Corrosion Of Metals And Its Prevention

Corrosion of Metals

Corrosion or Rust

What is Corrosion?

When an article made up of iron is exposed to the atmosphere, it is observed that a reddish coat has been formed on the surface of the article. This coating is known as rust, it is actually an oxide of the metal formed by the reaction with the oxygen present in the atmosphere. When the surface of a metal is attacked by moisture or any other substances around it, then the metal surface is known to be corroded and the phenomenon is known as corrosion. Therefore reactive metals such as potassium and sodium are kept in kerosene oil to avoid their exposure to the atmosphere.

What are the Factors affecting Corrosion?

There are many factors governing the corrosion of metals.

  • In presence of oxygen, the corrosion of metals increases.
  • The metals placed higher in the reactivity series gets corroded more easily than the ones place below them.
  • The dissolved salts in water act as an electrolyte and hence the rate of corrosion is enhanced. For example, iron corrodes faster in seawater. The presence of pollutants, for example, NO2 and CO2 increases rusting.

Types Of Corrosion

There are various types of corrosion such as:

  • Caustic Agent Corrosion
  • Localized Corrosion
  • General Corrosion
  • Stress Corrosion Cracking
  • Crevice Corrosion
  • Pitting Corrosion
  • Uniform Corrosion

Examples Of Corrosion

There are various examples of corrosion depending upon its type:

  • The uniform corrosion is the most basic and rusting is a good example.
  • Example of Pitting corrosion is pitting of stainless steel in the presence of water containing chloride
  • Crevice corrosion can be found in nuts and bolt. In the tiny gap between the nut and the threaded bolt and presence of a thin film of water in the humid condition
  • Galvanic corrosion’s example is a steel rivet in alloy 400 sheets which is made exposable to seawater

Methods for prevention of corrosion

The rusting of iron can be prevented by greasing, painting, galvanizing, anodizing or oiling the surface. These methods can be classified into the following categories:

  1. Barrier protection:

In this process, the metal surface is not allowed to come in contact with atmospheric agents like air and water. Hence it protects the metal from corrosion. The barrier protection can be done by a coating of one metal with another metal with the help of electricity (electroplating).

  1. Sacrificial protection:

In this method, the metal to be protected is covered with more electropositive metal such as zinc or magnesium, which gets oxidized and save the metal from corrosion.

  1. Cathode protection:

The metal object that is to be protected from rusting is connected to a piece of more electropositive metal like zinc. The anode is made up of a more reactive element which loses electrons and gets oxidized. The anode goes on disappearing and thus saves the cathode form rusting.

We have seen the process and methods for prevention of corrosion. For any further query call the mentor support team at Byju’s.

Practise This Question

Alloying is a very good method of improving the properties of a metal. Alloys are mixtures of metals with ___.