A study on magnesium corrosion by real-time imaging and electrochemical methods: relationship between local processes and hydrogen evolution

Abstract This work investigates the hydrogen evolution process on magnesium by real time imaging of the corroding surface at the free corrosion potential and during potentiodynamic polarization in alkaline and neutral environments, in the presence and absence of chloride ions. High-magnification imaging of the corrosion process from side view discloses that three different types of hydrogen bubbles are generated during corrosion: i) large and stable bubbles on the uncorroded regions, ii) a stream of fine bubbles at the corrosion front and iii) medium size bubbles behind the corrosion front. It is proposed that the generation of streams of bubbles at the corrosion front is due to the disruption of the oxide/hydroxide film that is possible when an anodic current is available and environmental conditions can induce depassivation. This results in direct exposure of the underlying magnesium to the electrolyte and, due to the large overpotential available, in hydrogen evolution. Thus, the corrosion front act as a current amplifier where the rate of magnesium oxidation is proportional to the sum of the current produced remotely, that maintains the depassivation, and the current produced at the corrosion front by hydrogen evolution.

[1]  M. Pourbaix.  Atlas of Electrochemical Equilibria in Aqueous Solutions , 1974 .

[2]  M. Liu,et al.  Influence of pH and chloride ion concentration on the corrosion of Mg alloy ZE41 , 2008 .

[3]  N. Birbilis,et al.  Observations of the galvanostatic dissolution of pure magnesium , 2012 .

[4]  A. Atrens,et al.  The Negative Difference Effect and Unipositive Mg+ , 2007 .

[5]  N. Birbilis,et al.  The source of hydrogen evolved from a magnesium anode , 2013 .

[6]  John R. Scully,et al.  Accurate Electrochemical Measurement of Magnesium Corrosion Rates; a Combined Impedance, Mass-Loss and Hydrogen Collection Study , 2014 .

[7]  M. Curioni,et al.  The Mechanism of Hydrogen Evolution During Anodic Polarization of Aluminium , 2015 .

[8]  G. Frankel,et al.  Evidence for enhanced catalytic activity of magnesium arising from anodic dissolution , 2014 .

[9]  Sviatlana V. Lamaka,et al.  The effect of iron re-deposition on the corrosion of impurity-containing magnesium. , 2016, Physical chemistry chemical physics : PCCP.

[10]  G. Song.  Recent Progress in Corrosion and Protection of Magnesium Alloys , 2005 .

[11]  Quanjie Gao,et al.  Advanced engineering materials , 2015 .

[12]  N. Birbilis,et al.  Evolution of hydrogen at dissolving magnesium surfaces , 2013 .

[13]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[14]  M. Curioni.  The behaviour of magnesium during free corrosion and potentiodynamic polarization investigated by real-time hydrogen measurement and optical imaging , 2014 .

[15]  G. Frankel,et al.  Corrosion mechanism and hydrogen evolution on Mg , 2015 .

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

[17]  J. McDermid,et al.  Towards a Physical Description for the Origin of Enhanced Catalytic Activity of Corroding Magnesium Surfaces , 2014 .

[18]  G. Frankel,et al.  Effect of impurities on the enhanced catalytic activity for hydrogen evolution in high purity magnesium , 2015 .

[19]  C. Weber,et al.  The negative difference effect of magnesium and of the AZ91 alloy in chloride and stannate-containing solutions , 2010 .

[20]  F. Gan,et al.  Improvement of corrosion resistance of AZ91D magnesium alloy by holmium addition , 2006 .

[21]  G. Frankel,et al.  On the evidence for univalent Mg , 2015 .

[22]  P. Tabeling,et al.  A novel approach to on-line measurement of gas evolution kinetics: Application to the negative difference effect of Mg in chloride solution , 2014 .

[23]  F. Bellucci,et al.  Correlation between electrochemical impedance measurements and corrosion rate of magnesium investigated by real-time hydrogen measurement and optical imaging , 2015 .

[24]  Andrej Atrens,et al.  Recent Insights into the Mechanism of Magnesium Corrosion and Research Suggestions , 2007 .

[25]  O. Gharbi,et al.  Revisiting the electrochemical impedance spectroscopy of magnesium with online inductively coupled plasma atomic emission spectroscopy. , 2015, Chemphyschem : a European journal of chemical physics and physical chemistry.

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

[27]  G. Song,et al.  Corrosion mechanisms of magnesium alloys , 1999 .

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

[29]  Geraint Williams,et al.  Localized Corrosion of Magnesium in Chloride-Containing Electrolyte Studied by a Scanning Vibrating Electrode Technique , 2008 .

[30]  A. C. Chialvo,et al.  Kinetics of hydrogen evolution reaction with Frumkin adsorption : re-examination of the Volmer-Heyrovsky and Volmer-Tafel routes , 1998 .

[31]  O. Gharbi,et al.  Mg Dissolution in Phosphate and Chloride Electrolytes: Insight into the Mechanism of the Negative Difference Effect , 2015 .

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