The pH Dependence of Magnesium Dissolution and Hydrogen Evolution during Anodic Polarization

Rossrucker, Lisa; Samaniego, Alejandro; Grote, Jan-Philipp; Mingers, Andrea Maria; Laska, Claudius Alexander; Birbilis, Nick; Frankel, G. S.; Mayrhofer, Karl Johann Jakob

doi:10.1149/2.0621507jes

Cited by 71 publications

(61 citation statements)

References 33 publications

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“…[15][16][17] It has been reported that enrichment of surface impurities alone cannot account for the observed NDE since substantial enhanced catalytic activity was observed even for ultra-high purity Mg. 26 Recently, Mg surface films have been shown to sustain HER and may also contribute to increased rates of self-corrosion. 18,21,28,31,36 Studies also suggest that the impurities trapped in the film may provide cathodic sites to sustain HER. 16,27,37 We note that these mechanisms may have played a role in the high rates of self-corrosion observed, and that acceleration was likely facilitated at the high dissolution rates observed in our experiments.…”

Section: Resultsmentioning

confidence: 99%

Hydrogen Evolution during the Corrosion of Galvanically Coupled Magnesium

Banjade

Porter

McMullan

et al. 2016

J. Electrochem. Soc.

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In this study, the impact of galvanic coupling of magnesium to steel on the corrosion rate, surface morphology, and surface film formation was investigated. In particular, experiments were performed to examine and quantify the role of self-corrosion (also called negative difference effect (NDE) or anodic hydrogen) during the corrosion of galvanically coupled Mg. It was found that galvanic coupling at high cathode-to-anode area ratios resulted in high rates of corrosion that impacted hydrogen evolution on the Mg surface. Self-corrosion accounted for, on average, approximately one-third of the total observed corrosion. The self-corrosion fraction varied with time and was found to reach values in excess of 50%. Surface film formation was observed, and approximately 30% of the Mg lost to corrosion was found in the film at the end of our experiments. The surface morphology observed during galvanic corrosion was dramatically different from the filiform structures associated with free corrosion of our samples, but showed similarities to the morphology observed previously for anodically polarized samples. Film formation appeared to slow the rate of self-corrosion with time. These results complement previous studies of Mg corrosion and add important insight into the role of hydrogen evolution on the Mg surface during galvanic corrosion. New environmental regulations, good mechanical properties, abundant availability and reasonable cost have generated renewed interest in the wider use of magnesium (Mg), especially for automobile and aerospace applications.1-4 There has also been growing interest in the use of Mg for batteries and in hydrogen generation systems. 5-8A key obstacle to the use of Mg is its corrosion susceptibility. Consequently, several previous studies have focused on understanding the corrosion mechanisms that control the dissolution rate and surface morphology of Mg during corrosion. Both disk-shaped and filiform corrosion have been observed for unalloyed Mg, depending on the concentration of impurities in the metal and the concentration of Cl − in the electrolyte. [9][10][11] In both cases, the morphology is strongly influenced by the cathodic reaction, which limits the rate of corrosion. 11,12The situation changes dramatically when Mg is coupled to another metal because of the increased cathodic area that significantly diminishes limitations due to the cathodic reaction on the Mg surface. Although most hydrogen evolution occurs on the coupled metal, hydrogen evolution on the Mg surface does not cease. The purpose of this paper is to investigate the impact of galvanic coupling on Mg corrosion that is associated with hydrogen evolution on the Mg surface, and the extent to which such coupling influences both the morphology and rate of Mg self-corrosion.In this paper, we use the term "self-corrosion" to refer to the dissolution of Mg that is not associated with the galvanic current that passes between the coupled metal and the Mg, similar to the definition used previously by others in galvanically coupled st...

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Section: Resultsmentioning

confidence: 99%

Hydrogen Evolution during the Corrosion of Galvanically Coupled Magnesium

Banjade

Porter

McMullan

et al. 2016

J. Electrochem. Soc.

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“…Meanwhile, the water reduction reaction can be enhanced on some cathodic sites produced by active dissolution of Mg in the anodic zone due to the well-known anodic HE. 35 As a result, pH can increase to some extent in the anodic sites which enlarge the surface area with high pH on MgZn 2 . At pH 4, it is found that the lowest pH (pH = 5.5) on MgZn 2 is higher than the bulk solution pH, which is probably due to the anodic HE and the migration of OH − from the higher pH zone (Fig.…”

Section: Discussionmentioning

confidence: 99%

SVET and SIET Study of Galvanic Corrosion of Al/MgZn₂in Aqueous Solutions at Different pH

