抄録
The initial growth stage of etch pits in high-purity aluminum was examined in 3.6%HCl solution by applying galvanostatic pulse of 0.5A/cm2 for 10-2s, with the off time between pulses varied from 10-3 to 1s. The morphology of the etched aluminum surface was found to depend markedly on the off time. At off time longer than 0.1s, hemispherical pits composed of large numbers of minute hemispherical pits, were formed on the etched surfaces. These small pits were covered with a non-uniform fibrillar layer of etching products, which are thought to be deposits of aluminum hydroxide. The effect of the off time on pit morphology was examined further by measurement of potential changes and polarization curves. At longer off times, the electrode potential of the specimens shifted to the repassivation potential. An overshoot always occurred in the galvanostatic potential transients at application of the current pulses, suggesting the formation of an anodic film. This was supported by measurements of the polarization curves.
