Lots of researchers are making, by ‘growing,’ carbon nanotubes, so last week when researchers from Rice University and the University of Oulu in Oulu, Finland, announced finding that carbon nanotubes could significantly improve the performance of electrical commutators that are common in electric motors and generators, one gets an attention seizure. The research appeared online this month in the journal Advanced Materials.

Commutators have a stationary contacts known as “brushes” in motors, alternators and generators. They conduct the current into the electromagnets mounted on the rotating shaft. Their ability to energize those rotating magnets has a great deal to do with power output, efficiency and heat generation. For those who know, the announcement that the “brush contact” pads made of carbon nanotubes had 10 times less resistance than did the carbon-copper composite brushes commonly used today (do they mean 10% of the previous material?) is quite significant.

Lead researcher Pulickel Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science 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.”

This is to my recollection the first major probable use of carbon nanotubes making use of the combination of mechanical and electrical properties of nanotubes.

Carbon nanotubes are small, extremely lightweight and durable, and they are excellent conductors of heat and electricity. The carbon nanotubes used in the study are hollow tubes of pure carbon that are about 30 nanometers in diameter, whereas a human hair is about 100,000 nanometers in diameter.

Carbon Nanotube Pad or Brush. Click image for more.

Carbon Nanotube Pad or Brush. Click image for more.

Because of these properties, the researchers decided to test nanotubes as brush contacts. Brush contacts are conducting pads held against a spinning metal disc or rod known as the slip ring(s) or commutator by spring-loaded arms. Current is passed from the spinning disc through the brush contacts to other parts of the device. Other than some bearing friction and air resistance the brush contact is the prime source of internal heat and friction inside many motors, alternators and generators.

Carbon Nanotube Pads On Test. Click image for more.

Carbon Nanotube Pads On Test. Click image for more.

In testing 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. Under an electron microscope, these millimeter-square blocks look like a tightly packed forest.

In Ajayan’s previous work in carbon nanotube properties, 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 who worked on the study with Ajayan and a group of researchers in Finland led by University of Oulu Researcher Krisztian Kordas, 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.”

Here’s the payoff, and if you’ve watched generators spin sparking away electricity at the brush commutator surface you might agree with the research team that ‘believes the improved contact between the surface of the spinning disc and the brush accounts for the 90 percent reduction in lost energy.’ I for one suspect that’s the case.

Slip rings on the other hand haven’t any “breaks” in contacting between the brush and rotating ring so don’t spark much if at all. So these fellows have a product hit by my standards as motor, alternator and generators all can use every bit of efficiency gain possible. Eliminating resistance at the rotating connection should reduce heat generation in the whole rotating assembly, a waste of power and the main cause of wear and failure. I’m quite hopeful that the new carbon nanotube based pads will scale to larger applications and become available (please!) for older applications as replacement parts.

This news, if the engineering to scale works out, will be one of the quiet revolutions that while seemingly small, that have huge worldwide effects.


1 Comment so far

  1. samsung lcd on January 25, 2010 9:09 AM

    You have great blog and this post is good!

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