Abstract
The effect of oxygen composition on the crystal phases and flexural strength of AIN hot-pressed under 200 kg/cm2 for one hour at 1600-2100°C was examined. The A1N pseudo-polytype in 2Hδ structure was formed in the specimens hot-pressed at temperatures above 1900°C containing about 2.7 wt% oxygen. In these experiments, specimens from the powder with 2.7 wt% oxygen (97.6 mol% A1N) had the highest strength of 48 kg/mm2. The oxygen addition enhances densification and increases flexural strength because of forming spinel-type aluminum oxynitride and/or needle-shaped pseudo-polytypes in the grain boundary of A1N. The excess formation of the pseudo-polytype, however, seemed to be undesirable in the attainment of strong material.
