Nickel electrolytic colouring of anodic alumina for selective solar absorbing films

The influence both of the waveform of the pigmentation current and of the type of electrolyte on the quality of nickel-pigmented aluminium solar-absorbing coatings was investigated. Alternating current (AC) and rectified AC current with half-wave and full-wave rectification, respectively, were applied. As a pigmentation agent, Watts and citrate electrolytes on the nickel (Ni2+) basis were used. Thickness, weight, colour shade of the deposited coatings were recorded before and composition and microstructure ones after stripping procedure. The stripping procedure of anodic alumina was carried out in the chrome/phosphoric acid mixture. It was confirmed that the negative half wave of anodising current is responsible for nickel deposition. Morphology study revealed that the positive half wave causes softening/dissolution of the structure deposit. Complexing agent of the nickel-based electrolyte for pigmentation of anodic alumina causes high-degree arrangement of the nickel deposit at presented conditions.