GRAPHENE — HARDER THAN DIAMOND, THINNER THAN HUMAN HAIR
There is a new material in town, a stronger material than steel, as hard as diamond and a million times thinner than the diameter of the human hair. Seeker calls it the ‘Miracle material,’ and Business Insider says ‘the material will change the world.’ This material is none other than Graphene.
Graphene was discovered in 2004 by two professors from the University of Manchester; Andre Geim and Konstantin Novoselov. They isolated and characterized graphene using the Scotch tape method and went on to win the Nobel Prize in 2010.
Graphene is the thinnest form of material known to man, and because of its very close and tight packing of atoms in its crystal lattice, graphene is a highly stable material. Graphene is considered a smart material that possesses excellent mechanical, electrical, and thermal properties.
Over the last decade, the number of research publications related to various aspects of production, properties, and graphene applications has increased exponentially. With such keen interest in the material, it is essential to keep up with the current graphene technology as it has the potential to drive futuristic innovations.
STRUCTURE
Carbon exists in more than one allotropic form, which has distinct physical properties due to their different arrangement of atoms.
Diamond and Graphite are two major allotropes of carbon. Graphite is so soft that you can write with it, while diamond is so hard that you can only scratch it with another diamond.
Diamond
Structure and bonding
Diamond has a giant covalent structure in which:
- each carbon atom is joined to four other carbon atoms by covalent bonds
- the carbon atoms have a regular lattice arrangement
- there are no free electrons
Fig 1. Carbon atoms in diamond have a tetrahedral (pyramid-shaped) arrangement
Graphite
Structure and bonding
Graphite has a giant covalent structure in which:
- each carbon atom is joined to three other carbon atoms by covalent bonds
- the carbon atoms form layers with a hexagonal arrangement of atoms
- the layers have weak forces between them
- each carbon atom has one non-bonded outer electron, which becomes delocalized
Graphene is a crystallographic allotrope of carbon with 2-dimensional properties and it is the purest version of GRAPHITE. It can have plenty of height and width but no perceivable height, this makes it as close as you’ll ever get to a 2D material living in a 3D world.
Graphene is the thinnest form of material known to man having a single layer of carbon atoms arranged in one plane; more than ten layers of graphene make up graphite [ISO].
To fully appreciate the value of Graphene, we need to understand the microstructure of Carbon.
Carbon is a chemical element found in group 14 and period 2 of the period table. It is the sixth element in the periodic table, with a ground-state electronic configuration of 1s2s2P2. The nucleus of a carbon atom is surrounded by 6 electrons, four of which are valence electrons
These electrons in the valence shell of a carbon atom can form three types of hybridization; sp, sp2, and sp3. When carbon atoms share sp2 with three other neighboring carbon atoms, they form a layer of honeycomb network of planar structure, which is also called the monolayer graphene.
Graphene is a single layer of pure carbon atoms bonded together with sp2 bonds in a hexagonal lattice pattern. In graphene, each carbon atom is covalently bonded to three other carbon atoms. Since graphene is flat, every atom is on the surface and is accessible from both sides, so there is more interaction with surrounding molecules. Graphene also enjoys electron mobility that is higher than any known material.
The term ‘Graphene’ theoretically refers to monolayer graphene, and sometimes it could include bilayer graphene. The properties of bilayer graphene are similar to the properties of monolayer graphene. These properties include excellent electrical conductivity, high room temperature thermal conductivity, outstanding mechanical stiffness, and strength. It has been shown that the electronic structure of graphene rapidly evolves with the number of layers.
Ideal graphene has a highly ordered structure exhibiting zero band-gap, high tensile strength, and high thermal conductivity at room temperature.
CASE STUDY — A PENCIL
So let’s break it down, I’m sure we all used pencils while of growing up.
The black ‘stuff’ that rubs off on our paper when writing is called Graphite. Now take a piece of cello-tape and strip off a layer of the graphite from your pencil. If you continue to strip off layers from the first layer, what you have as your final product is graphene.
To paint a better picture, if you put together a million layers of graphene, you would eventually have enough to make just one millimeter of your pencil (graphite).
METHOD OF PRODUCTION
There are two major ways of producing graphene.
- The top-down method — involves the production of graphene from bulk graphite using methods such as the exfoliation of graphite with Scotch tape (also referred to as Mechanical exfoliation), liquid-phase exfoliation, etc.
- Bottom-up Method — this involves the production of graphene from the molecular growth of carbon precursors. E.g. Chemical Vapor Deposition (CVD) etc.
Mechanical Exfoliation- this method is used to produce graphene by systematically peeling graphite with the use of adhesive tape. During this process, graphene is separated from graphite crystals. Geim and Novoselov initially used adhesive tape to pull graphene sheets away from graphite. After exfoliation, the flakes are deposited on a silicon wafer. In this process, layers of graphene are bonded strongly by van der Waals bonding. It is a straightforward, easy manufacturing method for producing graphene but its disadvantage is that it is not suitable for large scale production.
