Abstract
The action of water at 100°C on barrier anodic aluminum oxide has been studied for reaction times up to 30 min. The hydrated product is essentially the same as that formed when aluminum metal reacts with water under the same conditions. Furthermore, the rate of hydration of anodic oxide is remarkably similar to the rate of aqueous oxidation of the metal, suggesting that the same mechanism produces the hydrated film in each case.
The electrolyte used to form anodic films leaves a tenacious layer on the surface of the oxide. This layer must be penetrated or removed by the boiling water before hydration of the oxide can begin. This process gives rise to an "inhibition period" which is distinguished from a similar time lapse which occurs in the direct reaction of water with aluminum. The latter effect is due to the presence of the natural oxide film on the metal.