Application of CuCoMnO x coat by sol gel technique on aluminum and copper substrates for solar absorber application

Abstract

Solar thermal heaters are used widely in domestic and industrial applications. The main part of solar thermal heaters is the absorber surface which must have a maximum absorptivity (α) and minimum emissivity (e) of solar radiation. This is achieved by application of selective coating on the absorber surface. In the present work, solar selective CuCoMnO x spinel films are deposited by sol gel technique using a dip-coating technique on copper and aluminum sheets. The precursor’s ratio Co:Cu:Mn applied is 1:3:3. Different precursor molar ratios were combined with a fixed amount of solvents for the coating process. Process parameters such as withdrawal rate, heat treatment, and substrate materials on the coat characteristics and optical properties were studied. The coated metallic samples were heat treated at 450°C for 30 min in the case of aluminum and at 200°C at different times in the case of copper. Optical properties of the coatings, namely absorptivity (α) and emissivity (e) were measured and the deposition process parameters were optimized in order to produce the maximum selectivity (α/e) values. The deposition parameters were found to influence both the thickness and surface roughness of the coatings. As the coating thickness decreases, the absorptivity increases while the emissivity decreases irrespective of the substrate material. It was also observed from the results that when applying the coat on aluminum substrates, a maximum selectivity value of (α/e) = 31 was realized while for the copper substrates a maximum value of (α/e) = 81.8 was obtained. The deposited coatings were analyzed using SEM, XRD, and AFM.