Liquid-Phase Exfoliation- this method involves using solvents like acetic acid, sulfuric acid, and hydrogen peroxide, to exfoliate graphite through ultrasonication. This method used to create graphene is difficult for large-scale production. Graphene produced from graphite by direct exfoliation methods have relatively high crystal quality; this, in turn, leads to high electrical conductivity and less crystal defect but the production yield is still very low and not enough for practical application.
Chemical Vapor Deposition- CVD is one of the important deposition methodologies. Chemical Vapor Deposition is a bottom-up approach for the direct synthesis of graphene from carbon sources such as methane, which is then transferred to a substrate. In the CVD process, nickel and copper are used for large scale production of graphene. During the CVD process, a film of metallic catalyst deposits on the substrate. Chemical etching is performed on the deposited material on the substrate. After chemical etching, a mixture containing the carbon is then passed into the reaction chamber. The quality of graphene from CVD is of high quality, and it is also suitable for mass production.
Other methods for creating graphene are growth from a solid carbon source (using thermo-engineering), sonication, cutting open carbon nanotubes, carbon dioxide reduction, and also graphite oxide reduction. This latter method of using heat (either by atomic force microscope or laser) to reduce graphite oxide to graphene has received a lot of publicity of late due to the minimal cost of production. However, the quality of graphene produced currently falls short of theoretical potential and will inevitably take some time to perfect.
APPLICATIONS
FLEXIBLE ELECTRONICS:
Ever wish you could sit on your phone without breaking it? If it was made with graphene, you could. Graphene can be made into a transparent material and flexible with some excellent mechanical properties. With graphene’s amazing strength, 100% transparency, and astounding flexibility, it would usher us into a whole new consumer electronics world. Graphene is also one of the best conductors of both heat and electricity, as it has a zero band-gap.
WATER FILTRATION:
Only 3% of the water’s supply is fresh, scientists at Rice University have discovered the ability of graphene oxide to decontaminate and remove radioactive materials from contaminated water.
PHOTOVOLTAIC CELLS:
Graphene is the ideal material to be used in Solar Cells due to its high conductive capacities. It is very effective at absorbing ambient heat and light.
Graphene is highly inert and so can act as a corrosion barrier between oxygen and water diffusion. This could mean that future vehicles could be made to be corrosion resistant as graphene can be made to be grown onto any metal surface (given the right conditions).
· Due to its strength, graphene is also currently being developed as a potential replacement for Kevlar in protective clothing, and will eventually be seen in vehicle manufacture and possibly even used as a building material.
· IBM announced in 2014 that it had used graphene to create a chip that is 10,000 times faster than the normal chip.
· Graphene is the ultimate material for overcoming friction and can potentially increase the lifespan of machinery. If you apply a one-atom-thick layer of graphene to a two moving metal equipment, the graphene could last an astonishing 6500 cycles.
This just shows you the future potential for graphene once production becomes cheaper. The commercial potential of graphene is staggering, already portrayed as the material of the future:
· Companies like Ford already use graphene nanoplates in their trucks to improve noise reduction and increase the strength and heat endurance of the polyurethane foams used in their engine compartment.
· Oakley uses graphene for heat dissipation in their ‘aero jerseys’.
· Callaway infuses graphene in their golf balls to improve the compression-to-resilience ratio.
REFERENCES
https://grapheneamerica.com/blog
http://www.graphenesq.com/whatis/how.asp
https://www.bbc.co.uk/bitesize/guides/z3ntjty/revision/1
https://ui.adsabs.harvard.edu/abs/2008Sci...321..385L
https://www.graphene-info.com/graphene-structure-and-shape
https://doi.org/10.1080/14686996.2018.1494493
http://dx.doi.org/10.5772/intechopen.92258
AUTHORS BIOGRAPHY
Christian E. Emeodi holds a national diploma degree in Mechanical Engineering and currently a final year student at the department of Metallurgical and Materials Engineering, University of Lagos, Akoka. He was an Engineering intern at the AJAOKUTA STEEL COMPANY LIMITED where he gained practical knowledge on the production of Steel. Christian led a team of students that discovered a way to recycle plastic waste into paver bricks. He is currently a member of Institute of Engineering and Technology, Unilag chapter. He is also a student member of ASTM and NSBE.
Bukola F. Animashaun interned at the AJAOKUTA STEEL COMPANY LIMITED where she learnt the technical know-how of commercial production of steel, with exposures at the Sintering and Raw Materials Handling Plant, Coke Oven and By-product Plant, Blast Furnace Plant, and Pig Casting Shop. Bukola was awarded the best student in Physical Metallurgy and the overall best student in 400 level at the department of Metallurgical and Materials Engineering, University of Lagos, Akoka. She is currently the regional Vice President of ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (Unilag Nigeria Chapter).
