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Magnesium is widely used as a sacrificial anode for protecting steel from corrosion. In this paper, the electrochemical behaviour of magnesium sacrificial anodes has been studied using electrochemical impedance spectroscopy (EIS) and polarisation curves, completed by Evans’ diagrams (under galvanic conditions) and SEM observations. The impedance diagrams are composed of two capacitive loops at the high and middle frequencies; the first one is related to the charge transfer resistance in parallel to the double layer capacity, the other one is attributed to the magnesium ion concentration. An inductive loop at low frequencies appeared as due to the formation, adsorption and desorption of the corrosion products, on the surface of the anodes. The intensiostatic curves permit the evaluation of the anodes efficiency as a function of the current flow. The obtained Evans’ diagrams are discussed taking into account the polarization effects at the electrodes for different experimental conditions.
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