Electrochemical processes, corrosion

Electrochemistry is a field, where control of experiments and data acquisition methods do not differ greatly, but proper interpretation of measured data gives information on several different phenomena. In electrochemical experiments one controls the system with electrical quantities and also measures electrical quantities, i.e. voltage and current. The electrochemical corrosion process, its probability and rate can be described as a function of three variables potential, current and time. Other electrical and electrochemical parameters can be derived from these variables. As an electrochemical process, corrosion can also be studied with electrical measurement methods. The measurements are suitable for automation which has the following advantages ... 

M N Alias and R Brown, Damage to composites from electrochemical processes , Corrosion 1992 48(5) 373-378. 

We then study a spontaneous electrochemical process—corrosion—and leam ways to prevent it. (19.7)... 

G lv nic Corrosion. Galvanic corrosion is an electrochemical process with four fundamental requirements (/) an anode (magnesium), 2) a cathode (steel, brass, or graphite component), (J) direct anode to cathode electrical contact, and (4) an electrolyte bridge at the anode and cathode interface, eg, salt water bridging the adjacent surfaces of steel and magnesium components. If any one of these is lacking, the process does not occur (133,134). 

The industrial economy depends heavily on electrochemical processes. Electrochemical systems have inherent advantages such as ambient temperature operation, easily controlled reaction rates, and minimal environmental impact (qv). Electrosynthesis is used in a number of commercial processes. Batteries and fuel cells, used for the interconversion and storage of energy, are not limited by the Carnot efficiency of thermal devices. Corrosion, another electrochemical process, is estimated to cost hundreds of millions of dollars aimuaUy in the United States alone (see Corrosion and CORROSION control). Electrochemical systems can be described using the fundamental principles of thermodynamics, kinetics, and transport phenomena. 

The active and passive electrochemical processes on which present-day corrosion protection is based were already known in the 19th century, but reliable protection for pipelines only developed at the turn of the 20th century. 

Corrosion is essentially an electrochemical process, wherein the oxidation of metals or alloys to their (lower energy state) oxides or cations takes place. 

Section 8 deals with reactions which occur at gas—solid and solid—solid interfaces, other than the degradation of solid polymers which has already been reviewed in Volume 14A. Reaction at the liquid—solid interface (and corrosion), involving electrochemical processes outside the coverage of this series, are not considered. With respect to chemical processes at gas-solid interfaces, it has been necessary to discuss surface structure and adsorption as a lead-in to the consideration of the kinetics and mechanism of catalytic reactions. 

Corrosion is the unwanted oxidation of a metal. It cuts short the lifetimes of steel products such as bridges and automobiles, and replacing corroded metal parts costs billions of dollars a year. Corrosion is an electrochemical process, and the electrochemical series is a source of insight into why corrosion occurs and how to prevent it. 

The recovery of petroleum from sandstone and the release of kerogen from oil shale and tar sands both depend strongly on the microstmcture and surface properties of these porous media. The interfacial properties of complex liquid agents—mixtures of polymers and surfactants—are critical to viscosity control in tertiary oil recovery and to the comminution of minerals and coal. The corrosion and wear of mechanical parts are influenced by the composition and stmcture of metal surfaces, as well as by the interaction of lubricants with these surfaces. Microstmcture and surface properties are vitally important to both the performance of electrodes in electrochemical processes and the effectiveness of catalysts. Advances in synthetic chemistry are opening the door to the design of zeolites and layered compounds with tightly specified properties to provide the desired catalytic activity and separation selectivity. 

Electrochemical processes (e.g., electrolysis, electroplating, electromachirring, crrnetrt generation, and corrosion [Plate 8]) are distinguished by their occturence in a boundary region between an electrolyte (liqtrid or solid) and an electrode. The corrrse of these processes is strongly dependent on the potential at the electrode surface, the composition and stmcture of the electrode, the composition of the electrolyte, and the microstmcture of the electrolyte in the boundary layer near the electrode surface. In certain applications, the pore size and coimectivity of the electrode can also be important. 

