Enhancing bonding strength and oxidation resistance of high-temperature silicone composite coatings using submicron low-melting glass powder

This study comparatively investigated the influence of micron low-melting glass (LMG) powder and submicron LMG powder on the bonding strength and oxidation resistance of high-temperature silicone composite coatings. Compared with the micron counterpart, submicron LMG powder reduced porosity, enhancing the structural integrity and cohesive strength of the coating. At high temperatures, the thermo-oxidative decomposition of silicone resin generated numerous cavities within the coating. At 650 °C, LMG powder underwent viscosity softening, transitioning into a viscous flow regime. Under capillary forces, the viscous LMG phase infiltrated surrounding cavities, followed by coalescence. The uniform distribution of submicron LMG powder within the coating promoted the formation of a homogeneous LMG phase, thereby establishing a barrier effect on oxygen ingress. Hence, at 650 °C, the silicone composite coating formulated with submicron LMG powder, Al flakes and other heat-resistant pigments exhibited superior oxidation resistance. Moreover, owing to the higher bond energy of covalent bonds formed by the glass network compared to the secondary bonds formed by the decomposed silicone resin, the cohesive strength of the coating containing submicron LMG powder increased from 2.11 MPa to 2.61 MPa.