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question 25: what's the world's strongest material?

For a long time people thought that graphite and diamond were the only stable forms in which pure carbon could occur. Then fullerenes, carbon balls, rolled into the arena, and nothing's been quite the same since. Absolutely nothing comes stronger than a carbon nanotube!

Text by Eva Krutmeijer

It all started in outer space. And in Harold Kroto's laboratory in England. Kroto was studying the spectra from distant giant stars. In these spectra you can see what chemical elements are present in a star - from lightest to heaviest. You can also find evidence of quite large carbon-chain molecules. Kroto thought that these molecules might be formed in the giant stars and wanted to study how this might happen.

Kroto arranged an experiment with American scientists Robert Curl and Richard Smalley. By gasifying graphite using laser light in a cloud of helium gas they succeeded in mimicking the environment in the stars. They eventually found the carbon-chain molecules they had been looking for. But, to their great surprise, stable clusters of 60 and 70 carbon atoms were also formed.

The carbon balls turned out to resemble hollow footballs constructed of alternate pentagons and hexagons, with carbon atoms at each corner. This was the roundest molecule ever seen - and there was more to come: it could hide other atoms inside it.

The year was 1985. Just over ten years later, in 1996, the three scientists were awarded the Nobel Prize in chemistry.

The fullerenes, as the carbon footballs came to be called, opened up a whole new research field and rapidly became one of the most important factors in the rapidly advancing field of nano research.

A close relation to the fullerene is the carbon nanotube. You can see it as a rolled-up chicken net of carbon atoms, ten thousand times thinner than a strand of hair.

Professor Eleanor Campbell explains:

"We haven't found carbon nanotubes occurring anywhere naturally yet. They need extreme conditions. A Japanese scientist called Iijima discovered them in 1991 in an apparatus he used to produce fullerene molecules. They had actually been made many times before but hadn't been regarded as anything special until Iijima saw them properly for the first time in his electron microscope.

"Scientists have recently discovered carbon nanotubes in the damascene steel they used in the Middle Ages to make Saracen swords which might explain what made them so exceptional."

Research on carbon nanotubes has grown enormously since 1991. Why?

"Nanotubes are extremely strong. They're unique in their combination of stiffness and toughness. They can stretch beyond 20% of their rest length and they can be tied in knots and bent double without any difficulty. Nanotubes are the strongest fibre we know of today."

And what can we use this super strong material for?

"Well, for a start we can produce molecular electrical components. For example we can make computer chips much smaller and more energy efficient than they are today. We'll be able to use the strength of carbon nanotubes in all kinds of ways: radiation-proof textiles, thin bullet-proof jackets and entirely new super strong constructions. Perhaps even the science-fiction dream of an elevator to take us into outer space can come true!"

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