Corrosion definition and types

Corrosion definition
Photo by Mike Bird

Corrosion definition

Corrosion is a significant term in chemistry. The matter is divided into three groups based on their physical and chemical properties. These are metal, nonmetal, and metalloid. Metals, which are chemically active, are corroded in the presence of atmospheric air and moisture. Metals that are highly reactive, such as magnesium, iron, aluminum, etc. are more corroded. Corrosion definition is a natural phenomenon that we often witness in our daily life. This is a chemical change, which is accomplished in the presence of air and moisture (1).

What is corrosion?

The definition of corrosion is the breakdown of elements due to chemical processes usually oxidized by the presence of the air and water. It is a process of degradation of elements as a result of chemical, electro-chemical, or other reactions. Corrosion occurs when the substance comes in contact with air or certain chemicals. When an element corrodes, its physical properties change. This natural process converts the metal to a more chemically stable form such as oxide, sulfide, or hydroxide (1) & (2).

Example of corrosion

  • When iron is kept in the open air for a long time after it has a reddish-brown coating on it called rust. Under open atmosphere iron for long periods of time, it reacts with oxygen and water in the air to form a reddish-brown coating on the iron, which is rust. Rust is a form of rust.

4Fe + 3O₂ + 2H₂O = 2Fe₂O₃ + 2H₂O

  • When silver is left in the open for a while, it reacts with sulfur in the atmosphere and forms a layer of silver sulfide on the surface of the silver, which is black in color. It is called silver tarnishing. In this process, silver forms silver sulfide as it reacts with hydrogen sulfide, which is present in the atmosphere.

4Ag + 2H₂S + O₂ = 2Ag₂S + 2H₂O

Condition of corrosion formation

Corrosion is a chemical process in this process, new substances are produced by changing the physical properties of the substance. The presence of three materials is required for this process to be completed. These are

  1. The presence of oxygen or air in the atmosphere.
  2. The presence of moisture or water.
  3. Substance (metal) (1) & (2)

Corrosion factor

The rate of corrosion is controlled by some factor. These are

  1. The integrity of the metal.
  2. The electrical sensing nature of the metal.
  3. The presence of reactionary gases in the atmosphere.
  4. The presence of salt in the water (1).

Types of corrosion

There are different types of is discussed below (3).

Type of corrosion

Explanation or definition of corrosion type


1.     Uniform corrosion This corrosion occurs as a result of the continuous transfer of electrolyte to the anode and cathode regions of a metallic surface and continues to corrode almost over the entire surface. A piece of zinc and steel immersed in mixed sulfuric acid usually dissolves over the surface at a certain rate.
2.     Galvanic corrosion Two different metals come in contact with a corrosive environment, electrical potential differences are present.

When two metals are electronically connected, the resulting galvanic cell becomes a more active metal anode and its corrosion will increase.

Aluminum and carbon steel are attached and immersed in water, then aluminum corrodes very quickly. And steel is preserved.
3.     Crevice corrosion Whenever there is a difference in the ionic density between any two local regions of metal, the forms of local decay is known locally because the crystalline corrosion may occur. Crevice corrosion occurs in aluminum and stainless steel.
4.     Pitting corrosion Pitting corrosion definition is it is a form of localized corrosion. It is the most damaging form of corrosion.

This corrosion occurs at a local point. It proceeds by forming a corrosion cell around the metallic surface. Once the pitting corrosion formed, it continuously growing. It can take on different shapes.

A droplet of water on a steel surface, pitting will start at the center of the water droplet.
5.     Intergranular corrosion This corrosion occurs due to the presence of excrement at the boundary of the grain which separates the grain formed during solidification of the metal alloys. This corrosion occurs in the aluminum-based products.
6.     Stress corrosion cracking This corrosion can be summarized to ‘SCC’. It refers to the cracking of the metal as a result of the corrosive environment. This corrosion occurs at high temperatures. Examples of stress corrosion cracking are brass and stainless steel alloys.

When a minimum marginal tensile pressure is reached certain brass alloys will crack into the ammonia.

Stainless steel alloys do not crack in ammonia but crack in chloride solutions.

Prevention of corrosion

There are many methods to prevent corrosion. These are

  1. Electroplating is a process by which corrosion is prevented. In this process, the metal is coated by electrolysis with silver, chromium, or any other metal. It is the most popular method to prevent corrosion.
  2. Galvanization is a process of preventing corrosion. This process involves a layer of zinc coating on the iron. This is usually done by dipping iron in molten zinc. This zinc layer coating thus protects the iron inside from corrosion.
  3. Applying a coating of paint or grease on the metal can prevent exposure to the metal to the external environment. Which makes it possible to prevent corrosion.
  4. An easy way to prevent corrosion is to use corrosion-resistant metal such as aluminum, stainless steel, etc.
  5. An alloy is a mixture of two or more metals. Alloying is a process where metals like iron or steel are mixed with a less reactive metal like chromium, magnesium, etc. to protect them from corrosion (1).

Battery corrosion

Corrosion in the terminals is due to the release of hydrogen gas from the battery acid. It mixed with other substances in the atmosphere and produced corrosion. If the corrosion continues to occur at the negative terminal the system is probably going to undercharging. And if the corrosion occurs at the positive terminals the system is probably going to overcharging. Most of the corrosion occurred on the negative side of the battery because the battery is usually in an undercharge situation.

Causes of battery corrosion

  1. Hydrogen gas is released from battery acid in the terminals. The hydrogen gas mixed with other particles is present in the atmosphere. And produced the corrosion in battery terminals.
  2. Copper does not corrode easily. And it is a good conductor. When electric currents cross the copper, which is present in the terminals, there is copper sulfate produced. That leads to the corrosion of battery terminals.
  3. Due to the damage of the battery, the electrolyte in the battery leaks and accumulates on the terminals and corrosion occurs.
  4. When the battery is overcharged the electrolyte gets charged upon kinetic energy and overflows to the terminals. That is why corrosion occurs in the terminal of the battery (6).

Prevention of battery corrosion

  • When the battery is overcharged or undercharged, then corrosion occurs. There is a recommendation of the battery voltage in the manufacturer’s manual. If the terminal’s corrosion is to be prevented, it must be complied with.
  • There are different sprays on the market to prevent terminal corrosion. These can also prevent battery corrosion.
  • Battery terminal corrosion can also be prevented with Vaseline or grease coating (4) & (5)