Accurate Electrochemical Measurement of Magnesium Corrosion Rates; a Combined Impedance, Mass-Loss and Hydrogen Collection Study

Abstract

Experiments were conducted to enable the simultaneous measurement of electrochemical impedance and collection of hydrogen gas during the corrosion of pure magnesium in NaCl solutions. These results were then assessed along with the attendant specimen mass loss, providing three unique measures of magnesium corrosion for the same specimen. It was determined that analysis of impedance data, while accounting for a physically justified inductive response at low frequencies, enabled the determination of the polarization resistance, RP at the zero frequency limit. The determination of RP, as evaluated herein from electrochemical testing, provided excellent correlation to the mass loss and volume of hydrogen collected. This finding is elaborated in a broader discussion that critically addresses previous studies which have utilized the impedance behavior of magnesium and which claim electrochemical tests may underestimate Mg corrosion when attempting to use a charge transfer resistance at intermediate frequencies.