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Encyclopedia > Corrosion
Mechanical failure modes
Buckling
Corrosion
Creep
Fatigue
Fracture
Melting
Rupture (engineering)
Thermal shock
Wear
Yielding
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Corrosion is breaking down of essential properties in a material due to reactions with its surroundings. In the most common use of the word, this means a loss of an electron of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a well-known example of electrochemical corrosion. This is commonly known as rust. This type of damage usually affects metallic materials, and typically produces oxide(s) and/or salt(s) of the original metal. Corrosion also includes the dissolution of ceramic materials and can refer to discoloration and weakening of polymers by the sun's ultraviolet light. Corrosion is the destructive reaction of a metal with another material, e. ... This article is about engineering. ... Creep is the term used to describe the tendency of a material to move or to deform permanently to relieve stresses. ... In materials science, fatigue is the progressive, localised, and permanent structural damage that occurs when a material is subjected to cyclic or fluctuating strains at nominal stresses that have maximum values less than (often much less than) the static yield strength of the material. ... For other uses, see Fracture (disambiguation). ... In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns into a liquid. ... Rupture, or ductile rupture describes the ultimate failure of tough ductile materials loaded in tension. ... Thermal shock and thermal loading refer to the disfuntion (and perhaps, crack) of a material due to the heating, especially non-stationary and non-uniform. ... In materials science, wear is the erosion of material from a solid surface by the action of another solid. ... Yield strength, or the yield point, is defined in engineering and materials science as the stress at which a material begins to plastically deform. ... Look up material in Wiktionary, the free dictionary. ... This article is about metallic materials. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... For other uses, see Iron (disambiguation). ... Properties For other meanings of Atom, see Atom (disambiguation). ... A blacksmith removing rust with sand prior to welding Rust damage in automobiles can create hidden dangers. ... This article is about metallic materials. ... An oxide is a chemical compound containing an oxygen atom and other elements. ... For other uses, see Salt (disambiguation). ... Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικός (keramikos). ... A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... Sol redirects here. ... For other uses, see Ultraviolet (disambiguation). ...


Most structural alloys corrode merely from exposure to moisture in the air, but the process can be strongly affected by exposure to certain substances (see below). Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area to produce general deterioration. While some efforts to reduce corrosion merely redirect the damage into less visible, less predictable forms, controlled corrosion treatments such as passivation and chromate-conversion will increase a material's corrosion resistance. An alloy is a homogeneous hybrid of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. ... Look up air in Wiktionary, the free dictionary. ... For the hazard, see corrosive. ... Passivation is the process of making a material passive in relation to another material prior to using the materials together. ... Zinc chromate conversion coating on small steel parts. ...

Rust, the most familiar example of corrosion.

Contents

Image File history File linksMetadata Download high resolution version (1904x1504, 3724 KB) Summary Rust and dirt on a baking plate. ... Image File history File linksMetadata Download high resolution version (1904x1504, 3724 KB) Summary Rust and dirt on a baking plate. ...

Corrosion in nonmetals

Influences of selected glass component additions on the chemical durability against water corrosion of a specific base glass (corrosion test ISO 719). (Reference: Glassproperties.com)
Influences of selected glass component additions on the chemical durability against water corrosion of a specific base glass (corrosion test ISO 719). (Reference: Glassproperties.com)

Most ceramic materials are almost entirely immune to corrosion. The strong ionic and/or covalent bonds that hold them together leave very little free chemical energy in the structure; they can be thought of as already corroded. When corrosion does occur, it is almost always a simple dissolution of the material or chemical reaction, rather than an electrochemical process. A common example of corrosion protection in ceramics is the lime added to soda-lime glass to reduce its solubility in water; though it is not nearly as soluble as pure sodium silicate, normal glass does form sub-microscopic flaws when exposed to moisture. Due to its brittleness, such flaws cause a dramatic reduction in the strength of a glass object during its first few hours at room temperature. Image File history File links Size of this preview: 800 × 547 pixelsFull resolution (911 × 623 pixel, file size: 22 KB, MIME type: image/png) Influences of selected glass component additions on the chemical durability against water corrosion of a specific base glass (glass corrosion test procedure ISO 719). ... Image File history File links Size of this preview: 800 × 547 pixelsFull resolution (911 × 623 pixel, file size: 22 KB, MIME type: image/png) Influences of selected glass component additions on the chemical durability against water corrosion of a specific base glass (glass corrosion test procedure ISO 719). ... Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικός (keramikos). ... Calcium oxide (CaO), commonly known as lime, quicklime or burnt lime, is a widely used chemical compound. ... This article is about the material. ... Sodium silicate, also known as water glass or liquid glass, available in aqueous solution and in solid form, is a compound used in cements, passive fire protection, refractories, textile and lumber processing. ... A material is brittle if it is subject to fracture when subjected to stress i. ...


