Corrosion electrochemistry practical processes

The processes of cathodic protection can be scientifically explained far more concisely than many other protective systems. Corrosion of metals in aqueous solutions or in the soil is principally an electrolytic process controlled by an electric tension, i.e., the potential of a metal in an electrolytic solution. According to the laws of electrochemistry, the reaction tendency and the rate of reaction will decrease with reducing potential. Although these relationships have been known for more than a century and although cathodic protection has been practiced in isolated cases for a long time, it required an extended period for its technical application on a wider scale. This may have been because cathodic protection used to appear curious and strange, and the electrical engineering requirements hindered its practical application. The practice of cathodic protection is indeed more complex than its theoretical base. 

We saw above that the study of the competition between Fe3+ and H + reduction on illuminated p-GaP led to an increased understanding of the nature of surface electrochemical processes on that material. For many n-type materials, however, the most serious competing reaction with the oxidation of some redox couple in solution is the oxidative corrosion of the semiconductor itself. This has considerable practical consequencies a photoelectrochemical device for the conversion of solar energy must be one in which the desired electrochemical route is overwhelmingly probable compared with semiconductor dissolution. So essential is this requirement, and so difficult has it proved to find satisfactory solutions for n-type semiconductors, that a substantial fraction of the recent literature on semiconductor electrochemistry has been devoted to both practical and theoretical considerations of the problem. 

In our examples of the electrolysis of NaCl, the electrodes are inert they do not react but merely serve as the surface where oxidation and reduction occur. Several practical applications of electrochemistry, however, are based on active electrodes—electrodes that participate in the electrolysis process. Electroplating, for example, uses electrolysis to deposit a thin layer of one metal on another metal to improve beauty or resistance to corrosion. Examples include electroplating nickel or chromium onto steel and electroplating a precious metal like silver onto a less expensive one. 

It is important to emphasise that the above theoretical approach for the electrochemical decomposition of PFC has been developed for the whole electrochemical system without separating it into the cathode and anode sub-systems. Remembering modem theoretical electrochemistry, we must admit that such approach is not common. Really, the partial cathode and anode processes used to be studied separately at different electrodes (except for corrosion studies). It is believed that the adequate pattern can be obtained for the whole system by mechanical joining the separate mechanisms together. Is it valid every time and everywhere The answer is no. We should consider it only as practically useful simplification and remember that there are situations where it is no longer true. 

Although corrosion is an important example of electrochemical processes, we need to realize that it alone does not define electrochemistry. There are many important applications of electrochemistry that provide useful products for society rather than degrading them. The refining of some metal ores into useable materials and the production of batteries are two obvious examples of the practical utility of electrochemistry. But even in the production of batteries, we need to consider additional manufacturing steps to reduce the impact of corrosion on the useful lifetime of the battery. Where does corrosion occur in a battery, and what can be done to combat it The study of electrochemical principles will help us answer these questions. 

Fortunately, the rewards of research are complementary, and whatever direction or thrust a particular spectroelectrochemical project may take, several fields of science ultimately may benefit. The interchange of knowledge and ideas in electrochemistry and surface science at the analytical-physical interface, for example, is notable. Such progress offers a better understanding of electrochemical processes through theoretical advances and experimental discovery or validation, by both pure and applied motivation. These new electroanalytical techniques permit reevaluation of important practical electrochemical systems such as corrosion mechanisms, biochemical redox intermediates, kinetic and catalytic processes of analytical and chemicals production importance, and optical devices. Spectroelectrochemistry continues to be an exciting and challenging field in which to work. 

In this chapter, we will see how chemical reactions can be used to produce electricity and how electricity can be used to cause chemical reactions. The practical applications of electrochemistry are countless, ranging from batteries, fuel cells, and biological processes to the manufacture of key chemicals, the refining of metals, and methods for controlling corrosion. Before we can understand such applications, we must first discuss how to carry out an oxidation-reduction reaction in an electrochemical cell and explore how the energy obtained from, or supplied to, an electrochemical cell is related to the conditions under which the cell operates. 

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