Nickel pigmented anodized aluminium as solar selective absorbers

Abstract

The effect of various anodization parameters on the structural features and optical properties of solar absorbing nickel pigmented anodic alumina coatings has been studied. A correlation between the microstructural features and the solar selectivity of these coatings has been established. Stable coatings with low thermal emittance, ≈0.06 (at 100°C), and solar absorptance ≥ 0.90 have been prepared by anodizing in a phosphoric acid electrolyte. Addition of H₂SO₄ in the anodizing bath leads to an increase in the α and ε values of the film due to the formation of a thicker and alumina rich anodic film. By using a mixture of H₃PO₄ and H₂SO₄, α and ε values can be varied over a wide range of 0.90 ≤ α ≤ 0.96 and 0.06 ≤ ε (100°C) ≤ 0.46.