This chapter develops a corrosion model that accounts for solution potentials and the effects of coupling between cathodic and anodic reactions. It begins by examining potential differences at various points (in the solution) along a path from the anode to the cathode area. It then presents a simple model of a galvanically coupled electrode, in which the metal is represented as an array of anode and cathode reaction surfaces. The chapter goes on to develop the related theory of mixed electrodes, showing how it can be used to predict corrosion rates based on measured potentials and current densities, polarization characteristics, and physical variables such as anode-to-cathode area ratios and fluid velocity. It also discusses the effect of corrosion inhibitors, galvanic coupling, and external currents, making extensive use of polarization curves.

This chapter discusses the principles of corrosion of metals in aqueous environments. The thermodynamics of aqueous corrosion is the subject of the first half of this chapter, which addresses concepts such as corrosion reactions and free-energy change, the relationship between free energy and electrochemical potential, the effect of ionic concentration on electrode potential, and the corrosion behavior of a metal based on its potential-pH diagram. The corrosion (potential-pH) behavior of iron, gold, copper, zinc, aluminum, and titanium are described. Understanding the kinetics of corrosion and the factors that control the rates of corrosion reactions requires examination of the concepts of polarization behavior and identification of the various forms of polarization in an electrochemical cell. These concepts, addressed in the remaining of this chapter, include anodic and cathodic reactions, the mixed-potential theory, and the exchange currents.

Corrosion involves chemical reactions in equilibrium that that are understood through principles of thermodynamics. In practice, the rate at which corrosion reactions occur is the most important consideration. This chapter deals with corrosion kinetics, which allows engineers to to understand rates of corrosion. The discussion covers two kinetic processes, namely electrode reactions at the cathode and anode and conduction of ions in the electrolyte. The chapter also provides information on passivation and its effect on polarization diagrams.

This chapter first covers some basic principles of electrochemical corrosion and then some of the various types of corrosion. Some of the more common types of corrosion discussed include uniform corrosion, galvanic corrosion, pitting, crevice corrosion, erosion-corrosion, cavitation, fretting corrosion, intergranular corrosion, exfoliation, dealloying corrosion, stress-corrosion cracking, and corrosion fatigue. The chapter discusses the processes involved in corrosion control by retarding either the anodic or cathodic reactions. The rate of corrosion is reduced by conditioning of the metal, by conditioning the environment, and by electrochemical control. Finally, the chapter deals with high-temperature oxidation that usually occurs in the absence of moisture.

Corrosion can be defined as a chemical or electrochemical reaction between a material and its environment that causes the material and its properties to degrade. In most cases, it refers to the electrochemical oxidation of metals accompanied by the production of oxides or salts of the base material. This chapter discusses the process of corrosion and how to prevent or mitigate its effects. It describes several forms of corrosion, including uniform, intergranular, pitting, crevice, and stray-current corrosion, and the effects of stress-corrosion cracking, corrosion fatigue, and selective leaching. It discusses the use of corrosion inhibitors, cathodic and anodic protection, pH control, and Pourbaix diagrams.

This article describes in detail the process of corrosion control by cathodic and anodic protection. The discussion covers the basic concept of cathodic and anodic protection systems, their types and equipment used, and the advantages, limitations, and applications of these protection systems. The types of cathodic protection systems include sacrificial cathodic protection and impressed-current cathodic protection systems. Some of the technical problems associated with cathodic protection include the effects of stray currents on the corrosion of adjacent metal structures, the effects of the chemical reactions occurring at the surface of the protected structure, and the effects of cathodic protection on coatings.

This chapter familiarizes readers with the basic concepts of corrosion, discussing chemical reactions, ion transfer mechanisms, electrochemical processes and variables, and the formation of solid corrosion products. It presents a simple but effective teaching tool, the elementary electrochemical corrosion circuit, using it to explain how electric potential differences drive the corrosion process and how corrosion rates vary in proportion to current density. The chapter concludes with a discussion on the importance of corrosion products, such as oxides and hydroxides, and how their formation can be a major factor in controlling corrosion.

This chapter discusses the formation and control of aqueous corrosion in iron and steel. It also provides information on passivation, stress corrosion, rust, and direct oxidation.

