Ever since scientists first figured out how to make carbon nanotubes—tiny cylinders of carbon with diameters of a few tens of nanometers—they’ve been touted as the material of the future: as strong as steel but far lighter, with the ability to conduct electricity in useful ways. The problem is that because they’re so small, it’s been difficult to make them at scales that would be useful to industry. You can’t really build a lightweight airplane a few microns at a time, after all.
Now a New Hampshire company, Nanocomp Technologies of Concord, says it has overcome that limitation, producing sheets of carbon nanotubes that measure three feet by six feet and promising slabs 100 square feet in area as soon as this summer.
“From the get-go, we wanted to build something that would be manufacturable,” says Peter Antoinette, CEO and co-founder of Nanocomp. “We’re out to make value-added components out of that material.”
The sheets, which the company can produce on its single machine at a rate of one per day, are composed of a series of nanotubes each about a millimeter long, overlapping each other randomly to form a thin mat. The tensile strength of the mat ranges from 200 to 500 megapascals—a measure of how tough it is to break. A sheet of aluminum of equivalent thickness, for comparison, has a strength of 500 megapascals. If Nanocomp takes further steps to align the nanotubes, the strength jumps to 1,200 megapascals.
The trick, says Antoinette, is being able to make the tubes a millimeter long. Many carbon nanotubes, in addition to having vanishingly tiny diameters, are at best a few tens of microns long (a micron is one-thousandth of a millimeter). So most production processes create what is essentially a powder of nanotubes, Antoinette says.
He won’t go into great detail about Nanocomp’s recipe for cooking up the tubes, but essentially the process works by taking a carbon-containing fuel, such as ethanol or methane, heating it up, and flowing it past a catalyst—a nanoparticle that can be made from any number of materials, including oxides of nickel, cobalt, or iron. Heat causes the flowing fuel to react with the catalyst, breaking off the carbon atoms, which build up on the catalyst, atom by atom, into a nanotube. The size of the catalyst determines the diameter of the nanotube.
Antoinette says Nanocomp’s technical achievement was to figure out a way to maintain the catalyst particle at the desired size and hold it stable long enough for the nanotube to grow to millimeter length. A computer controlling about 30 different parameters in the process—including temperature, temperature gradient, gas flow rates, and the chemistry of the mix—allows the builders to control the properties of the tubes. One setting gives them single-walled tubes, and another gives multi-walled versions, with one cylinder inside another, which provide different properties. “We can dial it in,” he says.
So what do you do with the stuff once you’ve made it? Antoinette says the sheets would be particularly good for shielding electronic components from electromagnetic interference. He’s talked to manufacturers of cell phones and PDAs who are looking at the material as something they could use to build handsets that are less vulnerable to the noise from stray transmissions. It might also make a nice housing for a computer, with aligned nanotubes acting as an antenna for wireless connections and randomly oriented nanotubes protecting the computer from electrical surges, while the material also dissipates heat from the processor.
Someday Antoinette would like to see the nanotubes built into composites, similar to the carbon fiber composites being used for next-generation airplanes such as the Boeing 787. But even before that’s done, the current material can solve a problem designers are having with those carbon fiber composites—the fact that