AC-impedance measurements on aluminium barrier type oxide films

Abstract

AC-impedance measurements in the frequency range 5 × 10 −3 Hz ≤ f ≤ 10 4 Hz were performed in the system polycrystalline pure aluminium/0.16 M NH 4-tartrate at pH 5–7, in the potential range −900 mV ≤ E H ≤ 400 mV. The impedance of the system is characterized by a high-frequency capacitive and a low-frequency inductive behaviour. The capacity is unequivocally related to the thickness and dielectric properties of the barrier oxide film. The faraday impedance corresponds to a metal dissolution process at the oxide film/electrolyte interphase and can be interpreted by a model previously proposed by Armstrong.