Effect of sealing on characteristics of nano-porous aluminum oxide as black selective coatings

This study aimed to investigate the effect of sealing on improvement of optical characteristics of black anodized aluminum that was first anodized and re-anodized. Various types of selective coatings were studied, nano-porous anodized aluminum was black colored using electrolytic coloring technique. The anodization process was performed to build up the first and second nano anodized aluminum oxide film. Copper, tin and nickel ions were deposited within the porous layer using AC current. The optical characteristics of different types of black coatings were recorded. In case of first anodized black colored samples, the optical and potentiodynamic polarization data, showed that the sealing step was highly effective and essential step. As, it enhanced the absorbance value, decreased the rate of corrosion and increase the stability and protection of colored anodized sample. However, in case of tin coating that was re-anodized sealing can be neglected. The surface was characterized by different analysis; SEM, FTIR and solar absorption. The data revealed that the prepared selective coating can be beneficially used for solar panel industries e.g. solar water heaters and consequently solar desalination units