Abstract
The solubility of anodic oxide films formed on aluminum in sulfuric acid solutions was studied by measuring transient anode potential observed by the change in anodizing current and temperature and concentration of electrolyte during electrolysis.
The results obtained were as follows.
1) Important factors affecting the transient anode potential during electrolysis were concentration and temperature of the sulfuric acid solution.
2) When aluminum was anodized in sulfuric acid solution at a constant current density, a linear relationship was found between the logarithmic value of anode potential and the time of electrolysis; the constant ratio between the two was assumed to be k.
3) Since it is well known that the thickness of the barrier layer on the anodic oxide film was proportional to the cell voltage in the ratio of 10Å/V, k is considered to correspond with the constant rate of dissolution of barrier layer into the electrolyte.
4) When the concentration of sulfuric acid was kept constant, Arrhenius' Plot was obtained between log k and 1/T (inverse number of absolute temperature of the electrolyte) and the activation energy of anodic dissolution of the barrier layer was determined to be 0.44eV by calculation.
5) When the temperature of electrolyte was constant, log k was found to be proportional to log C (logarithmic value of concentration of sulfuric acid) in the constant ratio of 0.81.
