The electrochemical behaviors of barrier-type anodic films on aluminum in ammonium adipate solution

To investigate the effect of applied voltage and anodizing time on the form ation and characteristics of barrier-type oxide layer, aluminum was anodize d in 150 g/L ammonium adipate solution at 65 degrees C. The electrochemical behavior of oxide layers on aluminum was studied using impedance spectrosc opy. The fitted results of impedance spectroscopy show clearly that the thi ckness of the oxide film subjected to applied anodic voltage increased line arly at a ratio of 1.42 nm/V, but the effect of the anodizing duration at c onstant voltage on film thickness was not remarkable. From a comparison of the fitting results and the observed microstructure using TEM, the fitted c apacity by equivalent circuit can be directly converted to an oxide thickne ss.