An Introduction to Corrosion and Protection of Metals

Corrosion may be defined as an unintentional attack on a material through reaction with a surrounding medium. The term can refer to a process or to the damage caused by such a process. According to this general definition, materials other than metals, such as ceramics, plastics or concrete, may also be subject to corrosion (or corrode). When no particular reference is made to the material, however, it is normally understood that a metal is being attacked. It is entirely in this limited sense that the term is used in this book. There are good reasons for treating the corrosion of metals separately, apart from deterioration or decay of other materials. Since metals have a high electric conductivity, their corrosion is usually of an electrochemical nature. The chemical deterioration of electrically non-conducting ma terials, such as plastics and ceramics, is governed by other physico-chemical principles. It is necessary to devote more attention to metallic corrosion nowadays than earlier, due to 1. An increased use of metals within all fields of technology. 2. The use for special applications, e.g. within the atomic energy field, of rare and expensive metals, whose preservation requires particular precautions. 3. A more corrosive environment due to the increasing pollution of air and water. 4. The use of metallic constructions of more slender dimensions which do not tolerate corrosive attacks to the same extent as did the heavy constructions used in the old days.

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1 Electrochemical elements.- 1.1 Electric conductance.- 1.2 Electrode potentials.- 1.3 Polarization.- 1.4 Potential-distance diagrams and potential-arrow diagrams.- 1.1 Measurement of electrode potentials and polarization.- 1.2 Polarization curves.- 2 Metallurgical elements.- 2.1 Metals and alloys.- 2.2 Carbon and low-alloy steels.- 2.3 Stainless steels.- 2.4 Heat treatment of steels.- 2.5 Slag inclusions in steel.- 2.6 Some important copper and nickel alloys.- 3 Metallic corrosion in various environments.- 3.1 Various methods of systematization of the corrosion field.- 3.2 Systematization of corrosion phenomena according to environment.- 3.3 Corrosion in moist environments, electrochemical mechanism.- 3.4 Corrosion in fused salts and slags, electrochemical mechanism.- 3.5 Corrosion (oxidation) in dry gases (air, smoke gases, steam at high temperature); chemical mechanism.- 3.6 Corrosion in water-free organic liquids and gases; chemical mechanism.- 3.7 Corrosion in molten metals; physical mechanism.- 4 Potential-pH diagrams.- 5 The kinetics of electrochemical corrosion; passivity.- 5.1 Electrode potentials of corroding system: the galvanic series.- 5.2 Mixed potentials: potential-current diagrams.- 5.3 Experimental demonstration of the electrochemical nature of metallic corrosion.- 5.4 Local and general electrochemical corrosion.- 5.5 Passivity.- 6 Hydrogen evolution and oxygen reduction corrosion.- 6.1 Different cathode processes in electrochemical corrosion.- 6.2 Hydrogen evolution corrosion.- 6.3 Oxygen reduction corrosion.- 7 Some important types of electrochemical corrosion.- 7.1 Corrosion cells, acting in electrochemical corrosion.- 7.2 Galvanic macro-cells; galvanic corrosion.- 7.3 Galvanic micro-cells (local cells).- 7.4 Oxygen concentration cells(differential aeration cells).- 7.5 Metal ion concentration cells.- 7.6 Active-passive cells.- 7.7 Electrolytic cells.- 8 Corrosion types, influenced by mechanical factors.- 8.1 Stress corrosion cracking.- 8.2 Hydrogen-induced cracking (HIC) and sulphide stress cracking (SSC).- 8.3 Corrosion fatigue.- 8.4 Erosion corrosion.- 8.5 Cavitation corrosion.- 8.6 Fretting corrosion (frettage).- 9 Atmospheric corrosion.- 10 Corrosion in soil.- 10.1 Soil as a corrosion medium.- 10.2 Comparison between corrosion in soil, air and water.- 10.3 Pitting in soil corrosion.- 10.4 Corrosion of archaeological finds.- 10.5 Corrosion in soil as a method for refining iron.- 10.6 Corrosion problems in the final disposal of spent nuclear fuel rods.- 11 Corrosion in dry gases.- 12 Corrosion protection by change of metal and by design.- 12.1 Change of composition or structure and of stress or surface condition of the metal.- 12.2 Design for corrosion prevention.- 13 Corrosion protection by change in the corrosive medium.- 13.1 Removal of corrosive constituents.- 13.2 Addition of corrosion-retarding substances (inhibitors).- 14 Corrosion protection by change of the electrode potential metal/corrosive medium.- 14.1 Electrochemical (cathodic and anodic) corrosion protection.- 14.2 Cathodic protection.- 14.3 Anodic protection.- 15 Corrosion protection by means of surface coatings.- 15.1 Pretreatment of metal surfaces before the application of surface coatings.- 15.2 Metallic surface coatings.- 15.3 Inorganic, non-metallic coatings.- 15.4 Organic coatings.- 16 Corrosion testing.- 16.1 Different types of corrosion test.- 16.2 Variation of corrosion velocity with time.- 16.3 Characterization of test materials.- 16.4 Control of experimental conditions in laboratory tests.- 16.5 Various methodsfor the evaluation of corrosion tests.- 16.6 Some applications of accelerated laboratory testing.- 17 Potential-pH diagrams for some technically important metals.- General Bibliography.- Appendix: Conversion factors from some American to SI units.