Catalytic and Radiative Properties of Ultra-High Temperature Ceramic Coatings

The high temperature catalytic and radiative performance are the intrinsic properties of the thermal protection materials, and the low catalytic coefficients and high emissivity reduce the thermal loads, which could enhance the heat resistance and prolong the service life under high temperature conditions. In this study, ZrB₂-SiC, ZrC-SiC, HfC-SiC and HfC ultra-high temperature ceramic (UHTC) coatings were fabricated using vacuum plasma spray technique. The catalytic coefficients and emissivity of the coatings were measured by the inductive coupled plasma wind tunnel and related equipments, and the effects of main and additive phases of the coatings on them were analyzed. Results demonstrated that the catalytic coefficients and emissivity of the ZrB₂-SiC and ZrC-SiC coatings exhibited similar values at 1500 °C, which is about 1.3 × 10⁻² and 0.8, respectively. Compared with the Zr-based coatings, the HfC-SiC coating possessed lower catalytic coefficients (1.053 × 10⁻²) and higher emissivity (0.92). Moreover, the addition of SiC was beneficial to the decrease of the catalytic coefficients of the HfC-SiC coating, but also led to a decrease of the emissivity. The catalytic and radiative behaviors of UHTC coatings were closely related to the oxidation products.