Let's discuss some scientific facts. What do you know about corrosion? Maybe you remember learning this topic in school during one of your favorite subjects? Today you will find out some interesting and maybe new facts about this concept. So keep reading to learn 'what is corrosion'!
What is corrosion?
Corrosion is the destruction of metals as a result of chemical or electrochemical interaction with the environment. Corrosion leads to a lot of harm, including a direct and indirect damage associated with the destruction of metal structures.
The rapidity of corrosion processes depends on the conditions in which the products are manufactured and operated. Since it is practically impossible to eliminate the atmospheric effect on metal structures, corrosion should be recognized as an eternal metal companion. The process of corrosion includes 4 basic elements:
- The Cathode (or the electrode on which the cathodic reaction occurs);
- The Anode (or the electrode on which the anodic reaction occurs);
- The electron conductor (metal conducting electric current);
- The Ion conductor (electrically conductive liquid or electrolyte).
Causes of corrosion
Corrosion is an electrochemical reaction which has several forms. Among them are the chemical corrosion and atmospheric corrosion. The latter is the most common form. When acid substances including water come in contact with metals (iron/steel), the rust begin to form. It is the result of steel corrosion after the iron particles were exposed to oxygen and humidity. When steel is exposed to water, they are lost in the acid electrolytes of water. Subsequently, the iron particles become oxidized. This leads to the formation of Fe⁺⁺. As a result of its formation, two electrons are extracted which flow through the steel into another area - the cathode field.
Due to Oxygen, these electrons rise up and form hydroxyl ions. The OH ions react with the FE⁺⁺. After this rust is formed (a hydrous iron oxide). That means it is a corrosive product. When we talk about corrosion, you need to remember that it is necessary to take precautions.
Types of corrosion
By the nature of the surface's destruction, corrosion is divided into a continuous uniform, continuous uneven, and local (spot, ulcers, spots, intergranular, etc). According to the type of corrosive environment, it is subdivided into atmospheric, soil, marine, acidic, alkaline, microbiological, etc.
If you go with the mechanism of corrosion process, it is divided into chemical and electrochemical. Chemical - gas, and corrosion in liquids nonelectrolytes. Electrochemical - corrosion in electrolytes. By the nature of the additional impact, corrosion is divided into corrosion cracking, corrosion fatigue, frictional corrosion, cavitation erosion, and jet erosion.
There are a large number of common types of corrosion:
1. General Attack Corrosion.
2. Localized Corrosion.
3. Galvanic Corrosion.
4. Environmental Cracking.
5. Flow-Assisted Corrosion.
6. Intergranular Corrosion.
8. Fretting Corrosion.
9. High-Temperature Corrosion.
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Intergranular corrosion is one of the types of local metal corrosion. It leads to a selective destruction of grain boundaries. IC is a very dangerous form of destruction. Visually it cannot always be determined. Metal loses its plasticity and strength. Intergranular corrosion is most often found in metals and alloys, which easily become passive. These include chromium-nickel and chromium alloys (stainless steels), alloys of aluminum, nickel, and some others.
The cause of intergranular corrosion: structural transformations at the grain boundaries of the metal. The zone of structural transformations becomes an anode, which strongly dissolves. The connection between the grains of the metal is broken and their chipping occurs. As a result of these processes, metal structures lose their properties during operation and quickly deteriorate.
Biological corrosion is a type of corrosion destruction through exposure to microorganisms. The products of vital activity of various microorganisms that are present in water and soil intensify the process of corrosion. Biocorrosion can be considered as an independent type of destruction. But more often the processes of biological corrosion proceed in parallel with others. For example, soil, sea, atmosphere and corrosion in nonelectrolytes, aqueous solutions.
Various underground structures and pipelines in the water undergo damage from biocorrosion. Biocorrosion is an integral companion of the oil and gas industry. The first guesses about the effect on the process of corrosive destruction of biological organisms appeared only at the end of the nineteenth century.
What is exfoliation corrosion?
This type of corrosion is a form of intergranular corrosion. It includes a selective attack of a metal on the grain boundaries or next to them. In this process, corrosion products form the strength of the metal to move away from the material body. The result is in a multi-layered appearance. Exfoliating corrosion is also known as layer corrosion or lamellar corrosion.
Aluminum alloys which contain copper or zinc-magnesium-copper as alloying components, are susceptible to the exfoliation corrosion.
What is steel corrosion?
It is a deterioration and destruction of steel because of the electrochemical/chemical reaction of its surface to environmental factors (acids, oxygen, and moisture). It can't be reversible. Steel corrosion includes an electrolysis in which a metal surface releases electrons into an electrolyte (a layer of moisture in the presence of oxygen).
This electrochemical reaction is due to the tendency of metals to return to their natural state. Iron in steel in the moist air will tend to return to the original state of iron oxide as rust. Steel can be corroded by the chemical reaction of certain chemicals, such as sulfuric acid.
What is electrolytic corrosion?
It is a process of accelerated corrosion. The metal surface is continuously corroded by another metal that is in contact with the electrolyte and the flow of electric current between the two metals. Electric current is caused by an external source of electromotive force. This form of corrosion causes widespread damage to critical equipment.
We think today you have enriched your knowledge with new facts about corrosion. As you can see, there are many different kinds. And in most cases, corrosion occurs regardless of the type of environment. In fact, it can destroy everything under different circumstances.
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