The degradation of polymeric materials is due to a wide array of complex and often poorly-understood physiochemical processes. These are strikingly different from the other processes discussed here, and so the term "corrosion" is only applied to them in a loose sense of the word. Because of their large molecular weight, very little entropy can be gained by mixing a given mass of polymer with another substance, making them generally quite difficult to dissolve. While dissolution is a problem in some polymer applications, it is relatively simple to design against. A more common and related problem is swelling, where small molecules infiltrate the structure, reducing strength and stiffness and causing a volume change. Conversely, many polymers (notably flexible vinyl) are intentionally swelled with plasticizers, which can be leached out of the structure, causing brittleness or other undesirable changes. The most common form of degradation, however, is a decrease in polymer chain length. Mechanisms which break polymer chains are familiar to biologists because of their effect on DNA: ionizing radiation (most commonly ultraviolet light), free radicals, and oxidizers such as oxygen, ozone, and chlorine. Additives can slow these process very effectively, and can be as simple as a UV-absorbing pigment (i.e., titanium dioxide or carbon black). Plastic shopping bags often do not include these additives so that they break down more easily as litter. A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... For a less technical and generally accessible introduction to the topic, see Introduction to entropy. ... Polyvinyl chloride Polyvinyl chloride, (IUPAC Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. ... Plasticizers are additives that soften the materials (usually a plastic or a concrete mix) they are added to. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Radiation hazard symbol. ... For other uses, see Ultraviolet (disambiguation). ... In chemistry, radicals (often referred to as free radicals) are atomic or molecular species with unpaired electrons on an otherwise open shell configuration. ... Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... For other uses, see Ozone (disambiguation). ... General Name, symbol, number chlorine, Cl, 17 Chemical series halogens Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... Look up Additive in Wiktionary, the free dictionary When used as a noun, additive refers to something that is introduced to a larger quantity of something else, usually to alter characteristics of the larger quantity. ... Natural Ultramarine pigment in powdered form. ... Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. ... Carbon black is a material, today usually produced by the incomplete combustion of petroleum products. ... Plastic shopping bags/Carrier bags are a common type of shopping bag in several countries. ... The International Tidy Man For other meanings of litter, see Litter (disambiguation). ...


Corrosion of glasses

The corrosion of silicate glasses in aqueous solutions is governed by two mechanisms: diffusion-controlled leaching (ion exchange) and glass network hydrolytic dissolution [A.K. Varshneya. Fundamentals of inorganic glasses. Society of Glass Technology, Sheffield, 682pp. (2006)]. Both corrosion mechanisms strongly depend on the pH of contacting solution: the rate of ion exchange decreases with pH as 10-0.5pH whereas the rate of hydrolytic dissolution increases with pH as 100.5pH [M.I. Ojovan, W.E. Lee. New Developments in Glassy Nuclear Wasteforms. Nova Science Publishers, New York, 136pp. (2007)]. diffusion (disambiguation). ... For other uses, see PH (disambiguation). ...


Numerically corrosion rates of glasses are characterised by normalised corrosion rates of elements NRi (g/cm2 d) which are determined as the ratio of total amount of released species into the water Mi (g) to the water-contacting surface area S (cm2), time of contact t (days) and weight fraction content of the element in the glass fi:


NRi=Mi/S·fi·t


The overall corrosion rate is a sum of contributions from both mechanisms (leaching + dissolution) NRi=Nrxi+NRh. Diffusion-controlled leaching (ion exchange) is characteristic of the initial phase of corrosion and involves replacement of alkali ions in the glass by a hydronium (H3O+) ion from the solution. It causes an ion-selective depletion of near surface layers of glasses and gives an inverse square root dependence of corrosion rate with exposure time. The diffusion controlled normalised leaching rate of cations from glasses (g/cm2 d) is given by:


NRxi=2·ρ·(Di/π·t)1/2


where t is time, Di is the i-th cation effective diffusion coefficient (cm2/d), which depends on pH of contacting water as Di = Di0·10-pH, and ρ is the density of the glass (g/cm3).


