Oxidation of Ultra-High Temperature HfB2-SiC Ceramic Materials in Humid Air Flow

The effect of air humidity on the oxidation stability of the ultra-high temperature ceramics HfB2-30 vol % SiC manufactured by reactive hot pressing technique, was studied by thermal analysis. In the air flow with 100% humidity at 23 degrees C (where the water content was 3 vol %), the weight gain due to HfB2 oxidation started at lower temperatures, as well as the weight loss resulting from boron oxide evaporation at temperatures above 1140 degrees C, too. Optical and scanning electron microscopy with local microanalysis confirmed the observation that much less borosilicate glass appeared on the surface and a significantly different microstructure was in the presence of 3 vol % water in air flow.