Influence of Impurity Elements on Electrochemical Activity of Aluminum Activated by Indium

The electrochemical behavior of 99.999% aluminum (Al), 99.95% Al, and 99% Al in weak, acidic chloride solutions containing indium (In) salt was investigated. Activation of Al electrodes in the solution depended primarily on purity of the electrode. In all tests, time intervals between the addition of the In salt solution to the working electrolyte and the onset of activity (induction periods) were shorter for the 99.999% Al electrodes. It was found that activation with this electrode could be maintained indefinitely once initiated. Transient activation was observed only with the 99% Al electrode. However, activation was more effective after various surface pretreatments that effectively removed the surface iron (Fe)-containing phases. Large amounts of In were detected on the surface of immersed 99% Al. This was attributed to the deposition of In from indate solutions formed because of the build-up of alkaline regions adjacent to the Fe precipitates. The deposited In was rendered inactive.