Glass network dissolution is characteristic of the later phases of corrosion and causes a congruent release of ions into the water solution at a time-independent rate in dilute solutions (g/cm2 d):


NRh=ρrh,


where rh is the stationary hydrolysis (dissolution) rate of the glass (cm/d). In closed systems the consumption of protons from the aqueous phase increases the pH and causes a fast transition to hydrolysis [Corrosion of Glass, Ceramics and Ceramic Superconductors. Edited by: D.E. Clark, B.K. Zoitos, William Andrew Publishing/Noyes, 672pp. (1992)]. However further silica saturation of solution impedes hydrolysis and causes the glass to return to an ion-exchange, e.g. diffusion-controlled regime of corrosion. Hydrolysis is a chemical reaction or process in which a chemical compound reacts with water. ...


In typical natural conditions normalised corrosion rates of silicate glasses are very low and are of the order of 10-7 - 10-5 g/cm2 d. The very high durability of silicate glasses in water makes them suitable for hazardous and nuclear waste immobilisation.



The remainder of this article is about electrochemical corrosion.


Electrochemical theory

Main article: Electrochemistry

One way to understand the structure of metals on the basis of particles is to imagine an array of positively-charged ions sitting in a negatively-charged "gas" of free electrons. Coulombic attraction holds these oppositely-charged particles together, but the positively-charged ions are attracted to negatively charged particles outside the metal as well, such as the negative ions (anions) in an electrolyte. For a given ion at the surface of a metal, there is a certain amount of energy to be gained or lost by dissolving into the electrolyte or becoming a part of the metal, which reflects an atom-scale tug-of-war between the electron gas and dissolved anions. The quantity of energy then strongly depends on a host of variables, including the types of ions in a solution and their concentrations, and the number of electrons present at the metal's surface. In turn, corrosion processes cause electrochemical changes, meaning that they strongly affect all of these variables. The overall interaction between electrons and ions tends to produce a state of local thermodynamic equilibrium that can often be described using basic chemistry and a knowledge of initial conditions. English chemists John Daniell (left) and Michael Faraday (right), both credited to be founders of electrochemistry as known today. ... ... In physics, the free electron model is a possible model for the behaviour of electrons in a crystal structure. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... Electrostatics is the branch of physics that deals with the force exerted by a static (i. ... ... An electrolyte is a substance containing free ions that behaves as an electrically conductive medium. ... In thermodynamics, a thermodynamic system is in thermodynamic equilibrium if its energy distribution equals a Maxwell-Boltzmann distribution. ...


Galvanic series

Main article: Galvanic series

In a given environment (one standard medium is aerated, room-temperature seawater), one metal will be either more noble or more active than the next, based on how strongly its ions are bound to the surface. Two metals in electrical contact share the same electron gas, so that the tug-of-war at each surface is translated into a competition for free electrons between the two materials. The noble metal will tend to take electrons from the active one, while the electrolyte hosts a flow of ions in the same direction. The resulting mass flow or electrical current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a Galvanic series, and can be a very useful in predicting and understanding corrosion. The galvanic series determines the nobility of metals and semi-metals. ... Annual mean sea surface salinity for the World Ocean. ... Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. ... The galvanic series determines the nobility of metals and semi-metals. ...


Resistance to corrosion

Some metals are more intrinsically resistant to corrosion than others, either due to the fundamental nature of the electrochemical processes involved or due to the details of how reaction products form. For some examples, see galvanic series. If a more susceptible material is used, many techniques can be applied during an item's manufacture and use to protect its materials from damage. The galvanic series determines the nobility of metals and semi-metals. ...


Intrinsic chemistry

Gold nuggets do not corrode, even on a geological time scale.
Gold nuggets do not corrode, even on a geological time scale.

