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January 23, 2006
Volume 84, Number 4
p. 10

Nanomaterials

Making Nanotubes SuperStretchy

Rigid carbon structures become superplastic at high temperatures

Bethany Halford

Courtesy of Jianyu Huang

NanoTaffy Under a 2.3-V bias, a single-walled carbon nanotube becomes superplastic, stretching so that its diameter shrinks from 12 nm (right) to less than 1 nm (left).

More than 20 years after their discovery, single-walled carbon nanotubes (SWNTs) continue to surprise scientists with their remarkable properties. According to a new report, the tubes become unusually ductile at high temperatures, stretching to more than three times their original length and narrowing in diameter by a factor of 15 before breaking (Nature 2006, 439, 281).

Thanks to a strong structural network of carbon-carbon bonds, SWNTs are remarkably strong and rigid at room temperature. Theoretically, they should be able to stretch about 20% at normal temperatures, but experimentalists have been able to elongate the tiny tubes only 6% beyond their original length.

Boston College physics professors Jianyu Huang and Zhifeng Ren, graduate student Shuo Chen, and coworkers were therefore astonished to discover that a SWNT could be elongated to more than triple its original length when they ran a high current through it. One nanotube, for example, stretched from 24 nm to 91 nm while its diameter decreased from 12 nm to 0.8 nm.

"We think this elongated nanotube is highly disordered," Huang explains, adding that the stretching probably destroys the structure's characteristic honeycomb network of six-membered rings. "We think that the carbon atoms are very active at high temperature. Elongation creates defects, and the carbon atoms rearrange to heal those defects."

The researchers attribute the nanotube's newfound superplasticity to the elevated temperatures-roughly 2,000 oC-that the SWNT reaches when it's electrified. Because SWNTs become more ductile at extreme temperatures, Huang thinks they may be useful as reinforcing materials in ceramics and nanocomposites used in high-temperature applications.

Huang says this discovery has led his group to delve further into the properties of SWNTs at elevated temperatures. "The high-temperature properties of carbon nanotubes are a completely unexplored area," he says.

Chemical & Engineering News
ISSN 0009-2347
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