Do you think that rust is a problem for owners of 15-year-old Zhiguli cars? Alas, cars under warranty also become covered with red spots, even if the body is galvanized. Let's figure out how to properly care for metal and whether it is possible to protect it from corrosion once and for all.

What is a body? Thin construction sheet metal, and of different alloys and with many welded joints. And we must not forget that the body is used as a “minus” for the on-board network, that is, it constantly conducts current. Yes, it simply must rust! Let's try to figure out what is happening to the car body and how to deal with it.

What is rust?

Corrosion of iron or steel is the process of metal oxidation with oxygen in the presence of water. The output is hydrated iron oxide - a loose powder that we all call rust.

Destruction of a car body is considered a classic example of electrochemical corrosion. But water and air are only part of the problem. In addition to conventional chemical processes important role it is played by galvanic pairs that arise between electrochemically inhomogeneous pairs of surfaces.

I can already see a bored expression appearing on the faces of humanities readers. Do not be alarmed by the term “galvanic couple” - we are not going to give complex formulas at a chemistry lecture. This same pair in a particular case is just a combination of two metals.

Metals, they are almost like people. They don’t like it when someone else snuggles up to them. Imagine yourself on a bus. A rumpled man pressed against you, who yesterday celebrated some High-Rise Fitter Day with friends. In chemistry this is called an unacceptable galvanic couple. Aluminum and copper, nickel and silver, magnesium and steel... These are “sworn enemies” who, in close electrical connection They will “eat” each other very quickly.

In fact, no metal can withstand close contact with a stranger for long. Think for yourself: even if a curvy blonde (or a slender brown-haired woman, depending on your taste) is pressed up to you, it will be pleasant at first... But you won’t stand like that all your life. Especially in the rain. What does the rain have to do with it? Now everything will become clear.

There are many places in a car where galvanic couples are formed. Not unacceptable, but “ordinary”. Welding points, body panels made of different metals, various fasteners and assemblies, even different points on the same plate with different machining surfaces. There is always a potential difference between them all, which means that in the presence of an electrolyte there will be corrosion.

Wait, what is an electrolyte? An inquisitive motorist will remember that this is some kind of caustic liquid that is poured into batteries. And he will be only partly right. An electrolyte is generally any substance that conducts current. A weak acid solution is poured into the battery, but it is not necessary to pour acid on the car to speed up corrosion. Works well with electrolyte functions plain water. In its pure (distilled) form it is not an electrolyte, but in nature clean water does not occur...

Thus, in each formed galvanic couple, under the influence of water, the destruction of the metal begins on the anode side - the positively charged side. How to overcome this process? We cannot prevent metals from corroding from each other, but we can exclude the electrolyte from this system. Without it, “permissible” galvanic couples can exist for a long time. Longer than the car lasts.

How do manufacturers fight rust?

The simplest method of protection is to cover the metal surface with a film through which the electrolyte will not penetrate. And if the metal is also good, with a low content of impurities that promote corrosion (for example, sulfur), then the result will be quite decent.

But don't take the words literally. The film is not necessarily polyethylene. The most common type protective film- paint and primer. It can also be created from metal phosphates by treating the surface with a phosphating solution. The phosphorus-containing acids included in its composition oxidize top layer metal, creating a very strong and thin film.

By covering the phosphate film with layers of primer and paint, you can protect the car body for many years; it was according to this “recipe” that bodies were prepared for decades, and, as you can see, quite successfully - many cars produced in the fifties and sixties were able to survive to this day.

But not all, because over time the paint is prone to cracking. At first the outer layers fail, then the cracks reach the metal and phosphate film. And in case of accidents and subsequent repairs, coatings are often applied without maintaining the absolute cleanliness of the surface, leaving small points of corrosion on it, which always contain a little moisture. And under the film of paint a new source of destruction begins to appear.

You can improve the quality of the coating, use more and more flexible paints, the layer of which may be a little more reliable. Can be covered plastic film. But there is best technology. Coating steel with a thin layer of metal that has a more resistant oxide film has been used for a long time. The so-called tinplate - sheet steel coated with a thin layer of tin - is familiar to everyone who has seen a tin can at least once in their life.

Tin has not been used to coat car bodies for a long time, although there are stories about tinned bodies. This is an echo of the technology for straightening defects during stamping with hot solders, when part of the surface was manually covered with a thick layer of tin, and sometimes the most complex and important parts of the car body actually turned out to be well protected.

Modern coatings to prevent corrosion are applied at the factory before body panels are stamped, and zinc or aluminum are used as “saviors”. Both of these metals, in addition to having a strong oxide film, have another valuable quality - lower electronegativity. In the already mentioned galvanic couple, which is formed after the destruction of the outer paint film, they, and not the steel, will play the role of an anode, and as long as a little aluminum or zinc remains on the panel, they will be destroyed. This property can be used in another way by simply adding a little powder of such metals to the primer with which the metal is coated, which will give the body panel an additional chance for a long life.

In some industries, when the task is to protect metal, other technologies are used. Serious metal structures can be equipped with special protector plates made of aluminum and zinc, which can be changed over time, and even with electrochemical protection systems. Using a voltage source, such a system transfers the anode to some parts of the structure that are not load-bearing. These things don't happen on cars.

A multi-layer sandwich consisting of a layer of phosphates on the surface of steel or zinc, a layer of zinc or aluminum, anti-corrosion primer with zinc and several layers of paint and varnish, even in a very aggressive external environment such as ordinary city air with moisture, dirt and salt, allows you to keep body panels intact ten or two years.

In places where the paint layer is easily damaged (for example, on the bottom), thick layers of sealants and mastics are used, which additionally protect the paint surface. We used to call this “anticorrosive”. Additionally, compounds based on paraffin and oils are pumped into the internal cavities; their task is to displace moisture from surfaces, thereby further improving protection.

None of the methods alone provides 100% protection, but together they allow manufacturers to provide an eight- to ten-year guarantee against through-corrosion of the body. However, we must remember that corrosion is like death. Its arrival can be slowed down or postponed, but cannot be completely excluded. In general, what do we say to rust? Correct: “Not today.” Or, to paraphrase modern classic, “not this year.”

Keep the car body clean. Dirt absorbs moisture, which is thus stored on the surface and performs its destructive function for a long time, slowly penetrating through microcracks to the iron.

Repair paint damage in a timely manner, even if the body is galvanized. After all, the fact that “bare” metal does not rust is a consequence of the constant “consumption” of protective metals, and there are by no means kilograms of them on the surface.

Use the services of qualified body services, because proper recovery surface requires very careful and clean work, with a full understanding of the processes taking place. And suggestions to simply paint over everything with a thicker layer of paint will definitely lead you to the body shop again, and with much more serious damage to the metal.

a href=”http://polldaddy.com/poll/8389175/”Have you had to deal with rust on the body?/a

Classification of types of corrosion

Corrosion processes are characterized by a wide distribution and diversity of conditions and environments in which they occur. Therefore, there is not yet a unified and comprehensive classification of the occurrence of corrosion cases.

