Oxidation induced emissivity evolution of silicon carbide based thermal protection materials in hypersonic environments

The emissivity of typical SiC-based thermal protection materials was measured in-situ at a wide temperature range (800 similar to 2300 degrees C) inside a plasma wind tunnel that was capable of simulating hypersonic environments on-ground. Based on it, the evolution mechanism dominated by dynamic oxidation was discussed. The results suggest an emissivity of C-f/SiC 0.84 similar to 0.88 at 858 similar to 1502 degrees C, prior to "temperature jump". If "temperature jump" emerged, the emissivity was decreased rapidly to approximate to 0.76. The emissivity drop was explained by the microstructural transition of the oxidized surfaces that were triggered by the dissipation of SiO2 oxide scale at 1600 similar to 1900 degrees C. Similar emissivity evolution was observed in SiCf/SiC after "temperature jump". The effect of temperature on the emissivity of ZrB2-SiC was more pronounced. It was increased from approximate to 0.73 to approximate to 0.98 at 1009 similar to 1297 degrees C, and was plateaued at 1298 similar to 1497 degrees C, approximate to 0.98. This was a consequence of the formation of higher percentage SiO2-rich layers. However, due to the dissipation of SiO2 and B2O3, the emissivity of ZrB2-SiC was declined at higher temperatures, from approximate to 0.98 (approximate to 1497 degrees C) to approximate to 0.85 (approximate to 1768 degrees C).