The observation of cristobalite formed on the oxidized layer of silicon nitride by EPMA

Abstract

Hot-pressed silicon nitride test bars were oxidized in air flow at 1200°C for 480h. The observations by composition and topography image of SEM indicate that cristobalite crystals of 1-4μm are formed (appears as black spots) and cracks run in all directions all over the oxidized surface, and Y2O3⋅2SiO2 crystals are clearly convex and the SEM image of cristobalites indicate that they are concave to the surface and this aspect is correspond to the COMPO image. The concentration of Al in the glass phase on the grain boundary is presumed to be high from the characteristic X-ray analysis. EDS analysis showed that a large amount of SiO2 and a small amount of alkali were found in the cristobalite phase and a large amount of Fe2O3, CaO and K2O are dissolved in the glass phase.