Electrolytic coloring of anodic aluminum for selective solar absorbing films: use of additives promoting color depth and rate

An optically black coating on aluminum substrate having improved solar abso rption is disclosed along with an enhanced process for formation. The two-s tep electrolytic coloring process has been used. Porous anodic films have b een formed by de anodization of aluminum samples in 16% sulfuric acid. It i s followed by black coloration via ac electrolysis in nickel sulfate soluti on. In this step, we have investigated the effect of chloride and magnesium as additives. Evaluation of the test samples has been carried out by spect ral reflectance and nickel content measurements. Choride existance verifies two aspects: the promotion of the coloring process and higher black tones shades are attained. However, magnesium has a minor effect. (C) 2001 Publis hed by Elsevier Science Ltd.