Influence of heat transfer on DC-anodizing of aluminium in sulphuric acid

Heat is generated during anodizing of aluminium, leading to macroscopic anodic film thickness variations and to local burning effects. The precise reasons for this non-uniform film behaviour have yet to be elucidated In the present study, conventional anodizing in sulphuric acid has been investigated in a wall-jet electrode reactor, enabling introduction of controlled heat transfer variations. An increased local film thickness is associated with an increased local electrode temperature. It was found that the higher the local temperature, the greater the local film thickness. This is explained by considering thermal enhancement of the field-assisted oxide dissolution at the pore bases, which necessitates a local current density rise to maintain the local anodizing equilibrium. Local cyclic voltammetry and capacitance measurements reveal an unchanged barrier layer thickness on the anodized aluminium specimen, thus confirming the previous.