The materials most resistant to corrosion are those for which corrosion is thermodynamically unfavorable. Any corrosion products of gold or platinum tend to decompose spontaneously into pure metal, which is why these elements can be found in metallic form on Earth, and is a large part of their intrinsic value. More common "base" metals can only be protected by more temporary means. Commons:Image:GoldNuggetUSGOV.jpg File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Commons:Image:GoldNuggetUSGOV.jpg File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dynamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ...


Some metals have naturally slow reaction kinetics, even though their corrosion is thermodynamically favorable. These include such metals as zinc, magnesium, and cadmium. While corrosion of these metals is continuous and ongoing, it happens at an acceptably slow rate. An extreme example is graphite, whitch releases large amounts of energy upon oxidation, but has such slow kinetics that it is effectively immune to electrochemical corrosion under normal conditions. A reaction is the following: In physics, a reaction (physics) is defined by Newtons third law: For every action there is an equal and opposite reaction. The idea that any given force has a pair or opposite force. ... In physical chemistry, chemical kinetics or reaction kinetics is the study of reaction rates in a chemical reaction. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, Symbol, Number cadmium, Cd, 48 Chemical series transition metals Group, Period, Block 12, 5, d Appearance silvery gray metallic Standard atomic weight 112. ... For other uses, see Graphite (disambiguation). ... The most fundamental reactions in chemistry are the redox processes. ...


Passivation

Main article: Passivation

Given the right conditions, a thin film of corrosion products can form on a metal's surface spontaneously, acting as a barrier to further oxidation. When this layer stops growing at less than a micrometre thick under the conditions that a material will be used in, the phenomenon is known as passivation (rust, for example, usually grows to be much thicker, and so is not considered passivation, because this mixed oxidized layer is not protective). While this effect is in some sense a property of the material, it serves as an indirect kinetic barrier: the reaction is often quite rapid unless and until an impermeable layer forms. Passivation in air and water at moderate pH is seen in such materials as aluminium, stainless steel, titanium, and silicon. Passivation is the process of making a material passive in relation to another material prior to using the materials together. ... Passivation is the process of making a material passive in relation to another material prior to using the materials together. ... For other uses, see PH (disambiguation). ... Aluminum redirects here. ... The 630 foot high, stainless-clad (type 304L) Gateway Arch defines St. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery metallic Standard atomic weight 47. ... Not to be confused with Silicone. ...


These conditions required for passivation are specific to the material. The effect of pH is recorded using Pourbaix diagrams, but many other factors are influential. Some conditions that inhibit passivation include: high pH for aluminum, low pH or the presence of chloride ions for stainless steel, high temperature for titanium (in which case the oxide dissolves into the metal, rather than the electrolyte) and fluoride ions for silicon. On the other hand, sometimes unusual conditions can bring on passivation in materials that are normally unprotected, as the alkaline environment of concrete does for steel rebar. Exposure to a liquid metal such as mercury or hot solder can often circumvent passivation mechanisms. A Pourbaix diagram, also known as a potential/pH diagram, maps out possible stable (equilibrium) phases of an aqueous electrochemical system. ... For other uses, see PH (disambiguation). ... The chloride ion is formed when the element chlorine picks up one electron to form an anion (negatively-charged ion) Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. ... Fluoride is the ionic form of fluorine. ... This article is about the construction material. ... For other uses, see Steel (disambiguation). ... A tied rebar beam cage. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Standard atomic weight 200. ... A solder is a fusible metal alloy, with a melting point or melting range of 180-190°C (360-370 °F), which is melted to join metallic surfaces, especially in the fields of electronics and plumbing, in a process called soldering. ...


Surface treatments

Galvanized surface
Galvanized surface

Image:Galvanized surface. ... Image:Galvanized surface. ... Galvanization or galvanisation refers to any of several electrochemical processes named after the Italian scientist Luigi Galvani. ...

