Processes Involved in Reattainment of Steady‐State Conditions for the Anodizing of Aluminum Following Formation Voltage Changes

Abstract

The dissolution processes involved in the formation of porous films in sulfuric acid have been studied by suddenly lowering the formation voltage and observing changes in the current flowing and the barrier layer capacitance as steady‐state conditions are re‐established. It was found that current changes always follow capacitance changes, and that the dissolution processes involved are (a) initially a short time region of chemical dissolution is found up to some point where the minimum electric field strength required for ionic migration is approached, and (b) a second stage dissolution assisted by the presence of this electric field. The change from one dissolution rate to the other is continuous as this minimum electric field is approached. On the basis of the Keller model, the required pore base orientation is proposed to occur during the second stage field‐assisted process.