Corrosion is defined as the deterioration of a material as a result of an electrochemical attack by its environment. More generally, it can be understood as the general tendency that materials have to seek their form with the greatest stability or lowest internal energy. Whenever corrosion is caused by an electrochemical reaction (oxidation), the rate at which it takes place will depend to some extent on the temperature, the salinity of the fluid in contact with the metal and the properties of the metals in question. Other non-metallic materials also suffer corrosion through other mechanisms. The corrosion process is natural and spontaneous.
Corrosion is a chemical reaction (oxide-reduction) in which three factors intervene: the manufactured part, the environment and water, or through an electrochemical reaction.
The best known factors are the chemical alterations of metals due to air, such as the rust of iron and steel or the formation of green patina on copper and its alloys (bronze, brass).
It is an important industrial problem, as it can cause accidents (breakage of a piece) and, in addition, it represents a significant cost, since it is estimated that every few seconds five tons of steel are dissolved in the world, coming from a few nanometers or picometers, invisible in each piece but which, multiplied by the amount of steel that exists in the world, constitutes a significant amount.
Corrosion is a field of materials science that invokes both notions of chemistry and physics (physicochemistry).
Basic definitions
What causes corrosion is a massive flow generated by chemical differences between the parts involved (corrosion is an electrochemical phenomenon). A current of electrons is established when there is a potential difference between one point and another. When electrons are transferred from a chemical species and migrate to another species, it is said that the species that emits them behaves like an anode and oxidation occurs, and the species that receives them behaves like a cathode and reduction occurs.
For this to occur between species, an electrochemical differential must exist. If we separate a species and its half-reaction, it will be called electrochemical half-pair; If we put both semi-pairs together, an electrochemical pair will be formed. Each semi-pair is associated with a reduction potential (previously the concept of was used). That metal or chemical species that exhibits a more positive reduction potential will proceed as a reduction and, vice versa, that which exhibits a more negative reduction potential will proceed as an oxidation.
Review of corroded metal parts
Introduction
Corrosion is defined as the deterioration of a material as a result of an electrochemical attack by its environment. More generally, it can be understood as the general tendency that materials have to seek their form with the greatest stability or lowest internal energy. Whenever corrosion is caused by an electrochemical reaction (oxidation), the rate at which it takes place will depend to some extent on the temperature, the salinity of the fluid in contact with the metal and the properties of the metals in question. Other non-metallic materials also suffer corrosion through other mechanisms. The corrosion process is natural and spontaneous.
Corrosion is a chemical reaction (oxide-reduction) in which three factors intervene: the manufactured part, the environment and water, or through an electrochemical reaction.
The best known factors are the chemical alterations of metals due to air, such as the rust of iron and steel or the formation of green patina on copper and its alloys (bronze, brass).
It is an important industrial problem, as it can cause accidents (breakage of a piece) and, in addition, it represents a significant cost, since it is estimated that every few seconds five tons of steel are dissolved in the world, coming from a few nanometers or picometers, invisible in each piece but which, multiplied by the amount of steel that exists in the world, constitutes a significant amount.
Corrosion is a field of materials science that invokes both notions of chemistry and physics (physicochemistry).
Basic definitions
What causes corrosion is a massive flow generated by chemical differences between the parts involved (corrosion is an electrochemical phenomenon). A current of electrons is established when there is a potential difference between one point and another. When electrons are transferred from a chemical species and migrate to another species, it is said that the species that emits them behaves like an anode and oxidation occurs, and the species that receives them behaves like a cathode and reduction occurs.
oxidation potential
This pair of metals constitutes the so-called galvanic cell, where the species that is oxidized (anode) gives up its electrons and the species that is reduced (cathode) accepts electrons. When the galvanic cell is formed, the cathode becomes negatively polarized, while the anode becomes positively polarized.
In an aqueous medium, the oxidation of the medium is verified by a special electrode, called ORP electrode"), which measures the conductance of the medium in millivolts. Chemical metallic corrosion is due to direct attack of the aggressive medium on the metal, oxidizing it, and the exchange of electrons occurs without the need for the formation of the galvanic pair.
