An improved process for making large amounts of pure metallic carbon nanotubes could hold the key to overhauling the electrical power grid with more efficient transmission lines.
Researchers at Rice University plan to generate a large quantity of this material by the end of summer. They’ll use these nanotubes to make long and highly conductive fibers that could be woven into more efficient electrical transmission lines.
There are a few different classes of carbon nanotube, each with slightly different properties and different potential uses. Unfortunately, existing production methods result in a mixture of different nanotubes, with varying dimensions and wildly different electrical properties. Purely semiconducting nanotubes, useful for future integrated circuits, are in the mix with metallic nanotubes that could be used to make highly conductive wires. So nanotubes have to be separated by type, a slow and expensive process, says Andrew Barron, professor of chemistry and materials science at Rice.
“There is a subset of nanotubes that are the best conducting materials to be found, that don’t lose any energy to heat,” says Barron.
Barron is part of a group at Rice that wants to make something very large from these nanotubes: miles and miles of highly conductive electrical transmission lines for a more efficient energy grid, which will be important as the use of renewable energy grows. This was one vision of the late Rice professor Richard Smalley, who won the Nobel Prize in Chemistry for his codiscovery of fullerenes, a new type of carbon structure. The Rice researchers have made long, pure carbon nanotube fibers, but since they have been working from impure samples, these fibers are not as conductive as they could be.
Barron and his colleagues have now improved on a method for making pure nanotubes that they first developed in 2006. Called “amplification,” it should eventually allow them to turn a nanogram of pure carbon nanotubes into a gram, then a kilogram, then a ton. They start by separating a small amount of pure metallic nanotubes from a mixture, and then attach a catalyst to the tip of each tube. They then put the nanotubes into a pressurized, temperature-controlled chamber and feed in a mixture of gases. Under these conditions, the nanotubes double in size, growing from the catalyst at the tip. The existing nanotube acts as a template that dictates the diameter, structure, and properties of the extra length of the nanotube. The nanotubes are then cut and the process is repeated.