Modeling of Oxidation Effects on Heat Transfer Behavior of ZrB₂ and ZrB₂-SiC Ceramics at High Temperature

Hypersonic vehicles need thermal protection materials such as ultrahigh temperature ceramics (UHTCs). ZrB2 and ZrB2-SiC have been proposed as candidates for such applications. Even though they have excellent oxidation resistance, high temperature exposure of ZrB2 will result in its oxidations. After oxidation in air at high temperature, it will generate new products of ZrO2, B2O3, and SiO2. The material and geometric changes from the original ZrB2 and ZrB2-SiC ceramics will affect the heat transfer behavior due to the mismatch of thermal properties between the materials. A steady-state heat transfer analysis was conducted using finite element analysis (FEA) modeling. Adaptive remeshing technique was used to improve analytical accuracy. Thermal conductivity was calculated for liquid phase of B2O3 and SiO2 based on a theoretical formulation. In the FEA modeling, all thermal properties are temperature dependant. Simulated results indicate that the heat flux concentration occurs at the pore corner. ZrB2-SiC ceramic has higher thermal resistance than ZrB2 ceramic has after oxidation