The Video-Microscopy Linked Electrochemical Cell – An Innovative Method Allowing for a More Accurate Interpretation of Electrochemical Measurements of Magnesium Degradation

Abstract

An innovative miniature 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 magnesium samples. The setup consists of a miniature electrochemical cell that is clamped onto the magnesium sample before being filled with electrolyte, bringing a sample surface area of about 0.8 mm2 in contact with the electrolyte. The miniature cell comprises afferent/efferent electrolyte ducts as well as a connection to the Mini Cell System (MCS), a combination counter and reference electrode that itself is connected to a potentiostat. The transparent roof of the electrolytic cell allows optical microscopic access to the corroding magnesium surface. Consequently, all measured and induced currents and voltages refer 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 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 alloys and modifications for use as absorbable stents or orthopedic implants. Different electrochemical test can be run under various conditions, while being easy to set up and reproduce as well as being minimally destructive to the sample.