Applied coatings

Main article: Galvanization

Plating, painting, and the application of enamel are the most common anti-corrosion treatments. They work by providing a barrier of corrosion-resistant material between the damaging environment and the (often cheaper, tougher, and/or easier-to-process) structural material. Aside from cosmetic and manufacturing issues, there are tradeoffs in mechanical flexibility versus resistance to abrasion and high temperature. Platings usually fail only in small sections, and if the plating is more noble than the substrate (for example, chromium on steel), a galvanic couple will cause any exposed area to corrode much more rapidly than an unplated surface would. For this reason, it is often wise to plate with a more active metal such as zinc or cadmium. Galvanization or galvanisation refers to any of several electrochemical processes named after the Italian scientist Luigi Galvani. ... Plating is the general name surface-covering techniques in which a metal is deposited onto a conductive surface. ... This article does not cite any references or sources. ... In a discussion of art technology, enamel (or vitreous enamel, or porcelain enamel in American English) is the colorful result of fusion of powdered glass to a substrate through the process of firing, usually between 750 and 850 degrees Celsius. ... General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... For other uses, see Steel (disambiguation). ...


Reactive coatings

If the environment is controlled (especially in recirculating systems), corrosion inhibitors can often be added to it. These form an electrically insulating and/or chemically impermeable coating on exposed metal surfaces, to suppress electrochemical reactions. Such methods obviously make the system less sensitive to scratches or defects in the coating, since extra inhibitors can be made available wherever metal becomes exposed. Chemicals that inhibit corrosion include some of the salts in hard water (Roman water systems are famous for their mineral deposits), chromates, phosphates, and a wide range of specially-designed chemicals that resemble surfactants (i.e. long-chain organic molecules with ionic end groups). Corrosion inhibitor - Wikipedia /**/ @import /w/skins-1. ... Hard water water that has a high mineral content (water with a low mineral content is known as soft water). ... The route of the Eifel aqueduct, with its average slope. ... A sample of ammonium dichromate Chromates and dichromates are salts of chromic acid and dichromic acid, respectively. ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ... Surfactants, also known as tensides, are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids. ...

This figure-8 descender is annodized with a yellow finish. Climbing equipment is available in a wide range of anodized colors.
This figure-8 descender is annodized with a yellow finish. Climbing equipment is available in a wide range of anodized colors.

Download high resolution version (915x701, 44 KB)Figure Eight device for belaying File links The following pages link to this file: Climbing equipment Categories: GFDL images ... Download high resolution version (915x701, 44 KB)Figure Eight device for belaying File links The following pages link to this file: Climbing equipment Categories: GFDL images ... A wide range of equipment is used during rock climbing. ...

Anodization

Main article: Anodising

Aluminium alloys often undergo a surface treatment. Electrochemical conditions in the bath are carefully adjusted so that uniform pores several nanometers wide appear in the metal's oxide film. These pores allow the oxide to grow much thicker than passivating conditions would allow. At the end of the treatment, the pores are allowed to seal, forming a harder-than-usual surface layer. If this coating is scratched, normal passivation processes take over to protect the damaged area. These inexpensive carabiners have an anodised aluminium surface that has been dyed and are made in many colors. ... A nanometre (American spelling: nanometer) is 1. ...


Controlled Permeability Formwork

Main article: Controlled Permeability Formwork

Controlled Permeability Formwork (CPF) is a method of preventing the corrosion of reinforcement by naturally enhancing the durability of the cover during concrete placement. CPF has been used in environments to combat the effects of Carbonation, chlorides, frost and abrasion. Controlled Permeability Formwork (CPF) CPF is the only system proven to significantly enhances the durability of surface concrete during the casting process. ... In operant conditioning, reinforcement is an increase in the strength of a response following the presentation of a stimulus contingent on that response. ... Look up cover in Wiktionary, the free dictionary. ... For the chemical reaction forming calcium carbonate, see carbonatation. ... The chloride ion is formed when the element chlorine picks up one electron to form the negatively charged ion Cl−. The salts of hydrochloric acid HCl are also called chlorides. ... Frost on black pipes Frost is a solid deposition of water vapor from saturated air. ...


Cathodic protection

Main article: Cathodic protection

Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. Aluminium anodes mounted on a steel jacket structure Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. ... Diagram of a copper cathode in a Daniells cell. ... A demonstration electrochemical cell setup resembling the Daniell cell. ...


