Convection Patterns in Liquid Oxide Films on ZrB2-SiC Composites Oxidized at a High Temperature

During the high‐temperature oxidation of ZrB2–SiC composites, liquid boron oxide (B2O3) is formed at the zirconium diboride–zirconium oxide interface and transported through the overlying layer of silica liquid by convection, forming distinct convection cells arranged like the petals of a flower. The convection cells are localized by a viscous fingering phenomenon, as the fluid B2O3 rich liquid solution rises through the viscous silica layer. The upwelling B2O3 rich liquid contains dissolved zirconium dioxide, which deposits in the center of the flower‐like structure as the B2O3 evaporates. The driving force for the B2O3 liquid flow is the volume increase upon oxidation of ZrB2. Convective transport of B2O3 liquids suggests a novel mechanism for the high‐temperature oxidation of these materials.