Corrosion

Introduction: Corrosion can be generally defined as degradation of materials in a reaction between the material and its environment. The nature of the reactions leading to degradation depends on the class of materials: for metals, corrosion is an electrochemical process, whereas ceramics can fail by purely chemical dissolution. This article mainly discusses the corrosion processes of metallic materials, that is, electrochemical corrosion reactions. First, the thermodynamic and kinetic principles of electrochemical corrosion reactions are introduced, followed by a section on metals passivity. The most relevant modes of corrosion processes are briefly described. Physical–chemical principles of corrosion protection are described. At. | Corrosion S Virtanen University of Erlangen-Nuremberg Erlangen Germany 2009 Elsevier . All rights reserved. Introduction Corrosion can be generally defined as degradation of materials in a reaction between the material and its environment. The nature of the reactions leading to degradation depends on the class of materials for metals corrosion is an electrochemical process whereas ceramics can fail by purely chemical dissolution. This article mainly discusses the corrosion processes of metallic materials that is electrochemical corrosion reactions. First the thermodynamic and kinetic principles of electrochemical corrosion reactions are introduced followed by a section on metals passivity. The most relevant modes of corrosion processes are briefly described. Physical-chemical principles of corrosion protection are described. At the end selected examples of corrosion phenomena encountered in electrochemical power sources are briefly discussed. Basics Thermodynamics Corrosion reactions of metallic materials are of electrochemical nature that is the reaction can be divided into an oxidation reaction anodic reaction and a reduction reaction cathodic reaction . In the case of corrosion metal oxidation reaction eqn I is coupled with the reduction of species in the environment electrolyte - the two most typical reactions taking place in aqueous environments are the reduction of protons eqn II or reduction of oxygen dissolved in water eqn III . Me Men neT I 2H 2e II O2 2H2O le -lOH III The anodic and the cathodic reactions can either take place statistically distributed all over the surface leading to uniform corrosion or be separated at specific cathodic and anodic sites of the surface leading to localized corrosion. The latter phenomena localized corrosion take place when heterogeneities exist either on the material surface . different phases of a multiphase alloy or in the environment . water-line corrosion of partially immersed objects owing to .

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