Pound for pound, wet-spun carbon nanotube-based fibers have greater capacity to carry electrical current than copper cables of the same mass, according to new research.
While individual nanotubes are capable of transmitting nearly 1,000 times more current than copper, the same tubes coalesced into a fiber using other technologies fail long before reaching that capacity.
But a series of tests shows the wet-spun carbon nanotube fiber still handily beat copper, carrying up to four times as much current as a copper wire of the same mass.
That, say the researchers, makes nanotube-based cables an ideal platform for lightweight power transmission in systems where weight is a significant factor, like aerospace applications.
The analysis led by Rice University professors Junichiro Kono and Matteo Pasquali appeared online in the journal Advanced Functional Materials.
Just 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.
Present-day transmission cables made of copper or aluminum are heavy because their low tensile strength requires steel-core reinforcement.
Scientists working with nanoscale materials have long thought there’s a better way to move electricity from here to there. Certain types of carbon nanotubes can carry far more electricity than copper. The ideal cable would be made of long metallic “armchair” nanotubes that would transmit current over great distances with negligible loss, but such a cable is not feasible because it’s not yet possible to manufacture pure armchairs in bulk, says Pasquali, professor of chemical and biomolecular engineering, chemistry, and materials science and nanoengineering.
In the meantime, 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.
Running the tests
Pasquali turned to Kono and his colleagues, including lead author Xuan Wang, a postdoctoral researcher at Rice, to quantify the fiber’s capabilities.
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.
Electric cables heat up because of resistance. When the current load exceeds the cable’s safe capacity, they get too hot and break. The researchers found nanotube fibers exposed to nitrogen performed best, followed by argon and open air, all of which were able to cool through convection. The same nanotube fibers in a vacuum could only cool by radiation and had the lowest CCC.
“The outcome is that these fibers have the highest CCC ever reported for any carbon-based fibers,” says Kono, professor of electrical and computer engineering, of physics and astronomy, and of materials science and nanoengineering.
“Copper still has better resistivity by an order of magnitude, but we have the advantage that carbon fiber is light. So if you divide the CCC by the mass, we win.”
Kono plans to further investigate and explore the fiber’s multifunctional aspects, including flexible optoelectronic device applications.
Pasquali suggests the thread-like fibers are light enough to deliver power to aerial vehicles. “Suppose you want to power an unmanned aerial vehicle from the ground,” he muses. “You could make it like a kite, with power supplied by our fibers. I wish Ben Franklin were here to see that!”
The Department of Energy, the National Science Foundation, the Robert A. Welch Foundation, Teijin Aramid BV, the Air Force Office of Scientific Research, and the Department of Defense National Defense Science and Engineering Graduate Fellowship supported the research.
Source: Rice University