Depending on the type of aggressive environment in which the destruction process occurs, corrosion can be of the following types:

• gas corrosion;
• atmospheric corrosion;
• corrosion in non-electrolytes;
• corrosion in electrolytes;
• biocorrosion;
• corrosion under the influence of stray currents.

According to the conditions of the corrosion process, the following types are distinguished:

• contact corrosion;
• corrosion due to partial immersion;
• Full immersion corrosion;
• corrosion during alternating immersion;
• friction corrosion;
• Stress corrosion.

By nature of destruction:

The main classification is made according to the mechanism of the process. There are two types:

• chemical corrosion;
• electrochemical corrosion.

Corrosion of non-metallic materials

As operating conditions become more severe (increasing temperature, mechanical stress, environmental aggressiveness, etc.), non-metallic materials are also exposed to the action of the environment. In connection with this, the term “corrosion” began to be used in relation to these materials, for example, “corrosion of concrete and reinforced concrete”, “corrosion of plastics and rubber”. This means their destruction and loss operational properties as a result of chemical or physicochemical interaction with the environment. But it should be taken into account that the mechanisms and kinetics of processes for non-metals and metals will be different.

Metal corrosion

Rust is the most common type of corrosion.

Metal corrosion.

Corrosion of metals is the destruction of metals due to their chemical or electrochemical interaction with a corrosive environment. For the corrosion process, the term “corrosion process” should be used, and for the result of the process, “corrosion destruction”. The formation of galvanic couples is usefully used to create batteries and accumulators. On the other hand, the formation of such a pair leads to an unfavorable process, the victim of which is a number of metals - corrosion. Corrosion is understood as electrochemical or chemical destruction occurring on a surface. metal material. Most often, during corrosion, the metal is oxidized to form metal ions, which, upon further transformations, produce various corrosion products. Corrosion can be caused by either a chemical or an electrochemical process. Accordingly, a distinction is made between chemical and electrochemical corrosion of metals.

Types of corrosion

Electrochemical corrosion

The destruction of metal under the influence of galvanic elements arising in a corrosive environment is called electrochemical corrosion. Corrosion of a homogeneous material, for example, rusting of iron, etc., should not be confused with electrochemical corrosion. Electrochemical corrosion (the most common form of corrosion) always requires the presence of an electrolyte (Condensate, rainwater etc.) with which the electrodes are in contact - either different elements of the material structure, or two different contacting materials with different redox potentials. If ions of salts, acids, or the like are dissolved in water, its electrical conductivity increases and the speed of the process increases.

Corrosive element

When two metals with different redox potentials come into contact and are immersed in an electrolyte solution, for example, rainwater with dissolved carbon dioxide CO 2, a galvanic cell is formed, the so-called corrosion cell. It is nothing more than a closed galvanic cell. It slowly dissolves metallic material with a lower redox potential; the second electrode in a pair, as a rule, does not corrode. This type of corrosion is especially characteristic of metals with high negative potentials. Thus, a very small amount of impurity on the surface of a metal with a high redox potential is already enough for the appearance of a corrosive element. Particularly at risk are areas where metals come into contact with different potentials, e.g. welding seams or rivets.

If the dissolving electrode is corrosion-resistant, the corrosion process is slowed down. This is the basis, for example, for protecting iron products from corrosion by galvanizing - zinc has a more negative potential than iron, therefore, in such a pair, iron is reduced, and zinc must corrode. However, due to the formation of an oxide film on the surface of zinc, the corrosion process slows down greatly.

Hydrogen and oxygen corrosion

If reduction of H 3 O + ions or H 2 O water molecules occurs, they speak of hydrogen corrosion or corrosion with hydrogen depolarization. Ion reduction occurs according to the following scheme:

2H 3 O + + 2e − → 2H 2 O + H 2

2H 2 O + 2e − → 2OH − + H 2

If hydrogen is not evolved, which often happens in a neutral or strongly alkaline environment, oxygen is reduced and we speak of oxygen corrosion or corrosion with oxygen depolarization:

O 2 + 2H 2 O + 4e − → 4OH −

A corrosive element can be formed not only when two different metals come into contact. A corrosive element is also formed in the case of one metal, if, for example, the surface structure is heterogeneous.

Chemical corrosion

Chemical corrosion is the interaction of a metal surface with a corrosive environment, not accompanied by the occurrence of electrochemical processes at the phase boundary. In this case, the interactions of metal oxidation and reduction of the oxidizing component of the corrosive environment occur in one act. For example, the formation of scale when iron-based materials react at high temperatures with oxygen:

4Fe + 3O 2 → 2Fe 2 O 3

During electrochemical corrosion, the ionization of metal atoms and the reduction of the oxidizing component of the corrosive environment do not occur in one act and their rates depend on the electrode potential of the metal (for example, rusting of steel in sea water).

Types of corrosion

• Gas corrosion
• Atmospheric corrosion
• Partial immersion corrosion
• Waterline corrosion
• Fully immersed corrosion
• Corrosion under alternating immersion
• Underground corrosion
• Biocorrosion
• Corrosion by external current
• Stray current corrosion
• Contact corrosion
• Friction corrosion
• Fretting corrosion
• Complete corrosion
• Uniform corrosion
• Uneven corrosion
• Local corrosion
• Subsurface corrosion
• Pitting corrosion
• Corrosion spots
• Through corrosion
• Layer corrosion
• Filiform corrosion
• Structural corrosion
• Intergranular corrosion
• Selective corrosion
• Graphitization of cast iron
• Dezincification
• Crevice corrosion
• Knife corrosion
• Corrosion ulcer
• Corrosion cracking
• Stress Corrosion
• Corrosion fatigue
• Corrosion fatigue limit
• Corrosion brittleness

Anti-corrosion

Corrosion causes billions of dollars in losses every year, and solving this problem is important task. The main damage caused by corrosion is not the loss of metal as such, but the enormous cost of the products destroyed by corrosion. That is why the annual losses from it in industrialized countries are so great. True losses from it cannot be determined by assessing only direct losses, which include the cost of a collapsed structure, the cost of replacing equipment, and the costs of measures to protect against corrosion. Even greater damage comes from indirect losses. These include equipment downtime when replacing corroded parts and assemblies, product leakage, and disruption of technological processes.

Ideal corrosion protection of 80% is ensured proper preparation surface, and only 20% by the quality of the paints and varnishes used and the method of their application. . The most productive and effective method of surface preparation before further protection of the substrate is abrasive blasting.

