Technology & Engineering
Oxidation and Corrosion
Oxidation is a chemical reaction in which a substance loses electrons, leading to the formation of oxides. Corrosion, on the other hand, is the deterioration of a material as a result of chemical or electrochemical reactions with its environment. Both processes can cause damage to metals and other materials, leading to structural weakening and potential failure.
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12 Key excerpts on "Oxidation and Corrosion"
eBook - PDFElectrochemistry for Technologists
Electrical Engineering Division
- G. R. Palin, N. Hiller(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
CHAPTER 5 Corrosion 5.1 Introduction The word corrode derives from the Latin corrodere, meaning to eat away or destroy by degrees. The term corrosion is most commonly applied to metals, and it is in this context that it will be discussed here. Corrosion of a metal involves an attack on it by its environment, leading to a change in its form. Very few metals occur naturally in the uncombined state, and a great deal of energy is expended in the extraction of metals from their ores. In a general sense, therefore, the combined state can be thought of as the stable form of a metal, with the uncombined state a metastable form. In all but a few special cases the change in a metal resulting from environmental attack is a chemical combina-tion. The change is usually slow, because metals are not used in environments in which they are rapidly attacked, but the end result may be the failure of the metal to fulfil its function. To combat corrosion hundreds of millions of pounds are spent annually in the U.K. on protective coatings for metals, and on the replacement of corroded parts. Most metallic compounds are electrovalent, and all corrosion processes involve ionisation, and are electrochemical. It is con-venient to discuss the various corrosion mechanisms separately, but it must be remembered that the corrosion of a metal in a given environment may not be confined to only one of these processes. Detailed study of corrosion processes enables the choice of a metal for a given function to be made with greater certainty about its freedom from corrosion, and also ensures that the best means of protection is employed. E.F.T.—5* 129 130 CORROSION 5.2 Oxidation Metals combine with oxygen giving oxides. A metallic oxide is an electrovalent compound which exists in the solid state as an array of metal ions and oxygen ions, O 2 . All metals, with the exception of gold, react with oxygen even at normal temperatures, and in the absence of moisture.
eBook - PDF- DENNIS A SNOW(Author)
- 2013(Publication Date)
- Newnes(Publisher)
This page intentionally left blank Corrosion basics 30/3 30.1 Corrosion basics 30.1.1 Definitions of corrosion Corrosion is generally taken to be the waste of a metal by the action of corrosive agents. However, a wider definition is the degradation of a material through contact with its environment. Thus corrosion can include non-metallic materials such as concrete and plastics and mechanisms such as cracking in addition to wastage (i.e. loss of material). This chapter is primarily concerned with metallic corrosion, through a variety of mechanisms. In essence, the corrosion of metals is an electron transfer reaction. An uncharged metal atom loses one or more electrons and becomes a charged metal ion: M ^ ± M + + electron In an ionizing solvent the metal ion initially goes into solution but may then undergo a secondary reaction, combining with other ions present in the environment to form an insoluble molecular species such as rust or aluminium oxide. In high-temperature oxidation the metal ion becomes part of the lattice of the oxide formed. 30.1.2 Electrochemical corrosion The most important mechanism involved in the corrosion of metal is electrochemical dissolution. This is the basis of general metal loss, pitting corrosion, microbiologically induced corrosion and some aspects of stress corrosion cracking. Corrosion in aqueous systems and other circumstances where an electrolyte is present is generally electrochemical in nature. Other mechanisms operate in the absence of electrolyte, and some are discussed in Section 30.1.4. Figure 30.1 depicts a metal such as iron, steel or zinc immersed in electrolyte such as sodium chloride solution. The fundamental driving force of the corrosion reaction is the difference in the potential energies of the metal atom in the solid state and the product which is formed during corrosion. Thus corrosion may be con- sidered to be the reverse of extractive metallurgy. Metals are obtained by the expenditure of energy on their ores.
