The formation and dissolution of anodic oxide films on pure aluminium in alkaline solution

The mechanisms of formation and dissolution of anodic oxide films on pure a luminium rotating disc specimens in alkaline solution have been investigate d using galvanostatic anodizing, potentiostatic anodizing, potential drop e xperiments and impedance spectroscopy. It was found that in alkaline soluti on the strength of the applied electric field accelerates the formation of the anodic oxide film, while it retards its dissolution, indicating electro chemical formation of the film and a complete lack of its field-assisted di ssolution. The rate of growth and the thickness of the anodic oxide film we re observed to decrease with an increasing rate of specimen rotation as a r esult of accelerated chemical film dissolution due to rapid removal of alum inate ions from and fast supply of hydroxide ions towards the film/solution interface. (C) 1999 Elsevier Science Ltd. All rights reserved.