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.