Typically, there are three areas of corrosion protection methods:

1. Structural
2. Active
3. Passive

To prevent corrosion as construction materials Stainless steels, Corten steels, and non-ferrous metals are used. When designing structures, they try to isolate them as much as possible from corrosive environments, using adhesives, sealants, and rubber gaskets.

Active methods of combating corrosion are aimed at changing the structure of the electrical double layer. Permanent overlay is applied electric field using a direct current source, the voltage is selected in order to increase the electrode potential of the metal being protected. Another method is to use a sacrificial anode, a more active material that will be destroyed, protecting the product being protected.

As protection against corrosion, application of any coatings, which prevents the formation of a corrosive element (passive method).

Oxygen corrosion of galvanized iron

Oxygen corrosion of tin-coated iron

Colorful coating, polymer coating and enameling must, first of all, prevent the access of oxygen and moisture. Coating, for example, of steel with other metals such as zinc, tin, chromium, and nickel is often also used. The zinc coating protects the steel even when the coating is partially destroyed. Zinc has a more negative potential and corrodes first. Zn 2+ ions are toxic. During production tin cans tin coated with a layer of tin is used. Unlike galvanized sheet, when the tin layer is destroyed, the iron begins to corrode, and more intensely, since tin has a more positive potential. Another way to protect metal from corrosion is to use a protective electrode with a high negative potential, for example, made of zinc or magnesium. For this purpose, a corrosion element is specially created. The protected metal acts as a cathode, and this type of protection is called cathodic protection. The dissolving electrode is called, accordingly, the sacrificial protection anode. This method is used to protect sea vessels, bridges, boiler plants, and underground pipes from corrosion. To protect the ship's hull outer side the housings are secured with zinc plates.

If you compare the potentials of zinc and magnesium with iron, they have more negative potentials. Nevertheless, they corrode more slowly due to the formation of a protective oxide film on the surface, which protects the metal from further corrosion. The formation of such a film is called metal passivation. In aluminum it is enhanced by anodic oxidation (anodizing). When a small amount of chromium is added to steel, an oxide film forms on the surface of the metal. The chromium content in stainless steel is more than 12 percent.

Cold galvanizing system

The cold galvanizing system is designed to enhance the anti-corrosion properties of a complex multi-layer coating. The system provides complete cathodic (or galvanic) protection of iron surfaces from corrosion in various aggressive environments

The cold galvanizing system is available in one, two or three packages and includes:

• binder - compositions based on chlorinated rubber, ethyl silicate, polystyrene, epoxy, urethane, alkyd (modified) are known;
• anti-corrosion filler - zinc powder (“zinc dust”), containing more than 95% metallic zinc, having a particle size of less than 10 microns and a minimum degree of oxidation.;
• hardener (in two- and three-pack systems)

One-pack cold galvanizing systems are supplied ready to use and require only thorough mixing of the composition before application. Two- and three-pack systems can be supplied in several packages and require additional operations to prepare the composition before application (mixing binder, filler, hardener).

After preparation (two- and three-pack systems), application of the composition to the protected metal surface with a brush, roller, pneumatic or airless spraying and drying, a zinc-filled anti-corrosion coating is formed on the metal surface - a polymer-zinc film that retains all the properties of the polymer coating that was used as binder, and at the same time possessing all the protective advantages of a conventional zinc coating.

Advantages of the cold galvanizing system compared to the hot galvanizing method:

1. Simplicity and less labor intensity of the technology for applying protective zinc coating. No special equipment is required to apply the coating.
2. Possibility of anti-corrosion protection of metal structures of any size, both in factory and field conditions.
3. Possibility of correcting abrasive damage to the coating and defects that occur during welding of metal structures directly on site.
4. Environmentally friendly coating process: no need to carry out work in a hot shop.
5. Creation of a flexible zinc layer on the surface of iron (which does not form microcracks when bending the metal product).

The cold galvanizing system is used in all types of industry and in everyday life, where reliable and durable protection of iron surfaces from corrosion is required.

In addition to being used as a primer layer in a complex multilayer coating, the cold galvanizing system can be used as an independent anti-corrosion coating for metal surfaces.

Thermal spraying

To combat corrosion, thermal spray methods are also used.
Using thermal spraying, a layer of another metal/alloy is created on the surface of a metal, which is more resistant to corrosion (insulating) or, conversely, less resistant (protective). This layer allows you to stop corrosion of the protected metal. The essence of the method is as follows: particles of a metal mixture are applied to the surface of the product with a gas jet at high speed, resulting in the formation protective layer thickness from tens to hundreds of microns. Thermal spraying is also used to extend the life of worn-out equipment components: from restoring steering racks in car repair shops to oil production companies.

Thermal diffusion zinc coating

(GOST 9.316-2006). To operate metal products in aggressive environments, a more resistant anti-corrosion protection surfaces of metal products. Thermal diffusion zinc coating is anodic in relation to ferrous metals and electrochemically protects steel from corrosion. It has strong adhesion (adhesion) to the base metal due to the mutual diffusion of iron and zinc in the surface intermetallic phases, so peeling and chipping of coatings does not occur during impacts, mechanical loads and deformations of processed products.

Diffusion galvanizing, carried out from the vapor or gas phase at high temperatures(375-850 °C), or using vacuum (vacuum) - at a temperature of 250 °C, used for coating fasteners, pipes, fittings and other structures. Significantly increases the durability of steel, cast iron products in environments containing hydrogen sulfide (including against hydrogen sulfide corrosion cracking), industrial atmosphere, sea water, etc. The thickness of the diffusion layer depends on temperature, time, galvanizing method and can be 0.01-1.5 mm. The modern process of diffusion galvanizing allows the formation of a coating on threaded surfaces fasteners, without complicating their subsequent screwing. Microhardness of the coating layer Hμ = 4000 - 5000 MPa. Diffusion zinc coating also significantly increases the heat resistance of steel and cast iron products, at temperatures up to 700 °C. It is possible to obtain alloyed diffusion zinc coatings, which are used to improve their performance characteristics.

Galvanizing

Galvanizing is the process of applying zinc or its alloy to a metal product to impart certain physical and chemical properties to its surface, primarily high corrosion resistance. Galvanizing is the most common and economical metallization process used to protect iron and its alloys from atmospheric corrosion. Approximately 40% of world zinc production is spent for these purposes. The thickness of the coating should be greater, the more aggressive the environment and the longer the expected service life. Steel sheets, tape, wire, fasteners, machine and instrument parts, pipelines and other metal structures are subjected to galvanizing. Zinc coating usually does not have a decorative purpose; some improvement presentation acquires after passivation of galvanized products in chromate or phosphate solutions, which give the coatings a rainbow color. The most widely used is galvanized strip, produced on automated hot-dip galvanizing lines, that is, by immersion in molten zinc. Spraying and metallization methods make it possible to coat products of any size (for example, power transmission towers, tanks, bridge metal structures, road barriers). Electrolytic galvanizing is carried out mainly from acidic and alkali-cyanide electrolytes; special additives make it possible to obtain shiny coatings.

