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April 26, 2010

Macroscale Carbon Nanotube Fibers

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In a Rice University lab, a black fiber the diameter of a human hair spools into a beaker of ether. Made up of pure nano­tubes, the strand is the culmination of nearly a decade of experimentation. Chemical engineer Matteo Pasquali and his colleagues have spun nanotubes into fibers several hundred meters long"

Update - the carbon nanotube fibers they are producing are weak and held together with friction. They are not chemically bonded rope (the individual pieces are but the whole is not). They are pieces that they mix together in super acid and extrude. They want to have more surface area and longer pieces. So it becomes like longer pieces of spaghetti that are boiled in a swimming pool or pond until mushy and formed into long pipes meters across. They just are targetting making the extruded carbon nanotube tangle strong enough to make electrical cable with better properties than copper. They are not there yet. I think nanocomp technologies is farther ahead in forming conducting macroscopic pieces of carbon nanotube rope and tapes. They use a process which looks like a cotton candy machine. This site has covered the nanocomp technologies before.
The fibers can currently withstand about 350 megapascals of pressure before failing--slightly less than a human hair, which is considered fairly strong for its diameter.

The fibers' strength depends on the friction generated where nanotube surfaces interact. Longer nanotubes generate more friction and, thus, stronger fibers. The Rice nanotubes--which Pasquali is using for the sake of convenience--are relatively short. But he's exploring partnerships with fiber-spinning companies and carbon-nanotube manufacturers who can provide additional spinning expertise and longer nanotubes. Pasquali hopes to ultimately increase the fibers' tensile strength more than tenfold.

There is still one major obstacle to realizing Smalley's dream of using nanotubes to remake the electrical grid. Pasquali's fibers have an electrical resistance of 120 microöhms per centimeter, about eight times greater than that of copper wires.

The Rice group plans to make fibers from conducting nano­tubes separated from the nonconducting tubes to determine whether such conductivities are possible. But today's sorting process makes the nanotubes too expensive for use in electrical transmission.

Pasquali remains optimistic, however, that this second challenge will be overcome, just as he solved the problem of spinning nanotubes into long fibers. And he's sure that when it is, strong, lightweight nano­tube wires can at last replace the heavy and in­efficient steel-reinforced aluminum cables used in today's power grid


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