Friday, September 09, 2011

Carbon nanotubes handle line voltages in key step to reality



By Nick Flaherty www.flaherty.co.uk

Carbon nanotubes have been are inching toward electrical conductivities seen in metal wires in the labs, but researchers have now been able to use them at line voltages, lighting up interest among a range of industries.
Researchers at Rice University in the US made such a cable from double-walled carbon nanotubes and powered a fluorescent light bulb at standard line voltage.
Highly conductive nanotube-based cables could be just as efficient as traditional metals at a sixth of the weight, said Enrique Barrera, a Rice professor of mechanical engineering and materials science. They may find wide use first in applications where weight is a critical factor, such as aircraft and cars and in the future could even replace traditional wiring in homes.

The cables developed in the study are spun from pristine nanotubes and can be tied together without losing their conductivity. To increase conductivity of the cables, the team doped them with iodine and the cables remained stable. The conductivity-to-weight ratio (called specific conductivity) beats metals, including copper and silver, and is second only to the metal with highest specific conductivity, sodium.
Yao Zhao built the demo rig that let him toggle power through the nanocable and replace conventional copper wire in the light-bulb circuit. He left the bulb burning for days on end, with no sign of degradation in the nanotube cable. He's also reasonably sure the cable is mechanically robust; tests showed the nanocable to be just as strong and tough as metals it would replace, and it worked in a wide range of temperatures. Zhao also found that tying two pieces of the cable together did not hinder their ability to conduct electricity.
The few centimeters of cable demonstrated in the present study seems short, but spinning billions of nanotubes (supplied by research partner Tsinghua University) into a cable at all is quite a feat, Barrera said. The chemical processes used to grow and then align nanotubes will ultimately be part of a larger process that begins with raw materials and ends with a steady stream of nanocable, he said. The next stage would be to make longer, thicker cables that carry higher current while keeping the wire lightweight. "We really want to go better than what copper or other metals can offer overall," he said.
Carbon nanotubes can now make cables one sixth the weight of metal

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