Economic damage from corrosion

Economic losses from metal corrosion are enormous. In the United States, according to the latest NACE data, corrosion damage and costs to combat it amounted to 3.1% of GDP ($276 billion). In Germany, this damage amounted to 2.8% of GDP. According to experts from various countries, these losses in industrialized countries range from 2 to 4% of the gross national product. At the same time, metal losses, including a mass of failed metal structures, products, and equipment, amount to 10 to 20% of annual steel production.

Collapse of the Silver Bridge.

Rust is one of the most common causes of bridge failures. Since rust has a much larger volume than the original mass of iron, its build-up can lead to uneven fit of structural parts to each other. This caused the destruction of the Mianus River Bridge in 1983 when bearings lifting mechanism rusted inside. Three drivers died when they fell into the river. Investigations showed that the road drain was blocked and not cleaned, and waste water penetrated the bridge supports. On December 15, 1967, the Silver Bridge connecting Point Pleasant, West Virginia, and Kanauga, Ohio, unexpectedly collapsed into the Ohio River. At the time of the collapse, 37 cars were moving on the bridge, and 31 of them fell along with the bridge. Forty-six people were killed and nine were seriously injured. In addition to the loss of life and injuries, the main transportation route between West Virginia and Ohio was destroyed. The cause of the collapse was corrosion.

The Kinzu Bridge in Pennsylvania was destroyed in a 2003 tornado primarily because the central main bolts had rusted, significantly reducing its stability.

See also

Notes

Links

• “Blasting: A Guide to Highly Efficient Abrasive Blasting Cleaning” - Ekaterinburg: OOO Publishing House Origami, 2007-216 pp., ISBN 978-5-9901098-1-0

Basic material for studying the topic:

§ 13, page 81.

Gabrielyan, O. S.

Chemistry. 9th grade: Bustard, 2013.

Additional material on the topic “Corrosion of metals”

Corrosion, rusting, rust is the spontaneous destruction of metals as a result of chemical or physico-chemical interaction with the environment. In general, this is the destruction of any material, be it metal or ceramics, wood or polymer. The cause of corrosion is the thermodynamic instability of structural materials to the effects of substances in the environment in contact with them. Example - oxygen corrosion of iron in water:

Iron hydroxide Fe(OH) 3 is what is called rust.

In everyday life, the term “rusting” is more often used for iron (steel) alloys. Less well known are cases of corrosion of polymers. In relation to them, there is the concept of “aging”, similar to the term “corrosion” for metals. For example, the aging of rubber due to interaction with atmospheric oxygen or the destruction of some plastics under the influence of precipitation, as well as biological corrosion. The rate of corrosion, like any chemical reaction, is very dependent on temperature. An increase in temperature of 100 degrees can increase the corrosion rate by several orders of magnitude.

Classification of types of corrosion

Corrosion processes are characterized by a wide distribution and diversity of conditions and environments in which they occur. Therefore, there is not yet a unified and comprehensive classification of the occurrence of corrosion cases.

Depending on the type of aggressive environment in which the destruction process occurs, corrosion can be of the following types:

gas corrosion;

atmospheric corrosion;

corrosion in non-electrolytes;

corrosion in electrolytes;

underground corrosion;

biocorrosion;

corrosion under the influence of stray currents.

According to the conditions of the corrosion process, the following types are distinguished:

contact corrosion;

crevice corrosion;

corrosion due to partial immersion;

Full immersion corrosion;

corrosion during alternating immersion;

friction corrosion;

intergranular corrosion;

Stress corrosion.

By nature of destruction:

continuous corrosion covering the entire surface:

• uniform;

  uneven;

  selective;

local (local) corrosion covering individual areas:

• ulcerative;

  point;

  end-to-end;

  intergranular (delamination in deformed workpieces and knife-edge in welded joints).

The main classification is made according to the mechanism of the process. There are two types:

chemical corrosion;

electrochemical corrosion.

Corrosion of non-metallic materials

As operating conditions become more severe (increasing temperature, mechanical stress, environmental aggressiveness, etc.), non-metallic materials are also exposed to the action of the environment. In connection with this, the term “corrosion” began to be used in relation to these materials, for example, “corrosion of concrete and reinforced concrete”, “corrosion of plastics and rubber”. This refers to their destruction and loss of operational properties as a result of chemical or physico-chemical interaction with the environment. But it should be taken into account that the mechanisms and kinetics of processes for non-metals and metals will be different.

Metal corrosion

Rust is the most common type of corrosion.

Metal corrosion.

Corrosion of metals is the destruction of metals due to their chemical or electrochemical interaction with a corrosive environment. For the corrosion process, the term “corrosion process” should be used, and for the result of the process, “corrosion destruction”. The formation of galvanic couples is usefully used to create batteries and accumulators. On the other hand, the formation of such a pair leads to an unfavorable process, the victim of which is a number of metals - corrosion. Corrosion refers to the electrochemical or chemical destruction of a metal material that occurs on the surface. Most often, during corrosion, the metal is oxidized to form metal ions, which, upon further transformations, produce various corrosion products. Corrosion can be caused by either a chemical or an electrochemical process. Accordingly, a distinction is made between chemical and electrochemical corrosion of metals.

Types of corrosion

There are 4 main types of corrosion: electrochemical corrosion, hydrogen, oxygen corrosion and chemical.

Electrochemical corrosion

The destruction of metal under the influence of galvanic elements arising in a corrosive environment is called electrochemical corrosion. Corrosion of a homogeneous material, for example, rusting of iron, etc., should not be confused with electrochemical corrosion. Electrochemical corrosion (the most common form of corrosion) always requires the presence of an electrolyte (Condensate, rainwater, etc.) with which the electrodes are in contact - either different elements of the material structure, or two different contacting materials with different redox potentials. If ions of salts, acids, or the like are dissolved in water, its electrical conductivity increases and the speed of the process increases.

Corrosive element

When two metals with different redox potentials come into contact and are immersed in an electrolyte solution, for example, rainwater with dissolved carbon dioxide CO 2, a galvanic cell is formed, the so-called corrosion cell. It is nothing more than a closed galvanic cell. It slowly dissolves metallic material with a lower redox potential; the second electrode in a pair, as a rule, does not corrode. This type of corrosion is especially characteristic of metals with high negative potentials. Thus, a very small amount of impurity on the surface of a metal with a high redox potential is already enough for the appearance of a corrosive element. Particularly at risk are areas where metals with different potentials come into contact, such as welds or rivets.

