TechFront Research and Development in Manufacturing and Technology
New Carbon Nanotubes Outperform Copper as Electrical Conductors
C
arbon nanotube-based fibers created at Rice Univer- sity (Houston) show that on a pound-per-pound basis, the nanotube fibers have more capacity to conduct electrical current than copper. Although individual nanotubes can transmit nearly 1000 times more current than copper, the same tubes coalesced into a fiber using other technologies fail long before reaching that capacity. In Rice’s research, tests show that wet-spun carbon nanotube fibers still easily beat copper, carrying up to four times as much current as a copper wire of the same mass. The research shows that nano- tube cables are ideally suited for lightweight power transmission applications where weight is a factor, particularly for aerospace use.
This analysis led by Rice professors Junichiro Kono and Matteo Pasquali appeared online in the journal Advanced Functional Materials. A year ago, the journal Science reported that Pasquali’s lab, in collaboration with scientists at the Dutch firm Teijin Aramid, created a very strong conductive fiber out of carbon nanotubes.
Current copper or aluminum transmission cables are heavy because their low tensile strength requires steel-core reinforcement. Researchers studying na- noscale materials have thought there may be better ways to move electricity, and certain types of carbon nanotubes can carry far more electricity than cop- per. The ideal cable would be made of long metallic “armchair” nanotubes that would transmit current over great distances with little loss, but such a cable is not feasible because it’s not yet possible to manufacture pure armchairs in bulk, Pasquali said.
Pasquali turned to Kono and his colleagues, including lead author Xuan Wang, a postdoctoral researcher at Rice, to quantify the fiber’s capabilities. Pasquali said there has been a disconnect between electrical engineers who study the current carrying capacity of conductors and materials scientists working on carbon nanotubes. “That has generated some confusion in the literature over the right comparisons to make,” Pasquali said.
Scanning electron microscope image shows typical carbon nanotube fibers created at Rice University and broken into two by high-current-induced Joule heating. Researchers broke the fibers in different conditions—air, argon, nitrogen and a vacuum—to see how well they handled high current.
The Pasquali lab has created a method to spin fiber from a mix of nanotube types that still outperforms copper. The cable developed by Pasquali and Teijin Aramid is strong and flexible even though at 20 microns wide, it’s thinner than a human hair.
The researchers analyzed the fiber’s “current carrying capacity” (CCC), or ampacity, with a custom rig that allowed them to test it alongside metal cables of the same diameter. The cables were tested while they were suspended in the open air, in a vacuum and in nitrogen or argon environments. “The outcome is that these fibers have the highest CCC ever reported for any carbon-based fibers,” Kono said. “Copper still
April 2014 |
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Image courtesy Kono Lab, Rice University
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