Abstract
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.
Highlights
Aqueous corrosion is probably the most important single cause of materials degradation and it occurs by the simultaneous oxidation of metal and reduction of species present in the environment
In the case of magnesium immersed in an electrolyte, hydrogen evolution largely dominates on oxygen reduction, as the potential of magnesium in aqueous environments remains at all times «1 V vs. SHE
Hydrogen evolution was initiated, the current associated with hydrogen evolution was larger than the current measured by the Figure 2 presents the behaviour recorded for high purity aluminium (99.99 wt.%) and AA2024-T3 during potentiodynamic polarisations and hydrogen evolution measurements
Summary
Aqueous corrosion is probably the most important single cause of materials degradation and it occurs by the simultaneous oxidation of metal and reduction of species present in the environment. In order to preserve charge neutrality, the oxidation (anodic) and reduction (cathodic) reactions must proceed at the same rate; the slower of the two processes determines the overall corrosion rate. The most important cathodic reaction in practical cases is the reduction of oxygen dissolved in the aqueous environment. For more reactive materials, i.e. with a low electrochemical potential for metal oxidation such as zinc, aluminium and magnesium, the reduction of hydrogen cations from water is thermodynamically possible and might provide a substantial contribution to the overall corrosion rate.[1] In the case of magnesium immersed in an electrolyte, hydrogen evolution largely dominates on oxygen reduction, as the potential of magnesium in aqueous environments remains at all times «1 V vs SHE. An improved understanding of the hydrogen evolution mechanism for both metals, and the identification of strategies to minimise it, would enable better alloy design and development of innovative protection measures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
