Examples of Corrosion

In corrosion, adsorbates react directly with the substrate atoms to fomi new chemical species. The products may desorb from the surface (volatilization reaction) or may remain adsorbed in fonning a corrosion layer. Corrosion reactions have many industrial applications, such as dry etching of semiconductor surfaces. An example of a volatilization reaction is the etching of Si by fluorine [43]. In this case, fluorine reacts with the Si surface to fonn SiF gas. Note that the crystallinity of the remaining surface is also severely disrupted by this reaction. An example of corrosion layer fonnation is the oxidation of Fe metal to fonn mst. In this case, none of the products are volatile, but the crystallinity of the surface is dismpted as the bulk oxide fonns. Corrosion and etching reactions are discussed in more detail in section A3.10 and section C2.9. 

Reactions that involve the transfer of electrons are immensely beneficial in a vast range of chemical processes, from the operation of a battery to the transmission of nerve impulses. However, in the form of corrosion, electron-transfer reactions also can be highly destructive. The rasting of iron objects is a prominent example of corrosion. 

Examples of corrosion-resistant designs of sewer systems are found in Kienow and Pomeroy (1978) and ASCE (1989), for example. 

Rusting is an example of corrosion, which is a spontaneous redox reaction of materials with substances in their environment. Figure 11.27 shows an example of the hazards that result from corrosion. 

Almost all metallic materials in practical environments perform their service in the state of spontaneous passivation, in which hydrated oxygen moleciiles or hydrogen ions act as oxidants to passivate the surfaces. Stainless steel is a good and widely known example of corrosion resistant metals it is spontaneously passivated and remains in the passive state with a thin passive oxide film even in fairly corrosive environments. 

Strong acids, bases, or oxidizers can cause permanent eye damage, skin bums, and, if swallowed, gastrointestinal damage. Examples of corrosive products include alkaline drain cleaners and oven cleaners, acid-based toilet bowl cleaners and rust removers, concentrated disinfectants, and some concentrated pesticides, especially fungicides. 

Corrosion> A process of gradual disintegration or decomposition of a chem nature. The most common example of corrosion is the rusting of iron in air or acidic water. Corrosion of metals is electrochemical in nature. Extensive info is available in the literature regarding measures that have been and can be taken to minimize or prevent various forms of corrosion which occur in industries. It is important to recognize the various forms of corrosion and to effectively apply the available info in or der to overcome corrosion problems. See the Refs given below... 

Another example of corrosion is electrochemical corrosion. A well-known example of this is the rust formation on the body of a car. Such a process requires two electrochemical elements, transport of electrons and a closed circuit . Suppose two steel tubes are connected by means of a copper fitting and water flows through them. In that case electrons from the iron atoms in the steel will move in the direction of the fitting and the thus formed Fe2+ ions will be given off to the flowing water. The tube decays . 

One can see from this how both kinetics factors (the i0 s) and thermodynamic ones, the s, affect the corrosion rate. The cathodic anodic tends to be a positive number so that the thermodynamic effects are very large. Finally, a number of practical examples of corrosion are given which show the two reactions that make up a corrosion saturation andjust where they occur. 

This example of corrosion provides a general reason why paint and coatings of various kinds are only a partial answer to the corrosion-prevention problem. They often tend to develop cracks or pinholes, and these exposed spots provide access to oxygen for the electronation reaction, which results in unseen corrosion of the surrounding areas. 

Examples of corrosion resistance of many metals and alloys in a variety of media and conditions that are available in the literature and given in the following books mentioned in the Bibliography [NACE Graver ed., 1985 ASM International, 1995 Schweitzer, 1986 De Renzo, 1985 McNaughton, 1980 ASM International, 1990 Climax Molybdenum Company, 1961]. 

The selective corrosion of cast iron (graphitization), the preferential corrosion of the steel welding (grooving corrosion), sensitization and knife line attack of welded stainless steels are typical examples of corrosion influenced by metallurgical parameters. 

Write the two half-reactions for this example of corrosion. 