Corrosion of metals is a natural phenomenon that occurs due to the thermodynamic instability of most metals. Indeed, with rare exceptions (gold, iron of meteoritic origin), metals are present on Earth in the form of oxides, in minerals (such as bauxite if it is aluminum or hematite if it is iron). Since prehistory, all metallurgy has consisted of reducing oxides in low furnaces, then in blast furnaces, to manufacture metal. Corrosion, in fact, is the return of metal to its natural state, rust.
Stainless steel is often talked about:.
• - This type of steel contains alloying elements (chromium) in at least 11%, which allows it to be stainless when exposed to oxygen, in addition to being a ferrite stabilizer.
• - Chromium causes the austenite region to contract, and the ferrite region decreases in size instead.
There are multiple varieties of steel called "stainless", which carry names such as "304", "304L", "316N", etc., corresponding to different compositions and treatments. Each steel corresponds to certain types of environment: ferritic, martensitic, austenitic, precipitation hardening (PH) and duplex stainless steel.
Types of corrosion
Contenido
Existen muchos mecanismos por los cuales se verifica la corrosión, que, tal como se ha explicado, es fundamentalmente un proceso electroquímico.
chemical corrosion
In chemical corrosion, a material that dissolves in a corrosive liquid will continue to dissolve until it is completely consumed or the liquid is saturated.
Copper (Cu)-based alloys develop a green varnish due to the formation of copper carbonate and hydroxides; This is the reason why the Statue of Liberty is seen with that greenish color.
Corrosive fluids are: hydrochloric acid and gas at all concentrations, sulfuric acid up to 90%, hydrofluoric acid up to 60%, all concentrations of phosphoric acid, acid stripping in surface treatment plants, electrolytes used in the mining industry, mixed acids, chlorinated hydrocarbons and catalysts such as aluminum chloride.
Liquid metals attack solids at their most critical energy points, such as grain boundaries, which will eventually generate several cracks.
It consists of separating solids from an alloy. Graphitic corrosion of gray cast iron occurs when iron is selectively diluted in water or soil, releasing graphite scale and a corrosion product, causing pipe leaks or failures.
Refractory ceramic materials used to contain molten metal during melting and refining can be dissolved by slag caused on the surface of the metal.
Plastics are considered resistant to corrosion; for example, Teflon and Viton") are some of the most resistant materials. These resist many acids, bases and organic liquids, but there are some solvents that are aggressive to thermoplastics; that is, the smaller solvent molecules separate the chains of the plastics, causing swelling that causes cracks. Solvents such as benzene and toluene tend to corrode plastics by chemical dissolution of their molecules, especially those such as polyethylene and polystyrene. Ergo, These liquids should be stored in metal or glass containers.
Types of electrochemical corrosion
They occur when two metals or alloys, such as copper and iron, form an electrolytic cell. Also called deposit attack or crevice corrosion. It is produced in small cavities formed by contact between a piece of metal the same or different from the first one, or a non-metallic element. It refers to the tendency of corrosion to accumulate more quickly in the cracks and crevices of a building or vehicle or structural joints. It is the deterioration of parts of a metal surface at different rates, due to the parts of the surface coming into contact with different concentrations of the same electrolyte. In other words, the deterioration at one point is faster than at another point. With the polarization effect of the alloy elements and the concentrations of the electrolyte, the emf series may not tell which region will be corroded and which will be protected.
Stress corrosion occurs due to galvanic action but can occur due to the filtration of impurities at the end of an existing crack. Failure occurs as a result of corrosion and applied stress; At greater efforts the time required for failure is reduced.
This type of corrosion generally occurs on surfaces exposed to diatomic oxygen dissolved in water or air; It is favored by high temperatures and high pressure (example: steam boilers). Corrosion in thermal machines (steam boilers) represents a constant loss of performance and useful life of the installation.
