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Corrosion is an electrochemical reaction of a metal and its environment. The aim of this paper is to provide an understanding of some of the electrochemical processes that result in corrosion and to provide a reference compendium of the present state of the art laboratory test methods used to evaluate these reactions. An analysis of the mechanism of electrochemical corrosion needs to try to identify anodic and cathodic corrosion partial processes, establish the thermodynamic possibility of these processes (the tendency to corrode), and determine the kinetics of these processes (the rate of corrosion). A study of the thermodynamic relationship of the solution pH to the system potential indicates the corrosion product ions or precipitates with the lowest free energy. When corrosion occurs, the current that flows between individual small anodes and cathodes on the metal surface causes the electrode potential of the system to change. While this current cannot be measured, it can be evaluated indirectly on a metal specimen with an inert electrode and an external electrical circuit. Kinetic polarization is described as the extent of the change in potential of an electrode from its equilibrium potential caused by a net current flow to or from the electrode, galvanic or impressed. This review covers the several laboratory electrochemical test methods used to identify and evaluate these metallic corrosion reactions.
corrosion, electrical resistance, electrochemical corrosion, impedance, velocity, immersion corrosion testing, controlled potential, Tafel extrapolation, linear polarization, potentiodynamic polarization, kinetic polarization, corrosion behavior diagram, pitting corrosion, crevice corrosion, thermodynamic EMF-pH diagrams, Poubaix diagrams, slow strain rate
Senior fellow, Monsanto Company, St. Louis, MO