Electrochemical kinetic study on the growth of porous anodic oxide films on aluminium

✍ Scribed by G. Patermarakis; K. Moussoutzanis

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 1004 KB
• Volume: 40
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(94)00347-4

✦ Synopsis

Aluminium specimens

were anodized galvanostatically in a thermostated and vigorously stirred bath of H,SO, 15% w/v at different bath temperatures and current densities and for long anodization times, suflicient to produce the maximum or near maximum limiting film thickness, and the anodic potential was followed. Results confirmed that the rate controlling step of the steady-state growth of the barrier layer is the charge transport across this layer, which is near solely due to the migration of anions; oxide is produced only in a region adjacent to the AI-AI,O, interface. Taking into consideration the structural features of the barrier layer oxide and by assuming a uniform oxide nature and one kind of migrating anions or cations, it has become possible to formulate simplified high field ion migration electrochemical kinetic equations.

They were found to be non-satisfactory when applied at low anodization temperatures, but become applicable at high temperatures or low barrier layer thicknesses. Their application postulated that the charge transfer at the AI-Al,O, interface, Al-3e --t AIS+, takes place rather through successive "one electron" transfer elementary steps. Also, the charge transport across the barrier layer oxide bulk takes place through a concomitant migration of the ions O"-, OH-and SO:-.

A model for the ions transport was suggested which gives a physical meaning to the field assisted oxide dissolution at pore bases, explains the incorporation of SO:-, SO,, OH-and H,O and predicts the change of their concentration, of the oxide nature and of the values of kinetic parameters across the barrier layer; it also predicts that an H+ migration may take place during oxide growth.