A thread of carbon nanotubes more than 100 metres long has been pulled from a fiery furnace. The previous record holder was a mere 30 centimetres long.
Carbon nanotubes are stronger than steel and better conductors than copper, but are often just a thousandth of a millimetre in length. By bundling the nanotubes together into much longer fibres, scientists hope to harness their properties on a larger scale. For example, embedding long carbon nanotube threads in plastic would give tougher composites for airplane hulls.
鈥淭his is ground-breaking research 鈥� but it鈥檚 early days鈥� says Harry Swan, whose company Thomas Swan of Consett, UK, is helping to finance the development of the new manufacturing technique.
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At present the ability to make the long nanotube fibres is confined to a laboratory at the University of Cambridge, where it the technology was invented by the research team of Alan Windle.
Gas stream
The carbon nanotubes are made by injecting ethanol into a fast-flowing stream of hydrogen gas. The gas carries the carbon-containing molecules into the centre of a furnace where temperatures soar above 1000 掳C.
The high temperature breaks the ethanol down and the carbon atoms reassemble into nanotubes, each about a micron in length. These float in the stream of hydrogen, loosely linked to each other in what Windle describes as an 鈥渆lastic smoke鈥�.
When a rod is poked into this amorphous cloud, it catches a few nanotubes. Rotating the rod pulls on these, which in turn pull on their neighbours, dragging out a continuous thread of closely-aligned nanotubes. This wraps around the rod at a rate of centimetres per second.
It is similar to spinning wool, Windle told New 杏吧原创: 鈥淵ou have this ball of entangled wool and you put a needle in to pull out the threads鈥�.
Scraped up
The 30-centimetre thread was made by scraping up nanotubes after they had been grown on the surface of a silicon wafer. In contrast, says Windle, the new process 鈥渋s really direct 鈥� you go straight from synthesis to fibre鈥�. This should not only make the fibres longer, but also cheaper.
However Windle admits that the properties of the threads they have made so far are 鈥渞eally quite modest鈥�. Their conductivity is only one per cent that of copper and it is no stronger than a conventional polyester thread.
That leads some to criticise the work. 鈥淚f they can spin it and get a fibre that has immense strength, then they鈥檝e won the battle 鈥� but they haven鈥檛 done that,鈥� says Malcolm Green, an expert on carbon nanotubes at the University of Oxford.
But Windle reckons that fine-tuning the manufacturing process to make the nanotubes pack more closely in the fibre will make the thread stronger. They are also trying to twist the individual threads together into a tougher rope.
Journal reference: Science (DOI:10.1126/science.1094982)