Author: Griffin-Smith Ben
Date: December 2007
A team of researchers at Cambridge University are using a new technique to make carbon nanotubes. For years now, carbon nanotubes have been one of the most promising new materials available to researchers. Carbon nanotubes are found commonly in the general environment. For example, they are formed, albeit in tiny concentrations, in candle flames. There has been massive speculation as to possible uses of these tubes. The material's impressive physical properties are coupled with controllable electrical properties, which make them possible candidates for nanoscale diodes, conductors and memory storage. Their incredible tensile strength and low mass makes them the perfect candidate for space elevators or orbital tethers, which would connect the ground we stand on to satellites or space stations. Televisions using carbon nanotubes have undergone trials and could soon replace plasma and LCD displays for large sets.
These applications are not yet fully realised, partly because of the difficulty in controlling the production of the tubes, making the right structures for the right application, in high purity. Carbon nanotubes exist in many structures, with names like zigzag and armchair, and all these structures have slightly different properties. Making a product containing only one of these structures is difficult.
Carbon Nanotubes, just a few billionths of a metre across, made by folding over layers of graphite so they join at each end, forming a cylinder image courtesy of www.nanotechia.co.uk
The New Kevlar
Researchers at the University of Cambridge have this year made a breakthrough in the field, by creating a nanotube fibre in a new way. To make the nanotubes, a simple feedstock containing carbon is injected into an incredibly hot furnace, able to break down the reactant into its component atoms. The free carbon then binds to particles of an iron catalyst as long nanotubes. Professor Windle explains that the forming carbon nanotubes look like smoke in the reaction chamber, but "because the nanotubes are entangled, the smoke we make is elastic". The formation process looks like a bizarre growing "sock". To make fibres which can be further processed, the nanotubes are stretched and woven into a thread. The pulling of the "sock" aligns the nanotubes with one another, packing them closer together. This gives rise to strong intermolecular forces, which hold the tubes together and increase the strength of the overall material.
One of the best features of the process is the simplicity of improvement. Marcello Motta, a post-doctorate researcher at the Cambridge department of Materials Science and Metallurgy, explains that, "It starts with a high temperature gas phase reaction, which gives you perfect control over the building blocks. That's a major advantage. If you have the need to improve your material, all you have to do is adjust the process, its balance, or chemistry to end up with better properties."
The nanotube thread can be woven into an incredibly strong cloth, which could be used to create body armor. Professor Windle, one of the researchers involved, says that "our fibre is up there with existing high-performance fibres such as Kevlar". In fact, the fibre has demonstrated many properties that are a significant improvement on those of Kevlar. The researchers say that their fibre is already several times stronger and stiffer than the best modern alternatives. The usefulness of the nanotube fibres lies not just in their strength, but in their ability to absorb and distribute impact. Professor Windle moreover explains that the speed of sound in the material is also important, because this determines the area of the armor that "knows the bullet is there", and the larger this area is the better the material is at absorbing energy from something like a bullet.
Scaling up
The Cambridge researchers have granted a licence to Q-Flo limited, a university spin-off company, to exploit the process. They are also seeking funds to investigate whether the process can be economically scaled up to an industrial scale process. How soon this happens remains to be seen, but the usefulness of this application is a great boost to nanotechnology, and the ingenious new technique the Cambridge researchers have developed is bound to be used elsewhere in the production of nanotubes. The fibre the Cambridge group is producing has also shown promise in other applications.
* A video showing the production of nanotubes and the "smoke sock" can be found at -
http://news.bbc.co.uk/1/hi/sci/tech/7038686.stm
Written by Ben-Griffin Smith
Reviewed by Antje Heidemann
Published by Pooja Ghatalia