POTENTIODYNAMIC AND AC IMPEDANCE INVESTIGATION OF ANODIC ZIRCONIUM-OXIDE FILMS

Potentiodynamically grown thin oxide films of zirconium were investigated as a function of the electrode potential (0V ≤ V ≤ 9V), the potential sweep rate (0.05 Vs−1 ≤ v ≤ 4.00 Vs−1) and the pH (1 ≤ pH ≤ 14) in phosphate electrolytes. The oxides were characterized by coulometric and impedance measurements in the frequency range 0.1 Hz ≤ f ≤ 6.0 × 104 Hz. The rate of oxide growth changes with the sweep rate according to the high field law. The oxide growth kinetics depends on the pH of the forming electrolyte. The results are interpreted in terms of anion incorporation into the film. The system impedance is characterized by a low-frequency capacitive behavior associated with the oxide film and by a high-frequency resistive behavior corresponding to the electrolyte. The oxide capacity was found to be frequency dependent. The oxide impedance can be interpreted in terms of a dielectric relaxation model. A complex dielectric constant ⊠ = 31.5 - i 1.3 was calculated at pH 14. © 1990, The Electrochemical Society, Inc. All rights reserved.