The Video Microscopy-Linked Electrochemical Cell: An Innovative Method to Improve Electrochemical Investigations of Biodegradable Metals

An innovative, miniature video-optical-electrochemical cell was developed and tested that allows for the conducting of electrochemical corrosion measurements and simultaneous microscopic observations over a small, well-defined surface area of corroding or degrading samples. The setup consisted of a miniature electrochemical cell that was clamped onto the metal sample and fixed under a video microscope before being filled with electrolyte. The miniature cell was comprised of afferent/efferent electrolyte ducts as well as a connection to the Mini Cell System (MCS) for electrochemical measurements. Consequently, all measured and induced currents and voltages referred to the same small area corroding completely within the field of view of the microscope, thus allowing for real-time observation and linking of surface phenomena such as hydrogen evolution and oxide deposition to electrochemical data. The experimental setup was tested on commercial purity (cp) and extra-high purity (XHP) magnesium (Mg) samples using open circuit potential and cyclic voltammetry methods under static and flowing conditions. The corrosion potential was shifted more anodically for cp Mg in comparison to XHP Mg under dynamic conditions. The corrosion current assessed from the cyclic voltametric curves were higher for the cp Mg in comparison to XHP Mg. However, there were no differences between static and flow conditions in the case of XHP Mg in contrast to cp Mg, where the current density was two times higher at dynamic conditions. The measurements and observations with this new method pave the way for a more detailed understanding of magnesium corrosion mechanisms, thus improving predictive power of electrochemical corrosion measurements on newly developed magnesium or other biodegradable alloys applied for medical devices. Different electrochemical tests can be run under various conditions, while being easy to set up and reproduce as well as being minimally destructive to the sample.