Characterization of Black Nickel Solar Absorber Coatings on Brass Substrates

Abstract

Solar Selective coatings have radiative characteristics which vary with wavelength. They are characterized by their high absorbance (α) in the visible region and low thermal emittance (ε) (or high reflection) beyond the visible region of the sun spectra. These coatings materials are of very great importance in the field of renewable energy sources (solar energy applications). In the present study, the influence of process parameters like the current density, concentration of particles, time of deposition, the thickness of the electrodeposited nickel (Ni), etc. was investigated. The objective of the research is to study solar selective coatings used in solar thermal collectors. i.e. black nickel (B-N) coatings, electrodeposited (ED) over brass substrates. Preparation and characterization of B-N coatings over brass substrates was performed. Low-cost solar selective absorbers (ED of B-N on brass) have been obtained. Trial to get rid of some structures or materials which are harm to the environment. (i.e. car batteries, by using lead sheets from recycled car battery as an anode during ED of B-N coating) was achieved. Reflectance measurements were used to evaluate both, (α) and (ε) of the coatings. The measurements of total or diffuse reflectance of samples were performed with instruments equipped with integrating spheres. Electrodeposited (ED) of black nickel BN on brass substrate has a moderate selectivity (α /ε =2.63, when α =0.95). The durability tests were carried out in the form of elevated temperature exposure in air (250 C°), temperature cycling (30-100 C°), and humidity tests (up to 90 % RH). The coatings have been re-characterized after ageing tests, using spectrophotometry and other techniques, such as X-ray techniques. Durability testing of the ED B-N coatings indicates that they are sensitive to humidity testing. However, efficient absorbers were obtained by using low-cost technique. Durability testing of the ED B-N coatings indicates that they are sensitive to humidity testing.