Microstructure, radiative property and thermal shock behavior of TaSi₂-SiO₂-borosilicate glass coating for fibrous ZrO₂ ceramic insulation

The objective of this research was to develop a high emissivity coating on the low thermal conductivity ZrO₂ ceramic insulation, which can be used in a reusable thermal protective system for short-term applications. The effects of SiB₆ and heat-treatment time on the microstructures and radiative properties of the TaSi₂-SiO₂-borosilicate glass composite coatings prepared on fibrous ZrO₂ ceramic with slurry dipping and subsequent sintering method were investigated. The coating prepared in the presence of SiB₆ with a heat-treatment time of 15 min maintains a dense structure and infiltrates into the ZrO₂ substrate, possessing a gradient structure and good compatibility. The emissivity of the coating is up to 0.9 in the range of 0.3-2.5 μm and 0.8 in the range of 3-30 μm at room temperature. The emissivity mechanism regarding electron transition absorption, lattice vibration absorption and the effect of surface roughness on the emissivity is discussed. The increased roughness leads to the increased emissivity, which can be explained by "circular grooves" and "pyramidal grooves" models. After thermal cycling between 1573 K and room temperature 10 times, the weight gain of the coating prepared with SiB₆ is only 0.29%. The high emissivity TaSi₂-SiO₂-borosilicate glass coatings with high temperature resistance show a promising potential for application in thermal insulation materials.