Commutating nanotubes

Researchers at Rice University and the University of Oulu in Oulu, Finland, have discovered that carbon nanotubes could improve the performance of electrical commutators that are common in electric motors and generators.

The research, which appeared online in the journal Advanced Materials, found that brush contacts made of carbon nanotubes had 10 times less resistance than the carbon-copper composite brushes commonly used today.

Brush contacts are conducting pads held against a spinning metal disc or rod by spring-loaded arms. Current is passed from the spinning disc through the brush contacts to other parts of the device. They are an integral part of commutators used in many battery-powered electrical devices, such as cordless drills.

Rice's Prof Pulickel Ajayan, said: 'The findings show that nanotubes have a great deal of practical relevance as brush contacts.

'The technology is widely used in industry, both in consumer gadgets as well as larger electrical machinery, so this could be a very interesting, near-term application for nanotubes.'

The carbon nanotubes used in the study are hollow tubes of pure carbon about 30 nanometres in diameter.

To test the feasibility of using carbon nanotube brush contacts, the research team replaced the ordinary copper-carbon composite brushes of an electric motor with small blocks that contain millions of carbon nanotubes.

From Ajayan's previous work, the team knew that these nanotube forests react something like a 'memory foam' pillow; they regain their shape very quickly after they are compressed.

Robert Vajtai, faculty fellow at Rice, said: 'This elasticity is something that's not found in existing composites that are used for brush contacts, and that's the essence of why the nanotube brush contacts perform better: they keep much more of their surface area in contact with the spinning disc.'

Vajtai worked on the study with Ajayan and a group of researchers in Finland led by University of Oulu researcher Krisztian Kordas.

The team believes that the improved contact between the surface of the spinning disc and the brush accounts for the 90 per cent reduction in lost energy.