Corrosion basic concepts

CORROSION CONSIDERATIONS 11.3.1 Corrosion—Basic Concepts Revisited... 

The subject is also closely related to fuel-ash corrosion which in most cases is caused by a layer of fused salts such as sulphates and chlorides Attention has been focused on the electrochemistry of this type of corrosion and the relevant thermodynamic data summarised in the form of diagrams . Fluxing and descaling reactions also resemble in some respects reactions occurring during the corrosion of metals in fused salts. A review of some of the more basic concepts underlying corrosion by fused salts (such as acid-base concepts and corrosion diagrams) has appeared. ... 

Considerable progress has been made during the past decade toward a better insight into the basic concepts and mechanism involved in metallic dissolution and corrosion. More emphasis has been placed on the "fundamental particles (metallic ions, electrons, and electron acceptors) and on the use of current-voltage characteristics. The wide recognition of dissolution and corrosion as electrode processes, and the idea of a polyelectrode exhibiting a mixed potential, have augmented the use of electrochemical techniques in the study and interpretation of corrosion phenomena. There is even some evidence that the phenomenon of passivity may soon be clarified. 

Oxidation-reduction processes are responsible for many t)q es of chemical change. Corrosion, the operation of a battery, and biochemical energy-harvesting reactions are a few examples. In this section we explore the basic concepts underlying this class of chemical reactions. 

The model had been originally proposed for a buried pipeline. The basic concept of the model was to divide the pipe and its surroundings into components and subsystems (Figure 4.50) and evaluate the risk of corrosion (and MIC) for each. 

For master s degree level and engineers. Basic concepts, electrochemical engineering, with an exhaustive study of industrial applications, including surface treatment, corrosion and sensors. 

Abstract Corrosion is basically the oxidation of metals, where electrons are transferred between oxidant and reductant. Therefore, corrosion is generally composed of redox reactions and should be analyzed from the viewpoint of electrochemistry. In this chapter, we describe the basic concept of electrochemistry and how various corrosion aspects can be explained by this discipline. We focus particularly on the equilibrium side because it could suggest possibilities that might be useful for corrosion prediction. The close relationship between redox reactions and corrosion are explained and stressed qualitatively and quantitatively. 

The specimen (after these tests) is evaluated for its extent of corrosion. If it would be genuine research, we could use various electron microscopies such as TEM, SEM, XPS, etc. However, we usually use a rating number method for the evaluation from the practical standpoint. Figure 10 shows schematic figures for the method. We can evaluate the distribution situation by the naked eye, by comparing the tested specimen to the standard samples. There are some other methods similar to the salt spraying test and the CASS test. However, the basic concept for the evaluation method is almost the same. The solution, temperature, and amount of spraying are varied from test to test. 

Under which conditions is it possible for metal corrosion to occur The answer to this fundamental question requires the study of chemical and electrochemical equilibria only then can we begin to understand and to quantify corrosion phenomena. The chapter begins with some basic concepts about chemical equilibrium these will... 

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