Graphene gleams from Graphite. “ Material of the Century”. “As if science fiction had become reality,” Youngjoon Gil, V.P. of the Samsung says. Yet it is probably the oldest elements, discovered by man. This was nothing other than the black pieces
left after they put out a wooden fire during the Hunting era. It was called by a multitude of names
ranging from charcoal, lamp black and soot to anthracite, bitumen and coke. By about the 19th Century, man discovered that
greasy black Graphite and brilliant
crystals of Diamond were extremely pure forms of the same element
. Fig.1. Strabge molecules of Carbon. The different forms of the same element are called Allotropes. So the names mentioned here are the allotropes of CARBON. Since 1962 still other forms were created by the scientists. Let us now look at the structure of this atom and try to understand how it behaves.  .Fig.1 A strange molecules of carbon. Fig 2. Structure of
the Carbon atom. Atomic No. 6. Atomic mass 12. It has 4 electrons in the outer shell which it closely hugs. As in the case of metallic atoms, where electrons are easily released, Carbon does not lend electrons forming positive ions. It form compounds by sharing electrons, the type of strong bonds referred to as co-valent bonds.  Fig.3. Carbon combines with other elements to form compounds.. Just as carbon combines with elements like chlorine, hydrogen etc, it can form strong chemical co-valent bonds with the atoms of the same element, forming giant molecules.. There are two ways by which they can occur.  Fig.4. Two allotropes of Carbon. In diamond we find the most stable bonds, where all four electrons in the outer shell of carbon are perfectly linked. It forms the hardest natural substance. There are no free electrons to conduct electricity. In graphite a carbon atom joins with only three other atoms. The remaining electron gets linked to another layer as shown in Fig 4. Weak force called a Van der wall’s force. The electrons are somewhat free to move which makes it an electrical conductor.  Fig.5. Different layers in graphite are linked by Van der Wall forces. CARBON has a pivotal position in the Periodic Table. It can either combine with the elements on its right or with metals, on the left. So it is on the boundary between a demarcation of metals and non metals slightly inclined towards right. Pure carbon atoms also combine with each other in different ways which has caused carbon to exist in varied forms, a phenomenon known as allotropy. It may not be simple for a layman to connect lamp black and diamond, but these two are two pure forms of the element Carbon, DIAMOND The most stable natural form of carbon is diamond. There is a very orderly arrangement of carbon atoms held firmly by covalent bonds. Each atom is attached to 4 other atoms of the same element. The lack of free electrons does not attract other elements and prevent the flow of electricity. It is chemically as well as physically very stable. It is 3.5 times as heavy as water and has a hardness of 10 according to the Moh’s scale. This property along with the transparency and high refractive index makes it ideal crystals for jewelery. The phrase, “Diamond cut diamond’ shows that it is used for cutting and drilling hard materials. Unfortunately the uses of diamond are limited partly as it is very rare . MP=3550ºC GRAPHITE This allotrope of carbon can be considered as the next most natural variety. Every Carbon atom is bound to 3 other atoms. This arrangement makes free electrons available that facilitate the conduction of electricity as in metals. This property makes it suitable as electrodes in cells and brushes for motors. The structure shows parallel layers which may slide, which makes it suitable as a lubricant that can be used at high temperatures. (NASA has recently discovered that this property negates in space.) The high melting point enables the material to be used in fire bricks and crucibles to pour molten metals MP= 3600ºC (approximately) COAL  Fig 6. Structure of coal This
is an impure form of carbon popularly used as fuel for generators and
heavy machinery such as locomotives and ships in the past. The best form of
coal, anthracite, is only 90% carbon bituminous coal, 75-90 percent
carbon, and lignite around 50 percent carbon. There are Hydrogen,
Nitrogen and even Sulphur and Phosphorous bonded to carbon atoms as shown in
the diagram. ‘Amorphous’ is the opposite of ‘crystalline’. Coal is usually an impure form of carbon which may be powdered easily. Charcoal and soot fall into this category. It has been now determined that even amorphous forms consist of crystalline verities mixed along with other impurities. FULLERINE In 1985, Harold Kroto, UK, Richard Smalley and Robert Curl of US, created a new carbon molecule. The structure was similar to a single layer of graphite folded into the shape of a soccer ball. By heating graphite rods surrounded by Helium gas, to avoid burning and condensing the vapour they obtained molecules consisting of 60 atoms of carbon. The structure was a sphere similar to a soccer ball. It had single and double bonds with 12 pentagons and 20 hexagons. They named it Buckminster Fuller or ‘Bucky ball’ for short. The trio shared the Nabel prize in 1996. Fig.5 Bucky ball. This is
considered as ‘the most beautiful molecule’, by some chemists. A
molecule of soccer ball structure consisting of 60 carbon atoms. Lampblack that
comes from a candle contains some of these microscopic variety of carbon. NASA
has recently found this to be present in cosmic space . They are black spheres
with an hollow space inside. Extremely hard and has strange magnetic
properties. A semi conductor of electricity, which can be transformed into
super conductors. Bonding is similar to graphite but only single
layer thick. The specific gravity is 1.7. Uses of Bucky balls.
CARBON NANO-TUBES Iijima Sumio of Japan folded the sheets into tubes and called them nano tubes.
 Fig.7. Carbon Nano-tube is a graphene sheet rolled into a cylindrical shape. These are similar molecules to 'buckyballs' but extended into tubes, cylindrical or cone shaped.. These have the highest tensile strength for any material discovered so far. A cable with a cross section of 1 mm2 can take a weight of over 6000kg. Though the smallest diameter is about 0.4 nm tubes up to 4cm length have been produced. Another phenomenon is the presence of many tubes in some cases as in a telescope. The strangest thing is that the interior tubes are telescopic without any friction. These provide the ideal bearings for linear or rotational movements and the scientists have plans for a frictionless nano-scale ideal motor.
GRAPHENE It is interesting to consider that everyone who has used an ordinary pencil has probably produced graphene-like structures without knowing it. A pencil contains graphite, and when it is moved on a piece of paper, the graphite is cleaved into thin layers that end up on the paper and make up the text or drawing that we are trying to produce. A small fraction of these thin layers will contain only a few layers or even a single layer of graphite, i.e. graphene. Thus, the difficulty was not to fabricate the graphene structures, but to isolate sufficiently large individual sheets in order to identify and characterize the graphene and to verify its unique two-dimensional (2D) properties. This is what Geim, Novoselov, and their collaborators succeeded in doing. In 2010, two
Russian born scientists claimed the physics prize for peeling out grapheme
layers, which is bound to initiate a new era in the use of materials National Graphene Institute (NGI)
in Manchester, which will be completed by 2015 at the cost of £61m, of which
£38m is coming from government research councils. Properties and Uses of Graphene.
The limiting factor at present is the rate of graphene production. Many research organizations are oriented towards peeling out larger and larger graphene sheets in a commercially viable manner. |
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