Abstract
The potentiodynamic oxidation of Zr at ν = 0.05 V s −1 was investigated in the potential range 0–90 V in the following electrolytes: H 2SO 4, HNO 3, H 3PO 4 and NaOH. After film growth, the oxides were characterized by ac impedance measurements in the frequency range 0.1 Hz ≤ f ≤ 10 kHz. The impedance responses of the films formed in H 2SO 4 and NaOH were modelled with a transfer function corresponding to a single-layer model. The impedance spectra of the oxides formed in H 3PO 4 and HNO 3 showed two time constants which were adequately simulated by a transfer function corresponding to a two-layer oxide structure. The nature of the outer layer of the films formed in H 3PO 4 was attributed to phosphate incorporation from the electrolyte, which was confirmed by X-ray photoelectron spectroscopy measurements. The variation of the oxide electrical parameters (resistance, capacitance etc.) with final formation potential is reported and the reasons leading to the complex film structure are discussed.
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