Anodizing of inner surface of long and small-bore aluminum tube

A method for anodizing the inner surface of long and small-bore aluminum tubes is described. Parameters affecting thickness, shape, porosity and stability of the oxide layer formed were investigated. The optimum conditions for electrolyte solution, temperature, applied voltage and anodizing time were found. The anodizing process was performed both in dynamic and static modes. The results obtained indicated that the quality of Al2O3 layer formed in dynamic mode was better than that of the static mode. Therefore the flow rate of the electrolyte solution in dynamic mode during the anodizing process was also optimized. In this study, the chemical characteristics of the Al2O3 layer formed were studied by adsorption quantity of fuchsin from aqueous solution on the coating layer and further desorption from it. Scanning electron microscopy was employed for the investigation of the physical characteristics of the Al2O3 layer. The results revealed that in the optimum conditions, a porous and stable layer, 45 μm thick, with a high surface area was formed on the inner surface of each aluminum tube.