Study of the electrochemical synthesis of selective black coatings absorbing solar energy

To set up a reproducible electrochemical preparation process of a black, adhesive and homogeneous film on a metallic substrate with well-defined optical and mechanical properties, we need to control all the electrochemical parameters and to understand their influence. For so doing, different coatings have been prepared in various conditions and their microstructures have been correlated with the synthesis parameters as well as the physical properties. Chromium oxide films on nickel-coated copper metallic substrates have been deposited from a chromate bath. In this paper, we present the evolution of the microstructure of the deposits according to some experimental parameters, more specifically the concentration of the hexafluorosilicic acid and trivalent chromium ions present in the electrochemical bath used in our experiments. A marked difference in the particle morphology has been put into evidence by modifying the source of the trivalent chromium ions: (i) from the addition of sucrose to the solution containing hexavalent chromium ions or (ii) from the addition of a trivalent chromium salt to the bath.