On the mechanism of dissolution of porous oxide films on aluminium during anodizing

✍ Scribed by M. Nagayama; K. Tamura

• Publisher: Elsevier Science
• Year: 1968
• Tongue: English
• Weight: 833 KB
• Volume: 13
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(68)80085-4

✦ Synopsis

The temperature distribution alongthe vertical pores of the anodicoxide films onalumhrium was calculated for usual conditions of anodizing in 10% sulphuric acid solution by taking into account the accumulation of both Joule heat and the heat of formation of oxide at the pore-base and the outward conduction of heat through the solution-filled pore. The results show that a steady state of distribution is established at any instant and at any film thickness during anodizing and that the temperature rise at the pore-base is-always negligibly &all.

This conclusion was conBrmed bv some exueriments on the dissolution behaviour of oxide films. It was demonstrated that small c&ges in the bulk solution temperature significantly affect the dissolution rate and anodizing current. It was also shown that the dissolution rate of oxide at the porebase is ahnost constant irrespective of the film thickness and of the time of anodizing. This rate was evaluated in the manner reported previously by subtracting the dissolution rate at the side walls of the pores from the total dissolution rate. These facts are in direct opposition to the 'thermal mechanism' and suggest that the extra-high rate of dissolution during anodizing almost certainly results from the high electrical field applied across the barrier layer.