Allotropes of carbon
Sreelakshmi P Vijayan
Yes! The chemical composition of the two are exactly the same. Can you believe it? This makes graphite and diamond allotropes of carbon. That is, graphite can be converted to diamond under high pressure (>100 k bar) and temperature (>2000oC).
Allotropy is the existence of an element in two or more forms, where there is a difference in the arrangement of atoms in crystalline solids or in the existence of molecules that contain different numbers of atoms. Allotropy is exhibited mainly by Carbon, Sulphur, Oxygen, Phosphorous, Tin etc.
Why 12C exhibits allotropy?
Carbon is capable of forming many allotropes due to its valency. Due to its property of catenation and pπ- pπ bond formation it can form various allotropes. Well-known allotropes of carbon include diamond and graphite. In recent periods, several allotropes have been discovered, including buckminsterfullerene and sheets such as graphene. Larger-scale structures of carbon include nanotubes, Nano buds and nanoribbons. Other unusual forms of carbon exist usually at elevated temperatures and pressures.
As we know both diamond and graphite consists of pure carbon. However, diamond is the hardest substance in the world. Do you know why this is? In diamond, the carbon atoms form 4 covalent bonds to give a tetrahedral structure (sp3 hybridization) whereas, in graphite the C-atoms are in sp2 hybridization forming 3 covalent bonds giving a layers of hexagonal ring structure and the remaining fourth electron forms layer by Van der Waal’s forces. Thus diamond exist in a rigid covalent structure which is difficult to break making it the hardest substance in the world while layers of graphite can be separated easily and hence it is soft in nature. Diamond is an insulator and graphite, as we know is a good conductor of electricity.
Buckminsterfullerene / Bucky balls was first invented by Richard Smalley, Harold Kroto and Robert Curl at Rice University, Houston. The trio won the Nobel Prize in Chemistry in 1996 for this discovery of a black solid, a kind of fullerene with formula C60. It consists of 20 hexagons and 12 pentagons, having a hollow cage-like structure, resembling a soccer ball. It was named due to its atomic similarity with Fuller’s geodesic domes. They are used as optical limiters in protective glasses, eye wears, optical sensors etc. due to their ability to decrease the transmittance.
A new material that is harder than diamonds
The ultra-hard material has been discovered by scientists in the Moscow Institute of Physics and Technology, whose hardness is twice than that of a diamond. The material is ultra-hard fullerite made of fullerenes, with hardness 150-300 GPa where the hardness of diamond is just 150 GPa. As in the past, fabrication of such hard materials where nearly impossible due to requirement of high pressure. However, the research team discovered a technique to synthesize such an ultra-hard material by adding carbon disulphide, CS2 which decreased the required pressure to nearly half providing scale-up synthesis by industries. The developed material can be used instead of diamonds for polishing, cutting, grinding etc.
Read more : Friction
Check your knowledge
Allotropes are two or more different physical forms/ states in which a chemical element (stable atom) can exist. These forms vary in their arrangement of constituent atoms in the solids.
It is the property of an element to exist in different forms having same chemical properties but different physical properties due to difference in bonding of atoms.
It is the property of carbon to form covalent bond with other carbon atoms to form long chains, rings and structures
Graphite, Diamond, Fullerene, CNTs, Graphene, Amorphous Carbon, Glassy carbon, Chaoite, Q-carbon, Schwarzites etc.
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