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    Nanotech Goes Big

    Large sheets made from carbon nanotubes could lead to lighter aircraft and more ­resilient space probes.
    December 20, 2011

    At a small factory in Concord, New Hampshire, workers at the startup Nanocomp Technologies are turning carbon nanotubes into paper-thin sheets many meters long. The nanotubes, which are each just a few billionths of a meter wide, are among the strongest and most conductive materials known. For decades researchers have dreamed of using them to make super-efficient electrical transmission lines, suspension bridges that can span several kilometers, and even elevators that convey satellites into space. But while some companies have succeeded in making useful products by mixing nanotubes with resins to create composites, it’s been difficult to make materials with properties that reflect those of the individual nanotubes. By making large sheets composed of nanotubes alone, Nanocomp has taken a big step in that direction.

    The sheets are still not as strong or conductive as individual nanotubes, but they can provide a lighter replacement for copper and other conventional materials in some applications, including protective shielding for coaxial cables. Nanocomp’s first customers are NASA, which has used nanotube sheets to shield a deep-space probe from radiation, and the U.S. military, which could use the sheets to reduce the weight of the electrical cables on unmanned drones by half, increasing flight times.

    Nanotubes are made by feeding alcohol and a catalyst into a furnace at high temperatures and pressures. Nanocomp has fine-tuned the process to produce relatively long nanotubes that emerge from the furnace to form networks that can serve as the basis for sheets. Practical large-scale manufacturing is the critical first step to futuristic applications, says John Dorr, the company’s vice president of business development. That will get nanotube products out of the lab and to the market at competitive prices.

    This mixture of alcohol and an iron catalyst, which makes the solution yellow, is fed into Nanocomp’s furnaces at high temperature and pressure. The action of the catalyst and the extreme conditions inside the furnace cause the carbon atoms in the alcohol to bind together to form long nanotubes.
    Pure nanotubes billow out of the furnace, which is operating in excess of 1,000 ºC. As they emerge, they tangle together, forming networks that will be key to the strength of the finished sheets.
    The tangled nanotubes accumulate on the surface of the spinning roller at the upper right of the picture.
    Nanocomp runs this process continuously for 18 hours to make a two-meter-square sheet of loosely packed nanotubes, shown here.
    A worker sprays the nanotube sheet with strong acid. As the acid dries, capillary forces pull the nanotubes together, compressing the sheet to form a dense, shiny mat of closely connected tubes. The acid treatment makes the sheet stronger and more conductive.
    Before the completed sheets are sent out to Nanocomp’s customers, the company tests their quality. Here a worker places a small piece of a sheet between two clamps, which will pull on it to test its tensile strength. The sheets are almost as strong as steel.
    Workers glue sheets together with an industrial adhesive, then roll them up and ship them to customers. This roll is 61 meters long. The company’s customers use the sheets as a layer in composite materials or to protect signals sent along coaxial cables from electromagnetic interference, among other applications.

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