Anodic polarization of aluminum

The ECOrr near -600 mV (SHE) in Fig. 5.22 results from the nearly constant current density (passive) anodic curve and a cathodic diffusion- 

It should be noted that there is no evidence of a peak or local maximum in the anodic curve related to a transition from the active to passive state. This is a result of the preexisting air-formed oxide film that effectively prepassivates the aluminum. Only under very restricted conditions is it possible to produce a sufficiently active surface to allow measurement of the active-to-passive transition (Ref 18). 

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