abstract
This article provides a contribution towards the mechanistic understanding of surface phenomena observed during the corrosion of Mg-based substrates particularly in the low anodic polarization range. The concept considers the recent literature explaining cathodic hydrogen evolution from noble acting areas even during global anodic polarization. Heavy metal impurities in the ppm range or intermetallics are always present even in highly pure magnesium. Their potential effect was investigated here in more detail. The experimental results contribute to understanding the role of iron impurities in dark area formation and suggest a way for linking the observed phenomena to the recent literature. The shown enhanced cathodic activity of dark areas especially at the corrosion front and the superfluous hydrogen are linked to an iron re-deposition mechanism due to iron reduction. The proposed mechanism is based on the results obtained from innovative characterisation techniques using magnetic fields, diffraction experiments and transmission electron microscopy, which show the formation of iron rich zones, especially at the corrosion front offering "in statu nascendi'' metallic Fe films acting as active cathodes for hydrogen reduction.
keywords
HYDROGEN EVOLUTION REACTION; ENHANCED CATALYTIC-ACTIVITY; PURE MAGNESIUM; ALKALINE-SOLUTION; GALVANOSTATIC DISSOLUTION; ANODIC POLARIZATION; ELECTROCHEMICAL BEHAVIOR; WATER ELECTROLYSIS; VOLMER-HEYROVSKY; MG SURFACES
subject category
Chemistry; Physics
authors
Hoche, D; Blawert, C; Lamaka, SV; Scharnagl, N; Mendis, C; Zheludkevich, ML
our authors
Mikhail Zheludkevich
Invited Principal ResearcherGroups
acknowledgements
Dr Hoche would like to thank Dr W. Dietzel for input and discussions, Dr A. Schwarz from University of Hamburg for assisting the ferrofluid application, Dr Marc Willinger and Michael Scherzer from the Department of Inorganic Chemistry at Fritz Haber Institute of the Max Planck Society for their contribution to the diffraction experiments and Eng. U. Burmester for setting up the experimental equipment. Dr Lamaka acknowledges the financial support of Alexander von Humboldt Foundation via the Experienced Researcher Grant.