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

Abstract

This work illustrates how side-view optical imaging, anodic potentiodynamic polarization, and real-time hydrogen evolution measurements can be applied and complementarily 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 is only covered by a poorly protective chloride-rich film. Regardless of the precise nature or morphology of the poorly protective (or absent)...