Graphite is a soft grayish-black greasy substance. The word ‘graphite’ comes from a Greek word meaning ‘to write’. The lead in our writing pencils is graphite mixed with clay. Graphite is also known as black lead or plumbago.
Graphite is also crystallized carbon. The carbon atoms of graphite form a crystal pattern that differs from that of the carbon atoms in diamond.
Natural graphite is mined in Bihar, Andhra Pradesh, Jammu and Kashmir, Odisha, Rajasthan, Tamil Nadu and Uttar Pradesh. Other than in Indian, it is found in Sri Lanka and Russia. In the United States it is mined in New York and Pennsylvania.
Synthetic graphite is made from hard coal or coke in an electric furnace.
Structure of graphite:
In graphite, the carbon atoms are arranged in flat planes of hexagonal rings stacked on one another.
Each carbon atom is attached to three others on the same plane. Thus, only three out of four valence electrons are used in carbon-carbon bonding. The fourth valence electron remains loosely between the planes. This free electron accounts for the electrical conductivity of graphite. The lack of carbon-carbon bonding between adjacent planes enables them to slide over each other making graphite soft, slippery and useful as a lubricant.
Properties of graphite:
Graphite has the following properties.
1. Graphite is a soft, slippery, grayish-black substance. It has a metallic luster and is opaque to light.
2. Specific gravity of graphite is 2.3.
3. Graphite is a good conductor of heat and electricity.
4. Although graphite is a very stable allotrope of carbon but at a very high temperature it can be transformed into artificial diamond.
5. Chemically, graphite is slightly more reactive than diamond.
Uses of graphite:
The important uses of graphite are as follows.
1. The major use of graphite is in making lead pencils of different hardness, by mixing it with different proportions of clay. The weakly held layers of carbon atoms in graphite easily slide over each other and are left behind on paper as black marks.
2. Due to its slippery nature, graphite is used as a dry lubricant in machine parts.
3. Being resistant to chemicals and having a high melting point and also because it is a good conductor of heat, graphite is used to make crucibles.
4. The presence of free electrons makes graphite a good conductor of electricity and it is used to make electrodes.
5. Graphite has the ability to absorb fast-moving neutrons, thus, it is used in nuclear reactors to control the speed of the nuclear fission reaction.