Influence of anion on the breakdown voltage of barrier-type anodic oxide film on aluminum.

Aluminum foil of 99 99% purity was anodized at a constant current (0.5mA/cm2) in ammonium adipate solutions until breakdown was observed and the voltage at that point was measured. Measurements were made in the four kinds of solution system-. 1) in varying concentrations at a fixed temperature (50°C), 2) at varying temperatures at a fixed concentration (100g/l), 3) in different combinations of temperature and concentration having the same specific resistance (13.5Ω·cm) and 4) at various pH in the same concentration (0 52M). It was found; 1) that the dependence of breakdown voltage (VB) on the specific resistance RS of the solution as shown by the heretofore accepted function VB=a+blog RS was entirely incorrect; 2) that the breakdown voltage depended substantially on anion concentration in such a way that it decreased linearly with increases in the logarithm of the concentration, i.e., VB=a-blog (anion); and 3) that strictly speaking, the breakdown voltage was more closely correlated with the anion charge according to the following relationship VB=a-blog (anion charge)