Fabrication and performance evaluation of a highly stable micro/nanostructured surface using rapid thermal treatment of Si-coated stainless steel for solar thermal applications

Nano-structured thin film multilayer is an ideal way to create solar absorber coatings due to its tunability. However, this is limited to mid-temperature applications as the structures are not generally high-temperature stable. Here, a thermally stable micro/nanostructured surface is created on stainless steel by Si deposition and heat treatment at various temperatures. An improved absorptance of 0.92 and emittance of 0.37 are obtained when the coating is heat-treated at 900 °C for a short duration. The roughness, composition, and morphology studies show the role of Si in creating nano-micro islands. The change in the composition of the surface with increasing temperatures was studied by micro-Raman analysis using different wavelength sources. Various stability tests were conducted on the optimized sample. The absorptance of the optimized sample is stable after 1000 hrs at 750 ℃ in air. The selectivity and emittance of the optimized sample were stable till 600 ℃ for 1000 hrs. The samples showed no signs of degradation after the corrosion test for 336 hrs (ASTM B117 standard) and the humidity test conducted at 90% relative humidity at 50 °C. The samples showed thermal shock resistance for 500 cycles at 700 °C and 750 °C. The efficiency calculations using real-time high-temperature emittance showed a high efficiency of 81% at 500 °C for the coating prepared at 900 °C.