An Impedance Investigation of the Mechanism of Pure Magnesium Corrosion in Sodium Sulfate Solutions

Abstract

The corrosion behavior of pure magnesium in sodium sulfate solutions was investigated using voltammetry and electrochemical impedance spectroscopy with a rotating disk electrode. The analysis of impedance data obtained at the corrosion potential was consistent with the hypothesis that Mg corrosion is controlled by the presence of a very thin oxide film, probably MgO, and that the dissolution occurs at film-free spots only. This hypothesis was substantiated both by the superposition of the EIS diagrams, obtained for different immersion times and for two Na 2 SO 4 concentrations once normalized, and by use of scanning electrochemical microscopy in the ac mode to sense the local conductivity of the material. On the basis of the electrochemical results, a model was proposed to describe magnesium corrosion at the open-circuit potential. Simulation of the impedance diagrams was in good agreement with the experimental results.

Effect of naturally formed oxide films and other variables in the early stages of Mg-alloy corrosion in NaCl solution

“…7) suggest either the presence of thinner films according to the inverse relationship between capacitance and film thickness of the flat capacitor formula [45], or more defective films which leaves a greater fraction of metallic surface area in contact with the electrolyte [46]. No significant differences in capacitance values have been observed as a function of surface conditions tested.…”

Formation of Corrosion Resistant Mg(OH)2 Film Containing Mg-Al Layered Double Hydroxide on Mg Alloy Using Steam Coating

“…The corrosion potential, E corr , and corrosion current density, i corr , values for the untreated AZ31 were estimated to be -1.435 V vs. Ag/AgCl and 5.395 X 10 -5 A/cm 2 , respectively. The anodic region of the curve for the bare AZ31 can be divided into three fields: (i) first region beginning from E corr (low anodic overpotential) that exhibits a linear increase in current density with potential; (ii) a range of abrupt increase in current density from -1.4 V, where the dissolution of Mg to Mg + or Mg 2+ ions predominantly occurred [18]; (iii) a current plateau at more positive potentials, where the electrode surface is covered with a film identified as Mg(OH) 2 [19]. In the cathodic branch, hydrogen evolution is more dominant at negative potentials than Ecorr, resulting in an increase in the cathodic current density.…”

High Functionalization of Magnesium Alloy Surface by Superhydrophobic Treatment

“…Their poor corrosion resistance, however, hinders their use on a larger scale. The corrosion of magnesium and magnesium alloys occurs via the following reaction (Baril et al, 2007;Song el al., 1997): 2Mg → 2Mg+ + 2e - …”