eBook - PDF- R. E. Smallman(Author)
- 2016(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 15 Oxidation and Corrosion 15.1 Introduction The use of nearly all metals and alloys at elevated temperatures is invariably limited by the way in which they react to their surrounding environment. The most common reaction is the oxidation of metals in air to form oxides. The process of oxidation usually involves a chemical reaction between a dry metal surface and an oxidizing gas which gives rise to a solid oxide film over the exposed surface. In practical application the solid-gaseous reaction which a metal undergoes is usually more complex than the simple metal-oxygen reaction, involving gaseous mixtures, e.g. jet engine and rocket nozzles in contact with combustion products. However, the basic principles governing these reactions are similar and hence in this chapter discussion is limited to oxidation. At ambient temperatures, oxidation is not normahy a serious problem for most commerical alloys. Instead of this dry corrosion phenomenon the major technological problem is wet, or aqueous, corrosion in which the chemical attack occurs through the medium of water. The nature and characteristics of this form of attack are also discussed. 15.2 Thermodynamics of oxidation The tendency for a metal to oxidize, like any other spontaneous reaction, is indicated by the free energy change AG accompanying the formation of the oxide. Most metals readily oxidize because AG is negative for oxide formation. The free energy released by the combination of a fixed amount (1 mol) of the oxidizing agent with the metal is given by AG° and is usually termed the standard free energy of the reaction. AG° is, of course, related to Δ / ί ° , the standard heat of reaction and AS° the standard change in entropy, by the Gibbs equation. The variation of the standard free energy change with absolute temperature for a number of metal oxides is shown in Figure 15.1, The noble metals which are easily reduced occur at the top of the diagram and the more reactive metals at the bottom.
eBook - PDF- Hong Shih(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
12 Corrosion of Metal – Oxide Systems Ramesh K. Guduru and Pravansu S. Mohanty University of Michigan, Dearborn, Michigan USA 1. Introduction Corrosion of materials occurs because of several factors; for example the application environment, operational conditions, presence of non-equilibrium phases, failure of the protective phases or layers in the materials, etc. In addition to the electro-chemical phenomena occurring in the corrosion process, operational conditions, such as temperature could influence the corrosion rates to different degrees depending on the materials involved. The effect of temperature is known to be severe on the corrosion phenomenon due to the dependence of corrosion rates on diffusion of materials. From the materials perspective, presence of non-equilibrium phases or second phases and their thermodynamic stability, microstructures, properties, and protective layers could affect the corrosion rates. Usually oxide systems are known for their protective behavior because of their stability and hindrance to the diffusion of different ionic species. Understanding their stability and role in prevention or slowing down of corrosion rates is, therefore, very important for engineers to design new material systems with desired properties and structures for corrosion resistant applications. Although metallic alloys with oxide second phase are extensively used in high temperature applications for creep resistance, literature suggests that addition of different kinds of oxide particles could help control the corrosion properties. In this chapter, an overview will be given on the corrosion behavior of different oxide systems and their role in corrosion resistant applications of the oxide particle embedded metallic systems in different environments, including low and high temperature applications. 2. Corrosion process and inhibition Corrosion is a continuous degradation process of a material.
eBook - PDF- Yongchang Huang, Jianqi Zhang, Yongchang Huang, Jianqi Zhang(Authors)
- 2018(Publication Date)
- De Gruyter(Publisher)
Metallic high-temperature corrosion frequently leads to the deterioration or destruction of metal materials or the descent of material properties; hence, research on high-temperature corrosion and the development of metallic alloys and coat- ings resisting high-temperature corrosion have an important position in the devel- opment of modern science and technology and engineering. It is a key science and technology and engineering problem that must be solved in the industries of energy resources, petrochemistry, power, chemical engineering, etc., and the high- technology industrial development of aerospace, nuclear energy, etc. It has impor- tant scientific significance and application value. https://doi.org/10.1515/9783110310054-004 110 4 Oxidation and hot corrosion of metals and alloys 4.2 High-temperature oxidation Narrow sense oxidation is the process of oxide formation caused by the reaction between metal and oxygen or an oxidizing medium. It can be expressed by the follow- ing reaction equation: M + n 2 O 2 MO n . In the reaction, the metal atom M loses an electron and turns into metallic ion to increase its positive atomic valence. And the oxygen atom obtains an electron and becomes oxygen ion. The metal ion and oxygen ion are combined into metal oxide. It is the most simple and basic chemical corrosion reaction, with high-temperature oxidation leading to the damage of metal material properties and the destruction of structure. For metals applied in the industries of mechanical engineering, chemical engineering, power, aerospace, etc., high-temperature oxidation resistance is a key property having the same important significance as the high-temperature mechan- ical property.
