TWO-STEP ELECTRODEPOSITION METHOD FOR A HIGHLY EFFICIENT SOLAR ABSORBING COATING

Highly effective selective absorbing coatings of Sn and Ni on polished copper sheets have been produced. A new method for improvement of the mechanical properties is proposed and investigated. It consists of a 2-step electrodeposition - the 1st step is electrodeposition of a high absorbing layer, and the 2nd step - electrodeposition at lower current density to increase the mechanical strength of the coating. The absorbance of the coating produced in the 1st step is calculated as 98% in the solar radiation range and the thermal emittance at 100 degrees C is 10%. Scanning electron microscopy micrographs show that the absorbing coatings consist of a highly branching layer of bimetallic needles. They serve as a radiation trap for the solar radiation because of multiple reflections. The selective absorbing coatings are investigated by electron microscopy. The selective absorbing coatings are investigated by electron microscopy, XRD, XPS and UV-vis., NIR and IR spectral analyses. The 2-step electrodeposited coatings have solar absorbance 96% and thermal emittance 18%.