It is one of the types of electrochemical corrosion. Some microorganisms are capable of causing corrosion on submerged metal surfaces. The biodiversity that is present in this type of corrosion will be:.
• - Bacteria.
• - Algae.
• - Fungus.
Some hydrogen-dependent species have been identified that use the dissolved hydrogen of water in their metabolic processes, causing a potential difference in the surrounding medium. Its action is associated with the pitting of oxygen or the presence of hydrogen sulfide in the medium. In this case, ferrobacteria are classified"). It is essential that the medium has the presence of water. Bacteria can live in a pH range of 0 to 10; this range does not imply that at a pH of 11 no bacteria can exist.
The oxygen present in a pipe, for example, is exposed to different partial pressures of the pipe. That is, one surface is more aerated than another next to it and a pile is formed. The area subject to less aeration (lower partial pressure) acts as an anode and the one with a greater presence of oxygen (higher pressure) acts as a cathode and the migration of electrons is established, oxide forming in one and reducing in the other part of the cell. This type of corrosion is common on very irregular surfaces where oxygen blockages occur.
It is the most common of all and is established when two different metals act as an anode and the other as a cathode. That which has the most negative reduction potential will proceed as an oxidation and, vice versa, that metal or chemical species that exhibits a more positive reduction potential will proceed as a reduction. This pair of metals constitutes the so-called galvanic cell. Where the species that is oxidized (anode) gives up its electrons and the species that is reduced (cathode) accepts the electrons.
It occurs in metal alloys, due to imperfections in the alloy.
Also called Evans effect. It occurs on flat surfaces, in humid and dirty places. The deposit of dirt causes, in the presence of humidity, the existence of a more electronegatively charged environment.
Examples of corrosion in daily life
automatic washing machine
When corrosion appears it is sometimes noticeable but in the case of the automatic washing machine we realize that there could be a corrosion problem when it makes some strange noises. When checking and emptying the drum, we may be surprised to find that it has a crack. There was no trace of rust; just strange noises.
The drum, despite being made of stainless steel, can suffer a certain type of corrosion, known by specialists as cracking corrosion due to the damage caused.
This type of corrosion, very localized in a certain area of the washing machine drum, is especially insidious and worrying because one does not realize its existence until the failure occurs.[1].
concrete constructions
In concrete constructions such as bridges, we can observe the effects of corrosion due to the appearance of rust spots on the surface of the structure. Other examples could be an underground parking lot, a bridge, or on power distribution line poles. These structures are reinforced internally with steel rods, which are covered with concrete.
Concrete is a mixture that, due to its high pH value, is compatible with steel. The same concrete in its characteristics has porosities through which oxygen and water from the external environment can infiltrate, thus initiating corrosion of the structure. When the concrete structure is in frequent contact with water containing chloride ions (seawater), through the porosity of the concrete itself it can reach the steel rods. The rust that forms as a result of the corrosion process in the steel, on the one hand, reduces the original section of the rod, and on the other hand, it causes the desired initial adhesion between the steel and the concrete to be lost.
As the corrosion process continues, cracks are observed in the concrete and subsequently stains appear on the surface. It not only happens in environments near the sea due to the salt in seawater; also in industrialized cities due to sulfur dioxide or sulfur dioxide, coming from industries that burn diesel (fuel) and car exhaust, among others.[1].
Metal containers for preserves
In cans, when stored for a long period of time, we can see that they are bulging and their metallic shine has changed to a dull appearance of the surface.
This bulging deformation is due to the accumulation of hydrogen gas and is an extreme manifestation of corrosion. Indicates that the useful life of the preserve has ended.
The most frequently used materials for the manufacture of containers are aluminum, tinplate and chrome plate, although tinplate continues to be the most widely used material.
The corrosion of tinplate by packaged foods is an electrochemical process due to the structure of the material that has several layers, which in turn in contact with the food that functions as an electrolyte form a galvanic cell. An additional contribution of corrosion to this system is the weld bead.[1].