eBook - PDF- R. E. Smallman, A.H.W. Ngan(Authors)
- 2011(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 9 Oxidation, corrosion and surface treatment 9.1 The engineering importance of surfaces The general truth of the engineering maxim that ‘most problems are surface problems’ is immediately apparent when one considers the nature of metallic corrosion and wear, the fatigue cracking of metals and the effect of catalysts on chemical reactions. For instance, with regard to corrosion, metal surfaces commonly oxidize in air at ambient temperatures to form a very thin oxide film (tarnish). This ‘dry’ corrosion is limited, destroys little of the metallic substrate and is not normally a serious problem. However, at elevated temperatures, nearly all metals and alloys react with their environment at an appreciable rate to form a thick, non-protective oxide layer (scale). Molten phases may form in the scale layer, being particularly dangerous because they allow rapid two-way diffusion of reacting species between the gas phase and the metallic substrate. ‘Wet’ or aqueous corrosion, in which electrochemical attack proceeds in the presence of water, can also destroy metallic surfaces and is responsible for a wide variety of difficult problems throughout all branches of industry. The principles and some examples of ‘dry’ and ‘wet’ corrosion will be discussed in Section 9.2. Conventionally, the surface properties of steels are improved by machining to produce a smooth surface texture (superfinishing), mechanically working (shot-peening), introducing small atoms of carbon and/or nitrogen by thermochemical means (carburizing, nitriding, carbo-nitriding), applying protective coatings (galvanizing, electroplating), chemically converting (anodizing), etc. Many of these traditional methods employ a liquid phase (melt, electrolyte). In contrast, many of the latest generation of advanced methods for either coating or modifying material surfaces use vapors or high-energy beams of atoms/ions as the active media.
- 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.
eBook - PDFMetals and Materials
Science, Processes, Applications
- R. E. Smallman, R J Bishop(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 12 Corrosion and surface engineering 12.1 The engineering importance of surfaces The general truth of the engineering maxim that 'most problems are surface problems' is immedi-ately apparent when one considers the nature of metallic corrosion and wear, the fatigue-cracking of metals and the effect of catalysts on chemical reactions. For instance, with regard to corrosion, metal surfaces commonly oxidize in air at ambient temperatures to form a very thin oxide film (tarnish). This 'dry' corrosion is limited, destroys little of the metallic substrate and is not normally a serious problem. However, at elevated tempera-tures, nearly all metals and alloys react with their environment at an appreciable rate to form a thick non-protective oxide layer (scale). Molten phases may form in the scale layer, being particularly dangerous because they allow rapid two-way diffu-sion of reacting species between the gas phase and the metallic substrate. 'Wet' or aqueous corrosion, in which electrochemical attack proceeds in the presence of water, can also destroy metallic surfaces and is responsible for a wide variety of difficult problems throughout all branches of industry. The principles and some examples of 'dry' and 'wet' corrosion will be discussed in Section 12.2. Conventionally, the surface properties of steels are improved by machining to produce a smooth surface texture (superfinishing), mechanically working (shot-peening), introducing small atoms of carbon and/or nitrogen by thermochemical means (carburizing, nitriding, carbo-nitriding), applying protective coatings (galvanizing, electroplating), chemically converting (anodizing), etc. Many of these traditional methods employ a liquid phase (melt, electrolyte). In contrast, many of the latest generation of advanced methods for either coating or modifying material surfaces use vapours or high-energy beams of atoms/ions as the active media.
eBook - PDFMaterials Science and Engineering, P-eBK
An Introduction
- William D. Callister, Jr., David G. Rethwisch, Aaron Blicblau, Kiara Bruggeman, Michael Cortie, John Long, Judy Hart, Ross Marceau, Ryan Mitchell, Reza Parvizi, David Rubin De Celis Leal, Steven Babaniaris, Subrat Das, Thomas Dorin, Ajay Mahato, Julius Orwa(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
In a microscopic sense, the oxidation and reduction reactions occur randomly over the surface. Familiar examples include general rusting of steel and iron and the tarnishing of silverware. This is probably the most common form of corrosion. It is also the least objectionable because it can be predicted and designed for with relative ease. Galvanic corrosion FIGURE 17.14 Photograph showing galvanic corrosion around the inlet of a single‐cycle bilge pump that is found on fishing vessels. Corrosion occurred at the interface between a magnesium shell and a steel core around which the magnesium was cast. Galvanic corrosion Steel core Magnesium shell Courtesy of LaQue Center for Corrosion Technology, Inc. Galvanic corrosion occurs when two metals or alloys having different compositions are electrically coupled while exposed to an electrolyte. This is the type of corrosion or dissolution that was described in section 17.2. The less noble or more reactive metal in the particular environment experiences corrosion; the more inert metal, the cathode, is protected from corrosion. As examples, steel screws corrode when in contact with brass in a marine environment, and if copper and steel tubing are joined in a domestic water heater, the steel corrodes in the vicinity of the junc- tion. Depending on the nature of the solution, one or more of the reduction reactions, equations 17.3 through 17.7, occurs at the surface of the cathode material. Figure 17.14 shows galvanic corrosion. The galvanic series in table 17.2 indicates the relative reactivities in seawater of a number of metals and alloys. When two alloys are coupled in seawater, the one lower in the series experiences corrosion. It is also worth noting from this series that some alloys are listed twice (e.g. nickel and the stainless steels), in both active and passive states.
