Effect of heating temperature on the optical properties of sol-gel synthesized C/NiO nanocomposite thin films

Abstract

For efficient photo-thermal conversion of solar energy a spectrally selective solar absorber surfaces are widely used. An ideal selective surface should have a high absorptance (low reflectance) in the solar wavelength range (0.3 to 2.5 µm) and low emittance (high reflectance) in the infrared wave length range (2.5 to 20 µm) in order to minimize heat losses. One of the designs that can be used to achieve a combination of high solar absorptance with low emittance is a tandem absorber. This can be realized by using a coating which contains metal particles embedded in an oxide matrix on a highly reflecting metal substrate. Due to its high absorptance in the visible and its metal-like characteristics, carbon is an excellent choice of material for solar absorber application. However, there are very few reports on carbon containing metal oxide materials. Sol-gel technique has been widely used to prepare spectrally selective coatings on aluminium substrate for solar absorber application in low temperature photo-thermal conversion have shown the feasibility of the C/NiO composite coatings for a selective solar absorber application, nonetheless, a detailed systematic investigation on the effect of the sol-gel fabrication process parameters on the structural and optical properties were not reported. It is expected that the heating temperature has a crucial effect on the properties of the final composite coatings. It is therefore the purpose of this work to investigate the effect of heating temperature on the optical properties of the C/NiO composite coatings.