Crevice corrosion is yet another example of corrosion caused by a difference in oxygen concentration between two areas on the metal surface. In this case, the region of low oxygen concentration lies inside a crevice caused by the overlapping of a piece of metal or other material, e.g. the crevice which exists under a washer pressed onto a metal surface (Fig.6). Even if the washer is insulating (e.g. nylon) as is used for mounting test coupons, corrosion will still occur. 

The clear liquid yielded saltpeter upon drying. The juxtaposition of these two methods—distillation vs. precipitation —relayed Geoffroy s hope that the laws of rapports could mediate between the different chemical procedures to shape a uniform terrain of chemical theory. By going through a variety of processes that produced corrosive sublimates, Geoffrey illustrated that the same order of rapports could explain all the varieties of chemical operations in a consistent manner. The theory of the process was the same, no matter what the variations in practice were. Through the example of corrosive sublimates, Geoffroy thus presented concisely and powerfully the descriptive, predictive, and explanatory functions of his table of rapports. 

In this chapter, corrosion protection of metal is used to illustrate the importance of interfacial factors and the role of system approach interface engineering. When a coating is applied in order to protect a substrate, the factors, particularly interfacial factors demonstrated by examples of corrosion protection, play important roles regardless of the nature of protection to be accomplished. An excellent coating cannot function well with poor interfaces. The creation of stronger interface is the core of SAIE. 

Fig. 27. Example of corrosion in processes using aluminum chloride-hydrocarbon complex as catalyst. Corrosion resulting from agitated pool of complex in bottom of line. The penetration rate of 5.3 in./yr. was determined during 455 hours of operation.

Both anodic and cathodic reactions occur uniformly over the surface in simple examples of corrosion, but the individual sites will depend very much on the surface characteristics such as grain boundaries, crevices and, of course, discontinuities in any protective oxide layer, as the protective film acts as an electrical barrier. The protection realized will depend on the uniformity of the protective layer and the intimacy of its contact with the underlying metal. The potential for corrosion will depend on the pH of the liquid in contact with the metal. 

An example of corrosion product formation is the rusting of iron as illustrated in Fig. 1.3. When the pH is greater than approximately 4, and under aerated conditions, a layer of black Fe304, and possibly Fe(OH)2, forms in contact with the iron substrate. In the presence of the dissolved oxygen, an outer layer of red Fe203 or FeOOH forms. The adherence... 

Give examples of corrosion processes that are not adequately modeled by the simplest equivalent electrical circuit of Fig. 6.18. 

Corrosion is the term usually applied to the deterioration of metals by an electrochemical process. We see many examples of corrosion around us. Rust on iron, tarnish on silver, and the green patina formed on copper and brass are a few of them (Figure 19.13). Corrosion causes enormous damage to buildings, bridges, ships, and cars. The cost of metallic corrosion to the U.S. economy has been estimated to be over 100 bil-... 

FIGURE 19.13 Examples of corrosion (a) a rusted ship, (bj a half-tarnished silver dish, and (c) the Statue of Liberty coated with patina before its restoration in 1986. 

By far the most familiar example of corrosion is the formation of rust on iron. Oxygen gas and water must be present for iron to rust. Although the reactions involved are quite complex and not completely understood, the main steps are believed to be as follows. A region of the metal s surface serves as the anode, where oxidation occurs ... 

Examples of corrosive liquids are concentrated acids and bases, acid chlorides, etc. Titanium tetrachloride, a solid, is also a corrosive material. 

Corrosives are acids or bases that, in small amounts, can cause damage to tissue. Tissue is damaged in much the same way as a thermal bum however, the bum is much more damaging. The type of damage is the same whether exposed to acids or bases. Examples of corrosive materials include nitric acid, sulfuric acid, phosphoric acid, sodium hydroxide, and potassium hydroxide. They are covered in detail in Chapter 10. 

Stress corrosion cracking (SCC) represents a process of crack nucleation in metals under the simultaneous action of corrosive medium and tensile (external or internal) stresses. A few typical examples of corrosive media for some metals and alloys are given in Table 4.1. 

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