Electrochemical methods applied to corrosion

The fundamental study of corrosion phenomena in a wet environment is essentially a matter of electrochemistry. The applied study of corrosion phenomena is a field of materials science that involves both chemistry and physics. Corrosion takes place on the surface of metallic materials exposed to a chemically aggressive environment. Not only the initiation of corrosion, but also its propagation are essentially surface processes, both chemical and electrochemical. To study these mechanisms, electrochemical techniques are essential.

This article, which deals with electrochemical techniques for the study of corrosion, first examines methods which focus on the macroscopic characterization of corrosion, i.e. the identification of the processes involved, averaged over the entire surface of the sample studied by methods using current-potential curves or impedances. On the other hand, in order to deepen our understanding of these processes, more detailed analyses are presented, at the level of the elementary events leading to corrosion, through the analysis of electrochemical noise, and at the microscopic level at the surface of the sample, through local characterization of corrosion processes using appropriate methods.

The first part of this article provides a general overview of corrosion, focusing in particular on the difference between uniform and localized corrosion.

The second part gives a brief overview of the instrumentation used to carry out steady-state corrosion studies. Standard cells are used, and only special cells for microelectrochemical techniques are reviewed. The classic electrical instrumentation – potentiostat, galvanostat, potential and current measuring devices – will be briefly reviewed.

The third part describes the oldest DC electrochemical methods, which are still widely used today. Polarization curves and the notion of polarization resistance are developed, and the parameters that can be derived from them are explained. Their use is illustrated by concrete examples. An application using the quartz crystal microbalance to measure weight loss is given.

Finally, the last part deals with measurements leading to local corrosion characterization. Techniques for obtaining current-potential curves on small parts of the surface of the sample under study, using microprobes or microcells, are reviewed.

Dynamic techniques, in particular impedance and electrochemical noise, are covered in the article