In situ microscopy observation of liquid flow, zirconia growth, and CO bubble formation during high temperature oxidation of zirconium diboride–silicon carbide

The oxidation of ZrB2–SiC composites at 1450–1650 °C was directly observed with in situ optical microscopy. Video frames showed the flow of silicate liquids, the formation of zirconia deposits, and the growth and collapse of gaseous bubbles on the oxide surface. Contrast in the incandescence of in situ images is analyzed as spatial variations in hue and intensity and related to differences in emissivity of the oxide scale surface features by comparing these hot images with room temperature images. Above 1450 °C, gaseous bubbles were observed to grow and collapse causing perturbations in the liquid oxide on the surface. The bubbles are associated with the evolution of CO from SiC oxidation and the onset is related to the critical temperature where the partial pressure of CO under the oxide scale exceeds atmospheric pressure.