Nickel pigmented anodized aluminium as solar selective absorbers

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