From: Matthew Brown <[EMAIL PROTECTED]> Date: 12 March, 2004 12:59:52 PM PST Subject: 100m Carbon Nanotube thread created
http://www.newscientist.com/news/news.jsp?id=ns99994769
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.
"This is ground-breaking research - but it's early days" says Harry Swan,
whose company Thomas Swan of Consett, UK, is helping to finance the
development of the new manufacturing technique.
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 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
"elastic smoke".
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 Scientist: "You have this
ball of entangled wool and you put a needle in to pull out the threads".
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 "is really direct - you go straight from synthesis to fibre".
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 "really quite modest". 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. "If they can spin it and get a fibre
that has immense strength, then they've won the battle - but they haven't
done that," 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)