Electrochemical processes in melts are often attended by side reactions and phenomena complicating the primary process. This is true, in particular, for the technically very important class of reactions in which a number of metals (calcium, barium, and others) are obtained electrometallurgically from molten salts. In many of these processes the metal that is deposited (sometimes in a highly disperse state) is found to interact with the corrosive melt for example, in a reaction such as... 

Metal-water and solution-metal interfaces is of primary importance since many electrochemical processes occur there that are relevant for electrocatalysis, corrosion. 

Modem electrochemistry has vast applications. Electrochemical processes form the basis of large-scale chemical and metaUnrgical production of a number of materials. Electrochemical phenomena are responsible for metallic corrosion, which causes untold losses in the economy. Modem electrochemical power sources (primary and secondary batteries) are used in many helds of engineering, and their production figures are measured in billions of units. Other electrochemical processes and devices are also used widely. 

In general, the physical state of the electrodes used in electrochemical processes is the solid state (monolithic or particulate). The material of which the electrode is composed may actually participate in the electrochemical reactions, being consumed by or deposited from the solution, or it may be inert and merely provide an interface at which the reactions may occur. There are three properties which all types of electrodes must possess if the power requirements of the process are to be minimized (i) the electrodes should be able to conduct electricity well, i.e., they should be made of good conductors (ii) the overpotentials at the electrodes should be low and (iii) the electrodes should not become passivated, by which it is meant that they should not react to form on their surfaces any compound that inhibits the desired electrochemical reaction. Some additional desirable requirements for a satisfactory performance of the cell are that the electrodes should be amenable to being manufactured or prepared easily that they should be resistant to corrosion by the elements within the cell that they should be mechanically strong and that they should be of low cost. Electrodes are usually mounted vertically, and in some cases horizontally only in some rare special cases are they mounted in an inclined manner. 

Metallic corrosion is essentially an electrochemical process. Four components are necessary to set up an electrochemical cell ... 

McNeil, M. and Selwyn, L.S. (2001). Electrochemical processes in metallic corrosion. In Handbook of Archaeological Sciences, ed. Brothwell, D.R. and Pollard, A.M., Wiley, Chichester, pp. 605-614. 

Electrochemical Characterization Technloues. Since corrosion Is an electrochemical process, It Is not surprising that a considerable amount of work has been reported over the years on electrical and electrochemical techniques for the study of the corrosion process. Leldhelser Ql.) and Szauer (12.> 11) have provided good reviews of the principal techniques. Walter has recently provided a review of DC electrochemical tests for painted metals (14). Both AC and DC methods have been employed to study a variety of Issues related to corrosion and corrosion protection. DC techniques are especially useful for studying substrate processes, while AC impedance techniques are most useful for studying processes relating to coated substrates and the performance of coatings. 

Flash rusting exhibited in neutral to alkaline water borne formulations appears to occur through a localised corrosion process probably Involving grit "activity" present from blasting, either directly or indirectly, in an electrochemical process. At such pH the rapid oxidation of ferrous to ferric ion produces... 

Metallic corrosion is an electrochemical process associated with the flow of current between surface sites having a difference in electrochemical potential. The assessment and evaluation of organic coatings to prevent metal corrosion has traditionally been accomplished through salt fog testing (ASTM B-117) and long term exposure tests in particular service environments. Electrochemical techniques have often been considered (, but are not routinely employed in practice. 

The corrosion process that occurs in de-adhered regions under paint is driven by an electrochemical process in which a portion of the area is anodic in nature and another portion is cathodic in nature. The reality of this electro-chemical process can be confirmed when pH indicators or substances sensitive to iron ions are placed beneath the coating such that the sharp distinction between... 

The measurements discussed above describe the effects of the BTA, PVI-1, and UDI on the electrochemical processes. believed to be Involved in Cu corrosion at relatively high overpotentials. Open-circuit potential and linear polarization measurements were made in UDI solutions in order to correlate the high overpotential measurements to practical corrosion potentials. 

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