Allotropes of Carbon: Graphite

Allotropes have two or more forms of the same elements with different physical structures but similar chemical structures. Graphite is a crystalline form of carbon, and the atoms are arranged in a hexagonal structure. It is one of the most stable forms of carbon under a standard condition of temperature and pressure. It consists of layers of carbon atoms and is a good conductor of heat and electricity. The use of allotropes of graphite is manufacturing pencil leads and lubricants due to its slippery property. As it is a good conductor of electricity, it is used in manufacturing electrodes and electric motors due to the free flow of electrons.

Structure of Graphite 

The allotrope of graphite has bonds in sp2 orbital hybridization. Each carbon atom is joined with three other carbon atoms with covalent bonds. Still, one side is free, which creates a delocalized pool of electrons, making it an excellent conductor of electricity. The carbon atoms form a layer with carbon atoms arranged in a hexagonal plane. Each layer of graphite is known as graphene, and it is arranged in a honeycomb lattice with a bond length of 0.142nm. The distance between the planes is 0.335 nm. The carbon layers are bonded together via a weak Van der Waals bond, which allows the layers to slide easily past each other.

Occurrence of Graphite 

It is formed under the Earth’s crust and upper mantle due to high temperature and pressure. It occurs in the metamorphic rocks due to the reduction of sedimentary carbon compounds due to metamorphism. Graphite is also mined from igneous rocks and extracted from meteorites. All the graphite deposits are mined from the metamorphism of carbonaceous sedimentary rocks, and hence it is produced by a geological process.

Properties of Graphite 

1. It has a very high melting point above 3650°C and is a good conductor of heat. The high thermal stability is highly anisotropic due to the quick propagation of phonons along tightly bound planes. Due to the thermal stability, it is used largely in manufacturing refractories.
2. It has an excellent electricity conductor due to vast electron delocalization. The presence of valence electrons in the carbon allows the free flow of electrons to conduct electricity.
3. Graphite has a slippery nature because of weak Van der Waals force. Due to the weak bonding of the carbon layers, it allows sliding the layers across each other. The loose interlamellar coupling between sheets makes graphite lubricating.
4. The density of graphite is in the range of 2.09 to 2.33 g/cc, and it has a specific gravity of 2.26g/cc. Natural forms have low specific gravity due to the trapped porosity.
5. It is insoluble in organic solvents and water. There are no attractive forces between the carbon atoms and solvent molecules, it does not dissolve, and the carbon-carbon bond within graphite is stronger.
6. It is chemically inert, and hence it is used in a range of applications as it is stable under high temperature.
7. Graphite is oxidised to form carbon dioxide when heated in the presence of concentrated sulfuric acid and potassium dichromate. 
8. It is one of the hardest naturally occurring substances due to its structure.  

Uses of Allotropes of Graphite

There are many applications and uses of allotropes of graphite across various industries. The excellent properties of heat and electricity conduction make it a great allotrope for various uses. Here are some of the uses:

1. It is used to manufacture leads in the pencil with a mixture of graphite and clay.
2. Graphite is a good conductor of electricity and is used in manufacturing electrodes, electric motors, batteries, solar panels, etc. The delocalized electrons move freely through the sheets.
3. It is slippery and used in manufacturing different types of lubricants. It is also used as a protective layering on different surfaces.
4. It is used in nuclear reactors because it can absorb high-speed neutrons. Hence, it helps in controlling nuclear fission reactions.
5. One of the prominent uses of allotropes of graphite is the development of heat-resistant refractories. These are used in lining the blast furnaces due to their high thermal conductivity.
6. It is used in manufacturing steel as graphite helps increase the carbon content of the steel and make it strong and sturdy. It is used as a carbon raiser, increasing steel content to a specific level.
7. Natural and fine flake graphite is used for developing brake linings and is a great substitute for asbestos.

Conclusion

The use of allotropes of graphite in the development of electric motors, electrodes, and batteries is due to it being an excellent conductor of electricity. Graphite is an allotrope of carbon and is a crystalline form arranged in hexagonal form. The layers of graphene are connected with the help of a weak Van der Waals bond, making it slippery. It is naturally extracted from metamorphic rocks, sedimented over millions of years under high pressure and temperature. The topic covers all the important points regarding graphite, its properties and its uses.