O tracer is used to investigate the development of porous anodic films at constant current in phosphoric acid on electropolished aluminum. A barrier layer and porous region form initially with the pore size related to the surface texture of the substrate. Subsequently, major pores emerge, with their sizes related to the anodizing voltage. The evolution of the film is accompanied by increases in growth rate and formation efficiency. The 18 O ions of a preformed oxide are retained in the film during anodization in a nonenriched electrolyte, with 18 O being partitioned among ͑i͒ the surface region of texture-dependent porosity, ͑ii͒ the walls of major pores, and, in diminishing amounts, ͑iii͒ the inner region of the barrier layer.

The growth of anodic alumina in sulphuric acid is investigated at constant current on bulk and sputtering-deposited aluminium. The ratio of the thickness of the film to the thickness of oxidized aluminium is shown to increase with increase of the current density (from 0.5 to 50 mA cm−2) and with decrease of the electrolyte temperature (from 20 to 0°C). In addition, the sulphur content of the films and the efficiency of film formation increase. It is suggested that pores are generated primarily by dissolution at current densities below ∼2 mA cm−2, with flow of film material dominating at higher current densities.

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Film morphologies and ionic migration are investigated for anodic oxides formed galvanostatically on electropolished aluminum in selenate electrolyte. Anionic selenium species that migrate at ∼0.2 to 0.3 times the rate of O 2− ions were present in barrier films. Further, porous films could be generated by the use of sputtering-deposited aluminum substrates, although the film thickness is limited to ∼70 nm. Re-anodizing in pentaborate electrolyte at high efficiency revealed also a cationic selenium species that migrates at ∼0.6 to 0.7 times the rate of Al 3+ ions, suggesting that the migration of selenium is affected by the morphology and growth mechanism of the film.