Electrochemical corrosion

This chapter summarizes some of the important electrochemical principles and mechanisms controlling the aqueous corrosion of metals and alloys. It describes the way principles in electrochemical thermodynamics are used to predict whether or not corrosion will occur for a given metal in a given electrolyte at a given temperature. Sufficient detail was provided to allow these calculations. The thermodynamics calculations are also related to Pourbaix diagrams to provide an understanding of the source of these useful summary diagrams. Simple Tafel or charge-transfer polarization behavior is defined for anodic and cathodic half-reactions and appropriate equations are given. This simple behavior is expanded to include diffusion effects and active-passive behavior. Analyses of individual polarization curves and experimentally determined polarization curves are discussed relative to determining the open-circuit corrosion potential and the corrosion current density. The chapter derives Faraday's law, which allows calculation of the corrosion intensity or corrosion penetration rate from corrosion current density under the assumption of uniform corrosion. Several examples of specific types of electrochemical corrosion measurements and characterizations are also described.