This chapter discusses common forms of corrosion, including uniform corrosion, galvanic corrosion, pitting, crevice corrosion, dealloying corrosion, intergranular corrosion, and exfoliation. It describes the factors that contribute to stress-corrosion cracking, hydrogen embrittlement, and corrosion fatigue and compares and contrasts their effects on mechanical properties, performance, and operating life. It also includes information on high-temperature oxidation and corrosion prevention techniques.

Anodic protection is used on a smaller scale than other corrosion control techniques due to the fundamental electrochemistry involved. This chapter provides a brief history of the technique, discusses anodic protection use, and compares anodic and cathodic protection. The background and theory of anodic protection are summarized. In addition to briefly describing the various items used for each component of an anodic protection system, the chapter presents design concerns as well as applications of the system. Factors concerning the economic justification of anodic protection are also described.

This chapter describes some of the chemical processes that have been developed to extract beryllium from different types of ore. It covers the Kjellgren-Sawyer sulfate method, the Degussa method, Copaux-Kawecki fluoride extraction, solvent extraction, and leaching and settling. It also provides information on electrolytic extraction and the use of electrorefining.

This chapter lays the groundwork for understanding electrode kinetics associated with corrosion. It presents a simple but useful theory relating kinetics to the polarization behavior of half-cell reactions. The theory is based on the observation that electrode potentials vary as a function of current density or charge transfer in a given area. The chapter explains how to measure and plot electrode potentials and currents and how to interpret the resulting polarization curves. It also discusses the effects of concentration gradients, explaining how they cause diffusion and, in some cases, produce changes in electrode potential.

This chapter focuses on stress-corrosion cracking (SCC) of metals and their alloys. It is intended to familiarize the reader with the phenomenological and mechanistic aspects of stress corrosion. The phenomenological description of crack initiation and propagation describes well-established experimental evidence and observations of stress corrosion, while the discussions on mechanisms describe the physical process involved in crack initiation and propagation. Several parameters that are known to influence the rate of crack growth in aqueous solutions are presented, along with important fracture features.

This chapter addresses the basic concepts important to understanding corrosion of metals. It begins with an overview of the three types of behaviors that a metal exhibits when immersed in an environment and of the four requirements of a corrosion cell. The chapter then covers the important characteristics of metals with respect to corrosion, namely the metallurgical characteristics, the inherent tendency to corrode, and the tendency to form insoluble corrosion products. The important characteristics of aqueous solutions with respect to corrosion are then addressed. The characteristics include: conductivity of the solution, acidity and alkalinity, oxidizing power, degree of ionization, and solubility in the solution. These characteristics, in combination with the characteristics of the metal, will determine the corrosion behavior of a metal/environment combination. The chapter concludes with a section on the determination of corrosion rates and corrosion rate allowances.

This chapter discusses the conditions and sequence of events that lead to stress-corrosion cracking (SCC) and the mechanisms by which it progresses. It explains that the stresses involved in SCC are relatively small and, in most cases, work in combination with the development of a surface film. It describes bulk and surface reactions that contribute to SCC, including dissolution, mass transport, absorption, diffusion, and embrittlement, and their role in crack nucleation and growth. It also discusses crack tip chemistry, grain-boundary interactions, and the effect of stress-intensity on crack propagation rates, and describes several mechanical fracture models, including corrosion tunnel, film-induced cleavage, and tarnish rupture models.

This chapter focuses on the effects of microscopic organisms and the by-products they produce on the electrochemical corrosion of metals. It begins by considering the characteristics of organisms that allow them to interact with the corrosion processes, the mechanisms by which organisms can influence the occurrence or rate of corrosion, and the types of corrosion most often influenced by microbes. The chapter then discusses the formation of biofilms on the surface of metals. This is followed by a list of industries most often reported as being affected by microbiological corrosion, along with the organisms usually implicated in the attack. The types of attack that have most commonly been documented are illustrated through generalized case histories for different classes of alloys. The chapter also describes the general approaches to be taken to prevent microbiologically influenced corrosion. It ends with some information on the inhibition of corrosion by the action of bacteria.

This chapter discusses the corrosion behavior of titanium, the types of corrosion that can occur, and the effect of alloying on corrosion resistance. It explains that, due to its tenacious oxide film, titanium has excellent corrosion resistance in oxidizing environments and that the resistance can be extended into the “reducing-acid” region by adding a small amount of palladium. It describes how different grades of titanium respond to different forms of attack, including uniform, crevice, and galvanic corrosion. It also identifies applications where corrosion is often a concern.