Protective coating
Rusting can be prevented, by applying a protective coating on the surface of the iron, so that the iron does not come in contact with air and moisture simultaneously. This coating can be of two types:
(i) Non-metallic coating (ii) Metallic coating.Non-metallic coating
Non-metallic coatings include painting, varnishing tarring, plastic coating, oiling, greasing, enamelling etc. As matter of fact, every housewife knows that applying a thin layer of oil on the surface of iron utensils and implements will prevent their rusting.
Metallic coating
Eelectroplating with metals like nickel, chromium, cadmium etc. prevents rusting. Galvanising and tinning are also very effective metallic coatings. Galvanising involves dipping of iron sheet into molten zinc. A thin layer of zinc sticks to the iron. In tinning, tin is used instead of zinc.
By alloy formation
The alloys of iron have a strong resistance to rusting. Iron can be converted to stainless steel by fusing it with carbon, chromium and nickel in a definite proportion.
By forming insoluble iron compounds on the surface
By treating iron with super heated steam, a layer of ferrosoferric oxide (Fe3O4) is formed on the surface of iron. This layer is not affected by moist air.
By electronic protection
Iron, which has to be continuously remain in contact with water, as in the body of ships, can be given a kind of electronic protection. Pieces of a more reactive metal, such as magnesium are attached to that part of the ship that remains under water. When in contact with water, the magnesium undergoes ionisation, and each atom of magnesium liberates two electrons, which flow to the iron. In other words, a simple voltaic cell is established. These electrons prevent the iron from ionising, and thus from rusting. Ionisation of iron can happen only if iron loses electrons. As it gets extra electrons from the more reactive metal magnesium, ionisation is prevented. In other words, corrosion or rusting is prevented.