Corrosion protection
Design
The design of the structures may seem of little importance, but can be implemented to isolate surfaces from the environment.
The coatings
These are used to isolate the synodic (anodic) and cathodic regions and prevent the diffusion of oxygen or water vapor, which are a major source that initiates corrosion or oxidation. Oxidation occurs in humid places but there are methods to prevent the metal from rusting, such as a layer of paint.
Choice of material
The first idea is to choose a material that does not corrode in the considered environment. Stainless steels, aluminum, ceramics, polymers (plastics), FRP, etc. can be used. The choice must also take into account the restrictions of the application (mass of the part, resistance to deformation, heat, ability to conduct electricity, etc.).
It should be remembered that there are no absolutely stainless materials; Even aluminum can corrode.
In conception, confinement zones, contacts between different materials and heterogeneities in general must be avoided.
It is also necessary to anticipate the importance of corrosion and the time in which the part will have to be changed (preventive maintenance).
Mastery of the environment
When working in a closed environment (for example, a closed water circuit), the parameters that influence corrosion can be controlled; chemical composition (particularly acidity), temperature, pressure... Products called "corrosion inhibitors" can be added. A corrosion inhibitor is a substance that, added to a certain medium, significantly reduces the rate of corrosion. The substances used depend on both the metal to be protected and the medium, and an inhibitor that works well in a certain system can even accelerate corrosion in another system.
Corrosion inhibitors
It is the transfer of physical products that are added to an electrolyte solution to the surface of the anode or cathode, which produces polarization.
Corrosion inhibitors are products that act either by forming films on the metal surface, such as molybdates, phosphates or ethanolamines, or by delivering their electrons to the medium. In general, inhibitors of this type are modified azoles, which act synergistically with other inhibitors such as nitrites, phosphates and silicates. The chemistry of the inhibitors is not fully developed yet. Its use is in the field of cooling systems or heat sinks such as radiators, cooling towers, boilers and chillers. The use of ethanolamines is typical in some fuels to protect containment systems (such as pipes and tanks). Much work has been done on corrosion inhibitors as viable alternatives to reduce the rate of corrosion in industry. Extensive studies on IC and on factors governing its efficiency have been conducted over the past 20 years. They range from the simplest ones that were trial and error, to the most modern ones, which propose the selection of the inhibitor through theoretical calculations.
Preventive protection methods
Before providing protection, the metal surface must be prepared, cleaning it of foreign materials (cleaning and degreasing). Also the addition of substances that prevent the passage of oxygen, water, etc.; For example, paint prevents corrosion.
• - Galvanic corrosion.
• - Corrosion due to erosion.
• - Anticorrosive paint.
• - Corrosive substance.
• - Cathodic protection.
• - [ASM96]: Corrosion 5, vol. 13 of ASM Handbook, ASM International (American Society for Materials), 1996.
• - [Ben62]: L'Oxydation des métaux, J. Bénard et al., Gauthier-Villars, 1962.
• - [Kof88]: High Temperature Corrosion in metallic surfaces, P. Kofstad, Elsevier, 1988.
• - [Lan93]: Corrosion et chimie de surfaces des métaux, D. Landolt, vol. 12 of Traité des matériaux, Presses Polytechniques et Universitaires Romandes, 1993.
• - [Now92]: Diffusion in Solids and High Temperature Oxidation of Metals, J. Nowotny, Trans Tech Publications, 1992.
• - [Phi98]: Métallurgie: du minerai au matériau, J. Philibert et al., Masson, 1998.
• - Wikimedia Commons hosts a multimedia category on corrosion.
For this to occur between species, an electrochemical differential must exist. If we separate a species and its half-reaction, it will be called electrochemical half-pair; If we put both semi-pairs together, an electrochemical pair will be formed. Each semi-pair is associated with a reduction potential (previously the concept of oxidation potential was used). That metal or chemical species that exhibits a more positive reduction potential will proceed as a reduction and, vice versa, that which exhibits a more negative reduction potential will proceed as an oxidation.
