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A new approach for studying the effect of temperature on anodic oxide growth on aluminium is presented in this paper. Using an in-house developed electrode holder, anodizing is performed under conditions of applied and controlled electrode temperature. The influence of temperature on the process is evaluated by experiments in a broad temperature range for both the electrode and the electrolyte temperature. The electrochemical behaviour of the aluminium electrodes is demonstrated to be more susceptible to variations of the electrode temperature than to variations of the electrolyte temperature. Concerning the morphology of the anodic film it is shown that by cooling the electrode a normal oxide layer could be grown at high electrolyte temperatures, whereas anodizing in a cool electrolyte at high electrode temperature results in a collapsed porous structure at the oxide surface. Furthermore, the electrode temperature affects the formation ratio of the oxide to a larger extent than the electrolyte temperature, indicating its important influence even on the level of the ionic conductivity during anodic oxide growth. All observations indicate that merely considering the electrolyte temperature upon studying the influence of temperature on the process is not sufficient; the electrode temperature is much more determining.

A new approach for studying the effect of temperature on electrochemical processes is presented in this paper. Using an in-house developed electrode holder, experiments are performed under conditions of applied and controlled electrode temperature. This new approach provides an improved temperature control during the experimental study and, additionally, allows distinguishing both the influences of the electrolyte and electrode temperatures. The advantages of the applied electrode temperature approach are illustrated by considering porous anodizing of aluminium. In a broad temperature range the electrochemical behaviour of the aluminium electrodes, recorded during the new and the conventional way of anodizing, are compared. Differences between the anodic potential evolutions in both approaches are observed, and are explained by a heat flux to the surroundings during the experiments at uncontrolled electrode temperature. These results illustrate the advantage of applying the electrode temperature. If the influence of temperature on a process is investigated by merely varying the electrolyte temperature, the electrode temperature is only indirectly influenced and can significantly differ from the electrolyte temperature. Therefore, when evaluating the influence of temperature on an electrochemical system the electrode temperature should be considered, and preferentially also controlled. Keywords: Temperature, Electrode temperature, Aluminium, Anodizing, Porous oxide

A study of burning during galvanostatic anodizing of aluminium in sulphuric acid is presented. Experiments are performed under controlled convection in wall-jet configuration, while in situ measuring local anode temperatures. Burning is a breakdown phenomenon manifesting itself in the local temperature evolutions and in the electrochemical behaviour of the electrode. Undulating oxide surfaces with protruding oxide hillocks, displaying a twofold microstructure, are formed. Focusing on short anodizing times the initiation of burning is determined in the period of declining potential following the maximum potential, linking burning to the development of the final porous structure. The influence of enhanced Joule heat generation during the onset of anodizing is investigated by anodizing electrodes covered by barrier-type oxide films, formed by an a priori performed barrier anodisation. Increased initial oxide thicknesses intensify burning, in the extreme case resulting in non-quenched phenomena involving quasi complete concentration of current in the burning area. However, the occurrence of burning during experiments on a priori barrier anodized electrodes at reduced current density exclude the conditions of heat transfer as key parameter for triggering burning. Results indicate the existence of a critical barrier layer thickness above which burning is encountered during the period of development of the regular porous structure.