Mar 302011

Coal waste could provide a strong, lightweight material for car manufacturers

Could coal be the key to manufacturing lighter, more energy-efficient vehicles, including electric cars?

It may seem counterintuitive to use coal to reduce a vehicle’s fuel consumption, and thus its CO2 output. But one scientist at a New York technical school thinks he’s found a way, and hopes to market it to automakers and the growing electric vehicle industry.

Dr. Nikhil Gupta, an instructor at the Polytechnic Institute of New York University in downtown Brooklyn, says the secret lies in the cumbersome and ubiquitous waste product from burning coal — fly ash. Less than half of the fly ash produced from power plants is captured to make a certain type of cement, while the rest ends up in landfills.

Gupta said his team is working on a proprietary technology to use part of that coal fly ash to make a gasoline- or diesel-powered car at least 10 percent lighter. The weight of electric cars can be further reduced by making their batteries 20 to 30 percent lighter, thus extending their range, he said.

“It provides us the possibility of maximum weight reduction without compromising the mechanical properties,” Gupta explained in an interview. “It adds volume but it does not add weight, so that’s the advantage.”

It’s possible because coal fly ash contains fine microscopic structures called cenospheres, basically strong but hollow bubbles that are part of the waste byproduct of burning coal. These cenospheres can be separated from the rest of the material using water, because they float while the rest sinks.

Coating these spheres with nickel, copper or any other composite metal or ceramic material that manufacturers might prefer creates an ultra-strong but lightweight material that can be mixed in with a variety of metals. Gupta and his colleagues estimate that any given piece of metal could contain up to 60 percent fly ash, although that proportion would need to be adjusted depending on how resilient the part needed to be.

A ‘definitely affordable’ source of raw material

Thus, the weight of steel or aluminum could be cut dramatically without compromising the strength of the metal. Though the technology could be used for potentially hundreds of different applications, Gupta at NYU-Poly said heavy vehicle manufacturers and the military seem to be most interested. Research findings from Gupta and colleagues of his at the University of Wisconsin, Milwaukee, on fly ash-composite metal fabrication were published last week in the Journal of Metals.

“If you take a bulk piece of metal and you put some holes inside, just holes, it reduces the mechanical properties quite a bit,” he said. “This porosity is enclosed inside this ceramic particle, and these ceramics are very strong, so when you put them inside metal this porosity is enclosed by the ceramic shell, so that provides lots of strength in the final product.”

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