CORROSION

Corrosion:-  

The process of slowly eating of metal due to attack of atmospheric gases on the surface of metal resulting into the formation of compounds such as oxides, sulphides, carbonates, sulphates etc. is called as corrosion.

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. The corrosion of iron occurs in the presence of air & water.

In iron sheet or object or a particular pot behaves like a where oxidation takes place.

Anode: – 2Fe (s) –> 2Fe2+ + 4e-

And these electron moves to another spot where reduction takes place in the presence of H+ ion (H2CO3)

At Cathode: – O2(g) + 4H+ (aq) + 4e- –> 2H2O (l)

The overall reaction being   2Fe + O2 + 4H+ –> 2Fe2+ + 2H2O

E0(cell) = 1.67 v

Fe2+ (ferrous ion) oxidised by O2to form ferric ion (Fe3+) which comes out as Rust Fe2O3.xH2O.

Methods for prevention 

The rust of iron can be prevented by greasing, painting, galvanizing, anodizing or oiling the surface. The following are the methods to prevent

Barrier protection:

In this process, the metal surface is not allowed to come in contact with the atmospheric agents like air and water so 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.

Sacrificial protection:

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

Cathode protection:

The metal object that is to be protected from rusting is connected to a piece of more electro positive 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.