It is a method used to protect metal structures from corrosion. Cathodic protection systems are most commonly used to protect steel, water, and fuel pipelines and tanks; steel pier piles, ships, and offshore oil platforms. For other uses, see Steel (disambiguation). ... A deep foundation installation for a bridge in Napa, California. ... Offshore has two principal meanings: Physical - in the sea away from the shore; not on the shoreline but out to sea. ... The Hibernia platform is the worlds largest oil platform. ...


For effective CP, the potential of the steel surface is polarized (pushed) more negative until the metal surface has a uniform potential. With a uniform potential, the driving force for the corrosion reaction is halted. For galvanic CP systems, the anode material corrodes under the influence of the steel, and eventually it must be replaced. The polarization is caused by the current flow from the anode to the cathode, driven by the difference in electrochemical potential between the anode and the cathode.


For larger structures, galvanic anodes cannot economically deliver enough current to provide complete protection. Impressed Current Cathodic Protection (ICCP) systems use anodes connected to a DC power source (a cathodic protection rectifier). Anodes for ICCP systems are tubular and solid rod shapes of various specialized materials. These include high silicon cast iron, graphite, mixed metal oxide or platinum coated titanium or niobium coated rod and wires. Aluminium anodes mounted on a steel jacket structure Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... Cathodic Protection Rectifiers are AC powered electrical equipment that provide direct current for impressed current cathodic protection systems. ... Not to be confused with Silicone. ... Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). ... For other uses, see Graphite (disambiguation). ... This article is about metallic materials. ... An oxide is a chemical compound containing an oxygen atom and other elements. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... General Name, Symbol, Number niobium, Nb, 41 Chemical series transition metals Group, Period, Block 5, 5, d Appearance gray metallic Standard atomic weight 92. ...


Corrosion in passivated materials

Passivation is extremely useful in alleviating corrosion damage, but care must be taken not to trust it too thoroughly. Even a high-quality alloy will corrode if its ability to form a passivating film is hindered. Because the resulting modes of corrosion are more exotic and their immediate results are less visible than rust and other bulk corrosion, they often escape notice and cause problems among those who are not familiar with them. Passivation is the process of making a material passive in relation to another material prior to using the materials together. ... A blacksmith removing rust with sand prior to welding Rust damage in automobiles can create hidden dangers. ...


Pitting corrosion

Main article: Pitting corrosion

Certain conditions, such as low concentrations of oxygen or high concentrations of species such as chloride which compete as anions, can interfere with a given alloy's ability to re-form a passivating film. In the worst case, almost all of the surface will remain protected, but tiny local fluctuations will degrade the oxide film in a few critical points. Corrosion at these points will be greatly amplified, and can cause corrosion pits of several types, depending upon conditions. While the corrosion pits only nucleate under fairly extreme circumstances, they can continue to grow even when conditions return to normal, since the interior of a pit is naturally deprived of oxygen. In extreme cases, the sharp tips of extremely long and narrow can cause stress concentration to the point that otherwise tough alloys can shatter, or a thin film pierced by an invisibly small hole can hide a thumb sized pit from view. These problems are especially dangerous because they are difficult to detect before a part or structure fails. Pitting remains among the most common and damaging forms of corrosion in passivated alloys, but it can be prevented by control of the alloy's environment, which often includes ensuring that the material is exposed to oxygen uniformly (i.e., eliminating crevices). Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. ... The chloride ion is formed when the element chlorine picks up one electron to form an anion (negatively-charged ion) Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. ... An anion is an ion with negative charge. ... Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... A stress concentration is a phenomenon encounterered in mechanical engineering where an object under load has higher than average local stresses due to its shape. ... Structural failure refers to loss of the load-carrying capacity of a component or member within a structure or of the structure itself. ...


