Published: Jan 1988
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Galvanic corrosion can be defined simply as that corrosion that occurs as a result of one metal being in electrical contact with another in a conducting corrosive environment. The corrosion is stimulated by the potential difference that exists between the two metals, the more noble material acting as a cathode where some oxidizing species is reduced, the more active metal, which corrodes, acting as the anode. To fully understand this process it is first necessary to understand the basic thermodynamics and kinetics of electrochemical reactions. These are considered with particular reference to exchange current densities and the factors that control them, linear and Tafel kinetics, concentration and mass transfer effects, and mixed potential theory. The practical side of galvanic corrosion and its relationship to electrochemical parameters is considered with particular reference to the most important cathodic processes, that is, oxygen reduction and hydrogen evolution, as they occur on engineering materials, for example, steel, stainless steel, copper base alloys, and so forth and to the general form of the anodic processes that occur. Finally the use of galvanic series as a predictive tool is discussed. In addition methods used to model galvanic situations with the aim of predicting corrosion are briefly mentioned and their advantages and limitations outlined.
galvanic corrosion, mixed potentials, galvanic series, mathematical modelling, oxygen reduction, hydrogen evolution, electrochemical theory
Manager of corrosion, Cortest Laboratories Ltd., Sheffield,