Ikeuba

Zhang

Wang

et al. 2018

J. Electrochem. Soc.

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The galvanic corrosion behavior of synthesized MgZn 2 intermetallic particle coupled with Al in 0.1 M NaCl solutions across pH 2 to12 has been studied using the scanning vibrating electrode technique (SVET), the scanning ion-selective electrode technique (SIET) and X-ray photoelectron spectroscopy (XPS). Results indicate the galvanic dissolution of MgZn 2 depends on pH as well as exposure time. SVET current density maps reveal that MgZn 2 is anodic relative to Al at pH 2 but cathodic at pH 12, while self-dissolution of MgZn 2 prevails at pH 4 and 6. However, the galvanic coupling effect is more pronounced at pH 2 and 12. SIET maps of H + and Cl − ion distribution reveal evidence of local alkalization on MgZn 2 and migration of Cl − ions away from MgZn 2 surface at pH 4 and 6 due to significant accumulation of OH − ions. High strength 7xxx series Al alloys, which are parts of structural components in the aerospace and automotive industry, are vulnerable to localized corrosion in the presence of chloride ions. The localized corrosion manifests in the form of pitting, crevice, inter-granular and exfoliation corrosion, which increase stress corrosion cracking susceptibility.1,2 Localized corrosion is initiated at microstructural inhomogeneities such as grain boundaries or coarse intermetallic phases. Anodic dissolution of grain boundary precipitates (intermetallic particles) such as MgZn 2 is always considered a probable reason for stress corrosion cracking in Al 7xxx series alloys.3 Galvanic corrosion can occur between the intermetallic particles and the surrounding alloy matrix due to the difference between the electrochemical activity of the particles and the matrix, this leads to the deterioration of Al alloys in engineering materials. 4 The electrochemical behavior of MgZn 2 and its role in corrosion of 7xxx series alloys has been investigated by various researchers using various traditional methods.5-8 For instance, electrochemical testing carried out on MgZn 2 by Birbilis et al. 6,7 and Wloka et al. 9 using the microcell method indicates that MgZn 2 is anodic relative to the matrix and corrodes freely above their corrosion potential. Potentiodynamic polarization carried out by Ramgopal et al. 4 on a thin film analog of MgZn 2 indicates that it is anodically very active. The scanning Kelvin probe force microscopy (SKPFM) investigations on Al 7075 by Andreatta and coworkers 5,10,11 revealed that the initiation of the attack at the intermetallic sites is caused by strong potential differences between the matrix and intermetallics, in particular, MgZn 2 particles along grain boundaries. However, the kinetic parameters relating to the galvanic couples could not be provided. It then becomes obvious that some issues remain regarding the galvanic corrosion behavior of MgZn 2 due to lack of information on the kinetics of local processes occurring at the matrix/ solution interface. 6,7,12,13 These issues include the galvanic current density distribution as well as the pH and ion distributions especially in near neutral...

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“…3,4,12,16,[21][22][23][24][25][26][27] On these metals, with relatively low electrochemical potential for oxidation, hydrogen evolution is always thermodynamically possible in the presence of water, but may be hindered by the presence of an oxide, hydroxide, or mixed film that physically separates the metal surface from the electrolyte. In some conditions, when the film is locally disrupted, such as for example during anodic polarisation in chloride-containing environment or at active corrosion sites (pits) during free corrosion, hydrogen evolution might occur locally, providing additional current sustaining corrosion propagation.…”

Section: Introductionmentioning

confidence: 99%

The contribution of hydrogen evolution processes during corrosion of aluminium and aluminium alloys investigated by potentiodynamic polarisation coupled with real-time hydrogen measurement

et al. 2017

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Water reduction, which leads to the evolution of hydrogen, is a key cathodic process for corrosion of many metals of technological interest such as magnesium, aluminium, and zinc; and its understanding is critical for design of new alloys or protective treatments. In this work, real-time hydrogen evolution measurement was coupled with potentiodynamic measurements on high-purity aluminium and AA2024-T3 aluminium alloy. The results show that both materials exhibit superfluous hydrogen evolution during anodic polarisation and that the presence of cathodically active alloying elements enhances hydrogen evolution. Furthermore, it was observed for the first time that superfluous hydrogen evolution also occurs during cathodic polarisation. Both the anodic and cathodic behaviours can be rationalised by a model assuming that superfluous hydrogen evolution occurs locally where the naturally formed oxide is disrupted. Specifically, during anodic polarisation, oxide disruption is due to the combined presence of chloride ions and acidification, whereas during cathodic polarisation, such disruption is due to alkalinisation. Furthermore, the presence of cathodically active alloying elements enhances superfluous hydrogen evolution in response to either anodic or cathodic polarisation, and results in 'cathodic activation' of the dissolved regions.

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The pH Dependence of Magnesium Dissolution and Hydrogen Evolution during Anodic Polarization

Cited by 71 publications

References 33 publications

Hydrogen Evolution during the Corrosion of Galvanically Coupled Magnesium

Hydrogen Evolution during the Corrosion of Galvanically Coupled Magnesium

SVET and SIET Study of Galvanic Corrosion of Al/MgZn₂in Aqueous Solutions at Different pH

The contribution of hydrogen evolution processes during corrosion of aluminium and aluminium alloys investigated by potentiodynamic polarisation coupled with real-time hydrogen measurement

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The pH Dependence of Magnesium Dissolution and Hydrogen Evolution during Anodic Polarization

Cited by 71 publications

References 33 publications

Hydrogen Evolution during the Corrosion of Galvanically Coupled Magnesium

Hydrogen Evolution during the Corrosion of Galvanically Coupled Magnesium

SVET and SIET Study of Galvanic Corrosion of Al/MgZn2in Aqueous Solutions at Different pH

The contribution of hydrogen evolution processes during corrosion of aluminium and aluminium alloys investigated by potentiodynamic polarisation coupled with real-time hydrogen measurement

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Product

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SVET and SIET Study of Galvanic Corrosion of Al/MgZn₂in Aqueous Solutions at Different pH