Weld decay and knifeline attack

Stainless steel can pose special corrosion challenges, since its passivating behavior relies on the presence of a minor alloying component (Chromium, typically only 18%). Due to the elevated temperatures of welding or during improper heat treatment, chromium carbides can form in the grain boundaries of stainless alloys. This chemical reaction robs the material of chromium in the zone near the grain boundary, making those areas much less resistant to corrosion. This creates a galvanic couple with the well-protected alloy nearby, which leads to weld decay (corrosion of the grain boundaries near welds) in highly corrosive environments. Special alloys, either with low carbon content or with added carbon "getters" such as titanium and niobium (in types 321 and 347, respectively), can prevent this effect, but the latter require special heat treatment after welding to prevent the similar phenomenon of knifeline attack. As its name applies, this is limited to a small zone, often only a few micrometres across, which causes it to proceed more rapidly. This zone is very near the weld, making it even less noticeable1. Intergranular corrosion (IGC), also termed intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides. ... The 630 foot high, stainless-clad (type 304L) Gateway Arch defines St. ... General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... Heat treatment is a method used to alter the physical, and sometimes chemical, properties of a material. ... Calcium carbide. ... A crystallite is a domain of solid-state matter that has the same structure as a single crystal. ... English chemists John Daniell (left) and Michael Faraday (right), both credited to be founders of electrochemistry as known today. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... To prevent any remaining gases from remaining in a free state in a vacuum tube, modern tubes are constructed with getters, which are usually small, circular troughs filled with metals that oxidize quickly, with barium being the most common. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery metallic Standard atomic weight 47. ... General Name, Symbol, Number niobium, Nb, 41 Chemical series transition metals Group, Period, Block 5, 5, d Appearance gray metallic Standard atomic weight 92. ...


Galvanic corrosion

Main article: Galvanic corrosion

Galvanic corrosion occurs when two different metals electrically contact each other and are immersed in an electrolyte. In order for galvanic corrosion to occur, an electrically conductive path and an ionically conductive path are necessary. This effects a galvanic couple where the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a retarded rate. When immersed, neither metal would normally corrode as quickly without the electrically conductive connection (usually via a wire or direct contact). Galvanic corrosion is often utilised in sacrificial anodes. What type of metal(s) to use is readily determined by following the galvanic series. For example, zinc is often used as a sacrificial anode for steel structures, such as pipelines or docked naval ships. Galvanic corrosion is of major interest to the marine industry and also anywhere water can contact pipes or metal structures. The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ... The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ... An electrolyte is a substance containing free ions that behaves as an electrically conductive medium. ... The Galvanic cell, named after Luigi Galvani, consists of two different metals connected by a salt bridge or a porous disk between the individual half-cells. ... Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. ... A sacrificial anode, or sacrificial rod, is a metallic anode used in an electrochemical process where it is intended to be dissolved to protect other metallic components. ... The galvanic series determines the nobility of metals and semi-metals. ...


Factors such as relative size of anode (smaller is generally less desirable), types of metal, and operating conditions (temperature, humidity, salinity, &c.) will affect galvanic corrosion. The surface area ratio of the anode and cathode will directly affect the corrosion rates of the materials.


Microbial corrosion

Main article: Microbial corrosion

Microbial corrosion, or bacterial corrosion, is a corrosion caused or promoted by microorganisms, usually chemoautotrophs. It can apply to both metals and non-metallic materials, in both the presence and lack of oxygen. Sulfate-reducing bacteria are common in lack of oxygen; they produce hydrogen sulfide, causing sulfide stress cracking. In presence of oxygen, some bacteria directly oxidize iron to iron oxides and hydroxides, other bacteria oxidize sulfur and produce sulfuric acid causing biogenic sulfide corrosion. Concentration cells can form in the deposits of corrosion products, causing and enhancing galvanic corrosion. Microbial corrosion, or bacterial corrosion, is a corrosion caused or promoted by microorganisms, usually chemoautotrophs. ... Microbial corrosion, or bacterial corrosion, is a corrosion caused or promoted by microorganisms, usually chemoautotrophs. ... A cluster of Escherichia coli bacteria magnified 10,000 times. ... Chemotrophs are organisms that obtain energy by the oxidation of electron donating molecules in their environments. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Sulfate-reducing bacteria comprise several groups of bacteria that use sulfate as an oxidizing agent, reducing it to sulfide. ... Hydrogen sulfide (hydrogen sulphide in British English) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs and flatulence. ... Sulphide stress cracking (SSC), or sulphide stress corrosion cracking (SSCC), is a special corrosion type, a form of stress corrosion cracking. ... There are very few or no other articles that link to this one. ... A Concentration Cell is an electrochemical cell that has two equivalent half-cells of of the same material differing only in concentrations. ... The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ...


