The negative difference effect of magnesium and of the AZ91 alloy in chloride and stannate-containing solutions

Thomaz, T.R.; Weber, Cristina Rejane; Pelegrini, T.; Dick, Luís Frederico Pinheiro; Knörnschild, Gerhard Hans

doi:10.1016/j.corsci.2010.03.010

Cited by 88 publications

(41 citation statements)

References 30 publications

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“…Abidin et al [20] stated a difference between instantaneously or short time and steady state or long time measurements and mentioned that the application of the Tafel extrapolation might have measured a valid corrosion rate for the moment. In contrast, Thomaz et al [24] and Nam et al [25] said that the extrapolation of the cathodic curve leads to erroneous results.…”

Section: Literature Surveymentioning

confidence: 99%

The Influence of MgH2 on the Assessment of Electrochemical Data to Predict the Degradation Rate of Mg and Mg Alloys

Müeller

Hornberger

2014

IJMS

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Mg and Mg alloys are becoming more and more of interest for several applications. In the case of biomaterial applications, a special interest exists due to the fact that a predictable degradation should be given. Various investigations were made to characterize and predict the corrosion behavior in vitro and in vivo. Mostly, the simple oxidation of Mg to Mg2+ ions connected with adequate hydrogen development is assumed, and the negative difference effect (NDE) is attributed to various mechanisms and electrochemical results. The aim of this paper is to compare the different views on the corrosion pathway of Mg or Mg alloys and to present a neglected pathway based on thermodynamic data as a guideline for possible reactions combined with experimental observations of a delay of visible hydrogen evolution during cyclic voltammetry. Various reaction pathways are considered and discussed to explain these results, like the stability of the Mg+ intermediate state, the stability of MgH2 and the role of hydrogen overpotential. Finally, the impact of MgH2 formation is shown as an appropriate base for the prediction of the degradation behavior and calculation of the corrosion rate of Mg and Mg alloys.

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Section: Literature Surveymentioning

confidence: 99%

The Influence of MgH2 on the Assessment of Electrochemical Data to Predict the Degradation Rate of Mg and Mg Alloys

Müeller

Hornberger

2014

IJMS

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“…In simple terms, the NDE relates to the increase in hydrogen evolution experimentally observed during anodic polarization and it is contrary to what would be predicted by electrochemical theory. The first interpretation of the NDE [11][12][13] assumes that unipolar magnesium ions are generated during anodic polarization. Once detached from the metal electrode, the unipolar magnesium ions oxidize further and reduce water, producing hydrogen gas and hydroxide ions.…”

Section: Introductionmentioning

confidence: 99%

Correlation between electrochemical impedance measurements and corrosion rate of magnesium investigated by real-time hydrogen measurement and optical imaging

Curioni

Scenini

Monetta

et al. 2015

Electrochimica Acta

196

130

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Please cite this article as: M.Curioni, F.Scenini, T.Monetta, F.Bellucci, Correlation between electrochemical impedance measurements and corrosion rate of magnesium investigated by real-time hydrogen measurement and optical imaging, Electrochimica Acta http://dx. AbstractThe corrosion behaviour of magnesium in chloride-containing aqueous environment was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) performed simultaneously with real-time hydrogen evolution measurements and optical imaging of the corroding surface. The potentiodynamic investigation revealed substantial deviations from linearity in close proximity of the corrosion potential. In particular, differences in the slope of the current/potential curves were observed for small polarizations above or below the corrosion potential. These observations, suggest that the usual method based on the use of the Stern-Geary equation to convert a value of resistance into a value of corrosion current is inadequate.Nonetheless, a very good correlation between values of resistances estimated by EIS and corrosion currents obtained from real-time hydrogen measurement was found. Real-time hydrogen measurement also enabled, for the first time, direct measurement of an 'apparent' Stern-Geary coefficient for magnesium. In order to rationalize the complex behaviours experimentally observed, an electrical model for the corroding magnesium surface is presented.

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“…Historically, one of the possible interpretations was the generation of univalent magnesium during anodic polarization 10,13,14 . The generation of univalent magnesium could in principle explain this behaviour, since univalent magnesium ions could oxidize to divalent magnesium after detaching and generate hydrogen after ejection into the electrolyte.…”

Section: Introductionmentioning

confidence: 99%

Application of Side-View Imaging and Real-Time Hydrogen Measurement to the Investigation of Magnesium Corrosion

et al. 2017

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This work illustrates how side-view optical imaging, anodic potentiodynamic polarization and realtime hydrogen evolution measurements can be applied and complementary used to study the processes occurring on a corroding magnesium surface. Side-view imaging reveals that hydrogen evolution takes three different forms: i) large and stable bubbles on the uncorroded regions, ii) a stream of fine hydrogen bubbles at the corrosion front and iii) medium-sized bubbles behind the corrosion front. The observation suggests that the relatively large bubbles ahead and behind the corrosion front are associated with a purely cathodic reaction that provides the 'remote current'. This current, combined with the depassivating role of chloride ions, maintains the corrosion front active, generating regions where either the metal is locally directly exposed to the electrolyte or it is only covered by a poorly protective chloride-rich film. Regardless of the precise nature or morphology of the poorly protective (or absent) surface film at the corrosion front, additional hydrogen evolution occurs due to the large overpotential available. Overall, the anodic current associated with magnesium oxidation is the sum of the 'remote current', which is manifested with hydrogen evolution ahead and behind the corrosion front, and the 'local' current associated with hydrogen evolution at the corrosion front. From the electrical viewpoint, the corrosion front acts as a current amplifier where the current amplification effect can be measured directly by real-time gravimetric hydrogen measurement performed simultaneously with anodic potentiodynamic polarization.

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The negative difference effect of magnesium and of the AZ91 alloy in chloride and stannate-containing solutions

Cited by 88 publications

References 30 publications

The Influence of MgH2 on the Assessment of Electrochemical Data to Predict the Degradation Rate of Mg and Mg Alloys

The Influence of MgH2 on the Assessment of Electrochemical Data to Predict the Degradation Rate of Mg and Mg Alloys

Correlation between electrochemical impedance measurements and corrosion rate of magnesium investigated by real-time hydrogen measurement and optical imaging

Application of Side-View Imaging and Real-Time Hydrogen Measurement to the Investigation of Magnesium Corrosion

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