Latest nano role: Brush contacts

New research from Rice and the University of Oulu in Oulu, Finland, finds that carbon nanotubes could significantly improve the performance of electrical commutators that are common in electric motors and generators.

Rice researchers found that “brush contact” pads made of carbon nanotubes outperformed the carbon-copper composite brushes commonly used today.

The research appeared online March 6 in the journal Advanced Materials. The researchers found that “brush contact” pads made of carbon nanotubes had 10 times less resistance than carbon-copper composite brushes. Brush contacts are an integral part of “commutators,” or spinning electrical switches, used in such battery-powered devices as cordless drills.

“The findings show that nanotubes have a great deal of practical relevance as brush contacts,” said lead researcher Pulickel Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science. “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 nanotubes used in the study are hollow tubes of pure carbon about 30 nanometers in diameter. A human hair is about 100,000 nanometers in diameter. In addition to being small, nanotubes are extremely lightweight and durable, and are excellent conductors of heat and electricity.

Because of these properties, the researchers decided to test nanotubes as brush contacts, which 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.

To test the feasibility of using 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. Under an electron microscope, these millimeter-square blocks resemble tightly packed forests.

From Ajayan’s previous work, the team knew the nanotube forests react like a “memory foam” pillow; they regain shape quickly after being compressed.

“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,” said Robert Vajtai, faculty fellow at Rice. Vajtai worked on the study with Ajayan and a group of researchers in Finland led by University of Oulu Researcher Krisztian Kordas.

Jade Boyd, Rice News