High temperature corrosion

High temperature corrosion is chemical deterioration of a material (typically a metal) under very high temperature conditions. This non-galvanic form of corrosion can occur when a metal is subject to a high temperature atmosphere containing oxygen, sulphur or other compounds capable of oxidising (or assisting the oxidation of) the material concerned. For example, materials used in aerospace, power generation and even in car engines have to resist sustained periods at high temperature in which they may be exposed to an atmosphere containing potentially highly corrosive products of combustion.


The products of high temperature corrosion can potentially be turned to the advantage of the engineer. The formation of oxides on stainless steels, for example, can provide a protective layer preventing further atmospheric attack, allowing for a material to be used for sustained periods at both room and high temperature in hostile conditions. Such high temperature corrosion products in the form of compacted oxide layer glazes have also been shown to prevent or reduce wear during high temperature sliding contact of metallic (or metallic and ceramic) surfaces. Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ...


Economic impact

The US Federal Highway Administration released a study, entitled Corrosion Costs and Preventive Strategies in the United States, in 2002 on the direct costs associated with metallic corrosion in nearly every U.S. industry sector. The study showed that for 1998 the total annual estimated direct cost of corrosion in the U.S. was approximately $276 billion (approximately 3.1% of the US gross domestic product). FHWA Report Number:FHWA-RD-01-156. The NACE International website has a summary slideshow of the report findings. Jones1 writes that electrochemical corrosion causes between $8 billion and $128 billion in economic damage per year in the United States alone, degrading structures, machines, and containers. This is when Dampney Company came up with a solution for corrosion or "corrosion under insulation" coatings to prevent this reaction. The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. ... This article is about GDP in the context of economics. ... NACE International is a professional organization for the corrosion control industry. ...


References

Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... Map highlighting Upper Saddle Rivers location within Bergen County. ... Pearson can mean Pearson PLC the media conglomerate. ...

See also

Corrosion Hazard label NFPA 704 standard hazard sticker. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ... A blacksmith removing rust with sand prior to welding Rust damage in automobiles can create hidden dangers. ... Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Controlled Permeability Formwork (CPF) CPF is the only system proven to significantly enhances the durability of surface concrete during the casting process. ... Aluminium anodes mounted on a steel jacket structure Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. ... Galvanization or galvanisation refers to any of several electrochemical processes named after the Italian scientist Luigi Galvani. ... The most fundamental reactions in chemistry are the redox processes. ... The Periodic Table redirects here. ... The Society of Tribologists and Lubrication Engineers (STLE) is a professional organization of individuals working in the fields of tribology and lubrication. ... Salt spray test is a standardized test method used to check corrosion resistance of coated samples. ... Stress corrosion cracking (SCC) is the unexpected sudden failure of normally ductile metals subjected to a constant tensile stress in a corrosive environment, especially at elevated temperature. ... Zinc pest, (from German Zinkpest), is a destructive, intercrystalline corrosion process of zinc alloys of poor purity. ...

External links

Wikimedia Commons has media related to:
  • NACE International -Professional society for corrosion engineers ( NACE )
  • corrosion-doctors.org -Site dedicated to corrosion of all forms
  • efcweb.org -European Federation of Corrosion
  • worldstainless.org-Corrosion Properties of Stainless Steel

  Results from FactBites:
 
Wiley-VCH - Materials and Corrosion (131 words)
Materials and Corrosion is the leading European journal in its field, providing rapid and comprehensive coverage of the subject and specifically highlighting the increasing importance of corrosion research and prevention.
Materials and Corrosion provides you with strictly peer-reviewed, high-quality papers on all aspects of the behavior of materials in corrosive environments as well as corrosion testing and protection.
Several sections exclusive to Materials and Corrosion bring you closer to the current events in the field of corrosion research and add to the impact this journal can make on your work.
Corrosion - Wikipedia, the free encyclopedia (2463 words)
Corrosion is deterioration of intrinsic properties in a material due to reactions with its environment.
Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area to produce general deterioration.
A common example of corrosion protection in ceramics is the lime added to soda-lime glass to reduce its solubility in water; though it is not nearly as soluble as pure sodium silicate, normal glass does form sub-microscopic flaws when exposed to moisture.
  More results at FactBites »

 
 

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