This pair of metals constitutes the so-called galvanic cell, where the species that is oxidized (anode) gives up its electrons and the species that is reduced (cathode) accepts electrons. When the galvanic cell is formed, the cathode becomes negatively polarized, while the anode becomes positively polarized.
In an aqueous medium, the oxidation of the medium is verified by a special electrode, called ORP electrode"), which measures the conductance of the medium in millivolts. Chemical metallic corrosion is due to direct attack of the aggressive medium on the metal, oxidizing it, and the exchange of electrons occurs without the need for the formation of the galvanic pair.
Corrosion of metals is a natural phenomenon that occurs due to the thermodynamic instability of most metals. Indeed, with rare exceptions (gold, iron of meteoritic origin), metals are present on Earth in the form of oxides, in minerals (such as bauxite if it is aluminum or hematite if it is iron). Since prehistory, all metallurgy has consisted of reducing oxides in low furnaces, then in blast furnaces, to manufacture metal. Corrosion, in fact, is the return of metal to its natural state, rust.
Stainless steel is often talked about:.
• - This type of steel contains alloying elements (chromium) in at least 11%, which allows it to be stainless when exposed to oxygen, in addition to being a ferrite stabilizer.
• - Chromium causes the austenite region to contract, and the ferrite region decreases in size instead.
There are multiple varieties of steel called "stainless", which carry names such as "304", "304L", "316N", etc., corresponding to different compositions and treatments. Each steel corresponds to certain types of environment: ferritic, martensitic, austenitic, precipitation hardening (PH) and duplex stainless steel.
Types of corrosion
Contenido
Existen muchos mecanismos por los cuales se verifica la corrosión, que, tal como se ha explicado, es fundamentalmente un proceso electroquímico.
chemical corrosion
In chemical corrosion, a material that dissolves in a corrosive liquid will continue to dissolve until it is completely consumed or the liquid is saturated.
Copper (Cu)-based alloys develop a green varnish due to the formation of copper carbonate and hydroxides; This is the reason why the Statue of Liberty is seen with that greenish color.
Corrosive fluids are: hydrochloric acid and gas at all concentrations, sulfuric acid up to 90%, hydrofluoric acid up to 60%, all concentrations of phosphoric acid, acid stripping in surface treatment plants, electrolytes used in the mining industry, mixed acids, chlorinated hydrocarbons and catalysts such as aluminum chloride.
Liquid metals attack solids at their most critical energy points, such as grain boundaries, which will eventually generate several cracks.
It consists of separating solids from an alloy. Graphitic corrosion of gray cast iron occurs when iron is selectively diluted in water or soil, releasing graphite scale and a corrosion product, causing pipe leaks or failures.
Refractory ceramic materials used to contain molten metal during melting and refining can be dissolved by slag caused on the surface of the metal.
Plastics are considered resistant to corrosion; for example, Teflon and Viton") are some of the most resistant materials. These resist many acids, bases and organic liquids, but there are some solvents that are aggressive to thermoplastics; that is, the smaller solvent molecules separate the chains of the plastics, causing swelling that causes cracks. Solvents such as benzene and toluene tend to corrode plastics by chemical dissolution of their molecules, especially those such as polyethylene and polystyrene. Ergo, These liquids should be stored in metal or glass containers.
Types of electrochemical corrosion
They occur when two metals or alloys, such as copper and iron, form an electrolytic cell. Also called deposit attack or crevice corrosion. It is produced in small cavities formed by contact between a piece of metal the same or different from the first one, or a non-metallic element. It refers to the tendency of corrosion to accumulate more quickly in the cracks and crevices of a building or vehicle or structural joints. It is the deterioration of parts of a metal surface at different rates, due to the parts of the surface coming into contact with different concentrations of the same electrolyte. In other words, the deterioration at one point is faster than at another point. With the polarization effect of the alloy elements and the concentrations of the electrolyte, the emf series may not tell which region will be corroded and which will be protected.