If the dissolving electrode is corrosion-resistant, the corrosion process is slowed down. This is the basis, for example, for protecting iron products from corrosion by galvanizing - zinc has a more negative potential than iron, therefore, in such a pair, iron is reduced, and zinc must corrode. However, due to the formation of an oxide film on the surface of zinc, the corrosion process slows down greatly.

An example of large-scale electrochemical corrosion is the incident that occurred in December 1967 with the Norwegian ore carrier Anatina. Anatina), traveling from Cyprus to Osaka. A typhoon in the Pacific Ocean led to the entry of salt water into the holds and the formation of a large galvanic couple: a copper concentrate with the steel hull of the ship, which soon softened, and the ship sent a distress signal. The crew was rescued by a German ship that arrived in time, and the Anatina itself barely made it to the port.

Hydrogen and oxygen corrosion

If reduction of H 3 O + ions or H 2 O water molecules occurs, they speak of hydrogen corrosion or corrosion with hydrogen depolarization. Ion reduction occurs according to the following scheme:

2H 3 O + + 2e − → 2H 2 O + H 2

2H 2 O + 2e − → 2OH − + H 2

If hydrogen is not released, which often happens in a neutral or strongly alkaline environment, oxygen is reduced and we speak of oxygen corrosion or corrosion with oxygen depolarization:

O 2 + 2H 2 O + 4e − → 4OH −

A corrosive element can be formed not only when two different metals come into contact. A corrosive element is also formed in the case of one metal, if, for example, the surface structure is heterogeneous.

Chemical corrosion

Electrocorrosion of heated towel rail

Chemical corrosion is the interaction of a metal surface with a corrosive environment, not accompanied by the occurrence of electrochemical processes at the phase boundary. In this case, the interactions of metal oxidation and the reduction of the oxidizing component of the corrosive environment occur in one act. For example, the formation of scale when iron-based materials react at high temperatures with oxygen:

During electrochemical corrosion, the ionization of metal atoms and the reduction of the oxidizing component of the corrosive environment do not occur in one act and their rates depend on the electrode potential of the metal (for example, rusting of steel in sea water).

Types of corrosion

Gas corrosion

Atmospheric corrosion

Partial immersion corrosion

Waterline corrosion

Fully immersed corrosion

Corrosion under alternating immersion

Underground corrosion

Biocorrosion

Corrosion by external current

Stray current corrosion

Contact corrosion

Friction corrosion

Fretting corrosion

Complete corrosion

Uniform corrosion

Uneven corrosion

Local corrosion

Subsurface corrosion

Pitting corrosion

Corrosion spots

Through corrosion

Layer corrosion

Filiform corrosion

Structural corrosion

Intergranular corrosion

Selective corrosion

Graphitization of cast iron

Dezincification

Crevice corrosion

Knife corrosion

Corrosion ulcer

Corrosion cracking

Stress Corrosion

Corrosion fatigue

Corrosion fatigue limit

Corrosion brittleness

Anti-corrosion

Corrosion causes billions of dollars in losses every year, and solving this problem is an important task. The main damage caused by corrosion is not the loss of metal as such, but the enormous cost of the products destroyed by corrosion. That is why the annual losses from it in industrialized countries are so great. True losses from it cannot be determined by assessing only direct losses, which include the cost of a collapsed structure, the cost of replacing equipment, and the costs of measures to protect against corrosion. Even greater damage comes from indirect losses. These include equipment downtime when replacing corroded parts and assemblies, product leakage, and disruption of technological processes.

Ideal corrosion protection is 80% ensured by proper surface preparation, and only 20% by the quality of the paints and varnishes used and the method of their application. The most productive and effective method of surface preparation before further protection of the substrate is abrasive blasting.

Typically, there are three areas of corrosion protection methods:

Structural

Active

Passive

To prevent corrosion, stainless steels, Corten steels, and non-ferrous metals are used as structural materials. When designing structures, they try to isolate them as much as possible from corrosive environments, using adhesives, sealants, and rubber gaskets.

Active methods of combating corrosion are aimed at changing the structure of the electrical double layer. A constant electric field is applied using a direct current source, the voltage is selected in order to increase the electrode potential of the protected metal. Another method is to use a sacrificial anode, a more active material that will be destroyed, protecting the product being protected.

As protection against corrosion, application of some kind of coating can be used that prevents the formation of a corrosive element (passive method).

Oxygen corrosion of galvanized iron

Oxygen corrosion of tin-coated iron

Paint coating, polymer coating and enameling must, first of all, prevent the access of oxygen and moisture. Coating, for example, of steel with other metals such as zinc, tin, chromium, and nickel is often also used. The zinc coating protects the steel even when the coating is partially destroyed. Zinc has a more negative potential and corrodes first. Zn 2+ ions are toxic. In the manufacture of cans, tin coated with a layer of tin is used. Unlike galvanized sheet, when the tin layer is destroyed, the iron begins to corrode, and more intensely, since tin has a more positive potential. Another way to protect metal from corrosion is to use a protective electrode with a high negative potential, for example, made of zinc or magnesium. For this purpose, a corrosion element is specially created. The protected metal acts as a cathode, and this type of protection is called cathodic protection. The dissolving electrode is called, accordingly, the sacrificial protection anode. This method is used to protect sea vessels, bridges, boiler plants, and underground pipes from corrosion. To protect the ship's hull, zinc plates are attached to the outside of the hull.

If you compare the potentials of zinc and magnesium with iron, they have more negative potentials. Nevertheless, they corrode more slowly due to the formation of a protective oxide film on the surface, which protects the metal from further corrosion. The formation of such a film is called metal passivation. In aluminum it is enhanced by anodic oxidation (anodizing). When a small amount of chromium is added to steel, an oxide film forms on the surface of the metal. The chromium content in stainless steel is more than 12 percent.

Thermal spraying

To combat corrosion, thermal spray methods are also used. Using thermal spraying, a layer of another metal/alloy is created on the surface of a metal, which is more resistant to corrosion (insulating) or, conversely, less resistant (protective). This layer allows you to stop corrosion of the protected metal. The essence of the method is as follows: particles of a metal mixture, such as zinc, are applied to the surface of the product with a gas jet at high speed, resulting in the formation of a protective layer with a thickness of tens to hundreds of microns. Thermal spraying is also used to extend the life of worn-out equipment components: from restoring steering racks in car repair shops to oil production companies

Thermal diffusion zinc coating

To operate metal products in aggressive environments, more durable anti-corrosion protection of the surface of metal products is necessary. Thermal diffusion zinc coating is anodic in relation to ferrous metals and electrochemically protects steel from corrosion. It has strong adhesion (adhesion) to the base metal due to the mutual diffusion of iron and zinc in the surface intermetallic phases, so peeling and chipping of coatings does not occur during impacts, mechanical loads and deformations of the processed products.

