Metals react with air and form their oxides. This oxide formation tendency of metals affects their physical and chemical properties. For example, a green layer over old copper coin is due to oxidation leading to formation of copper oxide which is finally converted to basic copper carbonate on its surface due to its oxidation.
The processes of oxidation of metals are known as Corrosion. Corrosion leads to the destruction of metal surface by the action of air and moisture.
Generally the corrosion word is used for oxidation of different metals but in case of corrosion of iron, it is called rusting. When iron reacts with oxygen it produce brown powder called rust which is chemically hydrated ferric oxide.
4Fe (s) + xH2O + 3O2 → 2Fe2O3.xH2O (Brown Rust)
In rainy season maximum rusting takes place due to increased moisture in the air. For rusting of iron, two important conditions are required:
There are various methods of preventing corrosion and rusting of iron. Our main concern is to know the various methods to prevent the rusting of iron because iron is a strategic metal as it plays a very important role in the development of a nation.
Some of the important methods of prevention of corrosion are:
This is a common method of preventing iron from rusting. Painting prevents rusting by providing a coating over iron objects.
2. Oiling and Greasing
To put a layer of oil and grease on the iron objects also prevents them from rusting. Iron parts of various machines and vehicles are oiled and greased to prevent rusting and to minimize friction.
In this method we put a layer of zinc metal on the iron objects and this process is known as galvanization. This method is used on large scale for making galvanized iron sheets for making boxes and for roof covering.
Galvanised iron sheets are used to make drum, trunks and other iron containers. Galvanised iron sheets are also used for building roofs and manhole covers.
This is a very good method for improving the quality of different metals. In this method a particular metal with other metal or non-metal is mixed in a fixed proportion to improve its quality like resistance towards corrosion, strength, hardness, shining and high tensile strength.
For example iron metal can not be used for making utensils because it will rust but when it is mixed with nickel and chromium metal it becomes stainless steel.