What is graphite?
Unlike the tetrahedral arrangement of atoms in diamond, the carbon atoms in graphite are arranged in the form of hexagonal rings in layers (Fig.10.2). Each carbon is bonded to only three other carbon atoms in that layer.
Different layers of graphite are held together by rather weak forces. Hence they can slide over one another. This is one reason why graphite scales off easily and can mark impressions on substrates. Because of this property, it is also used as a lubricant.
Physical Properties of Graphite
- Graphite is greyish black crystalline substance.
- It has a soft and greasy texture, but has a metallic luster.
- The specific gravity of graphite is only 2.2 g cm-3.
- Due to the presence of a free valence electron, it is a good conductor of electricity.
- It is also one of the stable forms of carbon.
- The structure of graphite has hexagonal rings arranged in layers.
Chemical Properties of Graphite
- Graphite is inactive and inert to almost all chemicals.
- It does not burn in air, even if heated to high temperature. But if heated in oxygen, it burns completely to form only carbon dioxide.
- It also gets oxidised to carbon dioxide, when heated with concentrated sulphuric acid and potassium dichromate.
Uses of Graphite
- Graphite is used in making the ‘lead’ of pencils.
- It is used in the production of refractory crucibles, which can withstand very high temperature.
- Graphite being a conductor of electricity finds application in making electrodes.
- It is used in making polishes and paints.
- Graphite is used as lubricant in machines, which have to be operated at high temperatures. All such machines cannot be lubricated with oils, grease, etc. as they vaporize immediately at the high temperature.
- It is used for making electrotypes for printing
- Graphite is extensively used in nuclear reactors, to absorb neutrons.
- This helps in moderating the nuclear reaction.