Diffusion galvanizing, carried out from the vapor or gas phase at high temperatures (375-850 °C), or using rarefaction (vacuum) - at temperatures from 250 °C, is used to coat fasteners, pipes, fittings and other structures. Significantly increases the resistance of steel and cast iron products in environments containing hydrogen sulfide (including against hydrogen sulfide corrosion cracking), industrial atmosphere, sea water, etc. The thickness of the diffusion layer depends on temperature, time, galvanizing method and can be 0.01-1. 5 mm. The modern process of diffusion galvanizing allows the formation of a coating on the threaded surfaces of fasteners, without complicating their subsequent screwing. Microhardness of the coating layer Hμ = 4000 - 5000 MPa. Diffusion zinc coating also significantly increases the heat resistance of steel and cast iron products, at temperatures up to 700 °C. It is possible to obtain alloyed diffusion zinc coatings, which are used to improve their performance characteristics.

Cadmium plating

Coating steel parts with cadmium is done using methods similar to galvanizing, but gives more strong defense, especially in sea water. It is used much less frequently due to the significant toxicity of cadmium and its high cost.

Chrome plating

Corrosion impairs the performance of pipelines.

Economic losses from metal corrosion are enormous. In the United States, according to the latest NACE data [corrosion damage and costs to combat it amounted to 3.1% of GDP ($276 billion). In Germany, this damage amounted to 2.8% of GDP. According to experts from various countries, these losses in industrialized countries range from 2 to 4% of the gross national product. At the same time, metal losses, including a mass of failed metal structures, products, and equipment, amount to 10 to 20% of annual steel production.

Collapse of the Silver Bridge.

Rust is one of the most common causes of bridge failures. Since rust has a much larger volume than the original mass of iron, its build-up can lead to uneven fit of structural parts to each other. This caused the destruction of the Mianus River Bridge in 1983 when the bearings of the lifting mechanism rusted internally. Three drivers died when they fell into the river. Investigations showed that the road drain was blocked and not cleaned, and sewage had penetrated into the bridge supports. On December 15, 1967, the Silver Bridge connecting Point Pleasant, West Virginia, and Kanauga, Ohio, unexpectedly collapsed into the Ohio River. At the time of the collapse, 37 cars were moving on the bridge, and 31 of them fell along with the bridge. Forty-six people were killed and nine were seriously injured. In addition to the loss of life and injuries, the main transportation route between West Virginia and Ohio was destroyed. The cause of the collapse was corrosion

The Kinzu Bridge in Pennsylvania was destroyed in a 2003 tornado primarily because the central main bolts had rusted, significantly reducing its stability.

Homework

Alloys

Attention!!!

To get a “3” grade, it is enough to complete only the first part of the work; to get a “4” grade, you need to complete the entire part of the “3” grade of work without errors, and also without errors, the entire part of the “4” grade of work. To receive a grade of “5” you must complete all the work without errors!!!

Rating "3"

1. Which metal as a simple substance is more susceptible to corrosion?

1) 1s 2 2s 2 2p 6 3s

2) 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1

3) 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2

4) 1s 2 2s 2 2p 6 3s 2 3p 1

2. Chemical corrosion is caused by

1) water and oxygen

2) oxides of carbon and sulfur

3) salt solutions

4) all of the above factors.

3. When Ni and Fe come into contact in an acid solution

1) iron will dissolve

2) iron will be restored

3) nickel will dissolve

4) oxygen will be released

Rating "4"

4. Methods of protection against corrosion, in which work environment introduce substances that reduce the aggressiveness of the environment, called

5. A method of corrosion protection in which an iron sheet is coated with a layer of tin.

6. Corrodes most actively

1) chemically pure iron

2) iron coated with a layer of tin

3) technical hardware

4) iron-titanium alloy

Rating "5"

7. Alloying element that imparts corrosion resistance to steel

8. The mass of copper released on a plate placed in a solution of copper (II) chloride if zinc weighing 13 g reacted

8. The mass of copper released on an iron plate placed in a solution of copper (II) sulfate, if iron weighing 11.2 g reacted.

DEFINITION

When in contact with the environment, many metals, as well as metal-based alloys, can be subject to destruction due to chemical interaction (ORR with substances in the environment). This process is called corrosion.

A distinction is made between corrosion in gases (gas corrosion), which occurs at high temperatures in the absence of moisture on metal surfaces, and electrochemical corrosion (corrosion in electrolyte solutions, as well as corrosion in a humid atmosphere). As a result of gas corrosion, oxide, sulfide, etc. are formed on the surface of metals. films. Furnace fittings and engine parts are subject to this type of corrosion. internal combustion etc.

As a result of electrochemical corrosion, metal oxidation can lead to both the formation of insoluble products and the transition of the metal into solution in the form of ions. This type of corrosion affects pipelines located in the ground, underwater parts of ships, etc.

Any electrolyte solution is an aqueous solution, and water contains oxygen and hydrogen that are capable of reduction:

O 2 + 4H + +4e = 2H 2 O (1)

2H + +2e=H 2 (2)

These elements are oxidizing agents that cause electrochemical corrosion.

When writing about the processes occurring during electrochemical corrosion, it is important to take into account standard electrode potentials (EP). Thus, in a neutral environment, the EC of process 1 is 0.8B, therefore, metals whose EC is less than 0.8B (metals located in the activity series from its beginning to silver) are subject to oxidation by oxygen.

The EP of process 2 is -0.41V, which means that only those metals whose potential is lower than -0.41V (metals located in the activity series from its beginning to cadmium) are subject to oxidation with hydrogen.

The rate of corrosion is greatly influenced by impurities that a particular metal may contain. Thus, if a metal contains non-metallic impurities, and their EC is higher than the EC of the metal, then the corrosion rate increases significantly.

Types of corrosion

There are several types of corrosion: atmospheric (corrosion in humid air at normal conditions), corrosion in the soil, corrosion due to uneven aeration (access of oxygen to different parts metal product, located in the solution, is not the same), contact corrosion (contact of 2 metals with different EP in an environment where moisture is present).

During corrosion, electrochemical reactions occur on the electrodes (anode and cathode), which can be written by the corresponding equations. Thus, in an acidic environment, electrochemical corrosion occurs with hydrogen depolarization, i.e. Hydrogen is released at the cathode (1). In a neutral environment, electrochemical corrosion occurs with oxygen depolarization—water is reduced at the cathode (2).

