Study of the effect of an electric field on the kinetics of growth of oxide layers controlled by diffusion

International audienceThe metals oxidation kinetics controlled by the diffusion of charged species (ions, vacancy, etc.) has been theoretically treated since the thirties. Some authors, such as Hauffe and Wagner, propose that the gas-oxide interface is electrically negative with respect to the metal-oxide one and that the potential difference between two interfaces is one of the driving forces in oxidation. In this context, the application of an external electric field, which increases or decreases this potential difference, must act as an accelerator or a retarder of the system’s reactivity. However, in the literature the results of effect of an electric field are very different and there is no agreement on its dependence on the nature of the material, the temperature and the oxidizing atmosphere. This work concerns the study of the physico-chemical behavior of a zirconium alloy (Zicaloy-4) during its exposure to high temperature under oxygen and the influence of an external voltage. In this respect, thermogravimetric experiments at 850°C with the application in situ of an electric field were carried out. The general objective is to model the diffusion of charged species in the oxidation process under the influence of an electric field, taking into account chemical and electric potential as driving forces. The results show that a constant voltage (10 Volt) improves mass gain in 20% of the sample pretreated at high temperature under helium. The voltage-free oxidation kinetics exhibit a parabolic regime up to 4 hours in isothermal stage. In contrast, oxidation with electrical potential shows mixed behavior. Optical microscopy reveals that the thickness of the ZrO2 layer is globally greater on the oxidized sample under electrical field. In addition, the negatively polarized face is more oxidized according to theory