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

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 Na2SO4 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.

[1]  N. Pébère,et al.  The corrosion of pure magnesium in aerated and deaerated sodium sulphate solutions , 2001 .

[2]  D. Vermilyea,et al.  Studies of Inhibition of Magnesium Corrosion , 1969 .

[3]  L. A. Baker,et al.  Alternating current impedance imaging of membrane pores using scanning electrochemical microscopy. , 2005, Analytical chemistry.

[4]  M. Cohen,et al.  The Effect of Halides on the Capacity and Resistance of the Magnesium Electrode in Aqueous Solutions , 1959 .

[5]  L. Roué,et al.  Comparative study on the corrosion behavior of milled and unmilled magnesium by electrochemical impedance spectroscopy , 2004 .

[6]  N. Pébère,et al.  Investigation of magnesium corrosion in aerated sodium sulfate solution by electrochemical impedance spectroscopy , 1990 .

[7]  J. Greenblatt.  Gases Evolved at Magnesium Anodes And Cathodes in Neutral Salt Solutions , 1962 .

[8]  J. A. Harrison,et al.  The automation of electrode kinetics — III. The dissolution of Mg in Cl−, F− and OH− containing aqueous solutions , 1980 .

[9]  H. Takenouti,et al.  A model of the anodic behaviour of iron in sulphuric acid medium , 1975 .

[10]  S. D. Torresi,et al.  Ac-impedance and Raman spectroscopy study of the electrochemical behaviour of pure aluminium in citric acid media , 2001 .

[11]  M. Natta.  Evidence of Two Anodic Processes in the Polarization Curves of Magnesium in Aqueous Media , 2001 .

[12]  J. A. Harrison,et al.  The dissolution of magnesium in Cl− and F− containing aqueous solutions , 1979 .

[13]  J. Robinson,et al.  Electrochemical Behavior of the Magnesium Anode , 1961 .

[14]  F. Huet,et al.  Scanning Electrochemical Microscopy for Investigating Gas Bubble/Liquid Interfaces , 2003 .

[15]  P. F. King.  The Role of the Anion in the Anodic Dissolution of Magnesium , 1966 .

[16]  E. Gulbrandsen,et al.  The passive behaviour of Mg in alkaline fluoride solutions. Electrochemical and electron microscopical investigations , 1993 .

[17]  C. Blanc,et al.  AC Impedance Spectroscopy in Characterizing Time-Dependent Corrosion of AZ91 and AM50 Magnesium Alloys Characterization with Respect to Their Microstructures , 2001 .

[18]  J. Greenblatt.  A Mechanism for the Anodic Dissolution of Magnesium , 1956 .

[19]  G. Song,et al.  The anodic dissolution of magnesium in chloride and sulphate solutions , 1997 .

[20]  R. Tunold,et al.  The corrosion of magnesium in aqueous solution containing chloride ions , 1977 .

[21]  G. Song,et al.  Understanding Magnesium Corrosion—A Framework for Improved Alloy Performance , 2003 .

[22]  J. Jorcin,et al.  CPE analysis by local electrochemical impedance spectroscopy , 2006 .

[23]  M. Sluyters-Rehbach,et al.  The analysis of electrode impedances complicated by the presence of a constant phase element , 1984 .

[24]  A. Bard,et al.  Scanning electrochemical microscopy. Theory of the feedback mode , 1989 .

[25]  F. Huet,et al.  Scanning Electrochemical Microscopy Imaging by Means of High-Frequency Impedance Measurements in Feedback Mode , 2004 .

[26]  D. StJohn,et al.  The electrochemical corrosion of pure magnesium in 1 N NaCl , 1997 .

[27]  D. Tallman,et al.  Comparison of testing solutions on the protection of Al-alloys using a Mg-rich primer , 2006 .

[28]  E. Gulbrandsen.  Anodic behaviour of Mg in HCO−3/CO2−3 buffer solutions. Quasi-steady measurements , 1992 .

[29]  V. Vivier,et al.  Concentration mapping around copper microelectrodes studied by scanning electrochemical microscopy , 2005 .

[30]  R. L. Petty,et al.  The Anodic Oxidation of Magnesium Metal: Evidence for the Existence of Unipositive Magnesium1,2 , 1954 .

[31]  G. Song,et al.  Corrosion behaviour of AZ21, AZ501 and AZ91 in sodium chloride , 1998 .

[32]  Mark E. Orazem,et al.  Enhanced Graphical Representation of Electrochemical Impedance Data , 2006 .

[33]  G. G. Perrault,et al.  The potential-pH diagram of the magnesium-water system , 1974 .