K (cathode) (+): 2H + +2e=H 2 - reduction (1)

A (anode) (-): Me – ne →Me n + – oxidation

K (cathode) (+): O 2 + 2H 2 O + 4e → 4OH - - reduction (2)

In the case of atmospheric corrosion, the following electrochemical reactions occur on the electrodes (and at the cathode, depending on the environment, various processes can occur):

A (anode) (-): Me→Me n + +ne

K (cathode) (+): O 2 + 2H 2 O + 4e → 4OH - (in alkaline and neutral environments)

K (cathode) (+): O 2 + 4H + + 4e → 2H 2 O (in acidic medium)

Corrosion protection

The following methods are used to protect against corrosion: the use of chemically resistant alloys; protection of the surface of metals with coatings, which most often use metals that are coated in air with oxide films that are resistant to the effects of the external environment; treatment of corrosive environments; electrochemical methods (cathodic protection, protector method).

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Exercise

The part consists of an alloy of iron and nickel. Which metal will corrode faster? Write down the equations of the anodic and cathodic processes during atmospheric corrosion. The values ​​of standard electrode potentials are E(Fe 2+ /Fe) = - 0.444V, E(Ni 2+ /Ni) = -0.250V.

Solution

First of all, they undergo corrosion active metals(possessing the most negative values standard electrode potentials), in this case it is iron. Many materials, such as metal, ceramic, and wood, are susceptible to corrosion as a result of exposure to them. As a rule, this effect is achieved due to the instability of the structure, which is affected by thermodynamics environment. In this article we will look in detail at what metal corrosion is, what types it has, and how you can protect yourself from it. Some general information The word “rust” is quite popular among people, which refers to the process of corrosion of metal and various alloys. People use the term “aging” for polymers. In fact, these words are synonyms. A striking example is the aging of rubber products that actively interact with oxygen. Some plastic products Due to precipitation, they can quickly become unusable. How quickly the corrosion process occurs depends entirely on the conditions in which the product is placed. Ambient humidity is especially affected. The higher its indicator, the faster the metal will become unusable. Scientists have experimentally found that about 10% of products in production are simply written off due to corrosion. The types of this process are different, their classification depends on the type of environment in which the products are located, the speed and nature of the process. Next, let's look at the types of corrosion in more detail. Now every person should understand what metal corrosion is. Artificial aging The corrosion process does not always have a destructive effect and renders certain materials unusable. Often, due to corrosion, the coating acquires additional properties, necessary for a person. That's why it became popular artificial aging. Most often it is used if we're talking about about aluminum and titanium. Only with the help of corrosion can you achieve increased strength materials. In order to complete the destruction process correctly, it is necessary to use heat treatment. Considering that the natural aging of materials under some conditions is a rather slow process, there is no need to specify that when using this method the material must have a special hardening. You must also understand all the risks associated with this method. For example, although the strength of the material increases, its ductility decreases as much as possible. With ease, the reader can now answer the question of what artificial metal corrosion is. Reviews about heat treatment This method compacts the molecules of the material, and the structure changes accordingly. Often thermal protection is necessary to strengthen pipelines, as it helps protect the material from rust, as well as minimize the pressure that is exerted on the structure if it is located underground. Users of this technique leave reviews in which they describe that this method protection is as effective as possible and really shows good results. It is advisable to use this treatment only in the industrial sector. Due to the fact that chambers for firing and other processes necessary to obtain reliable protection, are expensive, the method is not popular. This protection of metal from corrosion is quite effective. Classification At the moment there are more than 20 rusting options. This article will describe only the most popular types of corrosion. Conventionally, they are divided into the following groups, which will help you understand in more detail what metal corrosion is. Chemical corrosion is interaction with a corrosive environment. In this case, the oxidation of the metal and the reduction of the oxidizing agent occur simultaneously in one cycle. Both materials are not separated by space. Let's look at other types of metal corrosion. Electrochemical corrosion is the interaction of a metal with an electrolyte. The atoms are ionized, the oxidizing agent is reduced, and these two processes occur in several cycles. Their speed depends entirely on the potential of the electrodes. With gas corrosion, metal with a small liquid content rusts. Moisture should not exceed 0.1%. Also this type corrosion can occur in gas environment at high temperatures. This species is most often found in the chemical and oil refining industries. In addition to those described above, there are many other types of corrosion of materials. There are biological, targeted, contact, local and other types of rust. Electrochemical corrosion and its features In electrochemical corrosion, the destruction of the material occurs due to its contact with the electrolyte. The last substance may be condensate or rainwater. It should be noted that the more salts there are in the liquid, the higher the electrical conductivity. Accordingly, the corrosion process will proceed quite quickly. If we talk about the most popular places that are susceptible to corrosion, we should note the rivets in metal structure, welded joints, as well as simply places where the material is damaged. It happens that when an iron alloy is created, it is coated with special substances that have anti-corrosion properties. However, this does not prevent the rusting process, but only slows it down. Enough a shining example can be called galvanizing. Zinc has a negative potential when compared to iron. Because of this latest material will be restored, and the zinc will be damaged. If there is an oxide film on the surface, the destruction process will take a long time. Electrochemical corrosion has several types, but it should be noted that they are all dangerous and, as a rule, it is impossible to stop this type of metal corrosion. Chemical corrosion Chemical corrosion is quite common. For example, if a person notices scale, then he must understand that it appeared as a result of the combination of metal, that is, interaction, with oxygen. As a rule, if the ambient temperature is high, the corrosion process will be noticeably accelerated. Liquids can participate in rusting, that is, water, salt, any acid or alkali, salt solutions. When it comes to chemical corrosion of metals such as copper or zinc, their oxidation leads to a persistent film corrosion process. The rest form iron oxide. Further, all the chemical processes that will occur will lead to the appearance of rust. It will not provide protection in any way, but rather promotes corrosion. Galvanizing can currently protect many materials. Other means of protection against chemical corrosion of metals have also been developed. Types of concrete corrosion Brittleness of concrete can be caused by one of three types of corrosion. It is quite common to see changes in the structure of this material. Let's look at why this happens. The most common type of corrosion is the destruction of cement stone. As a rule, this occurs when liquid and precipitation constantly affect the material. Because of this, the structure of the material is destroyed. Below there are more detailed examples metal corrosion: Interaction with acids. If the cement stone is constantly exposed to these materials, a rather aggressive element will be formed that is harmful to the coating. We are talking about calcium bicarbonate. Crystallization of sparingly soluble substances. We are talking about corrosion here. Due to the fact that fungi, spores and other substances enter the pores, concrete covering begins to deteriorate quickly. Corrosion: methods of protection Due to corrosion, manufacturers often suffer huge losses, so a lot of work is being done to avoid this process. Moreover, it should be noted that most often it is not the metal itself that is susceptible to corrosion, but huge metal structures. Manufacturers spend a lot of money on their creation. Unfortunately, it is almost impossible to provide 100% protection. However, if you properly protect the surface, that is, carry out abrasive blasting, you can delay the corrosion process for several years. They also combat it with paint and varnish. It reliably protects the material. If the metal is underground, it must be treated with special materials. This is the only way to achieve maximum metal protection from