Text: Carbon http://www.sussex.ac.uk/Users/kroto/workshop.html Everyone knows that diamonds are sparkling gemstones, and that graphite is the 'lead' in pencils. What is little known, and at first rather strange, is that these vastly different materials are actually made up of the same atomic building blocks - carbon atoms (ie. they are allotropes). Why are they so different ? The answer to this apparent contradiction was actually found almost a hundred years ago when scientists probed the materials with X-rays to determine their internal atomic structure. It turns out that the atoms in diamond are arranged in a rigid 3D structure, while the atoms in graphite are arranged in sheets of atoms. In graphite these sheets can move over each other fairly freely (see the picture over the page) but in diamond the atoms are held rigidly. Diamond is therefore hard while graphite is soft. Further analysis along these lines also explains why diamond is an insulator and crystal clear, while graphite is a conductor and opaque. People have been using diamonds and graphite for thousands of years, proof of this comes from the names which are derived from the ancient Greek. Diamond means 'invincible' related to its hardness, the hardest naturally occurring material. Graphite means 'to write' obviously this name was applied to an early use of the substance and we still use graphite today in pencils. Diamond and graphite are most important industrial materials. Diamonds can be mounted on to drill bits to extend the working life of the tip and allow them to cut into extremely hard materials. Graphite is used extensively in the manufacture of motors, heating equipment and electronic components. It is apparent that diamond and graphite are important materials. In fact the study of carbon materials is an extremely important area of research. The discovery of a third form of carbon would therefore caused a great stir in the scientific community if it were true. The brief story outlined below describes this new third form of carbon; buckminsterfullerene (more commonly called C60) and indeed it has caused an explosion of activity throughout science. Buckminsterfullerene is a tiny molecular cage of carbon having 60 atoms making up the mathematical shape called a truncated icosohedron. You actually know the shape of this structure very well because it happens to be the same shape as a football ! (12 pentagons and 20 hexagons count them). The experiments made during this workshop will allow you to make, analyse and purify C60 yourself. € Buckminsterfullerene - a strange name ? The round cage like structure of the fullerenes was reminiscent of the dome structures designed by the architect Richard Buckminster Fuller, and so C60 was named Buckminsterfullerene. These amazing buildings can cover large areas of land and the light weight and durable construction makes them ideal structures especially for building that have to withstand large changes in temperature and high winds such as found in the Arctic, for example. They also make good climbing frames and many small fuller type domes can be seen in playgrounds. € The discovery of microscopic amounts of Buckminsterfullerene C60, buckminsterfullerene, and a whole family of carbon cage molecules called the fullerenes, were first discovered in 1985 on a very sensitive laboratory instrument. The amount of C60 actually being produced in the experiment was very small. The scientists calculated that, even if the machine was run for ten years non-stop it would barely produce enough C60 to line the bottom of a test tube (a few milligrams perhaps). C60 was therefore initially discovered in microscopic amounts at levels too small to allow purification and analysis by any other techniques. However, from 1985 - 1990 the theoretical scientists started to calculate the physical and chemical properties of these curious molecules. € Making gram quantities of fullerenes The next scientific breakthrough came in 1990 when a German / American group and the Sussex group independently showed that C60 could be made in gram quantities using a carbon arc. The technique is essentially very simple; if a voltage is applied to two carbon rods, (just touching), an arc will develop between them. If the arc is maintained in helium or argon (instead of in air) clouds of black smoky carbon soot are produced. It turns out that at the correct arc temperature and gas pressure up to 10 % of the black soot is C60. Also present in the soots are 1% C70, and smaller quantities of larger fullerenes. The fullerenes are also found to be soluble in common solvents such as benzene, toluene or chloroform. If you shake up some of the fullerene soot with toluene and filter the mixture, one obtains a red solution. If you take a drop of this solution and place it under microscope, as the solvent evaporates, crystals of pure carbon appear in front of your eyes. These crystals are made up of millions and millions of tiny balls all packed together side by side and on top of each other. The beautiful pictures obtained using high power electron microscopes dramatically confirm this. € Fullerene Science Now the world has a method to make these fascination new carbon molecule we have started to investigate their physical and chemical properties. With the development of this incredibly simple technique the field of fullerene research has grown at an alarming rate. There are now thousands of articles and scientific publications on the fullerenes and it looks as though the new field of fullerene science is here to stay. € Has carbon any other 'tricks up its sleeves' Yes !, soon after the discovery that the fullerenes could be made in the carbon arc other interesting carbon structures were discovered lurking in the carbon soot. Electron microscopes have uncovered tiny carbon tubes ('buckytubes'), some having diameters as small as 2 nm or so, many are thousands of times as long as they are wide. Carbon 'onions' have also been found and these can be considered as carbon cages one inside the other, rather like a carbon version of the Russian doll toy. These carbon particles have many millions of atoms and some have been observed with dozens of concentric shells. The tubes and onions are likely to be composed of hexagonal and pentagonal carbon rings just like the fullerenes. However it looks as if structures having heptagonal (7 member) rings may also be possible. One such hypothetical structure is shown on the second page of this booklet. These nanoscale fullerene based structures (fullerenes, tubes and onions) represent a new range of carbon materials - materials destined to play a role in the technology of the 21st century. Fullerene Articles For further information etc. see contact name and address on the acknowledgements page. A new form of carbon is born, Jim Baggott New Scientist, 13 Oct. 1990 Great Balls of Carbon, Jim Baggott New Scientist, 6 July 1991 Buckyballs bounce into action, Jonathan Crane Chemistry Review, Jan 1995 Fullerene Books Perfect Symmetry Oxford University Press 1994 Jim Baggott SBN 0 19 8557906 about £19-00 The story of the discovery of the Fullerenes, from searching for chain molecules in space to some of the most important developments in Fullerene science. The Most Beautiful Molecule - An Adventure in Chemistry Aurum Press 1994 Hugh Aldersey-Williams about £19-00 The story of the discovery of C60 etc. etc. with emphasis on Fullers architectural domes etc. another good read. Designing the Molecular World - Chemistry at the frontier Princeton University Press 1994 Philip Ball ISBN 0 691 00058 1 about £20-00 A really great book on the latest excitement in chemistry, all about the research at the frontiers of chemistry (which naturally also contains physics and material sciences etc.). there's also a section on Fullerenes.

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