Selective paint and black chrome coatings development. Semiannual report, June 5-December 5, 1978

Solar selective black chrome and paint coatings were investigated to improve their performance and to develop techniques for large-scale applications. Formulations and processing conditions for thickness sensitive paint coatings were defined which consistently provide solar absorptance (..cap alpha..) of 0.90 and emittance (epsilon) of 0.10 on low emittance substrates. A significant improvement in abrasion resistance was achieved by decreasing the pigment volume concentration. Addition of aluminum flake to these formulations has resulted in a thickness insensitive coating with ..cap alpha.. = 0.90 and epsilon = 0.30. The critical bath components of a commercial black chrome plating process have been identified as hexavalent chromium, trivalent chromium, acetic acid and ferric ion. These components were varied and their effect on coating optical properties and durability at temperatures of 350-400/sup 0/C were studied. Coating thermal stability was significantly improved by reducing the trivalent chromium concentration from the normal 16 g/l to 12 g/l or less. Initial efforts have begun to optimize black chrome systems on aluminum substrates in terms of cost and durability