‘Armchair’ nanotubes could improve power grid’s efficiency

US researchers have found a way to produce carbon nanotubes for creating an electrical cable with negligible energy losses over long distances.

The scientists at Rice University, Texas, hope the armchair quantum wire (AQW) — named after the shape of the nanotubes used — could replace the existing copper-based grid in the US, which leaks electricity at an estimated five per cent per 100 miles.

The team, headed by chemist Andrew Barron, developed a way of manufacturing large quantities of the armchair nanotubes, which are good at carrying current but difficult to produce because they grow in batches and have to be individually separated out.

Barron’s lab demonstrated a way to take small batches of individual nanotubes and make them dramatically longer so they can be cut up. The nanotubes can then be re-seeded with a catalyst and re-grown indefinitely.

‘In the first demonstration, we got only one tube to grow out of hundreds or thousands,’ said Barron. The problem was that the catalyst would eat or ‘etch’ the nanotubes. ‘What we’re getting to is that sweet spot where most of the nanotubes grow and none of them etch.’

The key was finding the right balance of temperatures, pressures, reaction times and catalyst ratios to promote growth and retard etching, Barron added.

While initial growth took place at 1,000°C, the researchers found the amplification step required lowering the temperature by 200°C, in addition to adjusting the chemistry to maximise the yield of nanotubes that grow to 90 per cent.

Wade Adams, principal investigator on the AQW project, compared the technique to making sourdough bread. ‘You make a little batch of pure metallics and then amplify that tremendously to make a large amount,’ he said.

‘We know how to spin nanotubes into fibres and their properties are improving rapidly too. All this now has to come together in a grand programme to turn quantum wires into a product that will carry vast amounts of electricity around the world.’