Porous anodic alumina is used in nanotechnology, electronics, and corrosion protection with the film morphology tuned by appropriate selection of anodizing electrolyte and anodizing voltage or current. Specifically, tailored potential-time or current time regimes involving an initial voltage ramp may be used to modify the porous oxide morphology for improved corrosion resistance or nanotechnology applications. In this work, a fundamental study was performed on superpure aluminum to understand the processes of initiation and growth of the porous anodic oxide during anodizing under potentiodynamic conditions. The current-potential response comprises an initial current plateau followed by a region of quasi-exponential dependence of current on applied potential. The first region was associated with initial thickening of the air-formed oxide, and the subsequent quasi-exponential region was related to the establishment of porous anodic film growth. Phenomena related to cell reorganization associated with the continuous variation in the anodizing potential during the growth were examined by direct transmission electron microscopy of ultramicrotomed sections and stripped porous anodic films and compared with anodic oxides generated under steady potential conditions. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3230642] All rights reserved.