Why does iron get rusty?

          Rust is a brownish red substance that forms on the surfaces of iron and steel materials when they are exposed to damp air. Rust is a hydrated form of iron oxide.

          Rusting occurs when the oxygen in the air unites with iron by a process known as oxidation. It is also called “corrosion”. But rusting is not only a process of oxidation, because the presence of moisture is also necessary to produce the change. The complex rusting process is an electrochemical reaction that is speeded up by the presence of salts and acids. That is why rusting is more severe in coastal regions and industrial areas where the air may contain acidic sulphur dioxide fumes. 

          Rust not only corrodes the surface but also weakens the metal. Small cells are set up in the corroding metal. It occurs mainly at grain boundaries of metals and where it is stressed. A prolonged exposure to moist air causes rusting, in iron materials and holes in iron sheets.

          Rust can be removed by scrubbing the iron or steel or by using grinding abrasives. There are two basic methods to prevent rusting. The iron or steel may be coated with paint, plastic, or a corrosion-resistant metal such as tin or zinc so that oxygen is stopped from reaching the iron or steel beneath. Chemically coated paper wrapped around metal objects also prevents rusting. The metal may also be alloyed with corrosion resistant metals such as nickel and chromium.