Densification and microstructural development during the firing of compounds in the Si3N4-SiO2-Y2O3 system

Among the compounds in the Si3N4-SiO2-Y2O3 system, we examined densification/microstructural development during the firing of the melilite phase (Y2Si3O3N4), and evaluated the mechanical strength (Vickers hardness) and heat resistance of the resulting ceramic. Relative densities of Y2Si3O3N4 compacts fired at 1800 C for 4 h or more were as high as 95%. The Vickers hardness of the dense melilite ceramic was approximately 15 GPa. The oxidation of the melilite ceramic in air was inhibited below 1200 C, due to the formation of an oxide layer on the surface. (orig.)