Processes Involved in Reattainment of Steady-State Conditions for the Anodizing of Aluminum Following Fonnation Voltage Changes." 1

The dissolution processes involved in the formation of porous films in sulfuric acid have been studied by suddenly lowering the formation voltag.e and observing changes in the current flowing and the barrier layer capacl-tance as steady-state conditions are re-established. It was found that current changes always follow capacitance changes, and that the dissolution proc-esses involved are (a) initial ly 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 as-sisted by the presence of this electric field. The change from one dissolution rate to the other is continuous as this min imum electric field is approached. On the basis of the Keller model, the required pore base orientation is pro-posed to occur during the second stage field-assisted process. The structure of porous anodic oxide films on alu-minum has been investigated for many years, th