Carbon Nano Tubes

Carbon Nano tubes, tiny tubelike structures formed from carbon atoms, have shown promise as an alternative to metal used for electrical applications. They’re mechanically strong, yet flexible enough to be knotted or woven together into long lengths of wire. They carry about 100,000 amps of current per square centimeter of material, about the same amount as copper wires, but weigh one-sixth as much. They outperform copper on a metric called current density, which means they should be able to carry more electricity over longer distances without losing energy to heat—a problem with today’s electrical grid, and with computer chips. And because they’re made of carbon, not metal, they don’t corrode.

Making lightweight, efficient carbon nanotube wiring as conductive as copper has been a goal of nanotechnologists since the 1980s. Individual carbon nanotubes—hollow nanoscale tubes of pure carbon—are mechanically strong and an order of magnitude more conductive than copper. But unless carbon nanotubes are put together just so, larger structures made from them don’t have the superlative properties of the individual tubes.

Carbon nanotubes vary in their conductivity, length, and number of layers. The Rice group found that what worked best were relatively long, double-walled nanotubes provided by collaborators from Tsinghua University in Beijing. Electrons move through individual nanotubes very quickly, but current slows down when the electrons must jump from nanotube to nanotube. The longer the nanotubes, the fewer such jumps the electrons have to make in a given length of wire.

How is this done? I  Several different ways depending on the companies. Both companies in the end spool the cable as if you were to make yarn for clothing.

Nanocomp Technologies of Concord, New Hampshire first, it injects a proprietary mixture of iron and alcohol into one end of a large furnace, where heat activates the carbon atoms in the alcohol and binds them to iron. Then, as a cloud of nanotubes floats out of the other end of the furnace, a large spinning spool or drum gathers them. Finally Nanocomp uses machines to spin the tubes into yarn, called C-Tex, or spread them into sheets, called EmShield

The Rice group’s process of making nano cables begins with a lump of double-walled nanotubes that have been treated to remove impurities. The researchers add sulfuric acid to the nanotubes so they can spread them into a thin film. They then grasp the edge of the film with tweezers to start making a fiber, and pull with a steady force to yield a long cable They rinse the acid from the cable and expose it to iodine vapor at high temperatures. The iodine penetrates into the nanotubes within the cable and increases the cable’s conductivity without compromising its mechanical properties.

Both groups claim  that conductivity isn’t affected when the cables are knotted together to make greater lengths.

NASA is currently using Emshield sheets to protect the Juno spacecraft engines from electromagnetic radiation as it travels to Jupiter. By 2012, Nanocomp hopes to begin selling its yarn to airplane manufactures for use in its electrical wiring. I believe it’s only a matter of time before we see it in our new homes and new buildings.

 

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