Double layer SiO2/Al2O3 high emissivity coatings on stainless steel substrates using simple spray deposition system

High emissivity coatings (ɛ > 0.90) are widely used in spacecraft and industrial furnaces, which have attracted a great attention recently due to energy saving applications. In this study, a simple spray coating method was used to produce double layer high emissivity coatings on stainless steel (SS) substrate by sol-gel process at room temperature. Initially, silica (SiO2), sol prepared using sol-gel process, was deposited on sandblasted SS substrate with required thickness, followed by deposition of aluminium oxide (Al2O3) layer. The gradual increase in the thickness of Al2O3 layer resulted in increase in the emittance. The optimized double layer Al2O3 (23.0 μm)/SiO2 (9.13 μm) coating on SS substrate exhibited high emittance (ɛ = 0.92-0.94) and low absorptance (α = 0.30-0.34). The high emissivity coating, when exposed to a temperature of 1000 °C in air got crystallized but retained its optical properties. For example, the heat-treated coating exhibited an emittance of 0.92 (measured at 82 °C) and absorptance of 0.42. The SiO2/Al2O3 coating, thus, provides a simple and cost effective method for the preparation of high emissivity coatings.