What is corrosion

Corrosion is a destructive process that metallic materials are subject to under the influence of external factors, mainly due to chemical or electrochemical reactions. This process is the interaction of metal with the environment, which leads to a loss of strength and the destruction of its structure. The main factors that contribute to the development of corrosion are humidity, oxygen, salts and chemically active substances.

Ferrous metals such as iron, steel and cast iron are particularly susceptible to corrosion processes because they oxidize when exposed to oxygen and moisture. This process produces various compounds, including oxides and hydroxides.

For example, when iron reacts with oxygen from the air or water, iron hydroxide is formed, which then turns into rust. This reaction can be expressed by the equation:

4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃

Eventually, the originally durable metal that was used to create weapons, building structures and machinery gradually turns into a loose coating of rust, completely losing its useful properties. This process is natural, as metals obtained artificially tend to return to their natural state.

Corrosive destruction causes serious problems in industry, transport and construction. To protect metal from destruction, various methods are used, including the use of anti-corrosion alloys, the application of protective coatings and the use of electrochemical methods.

Causes of corrosion

Ferrous metals are most susceptible to rust because their structure is particularly susceptible to the effects of oxygen and water. However, humidity is not the only factor in corrosion, as much depends on the composition of the alloy. For example, one metal may remain resistant in a humid environment, but be subject to destruction in an acidic one.

Corrosion processes can occur in different environments:

Atmospheric corrosion - occurs in the open air due to exposure to oxygen, moisture, polluting gases and other atmospheric factors.
Soil corrosion — is associated with the contact of metal with soil. The rate of corrosion is determined by the chemical composition of the soil and its acidity: the lower the pH, the faster the metal is destroyed.
Aeration corrosion - occurs when one part of a metal object is in constant contact with air, while the other remains isolated.
Electrical corrosion — caused by stray currents, for example, near railway tracks or underground communications.
Biological corrosion — occurs under the influence of microorganisms that release hydrogen sulfide, carbon dioxide and other aggressive substances.
Corrosion in chemically active environments — caused by acids, alkalis, salts and other electrolytes, including fresh and sea water.

The main element that causes corrosion is oxygen, which reacts with the metal surface through air or water. As a result of this process, rust and other oxides are formed.

Main types of metal corrosion

Corrosion is classified according to the mechanism of destruction:

Chemical corrosion — is caused by the direct impact of aggressive substances on the metal, which leads to the formation of oxides. It occurs especially intensively in the presence of acids, alkalis and salts.
Electrochemical corrosion — is caused by the formation of galvanic elements on the metal surface. The difference in electrode potentials causes the movement of electrons, accelerating the destruction process.

There are also other types of corrosion:

Intercrystalline - is associated with a change in the structure of the metal, which makes it vulnerable to destruction.
Fatigue — develops under prolonged mechanical loads, leading to cracking of the material.

Chemical corrosion

The process of chemical corrosion involves oxidation-reduction reactions, during which the metal is transformed into oxide compounds. For example, iron, when interacting with moisture and oxygen, forms rust (Fe₂O₃), and aluminum forms an oxide film (Al₂O₃), which protects it from further destruction.

The destruction of metals is accelerated by exposure to acids and alkalis such as sulfuric acid, nitric acid or ammonia.

Various measures are used to protect against chemical corrosion:

application of protective coatings,
use of anti-corrosion additives,
use of special alloys resistant to chemical influences.

Electrochemical corrosion

This type of corrosion is caused by the interaction of the metal with the environment through electrochemical reactions. In such a system, the metal acts as an anode or a cathode, and the movement of electrons leads to its destruction.

An example is the interaction of iron with water and oxygen, where iron is oxidized and oxygen accepts electrons, forming iron oxides.

The rate of corrosion depends on humidity, temperature and the presence of aggressive substances. The process is especially intense in sea water, as it has high electrical conductivity.

Methods of protection against electrochemical corrosion include:

Cathodic protection — the use of special anodes, which are sacrificed to preserve the base metal.
Electrical protection — use of an external direct current source that creates a protective electric field.
Corrosion inhibitors — substances that slow down electrochemical reactions.

Methods of protecting metals from corrosion

To prevent corrosion, several basic methods are used:

1. Protective coatings

Paints and varnishes - create a barrier between the metal and the environment.
Polymer coatings — protect from moisture, ultraviolet radiation and temperature changes.
Galvanic coatings (zinc plating, chromium plating) — create a protective layer on the metal surface.

2. Electrochemical protection

Cathodic protection — use of sacrificial anodes (for example, made of zinc or aluminum).
Application of direct current - forms an electric field that prevents oxidation.

3. Corrosion inhibitors

These substances are applied to the metal, forming a protective film that slows down destruction.

Conclusion

Protection of metal from corrosion plays a key role in extending the service life of products and reducing operating costs. The use of protective coatings, special alloys and electrochemical methods allows minimizing destructive processes, which is especially important in construction, transport and industry. Modern technologies are constantly improving, offering increasingly effective solutions for combating corrosion.