About the Electrochemical Mechanism of Aluminum Corrosion in Acid Media by Electrochemical Impedance Spectroscopy

Abstract

AC-impedance measurements were performed in the alloy AA6061 in a mixture of sulfuric acid and sodium sulfate 0.05 M at pH of 1.45, 2 and 3, in the potential range of –0.8 V and 1.8 V_SSE. For all the ranges of potential and pH, the impedance of the system is characterized by three time constants, i.e., a capacitive behavior at high frequencies, an inductive loop at intermediate frequencies and a capacitive behavior at low frequencies. All impedance diagrams obtained were fitted with a single equivalent circuit. A theoretical impedance expression is presented based on a four-reactions physical model. Based on certain assumptions, this model allows evaluating the thickness of the film, the concentration and the velocity of charge carriers, as well as the potential distribution between the film and the interfaces and the electrical field on the oxide.