Preparation of a flexible high emissivity coating on quartz fiber fabric for thermal protection

Abstract A silica-sol-bonded flexible high emissivity coating, with MoSi 2 and SiC as emittance agents, was prepared on quartz fiber fabrics to improve surface radiant heat loss. The high-temperature behaviors of quartz fiber fabrics and the influence of silica sol dipping and alumina sol dipping on the fabrics were studied prior to coating preparation. The emissivity, tensile strength and bending properties of the coated fiber fabrics as functions of MoSi 2 contents were investigated. Results show that the tensile strength of quartz fiber fabrics decreased sharply as temperature increased because of cristobalite crystallization. Silica sol dipping increased the tensile strength of the fabrics and therefore was selected as the binder of the high emissivity coating. The coating emissivity was higher than 0.85. The coated fiber fabrics had higher tensile strength than raw fiber fabrics and showed high bending deflection and good flexibility, resulted from the abundant microcracks formed during sol drying. The tensile strength decreased after the coated fiber fabrics were calcined at 800 °C, and the coated fabrics with higher MoSi 2 contents had higher tensile strength, higher toughness and better flexibility, benefited from the pesting oxidation of MoSi 2 , which formed an interfacial gap at the fiber–coating boundary, and promoted interfacial debonding and fiber pull out.