Microstructures of Oxidized Si3N4-8%Y2O3
Introduction. There is considerable interest in the effect of oxidation on the microstructure of yttria-doped silicon nitride, since some compositions are unstable at low temperatures (=1000°C) despite their apparent stability at 1400°C (1). The material used in this study was the same commercial hotpressed Si3N4-8%Y2O3 (NCX-34) as one investigated previously, which had exhibited only passive oxidation during heating in air from 600° to 1400°C. Some thin (=100μm) specimens were oxidized at 800°, 1000° and 1450°C in ambient air and then ion-thinned from one side; others were ion-milled and oxidized. Specimens were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) along with energy dispersive x-ray (EDX) analysis.