Abstract
A high density of etch pits on high purity aluminum foil for electrolytic capacitors is produced by anodic dissolution in hot hydrochloric acid solution.Pit morphology and AC impedance characteristics were investigated under potentiostatic conditions for aluminum foil with (100) crystal orientation in 1mol/dm-3 hydrochloric acid solution at 363K, and the charge transfer resistance Rct, time constant τ0 and reaction uniformity parameter θ were estimated.Increase of anodic potential led to an increase in pit density and tunnel length, and to a decrease in pit size. The value of τ0 has a tendency to increase with time until becoming constant value at 0.4ms, and is independent of etching potential. In the steady state, when regular pits with small size and long tunnel length are made and large surface area are got, the value of τ0 is less than 0.4ms. When τ0 has a large constant value, pits proceed circumferentially around the walls of the pits without any preferred direction. This means that the change in τ0 value corresponds to the change in the morphology of pits formed at various potentials.
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