Stress corrosion occurs due to galvanic action but can occur due to the filtration of impurities at the end of an existing crack. Failure occurs as a result of corrosion and applied stress; At greater efforts the time required for failure is reduced.
This type of corrosion generally occurs on surfaces exposed to diatomic oxygen dissolved in water or air; It is favored by high temperatures and high pressure (example: steam boilers). Corrosion in thermal machines (steam boilers) represents a constant loss of performance and useful life of the installation.
It is one of the types of electrochemical corrosion. Some microorganisms are capable of causing corrosion on submerged metal surfaces. The biodiversity that is present in this type of corrosion will be:.
• - Bacteria.
• - Algae.
• - Fungus.
Some hydrogen-dependent species have been identified that use the dissolved hydrogen of water in their metabolic processes, causing a potential difference in the surrounding medium. Its action is associated with the pitting of oxygen or the presence of hydrogen sulfide in the medium. In this case, ferrobacteria are classified"). It is essential that the medium has the presence of water. Bacteria can live in a pH range of 0 to 10; this range does not imply that at a pH of 11 no bacteria can exist.
The oxygen present in a pipe, for example, is exposed to different partial pressures of the pipe. That is, one surface is more aerated than another next to it and a pile is formed. The area subject to less aeration (lower partial pressure) acts as an anode and the one with a greater presence of oxygen (higher pressure) acts as a cathode and the migration of electrons is established, oxide forming in one and reducing in the other part of the cell. This type of corrosion is common on very irregular surfaces where oxygen blockages occur.
It is the most common of all and is established when two different metals act as an anode and the other as a cathode. That which has the most negative reduction potential will proceed as an oxidation and, vice versa, that metal or chemical species that exhibits a more positive reduction potential will proceed as a reduction. This pair of metals constitutes the so-called galvanic cell. Where the species that is oxidized (anode) gives up its electrons and the species that is reduced (cathode) accepts the electrons.
It occurs in metal alloys, due to imperfections in the alloy.
Also called Evans effect. It occurs on flat surfaces, in humid and dirty places. The deposit of dirt causes, in the presence of humidity, the existence of a more electronegatively charged environment.
Examples of corrosion in daily life
automatic washing machine
When corrosion appears it is sometimes noticeable but in the case of the automatic washing machine we realize that there could be a corrosion problem when it makes some strange noises. When checking and emptying the drum, we may be surprised to find that it has a crack. There was no trace of rust; just strange noises.
The drum, despite being made of stainless steel, can suffer a certain type of corrosion, known by specialists as cracking corrosion due to the damage caused.
This type of corrosion, very localized in a certain area of the washing machine drum, is especially insidious and worrying because one does not realize its existence until the failure occurs.[1].
concrete constructions
In concrete constructions such as bridges, we can observe the effects of corrosion due to the appearance of rust spots on the surface of the structure. Other examples could be an underground parking lot, a bridge, or on power distribution line poles. These structures are reinforced internally with steel rods, which are covered with concrete.
Concrete is a mixture that, due to its high pH value, is compatible with steel. The same concrete in its characteristics has porosities through which oxygen and water from the external environment can infiltrate, thus initiating corrosion of the structure. When the concrete structure is in frequent contact with water containing chloride ions (seawater), through the porosity of the concrete itself it can reach the steel rods. The rust that forms as a result of the corrosion process in the steel, on the one hand, reduces the original section of the rod, and on the other hand, it causes the desired initial adhesion between the steel and the concrete to be lost.
As the corrosion process continues, cracks are observed in the concrete and subsequently stains appear on the surface. It not only happens in environments near the sea due to the salt in seawater; also in industrialized cities due to sulfur dioxide or sulfur dioxide, coming from industries that burn diesel (fuel) and car exhaust, among others.[1].
Metal containers for preserves
In cans, when stored for a long period of time, we can see that they are bulging and their metallic shine has changed to a dull appearance of the surface.
This bulging deformation is due to the accumulation of hydrogen gas and is an extreme manifestation of corrosion. Indicates that the useful life of the preserve has ended.
