The United States' copper-based electric grid is estimated to leak electricity at an estimated five percent per 100 miles (161 km) of transmission. With power plants usually located far from where the electricity they produce will actually be consumed, this can add up to a lot of wasted power. A weave of metallic nanotubes known as armchair quantum wire (AQW) is seen as an ideal solution as it can carry electricity over long distances with negligible loss, but manufacturing the massive amounts of metallic single walled carbon nanotubes required for the development of this "miracle cable" has proven difficult. Now researchers have made a pivotal breakthrough that could make the development of such a cable possible.
Armchair quantum wire gets its name from the metallic single-walled carbon nanotubes (SWCN) of which it is made. These SWCNs are dubbed armchairs due to their unique shape, and while they are great at carrying current, they can't yet be made on their own. They are currently grown in batches with other kinds of nanotubes and have to be separated out - not an easy task given that a human hair is 50,000 times larger than a single nanotube.
Rice University chemist Andrew R. Barron, graduate student Alvin Orbaek and undergraduate student Andrew Owens, are carrying on work instigated by the late Rice professor, nanotechnology pioneer and Nobel laureate Richard Smalley, whose dream was of an energy efficient grid that he predicted would provide solutions to many of the world's energy problems.
Working towards this ultimate goal, the team has found a way to take small batches of individual nanotubes and make them dramatically longer. They say that ideally, long armchair nanotubes could be cut, re-seeded with catalyst and re-grown indefinitely, potentially making the development of a cable that will make an efficient electric grid of the future possible.
The technique involves chemically attaching an iron/cobalt catalyst to the ends of nanotubes and then fine-tuning the temperature and environment in which amplification could occur. Barron says refining the process has taken years but the researchers' efforts are now paying off with up to 90 percent of the nanotubes in a batch now able to be amplified to significant lengths. They say that, although the latest experiments focused on SWCNs of various chiralities (ie. they lack an internal plane of symmetry), they feel the results would be as great, and probably even better, with a batch of pristine armchairs.
According to Barron, the key was finding the right balance of temperatures, pressures, reaction times and catalyst ratios to promote growth and retard etching. While initial growth took place at 1,000 degrees Celsius, the researchers found the amplification step required lowering the temperature by 200 degrees, in addition to adjusting the chemistry to maximize the yield. Barron and his team are continuing to fine-tune their process and hope that by summer's end they can begin amplifying armchair nanotubes with the goal of making large quantities of pure metallics.
"What we're getting to is that sweet spot where most of the nanotubes grow and none of them etch," Barron said.
Orbaek hopes the team's breakthrough will eventually lead to a single furnace to grow nanotubes from scratch, cap them with new catalyst, amplify them and put out a steady stream of fiber for cables.
"What we've done is a baby step," he said. "But it verifies that, in the big picture, armchair quantum wire is technically feasible."