Effect of Adipic Acid on DEIS Characteristics during the Aluminium Anodizing Process in Sulfuric Acid Bath

The formation process of anodic film on aluminium was investigated in the bath containing adipic acid and sulfuric acid (ASA bath) by using dynamic electrochemical impedance spectroscopy (DEIS). An interface reaction and ionic migration mechanism of anodic oxidation process in the ASA bath was established to interpreting the DEIS data. The impedance was decrease with the addition of adipic acid added in the anodizing bath, because of the adsorption of adipic anions on the surface of oxide film. An electrical equivalent circuit (EEC) model was established to analyse the relationship of the EEC model elements with the applied potential. The results indicated that the addition of adipic acid into the anodizing bath was beneficial to the grown of oxide film on aluminium, like faster in grown rate and thicker in thickness.