Titanium-tin oxide protective films on a black cobalt photothermal absorber

We report the effect of covering an electrodeposited black cobalt absorber film with a Ti : Sn oxide film at various atomic ratios prepared by the sol-gel dip process. The resulting composite was characterized in its optical, structural and morphological properties. After thermal treatment at 400 degrees C, the uncoated black cobalt him is oxidized and Co3O4 is formed. Samples covered with Ti:Sn films and thermally treated at the same temperature suffered lower oxidation maintaining in great extent the original metallic cobalt structure. The optical properties of the resulting material were affected by the presence of the Ti : Sn coating, and the best protective film obtained was a transparent Ti : Sn (8 : 2) atomic ratio oxide film, with a 210 nm thickness. This composite system exhibits an absorptance value of 0.91 and an emittance value of 0.34 after a 100 h, 400 degrees C thermal treatment. A photothermal material composed of a layer of black cobalt and a protective oxide film coating seems then a promising solar energy absorber capable of withstanding high operating temperatures (400 degrees C). (C) 1999 Published by Elsevier science B.V. All rights reserved.