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.
eBook - PDFSurface Modification and Mechanisms
Friction, Stress, and Reaction Engineering
- George E. Totten, Hong Liang, George E. Totten, Hong Liang(Authors)
- 2004(Publication Date)
- CRC Press(Publisher)
Protective coatings can be applied in many cases; inhibitors can be applied in others (e.g., as in Fig. 14). Separation of phases is important in cases of two-phase or multiphase flow (filters, separators) (Sec. IV.B). Last but Figure 14 Corrosion rate as a function of gas velocity in gas/condensate well. (From Ref. 13.) Corrosion and its impact on wear processes 565 not the least, many problems of erosion corrosion can be solved by appropriate design. Examples are the following: Pipe dimensions large enough to avoid velocities above the critical values everywhere. Suitable cross section and flow direction changes, and smooth joints and surface, which minimize turbulence and its effect [Fig. 15(a, b)]. Critical areas localized where corrosion makes less harm [Fig. 15(c)]. Increased material thickness. Corrosion-resistant or easily replaceable linings [Fig. 15(d)]. III. CORROSION IN DRY GASES (OXIDATION) A chemical reaction between oxygen in dry atmosphere and an engineering metallic material usually requires a high temperature to occur to a practically significant extent. However, under special conditions (e.g., wear conditions), oxidation of practical significance may also happen at ambient temperature. Reaction with oxygen causes an oxide film on the surface. Other oxidants that can react with metal in a similar way are, e.g., sulfur and halogens (chlorine, fluorine, bromine, iodine). The oxidation product may form a dense and relatively strong film, which is usually the case for oxide films on the most common engineering metals and alloys (iron and steel, Figure 15 Design for prevention of erosion corrosion. (From Ref. 15.) Surface modification and mechanisms 566 aluminum, chromium, copper, nickel, and their alloys). A divalent metal M may react with oxygen O 2 to the final product MO, but the reaction goes in steps.
- Yip-Wah Chung, Monica Kapoor(Authors)
- 2022(Publication Date)
- CRC Press(Publisher)
Zinc and magnesium in these cases are corroded instead and are known as sacrifcial anodes. This Photo by Unknown Author is licensed under CC BY-SA FIGURE 8.10 The Iron Pillar of Delhi. 261 Corrosion and Oxidation of Metals and Alloys This Photo by Unknown Author is licensed under CC BY-SA FIGURE 8.11 Galvanic protection of ship hull by attachment of zinc blocks. Cathodic protection : Another method is to apply a negative voltage to the mate-rial to be protected, forcing the material to become the cathode (cathodic protection). Natural gas lines and oil pipes are often protected against corrosion this way. A simple way to demonstrate cathodic protection is to take two pieces of the same metal (copper or iron), immerse them in a sodium chloride solution, and apply a small voltage, say 1.5 V, between them. Within a few minutes, the positively biased metal becomes dull due to oxidation/corrosion, while the negatively biased metal becomes shiny. 8.10 OXIDATION For most metals at room temperature, the free energy for the formation of the metal oxide is negative, meaning that such oxidation reactions are favorable. In some cases, these oxides form passivating layers protecting the underlying metals (e.g., alumi-num oxide); in other cases, they do not (e.g., iron oxides). In this section, we explore the process of oxidation and the conditions under which they may form protecting layers against corrosion. When we measure the weight gain Δ m of a metal due to oxidation as a function of time t , the results generally fall into two categories: (1) Δ m ∝ t 1/2 and (2) Δ m ∝ t . In the frst category (parabolic growth), the square-root dependence suggests a diffusion-based mechanism. There are two possibilities, depending on the relative diffusion rates of the metallic and oxygen ions, as shown in Figure 8.12. In the mechanism shown in Figure 8.12a, oxygen ions diffuse through the oxide and react with the metal to produce a thicker oxide layer.
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