Electrochemical Behavior of Thin Anodic Oxide Films on Zircaloy‐4: Role of the Mobile Defects

The first stages of the electrochemical oxidation of Zircaloy‐4 are investigated using simple electrochemical tests and modeling the passive film modifications occurring as a result of contact with the electrolyte. Variations in electrode potential (open‐circuit conditions) or current density (potentiodynamic scans) can be simply explained by a high field ( F ∼ 10 6 V / cm ) assisted passive film growth. Under open‐circuit conditions, this field does not vary with exposure time (in the 2 h to 48 h range). The minimum electric field for the onset of high‐field behavior is also evaluated and found smaller than the theoretical value which can be explained by a variation in the concentration of mobile defects throughout the film. Measurements of the electrode potential decay after a potentiodynamic scan confirm this model, allowing interpretation of the film modification as a combination of two separate phenomena: film growth under a high electric field and point defect annihilation.