Effect of TaSi2 content on the structure and properties of TaSi2-MoSi2-borosilicate glass coating on fibrous insulations for enhanced surficial thermal radiation

TaSi2-MoSi2-borosilicate glass coatings with high emissivity were prepared on mullite fibrous ceramics via a slurry technique to enhance surficial thermal radiation and serve in the thermal protection systems for aircrafts. The effect of TaSi2 dosages on the coatings' structure, phase composition, emissivity, thermal shock resistance and thermal endurance were investigated. The results show that all the coatings were flat and uniform, while the surface roughness and porosity increased with TaSi2 dosages. Part of TaSi2 was oxidized into Ta2O5 during the coating preparation, and finally, the coating with TaSi2 dosage of 45 wt% (C-45Ta) had the highest TaSi2 content. Emissivity of the coatings increased with TaSi2 contents. The total emissivity of C-45Ta was 0.855 in the range of 3-14.5 μm at 150 °C, while that of the coating without TaSi2 (C-0Ta) was 0.809. However, compared with C-0Ta, C-45Ta showed worse thermal shock resistance because of its higher CTE mismatch with the substrate and higher porosity. The thermal endurance of C-45Ta was worse due to the limited oxidation resistance of TaSi2 and the lower borosilicate glass content.