The temperature rise and burning for high rate anodizing of aluminum in oxalic acid

Abstract

The temperature rise in the substrate as well as in the bulk solution and the development of a local brown-coloured 'burnt' region on the anodic film are the characteristics of high rate anodizing of aluminum in oxalic acid. In this study, measurement of the barrier layer thickness in both the predicted burning region and the normal region indicates that they increase simultaneously as the voltage builds up to form the secondary voltage peak on the voltage/time transient; a depletion of oxalate anions allied with the temperature rise at the pore base is thought to govern this behaviour. Characteristic strong dotted anodic glows occurred simultaneously with a slight drop of voltage, about 1V, from the secondary peak value were observed just prior to the initiation of the local burning sector; also, the local substrate temperature always rises when burning is approaching. These studies suggest that a thermal modified electronic breakdown process is responsible for the burning phenomenon.