Technology & Engineering
Dry Corrosion
Dry corrosion refers to the chemical deterioration of a material due to exposure to the atmosphere without the presence of moisture. This type of corrosion typically occurs in environments with low humidity and can lead to the formation of oxide layers on the surface of the material, compromising its integrity. Preventative measures such as protective coatings or alloy selection are often employed to mitigate dry corrosion.
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6 Key excerpts on "Dry Corrosion"
eBook - PDF- F A A Crane, J A Charles, Justin Furness(Authors)
- 1997(Publication Date)
- Butterworth-Heinemann(Publisher)
Whilst corrosion is sometimes considered only in the context of metallic materials, in the more general sense of deterioration of materials through reaction with an environment it also includes the behaviour of glasses, ionic solids, polymers, concrete, etc. in a range of environ- ments, including electrolytes and non- electrolytes, molten metals and gases. It is difficult to classify the various types of corrosive attack. Traditionally, a broad division into 'wet' and 'dry' corrosion reactions has been employed, determined by the presence or absence of water or an aqueous solution. A more rational classification for metals has been given by Shreir I as follows: (1) Film-free chemical interaction in which there is direct chemical reaction of a metal with its environment. The metal remains film-free and there is no transport of charge. (2) Electrolytic systems: (a) Inseparable anode/cathode (insep. A/C) type. The anodes and cathodes cannot be distinguished by experimental methods although their presence is postulated by theory, i.e. the uniform dissolution of metals in acid, alkaline or neutral aque- ous solutions, in non-aqueous solution or in fused salts. (b) Separable anode/cathode type (sep. A/C). Certain areas of the metal can be distinguished experimentally as predom- inantly anodic or cathodic, although the distances of separation of these areas may be as small as fractions of a millimetre. In these reactions there will be a macroscopic flow of charge through the metal. (c) Interfacial anode/cathode type (inter- facial A/C). One entire interface will be the anode and the other will be the cathode. Thus a metal/metal oxide inter- face might be regarded as the anode and the metal oxide/oxygen interface as the cathode. 145 Selection for corrosion resistance In general, 2(a) and 2(b) include corrosion reactions which are normally classified as 'wet' while 2(c) includes those which are normally designated 'dry'.
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Intergranular corrosion—occurs preferentially along grain boundaries for specific metals/alloys (e.g., some stainless steels). Selective leaching—the case in which one element/constituent of an alloy is removed selectively by corrosive action. Erosion–corrosion—the combined action of chemical attack and mechanical wear as a consequence of fluid motion. Stress corrosion—the formation and propagation of cracks (and possible failure) re- sulting from the combined effects of corrosion and the application of a tensile stress. Hydrogen embrittlement—a significant reduction in ductility that accompanies the penetration of atomic hydrogen into a metal/alloy. • Several measures may be taken to prevent, or at least reduce, corrosion. These include material selection, environmental alteration, the use of inhibitors, design changes, ap- plication of coatings, and cathodic protection. • With cathodic protection, the metal to be protected is made a cathode by supplying electrons from an external source. • Oxidation of metallic materials by electrochemical action is also possible in dry, gase- ous atmospheres (Figure 17.25). • An oxide film forms on the surface that may act as a barrier to further oxidation if the volumes of metal and oxide film are similar, that is, if the Pilling–Bedworth ratio (Equations 17.32 and 17.33) is near unity. • The kinetics of film formation may follow parabolic (Equation 17.34), linear (Equation 17.35), or logarithmic (Equation 17.36) rate laws. • Ceramic materials, being inherently corrosion resistant, are frequently used at elevated temperatures and/or in extremely corrosive environments. Passivity Forms of Corrosion Corrosion Prevention Oxidation Corrosion of Ceramic Materials 684 • Chapter 17 / Corrosion and Degradation of Materials • Polymeric materials deteriorate by noncorrosive processes. Upon exposure to liquids, they may experience degradation by swelling or dissolution.
- Paul Angus, Carl Harrop, Steve Ingle, David Considine, Danny Davis, David Greenall, Allan Homewood, Lynne Jack, Brian Johnston, Derek King, John Turner(Authors)
- 2014(Publication Date)
Some woods are quite acidic and under damp conditions cause corrosion. Cementitious materials are very alkaline when fresh, and in the presence of moisture can attack certain metals such as zinc, aluminium and lead. Other materials such as plaster and stone etc. can also cause corrosion, but this is very dependent on their composition and the prevailing environmental conditions. 12.1.4 Causes and environments Corrosion is the term used to describe the process of conversion of metals into oxides or other compounds. There are two basic types of corrosion involved. 12.1.4.1 Aqueous corrosion This is the reaction between a metal and the atmosphere whereby a surface scale, usually oxide or sulphide, is formed, e.g. tarnishing or high temperature scaling. This process is only likely to affect the building services engineer in relation to heating and boiler plant where metal surfaces reach higher temperatures, i.e. greater than 200 °C. 12.1.4.2 Wet corrosion This is the most significant form of corrosion and occurs by an electrochemical mechanism which in most cases requires the presence of oxygen. Dissolution occurs where metals with dissimilar electrochemical potentials result in an electrochemical cell being set up (see section 12.2.2), where a complimentary reaction occurs in the anodic region and a complimentary reaction occurs at the cathode. Natural and supply waters contain dissolved salts which make them capable of carrying an electric current and sustaining the corrosion process. 12.1.4.3 Environments External corrosion occurs when moisture, in the form of rain, natural waters or in condensation comes into contact with the metal surface. Levels of pollutants can greatly affect the overall rate of corrosion as can the duration of wetness. Atmospheric pollutants in industrial regions include carbon, carbon compounds and sulphur dioxide along with smaller amounts of hydrogen sulphide, nitrogen oxides and other by-products from industrial processes.
