si2N2O/ZrO2 composite ceramic materials have been examined. Based on the reaction sintering of Si3N4 and ZrSiO4, high density composites were formed by the NPS technique from Si and ZrSiO4 with Y2O3/Al2O3 or CaMg(CO3)2 as stabilisation/sintering aid. The composites consisted of a submicron grain size Si2N2O phase of fibrous morphology, micron size irregularly shaped ZrO2 grains and an amorphous phase. XRD and TEM examination revealed that in the Y2O3/Al2O3 stabilised materials the tetragonal phase occured mainly as the non-transformable t′-ZrO2 polymorph while in the CaMg(CO3)2 stabilised materials XRD indicated the transformable t-ZrO2 polymorph to be present. Significant oxidation of the materials occurred only at temperatures >1000°C with the formation of porous scales containing SiO2 and ZrSiO4. At temperatures above 1250°C severe degradation of the materials occured following oxidation.
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