Evaluation of Nanostructured Metal-Ceramic Coatings for Solar Thermal Applications

Abstract

Metal- ceramic  thin film coatings has become an area of intense research particularly in applications related solar thermal, heat exchangers, filters, sensor technologies and many other optical applications such as laser windows, mirrors, reflectors and optics for digital projections. The composition of the W-Al₂O₃ thin film coating material, processing conditions and the resulting microstructure and surface finish influences the solar absorptance and thermal emittance behaviour of these coatings. The response of these nano-structured thin film coatings have been characterized using 410-Solar and ET-100 Emissometer. The solar absorptance and thermal emittance of metal-ceramic coatings on metallic substrates with and without consideration of nickel bond layer have been evaluated. Tungsten (W) and Alumina (Al₂O₃) coatings have been deposited using DC and RF magnetron sputtering process. The deposited Metal-Ceramic W-Al₂O₃ thin films coatings illustrated total solar absorptance of 0.8793 and hemispherical thermal emittance (HTE) of 0.1033 without effect of nickel bond layer while incorporating nickel bond layer solar absorptance was found to be of 0.9237 and thermal emittance of 0.0771 is observed. The microstructure of W-Al₂O₃ thin film are characterized using SEM to demonstrate crystal structure and orientation, topography and phase distribution of W and Al₂O₃ in deposited coatings. EDAX was performed for compositional characterization of W-Al2O3 thin films and these characterizations revealed that processing conditions have a direct influence on the solar absorptance and thermal emittance behaviour. The W-Al₂O₃ thin film coatings can be used as absorbers for solar thermal applications.