Allotropes of Carbon: Properties of Graphite

Graphite is a type of crystalline allotrope of carbon and is used in various applications due to the properties of graphite. It is a naturally occurring crystalline carbon allotrope formed from the carbon subjected to intense pressure and temperature under the metamorphic and igneous rocks. It is usually black or black-greyish in colour. The most critical properties of graphite are excellent conductors of electricity and heat. It is chemically inert, and hence it is the choicest form of element used in various industrial formulations as it does not impact the reagent, acids, chemicals, etc. In this topic, the properties of graphite allotrope will be discussed comprehensively.

Structure and Occurrence Graphite Allotrope of Carbon

• The graphic comprises two-dimension carbon atom layers arranged in a hexagonal structure
• Each of the individual layers of graphite is called graphene
• In each atom layer in graphite, each carbon atom is covalently linked to three adjacent or neighbouring carbon atoms
• The carbon atoms are in sp2 hybridisation with the fourth carbon forming pi-bond
• The carbon atoms in each layer are arranged in a honeycomb lattice
• The carbon atom layers have a bond length of 0.142nm with a distance of 0.335 nm between planes
• The layers of the graphite are held together with the help of Vander Waal forces
• This allows the graphite layers to slide past each other
• Only three of the four electrons of atoms are covalently bonded; the fourth electron is free and, hence, free to migrate, making it an excellent conductor of electricity
• The two forms of graphite majorly are alpha (hexagonal) and beta (rhombohedral)
• It is easy to convert the alpha form of graphite into beta form through mechanical treatment at a temperature above 1300°C

Types of Graphite 

There are majorly two types of graphite which are natural and synthetic graphite. Both types are excellent conductors of heat and electricity.

Natural Graphite

• The naturally occurring graphite is obtained from metamorphic and igneous rocks to reduce sedimentary carbon compounds
• It can be even extracted from meteorites that occur with troilite and silicate minerals
• It is stable over a temperature range with a high melting point of up to 3650°C
• Natural graphite has three types: high crystalline, amorphous, and flake

Synthetic Graphite

• It is produced by subjecting high carbon materials like coal tar pitch and petroleum coke to a very high temperature in the range of 2500 – 3000°
• It is less crystalline than natural graphite but has a purity of 99% of carbon

Properties of Graphite Allotrope

Graphite is a soft, shiny, greasy dark black or grey mineral used for a range of applications for its excellent properties. Here are some of the properties of graphite:

• Graphite is slippery, so it is used to produce lubricants and a protective coating. It is slippery due to the stack of tightly bonded one-atom thick carbon sheets, forming a hexagonal structure in each sheet. However, the carbon layers are held together by a weak Van der Waals Bond. The graphite’s lubricating properties are loose interlamellar coupling between graphene sheets.
• Graphite density is 2.265 g/cm3, giving it perfect crystal symmetry. The synthetic graphite has reduced particle size and reduced relative porosity. Isostatic pressing helps in providing a uniform product with high density and improved strength.  
• One of the excellent properties of graphite is that it is a good conductor of electricity
• It conducts electricity due to free delocalised electrons that move freely along the sheets
• It has a free electron as only three electrons of each carbon form bond while the fourth one is free
• Graphite is a good conductor of heat, making it resistant to high temperatures
• It has a melting point of around 3650°C
• Graphite is insoluble in water and organic solvents
• This is because the attraction between carbon atoms in graphite and solvent molecules is not strong enough compared to carbon-carbon bonds in graphite
• It has strong diamagnetic properties and is highly anisotropic
• It is odourless, soft, and has a greasy texture
• However, it is soft and flexible
• Graphite is chemically inert to most chemicals
• Due to its high temperature and inertness, it is used to construct refractory material
• When graphite is heated in concentrated sulfuric acid and potassium dichromate, it is oxidised to CO2
• One of the properties of graphite is its ability to absorb high–speed neutrons, and hence it is used in nuclear reactors
• Due to the high absorption of the neurons, it helps control the nuclear fission reaction
• Graphite is dimensionally stable, resilient, and impermeable to gases and liquids
• The carbon graphite allotropes are self-lubricating, resistant to chemical corrosion with high-temperature resistance

Conclusion 

Graphite is an important allotrope of carbon that has excellent properties and is used in manufacturing a range of products. The properties of graphite-like being a good heat and electricity conductor have made it an integral carbon allotrope in producing electric motors and many electrical products. Graphite is quite structured due to its honeycomb lattice formed by layers of atoms. The strong chemical and mechanical properties of each graphene layer make it an apt element for many applications. It is a chemically inert, slippery, and stable form of carbon.