corrosion. Anti-aging measures As mentioned above, the corrosion process cannot be stopped. But you can maximize the time during which the material will degrade. Also, in production, as a rule, they try to get rid of factors that affect the aging process as much as possible. For example, in factories, each structure is periodically treated with solutions and polishes. They are the ones who save the material from negative influence on metal from mechanical, temperature and chemical conditions. In order to understand this in more detail, you should study the definition of metal corrosion. If we talk about slowing down the aging effect, it should be noted that heat treatment can be used for this. Under normal operating conditions, this method will minimize the rapid destruction of the material. To ensure that the seams on the product do not come apart, welders use firing at a temperature of 650 degrees. This technique will reduce the intensity of aging. Active and passive methods of control Active methods of combating corrosion work by changing the structure of the electric field. To do this, you need to use direct current. The voltage must be such that the product has improved performance. A fairly popular method would be to use a “sacrificial” anode. It protects the material through its own destruction. The conditions for metal corrosion are described above. As for passive protection, a paint coating is used for this. It completely protects the product from liquids and oxygen. Thanks to this, the surface is maximally protected from destruction. Sputtering of zinc, copper, and nickel should be used. Even if the layer is severely damaged, it will still protect the metal from rust. Of course, you need to understand that passive protection methods will only be relevant if the surface does not have cracks or chips. Reviews about paint and varnish protection of metals At the moment, paint protection is particularly popular. It is effective, flexible in use, and inexpensive. However, if long-term use of a metal structure is necessary, then this method of protection will not work. Paint and varnish coatings will not be able to protect the material for more than 7-8 years. Accordingly, they will have to be updated. Most likely, you will have to carry out restoration and replace the surface of the material. Other disadvantages of this coating include limitations in terms of use. If it is necessary to strengthen pipes that are located underground or under water, then paint protection will not work. Therefore, it should be understood that if it is necessary for the structure to be used for more than 10 years, other methods of protection should be resorted to. Galvanizing in detail Having considered the main types of corrosion, it is also necessary to discuss the most effective methods of protection. One of these can be called galvanizing. It allows you to protect the material from severe destruction by changing the physical and chemical properties. At the moment, this method is considered economical and effective, given that almost 40% of all mined material on Earth is spent on zinc processing. It is important to treat the material with an anti-corrosion coating. Galvanizing is carried out for steel sheets, fasteners, appliances and large metal structures. In general, using this type of spraying you can protect products of any size and shape. Zinc has no decorative purpose, although occasionally it can be added to the alloy to produce shine. In general, you need to understand that this metal will provide maximum protection against corrosion even in the most aggressive conditions. Features of rust protective agents When working with metal, any person understands that before applying protective materials, it is necessary to prepare the surface. Often all the difficulties lie in this stage. In order to create a special barrier that will allow rust to reach the metal, it is necessary to introduce the concept of a compound. Thanks to it, the kit will provide protection against corrosion. In this case, electrical insulation takes place. It is usually quite difficult to protect against corrosion of ferrous metals. Due to the specific nature of the use of various protective agents, it is necessary to understand the operating conditions of the material. If the metal will be located underground, then it is necessary to use multilayer coatings that will have not only anti-corrosion properties, but also enhanced protection against mechanical damage. If we are talking about communications that actively interact with oxygen and gases, you should use a product that minimizes the effect of water and oxygen. Accordingly, increased attention from the manufacturer will be paid to insulation from moisture, steam and low temperatures. In this case, additives and special plasticizers should be added, because the causes of metal corrosion are different and should be protected from all types. Mixture "Urizol" The Urizol mixture should be considered separately, as it is used to coat the pipeline. It is also suitable for fittings, connecting parts, valve units and those products that are constantly in contact with oil or gases. This composition is needed in order to get rid of the influence of underground and atmospheric influences. Often this mixture is also used for insulation concrete materials. This substance is applied very simply, without any difficulty. In order to treat the surface, you must use a sprayer. This is the only way to avoid corrosion of metals and alloys of similar products. As soon as the components combine, the reaction begins. Because of this, polyurea occurs. After this, the mixture turns into a gel-like and non-flowing state, and after some time it becomes solid. If the polymerization rate is slow, smudges will begin to form. They are harmful because they make it difficult to increase the thickness of the coating. It should be noted that this mixture remains sticky for a long time. Due to this, all layers will be as uniform as possible, and intermediate thickness measurements will be equal to each other. If the polymerization process is too fast, the adhesion of the composition will decrease. In this case, the thickness of the resulting insulation layer will be uneven. By the way, the spray gun quickly becomes clogged if the coating speed is too fast. Metal corrosion factors will not appear if everything is done correctly. In order to prevent such situations, it is necessary to carefully select components and follow manufacturing rules. Paints and enamels Metal-plastic structures can be protected using three methods. Paint coatings have already been described previously. They are simple, come in a variety of colors, and can be used to easily process large surfaces. Since the process of metal corrosion is quite fast, you should immediately think about coating with materials. The second type is plastic coverings. As a rule, they are made of nylon and PVC. This coating will provide maximum protection against water, acids and alkalis. The third type is rubber coating. It is often used to protect tanks and other structures from the inside. Phosphating and chromating The metal surface must be properly prepared for the protection process. Which methods will be used depends entirely on the type of surface. For example, ferrous metals are protected by phosphating. Non-ferrous metals can be processed using both methods. In general, if we talk about chemical preparation, it is necessary to clarify that it takes place in several stages. To begin with, the surface is degreased. Then it is washed with water. Next, a conversion layer is applied. Afterwards it is washed again with two types of water: drinking and demineralized, respectively. Next, it remains to carry out passivation. Chemical treatment should be carried out using spray, immersion, steam and water jet methods. The first two methods must be used with the help of special units that will completely prepare the surface for work. Which method to choose depends on the size, configuration of the product, and so on. In order to better understand this issue, you should know the equations of metal corrosion reactions. Conclusion The article described what corrosion is and what types it has. Now any person after reading this article will be able to understand how to protect any material from aging. By and large, this is quite easy to do if you know everything necessary instructions. The main thing is to understand all the characteristics of the environment in which the material is used. If the products are located in a place where constant vibrations occur, and there are also severe loads, then paint coatings cracks will appear. Because of this, moisture will enter the metal, and accordingly, the corrosion process begins immediately. In such cases, it is better to additionally use rubber sealants and gaskets, then the coating will last a little longer. Additionally, it must be said that if the structure is prematurely deformed, it will quickly deteriorate and age. Accordingly, this can lead to completely unforeseen circumstances. This will cause material damage and may result in the death of a person. Accordingly, special attention should be paid to corrosion protection. Chicken fillet with spinach Most housewives... Mixture of nuts and dried fruits: benefits and harms Useful properties of raisins →