Electrochemical corrosion definition

Corrosion is a phenomenon that occurs spontaneously in the majority of metals and alloys as a result of their interaction with their environment, which makes them tend toward a situation of stable balance. According to the definition given by the European Corrosion Federation (1974), corrosion is the attack on a metal caused by its reaction to the environment, with the consequent degradation of its properties (Uhlig, 1985 Andrade, 1991). This environment could either be an electrolyte, which is when the process is called electrochemical corrosion, or another high-temperature atmosphere, whenitis called, oxidation, dry corrosion or high-temperature corrosion. 

Definitions of the anode and the cathode are among basic definitions in electrochemical corrosion. The area of the metal surface that corrodes i.e., where the metal dissolves and goes into solution) is called the anode. The cathode is the area of the metal surface that does not dissolve. In the literature of electrochemistry, reduction and oxidation reactions are defined as when metals lose electrons i.e., oxidation) or gain electrons (reduction) ... 

A commonly seen problem with steel piles in ports and jetty stmctures is a type of electrochemical corrosion called accelerated low water corrosion (ALWC) . An integral part of ALWC could be MIC [11]. In fact, some definitions of ALWC do consider MIC an integral part of the definition [12]. This type of corrosion has been observed and reported in ports all around the world, including the USA [13], Europe [12], and Australia [14]. In many cases of ALWC, microbial corrosion manifests itself as a mass which is orange in colour and collectively referred to as orange bloom (Figures 7.3a-d). 

Corrosion is the deterioration of a substance or its properties because of a reaction with its environment. For our purposes, we can be a little more precise in this definition therefore, corrosion is a destructive attack of a metal by either chemical or electrochemical reaction with a given environment [183J. 

The enormous scope of the subject of corrosion follows from the definition which has been adopted in the present work. Corrosion will include all reactions at a metal/environment interface irrespective of whether the reaction is beneficial or detrimental to the metal concerned —no distinction is made between chemical or electropolishing of a metal in an acid and the adventitious deterioration of metal plant by acid attack. It follows, therefore, that a comprehensive work on the subject of corrosion should include an account of batteries, electrorefining, chemical machining, chemical and electrochemical polishing, etc. 

There are many types of corrosion, as would be expected from its general definition. It has been traditional (4) to divide the study of corrosion into two areas the study of low temperature corrosion by aqueous or other solutions, controlled by electrochemical processes (wet) and the study of gaseous corrosion at high temperatures, controlled by thermodynamics and diffusion processes (dry). In addition to the obvious differences, the two areas have many phenomena in common. 

The ohmic drop exerts a sensible influence on the evaluation of the electrochemical parameters as well as on the definition of the reaction scheme that is most suitable for describing the behaviour of a metal in a given environment. It also determines the success of many operations, such as cathodic protection by means of sacrificial anodes or impressed current and corrosion rate monitoring. 

Corrosion may be defined as the spontaneous deterioration of a structure or part of a structure due to the action of the total environment or individual environmental agents. For the purposes of this chapter, the structure is assumed to be metallic and the environment is assumed to be aqueous. Using this definition and the constraints noted, this chapter will outline the electrochemical techniques used to develop criteria of corrosion and those used in the study of corrosion kinetics. 

These three points are very important as they not only imply that MIC is essentially an electrochemical process and, therefore, known corrosion nomenclature for describing electrochanical corrosion can also be applied to it they also imply that the mere existence of microorganisms in the system is not enough to infer that the case is definitely MIC. There are other factors that must be available too so that the case can be suspected to be MIC related. These points may seem to be obvious, but in fact, they are very much ignored in practice. We will get back to this matter later in this chapter (see Section 4.11). 

Corrosion is the destructive attack of a metal by chemical or electrochemical reaction with its environment. Deterioration by physical causes is not called corrosion, but is described as erosion, galling, or wear. In some instances, chemical attack accompanies physical deterioration, as described by the following terms corrosion-erosion, corrosive wear, or fretting corrosion. Nonmetals are not included in this definition of corrosion. Plastics may swell or crack, wood may split or decay, granite may erode, and Portland cement may leach away, but the term corrosion, in this book, is restricted to chemical attack of metals. 

Although there is no external current, anodic and cathodic processes can still occur at sites on the interface between solid and aqueous solution because of the electrolytic conductance of the corrosive medium. At electrochemical equilibrium, this leads to a definite jump in the electrical potential at the phase boundary. Kinetic barriers to certain partial reaction steps of the electrochemical process can cause the potential to be displaced from its equilibrium value. Thus, for example, instead of a dissolution of metal ... 

The two remaining components of the electrochemical industry are corrosion prevention and controlling and measuring devices. In both of these components, our interest is only in those devices whose operation is based on electrochemical principles. Such items fall within our definition of the electrochemical industry. There were no published figures available for the shipments value of either of these two components in 1958 or 1963. As a result, estimates based on interviews and correspondence with members of the industry are given. 

Any chemical transformation that implies the transfer of charge across the interface between an electronic conductor (the electrode) and an ionic conductor (the electrolyte) is referred to as an electrochemical reaction. An electrochemical reaction can include one or several electrode reactions. For example the reaction (1.3) is an electrochemical reaction each atom of iron that passes into solution implies the exchange of two electrons between the metal and the protons. Two electrode reactions are involved the oxidation of the iron and the reduction of the proton. According to the definition given above, all corrosion reactions that involve metal oxidation are electrochemical reactions. In order to understand and control corrosion phenomena it is essential to study the thermodynamics and kinetics of electrochemical reactions. 

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