Graphite

What is Graphite?

Graphite is one of the very common allotropes of carbon. It is also the most stable allotrope of carbon and thus used in electrochemistry as the standard state for defining the heat of formation of carbon compounds.  Graphite is a good conductor of heat and electricity with a density of 2.09–2.23 g/cm3. Graphite was accidentally synthesized by Edward G. Acheson for the first time when he was working on a high-temperature experiment on carborundum.  He found that at around 4150oC, the silicon in the carborundum gets vaporized, whereas leaving behind the carbon in the graphitic form. He was granted the patent for the graphite manufacture in 1896, and then the commercial production of the graphite started in 1897. Graphite is not an element or a compound, it's an allotrope of carbon. It doesn’t have any chemical formula of its own. 


Structure of Graphite

Graphite is a big covalent structure with each carbon atom joined with three other carbon atoms with covalent bonds. Each carbon atom is sp2 hybridized. These carbon atoms form a layer like structure with a hexagonal arrangement of carbon atoms. These layers have weak forces between them. Due to these weak forces, the layers can slip over each very easily. Each carbon atom has a one non bonded electron, which becomes delocalized.


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(These dotted lines denote the weak force between the layers of graphite.)


Properties of Graphite

Physical Properties of Graphite

  1. Graphite is a good conductor of electricity due to its free delocalized electron which is free to move throughout the sheets. 

  2. Graphite is insoluble in organic solvents and water, this is because the attraction between solvent molecules and carbon atoms is not strong enough to overcome the covalent bonds between the carbon atoms in the graphite.  

  3. Graphite is having a high melting point of 3650oC near to the melting point of Diamond. 

  4. Due to its layer-like structure, it is soft and slippery in nature.

  5. Graphite has the ability to absorb high-speed neutrons.


Important Chemical Reactions

  1. Reaction with air - Carbon in the form of Graphite, burns in the air to form Carbon Monoxide and carbon Dioxide depending upon the availability of air or oxygen.

C(s) + O₂(g) → CO₂(g)

2C(s) + O₂(g) → 2CO(g)

  1. Reaction with Water - Carbon in the form of Graphite doesn’t react with water in normal conditions.  Under certain circumstances, the given reaction becomes possible and forms water gas which is a mixture of carbon monoxide and hydrogen gas. 

C + H₂O → CO + H₂


Types of Graphite

Natural Graphite

Natural Graphite, an excellent conductor of heat and electricity, is a mineral composed of graphitic carbon. It is stable over a range of temperatures, with the melting point of around 3650°C. There are three types of natural graphite.

  • High crystalline

  • Amorphous

  • Flake

Synthetic Graphite

Synthetic graphite is produced from coke and pith. It is less crystalline in nature than the natural one. There are basically two types of synthetic graphites. The first one is electro graphite, pure carbon produced from coal tar pitch, and calcined petroleum coke in an electric furnace. The second one is synthetic graphite produced by heating calcined petroleum pitch to 2800°C.


Uses of Graphite

  • Graphite is used in making pencil lead.

  • Graphite is used in the nuclear reactor to control the nuclear fission reaction because of the ability of graphite to absorb fast-moving neutrons. 

  • Due to the slippery nature of Graphite, it is used as a lubricant in the machine parts.

  • Graphite is used as a conductor of heat and electricity in several processes due to its free electrons. 

  • Graphite is used in high-temperature applications like in the production of phosphorus and calcium carbide.

  • Graphite is used as an anode in aqueous electrolytic processes such as in the production of halogens.

  • Graphite is used as an electrical material in the electric motor as a carbon brush.

  • Due to its resistant nature towards chemicals and high melting temperatures, it is used to make crucibles.

  • Graphite materials are used as the anode material for lithium-ion batteries. 


Facts about Graphite

  • Graphite word comes from the word “Graphene” which means to write or draw in ancient greek. 

  • Graphite is the only non-metal that conducts electricity. This is due to the delocalized electron.  

  • Graphite is really tough to melt. It does not have a melting point at atmospheric pressure.

  • Most of the graphite used today is manufactured from coal in the electric furnace and not mined. 

  • Pencil manufacturing is one of the important uses of graphite. In 2011, around 7 % of the total graphite was used to make pencils.

FAQ (Frequently Asked Questions)

1. What are the Different Types of Natural Graphite?

Ans. There are three types of Natural Graphite-

  • High crystalline - Crystalline graphite has a  purity of around 90% and it comes in the size range of 1 cm to 1 m in thickness. It is believed crystalline graphite has come from crude oil deposits which have transformed into graphite over time. 

  • Amorphous - Although it is called amorphous, it is still crystalline in nature. It is the least graphitic among all the natural graphites.  

  • Flake - It can be found in the metamorphic rocks with concentration varying between 5% to 40%. Flake graphite can be found in numerous locations around the world.

2. “Graphite is a Good Conductor of Electricity Whereas Diamond is a Bad Conductor of Electricity” Explain why?

Ans. In diamond, each carbon is directly attached to four other carbon atoms via covalent bonds. Thus, all the valence electrons of carbon in diamonds are involved in bonding and are not free to conduct electricity which makes it a bad conductor of electricity. On the other side, each carbon atom in graphite is directly bonded to only three other carbon atoms, and the fourth valence electron is free which can move around freely in the layer. This makes it easier for graphite to conduct electricity. Hence, graphite is a good conductor of electricity.