High emissivity MoSi₂-ZrO₂-borosilicate glass multiphase coating with SiB₆ addition for fibrous ZrO₂ ceramic

To develop a high emissivity coating on the low thermal conductivity ZrO₂ ceramic insulation for reusable thermal protective system, the MoSi₂-ZrO₂-borosilicate glass multiphase coatings with SiB₆ addition were designed and prepared with slurry dipping and subsequent sintering method. The influence of SiB₆ content on the microstructure, radiative property and thermal shock behavior of the coatings has been investigated. The coating prepared with SiB₆ included the top dense glass layer, the surface porous coating layer and the interfacial transition layer, forming a gradient structure and exhibiting superior compatibility and adherence with the substrate. The emissivity of the coating with 3 wt% SiB₆ addition was up to 0.8 in the range of 0.3-2.5 μm and 0.85 in the range of 0.8-2.5 μm at room temperature, and the "V-shaped grooves" surface roughness morphology had a positive effect on the emissivity. The MZB-3S coating showed excellent thermal shock resistance with only 1.81% weight loss after 10 thermal cycles between 1773 K and room temperature, which was attributed to the synergistic effect of porous gradient structure, self-sealing property of oxidized SiB₆ and the match of thermal expansion coefficient between the coating and substrate. Thus, the high emissivity MoSi₂-ZrO₂-borosilicate glass coating with high temperature resistance presented a promising potential for application in thermal insulation materials.