The most frequently used materials for the manufacture of containers are aluminum, tinplate and chrome plate, although tinplate continues to be the most widely used material.
The corrosion of tinplate by packaged foods is an electrochemical process due to the structure of the material that has several layers, which in turn in contact with the food that functions as an electrolyte form a galvanic cell. An additional contribution of corrosion to this system is the weld bead.[1].
Corrosion protection
Design
The design of the structures may seem of little importance, but can be implemented to isolate surfaces from the environment.
The coatings
These are used to isolate the synodic (anodic) and cathodic regions and prevent the diffusion of oxygen or water vapor, which are a major source that initiates corrosion or oxidation. Oxidation occurs in humid places but there are methods to prevent the metal from rusting, such as a layer of paint.
Choice of material
The first idea is to choose a material that does not corrode in the considered environment. Stainless steels, aluminum, ceramics, polymers (plastics), FRP, etc. can be used. The choice must also take into account the restrictions of the application (mass of the part, resistance to deformation, heat, ability to conduct electricity, etc.).
It should be remembered that there are no absolutely stainless materials; Even aluminum can corrode.
In conception, confinement zones, contacts between different materials and heterogeneities in general must be avoided.
It is also necessary to anticipate the importance of corrosion and the time in which the part will have to be changed (preventive maintenance).
Mastery of the environment
When working in a closed environment (for example, a closed water circuit), the parameters that influence corrosion can be controlled; chemical composition (particularly acidity), temperature, pressure... Products called "corrosion inhibitors" can be added. A corrosion inhibitor is a substance that, added to a certain medium, significantly reduces the rate of corrosion. The substances used depend on both the metal to be protected and the medium, and an inhibitor that works well in a certain system can even accelerate corrosion in another system.
Corrosion inhibitors
It is the transfer of physical products that are added to an electrolyte solution to the surface of the anode or cathode, which produces polarization.
Corrosion inhibitors are products that act either by forming films on the metal surface, such as molybdates, phosphates or ethanolamines, or by delivering their electrons to the medium. In general, inhibitors of this type are modified azoles, which act synergistically with other inhibitors such as nitrites, phosphates and silicates. The chemistry of the inhibitors is not fully developed yet. Its use is in the field of cooling systems or heat sinks such as radiators, cooling towers, boilers and chillers. The use of ethanolamines is typical in some fuels to protect containment systems (such as pipes and tanks). Much work has been done on corrosion inhibitors as viable alternatives to reduce the rate of corrosion in industry. Extensive studies on IC and on factors governing its efficiency have been conducted over the past 20 years. They range from the simplest ones that were trial and error, to the most modern ones, which propose the selection of the inhibitor through theoretical calculations.
Preventive protection methods
Before providing protection, the metal surface must be prepared, cleaning it of foreign materials (cleaning and degreasing). Also the addition of substances that prevent the passage of oxygen, water, etc.; For example, paint prevents corrosion.
• - Galvanic corrosion.
• - Corrosion due to erosion.
• - Anticorrosive paint.
• - Corrosive substance.
• - Cathodic protection.
• - [ASM96]: Corrosion 5, vol. 13 of ASM Handbook, ASM International (American Society for Materials), 1996.
• - [Ben62]: L'Oxydation des métaux, J. Bénard et al., Gauthier-Villars, 1962.
• - [Kof88]: High Temperature Corrosion in metallic surfaces, P. Kofstad, Elsevier, 1988.
• - [Lan93]: Corrosion et chimie de surfaces des métaux, D. Landolt, vol. 12 of Traité des matériaux, Presses Polytechniques et Universitaires Romandes, 1993.
• - [Now92]: Diffusion in Solids and High Temperature Oxidation of Metals, J. Nowotny, Trans Tech Publications, 1992.
• - [Phi98]: Métallurgie: du minerai au matériau, J. Philibert et al., Masson, 1998.
• - Wikimedia Commons hosts a multimedia category on corrosion.