eBook - PDFMaterials Science and Engineering
An Introduction
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
Intergranular corrosion—occurs preferentially along grain boundaries for specific metals/alloys (e.g., some stainless steels). Selective leaching—the case in which one element/constituent of an alloy is removed selectively by corrosive action. Erosion–corrosion—the combined action of chemical attack and mechanical wear as a consequence of fluid motion. Stress corrosion—the formation and propagation of cracks (and possible failure) re- sulting from the combined effects of corrosion and the application of a tensile stress. Hydrogen embrittlement—a significant reduction in ductility that accompanies the penetration of atomic hydrogen into a metal/alloy. • Several measures may be taken to prevent, or at least reduce, corrosion. These include material selection, environmental alteration, the use of inhibitors, design changes, ap- plication of coatings, and cathodic protection. • With cathodic protection, the metal to be protected is made a cathode by supplying electrons from an external source. • Oxidation of metallic materials by electrochemical action is also possible in dry, gase- ous atmospheres (Figure 17.25). • An oxide film forms on the surface that may act as a barrier to further oxidation if the volumes of metal and oxide film are similar, that is, if the Pilling–Bedworth ratio (Equations 17.32 and 17.33) is near unity. • The kinetics of film formation may follow parabolic (Equation 17.34), linear (Equation 17.35), or logarithmic (Equation 17.36) rate laws. • Ceramic materials, being inherently corrosion resistant, are frequently used at elevated temperatures and/or in extremely corrosive environments. Passivity Forms of Corrosion Corrosion Prevention Oxidation Corrosion of Ceramic Materials 646 • Chapter 17 / Corrosion and Degradation of Materials • Polymeric materials deteriorate by noncorrosive processes. Upon exposure to liquids, they may experience degradation by swelling or dissolution.
- George Murray(Author)
- 1997(Publication Date)
- CRC Press(Publisher)
Environmental Degradation of Engineering Materials 2.1 Forms of Corrosion The several forms of corrosion to which a metal may be subjected are I. Electrochemical corrosion 2. Uniform corrosion 3. Intergranular corrosion 4. Galvanic corrosion 5. Crevice corrosion 6. Pitting 7. Erosion corrosion 8. Stress corrosion cracking (SCC) 9. Biological corrosion 10. Dezincification (dealloying) II. Concentration cell 12. Embrittlement 13. Filiform 14. Corrosion fatigue 15. Fretting 16. Graphitization 357 All of these forms of corrosion are not present in all applications, but it is possible to have more than one form present. Understanding when each of these forms of corrosion could be potentially present will permit the designer to take steps to eliminate the condition or to limit the corrosion to acceptable limits. Electrochemical Corrosion Corrosion of metals is caused by the flow of energy (electricity). This flow may be from one metal to another, or from one part of the surface of one metal to another part of the surface of the same metal, or from one metal to a recipient of some kind. This flow of electricity can take place in the atmosphere, underwater, or underground as long as a moist conductor or electrolyte, such as water, especially saltwater, is present. The differences in potential that causes the electric currents is mainly due to contact between dissimilar metallic conductors, or differences in concentration of the solution, generally related to dissolved oxygen in natural waters. Any lack of homogeneity on the metal surface may initiate attack by causing a difference in potentials that results in localized corrosion. The flow of electricity (energy) may also be from a metal to a metal recipient of some kind, such as soil. Soils frequently contain dispersed metallic particles or bacterial pockets that provide a natural electrical pathway with buried metal. The electrical path will be from the metal to the soil, with corrosion resulting.
eBook - PDFFundamentals of Corrosion
Mechanisms, Causes, and Preventative Methods
- P.E., Philip A. Schweitzer(Authors)
- 2009(Publication Date)
- CRC Press(Publisher)
During the first days of exposure, wet conditions (caused by high relative humidity or rainfall) cause higher corrosion rates than dry con-ditions. These effects will vary from one material to another. For example, zinc is more sensitive than steel. Differences are explained by the fact that different materials form different corrosion products with different protec-tive properties. A wide variety of structurally related corrosion products can be found on zinc, the nature of which depends on initial exposure condi-tions. The seasonal dependence on the concentrations of peroxide and ozone in the atmosphere might also be a contributing factor. During the third period of exposure, a constant corrosion rate is estab-lished — and thus the terminology “stationary period.” 4.2.5 Sheltering The design of the installation should eliminate all possible areas where water, dirt, and corrosion products can accumulate. The degree of shelter from particle fallout and rainfall can affect the initial and ultimate corrosion 86 Fundamentals of Corrosion rates. When pockets are present, the time of wetness increases, which leads to corrosive conditions. The design should make maximum use of exposure to the weather. Sheltering from rain should be avoided. 4.2.6 Wind Velocity Wind speed and type of wind flow have pronounced effects on the atmo-spheric corrosion rate. This is illustrated by the dry deposition velocity, which is defined as the ratio of deposition rate of any gaseous compound and the concentration of that compound in the atmosphere. 4.2.7 Nature of Corrosion Products The atmospheric corrosion rate is influenced by many parameters, one of the more important being the formation and protective ability of the corro-sion products formed. The composition of the corrosion products depends on the participating dissolved metal ions and the access to anions solved in the aqueous layer.
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