Treatment of antireflection on tin oxide coated anodized aluminum selective absorber surface

Nickel-pigmented anodic aluminum oxide, Ni–Al₂O₃ was pyrolytically coated with tin oxide (SnO₂). The undesirable increase of reflectance in the solar spectrum due to the high refractive index of the SnO₂ film was compensated by an antireflection layer. The layer was applied by a simple dipping technique in a bath containing a commercial colloidal silica sol which forms a silica (SiO₂) layer. The infrared reflectance is nearly unaffected by the silica sol treatment process. Preliminary test results indicate that treated samples are resistant to temperatures as high as 300°C as well as to corrosion in an 8% sulfuric acid solution. In addition, the optical properties were unaffected by outdoor exposure for two months.