Effects of low-melting glass powder on the thermal stabilities of low infrared emissivity Al/polysiloxane coatings

In this study, low infrared emissivity coatings with good thermal stabilities were fabricated using silicone resin as adhesive, flake aluminum powder as pigment, and low-melting glass powder as functional filler. The effects of the low-melting glass powder on the adhesions, thermal expansions, and infrared emissivity of the coatings were systematically investigated. In addition, the surface microstructures and thermal stability mechanisms of the coatings were analyzed in detail. Mechanical tests showed that the addition of the low-melting glass powder to the Al/polysiloxane coating enhanced its adhesion after a high-temperature treatment due to the mechanical interlocking of the particles by the secondary film-forming low-melting glass. Thermal analysis indicated that the oxidation resistance of the coating could be improved by the film-forming low-melting glass powder. The low-emissivity coating with a low-melting glass powder content of approximately 15 wt.% and Al/polysiloxane ratio of 1.5 exhibited good thermal stability. The adhesion of the coating increased to 9.0 ± 0.4 MPa after heating at 500 °C. When the content of the low-melting glass was increased from 0 to 15 wt.%, the oxidation exothermic peak of the coating shifted from 590 to 625 °C at a pigment/binder ratio of 1.5. The infrared emissivity of the coating was 0.25 after heating at 600 °C.