Programming Void Populations in the Passive Oxide of Aluminum in an Attempt to Correlate Evolving Nanostructure with Passivity Loss

Galvanostatic polarization in aqueous chloride media is shown to be a viable method for controlling the characteristics of a void and pore population within the passive oxide on aluminum thin films. Current density and anion type are demonstrated to be effective control parameters of nanoscale feature density and size. The use of the borate anion with chloride regulates the void formation and points to a mechanism where competitive anion adsorption at the barrier layer dictates the fraction of current density that is channeled into void formation versus oxide growth. Preliminary results are presented for microcapillary-based measurements of pit initiation in the presence of a pre-programmed void population. These results show the presence of an induction time with pre-existing voids. These findings suggest that where voids may play a role in pit initiation, other factors may be necessary in a more concerted mechanism of oxide breakdown and pit initiation.