From toxic waste to green cars

NYU (US) — Millions of tons of toxic waste could be kept out of landfills by using it to create lightweight composite metal foams for use in automotive and consumer products.

More than 70 million tons of fly ash—a poisonous by-product of coal combustion—are produced by coal power plants in the U.S. every year, and more than half that amount is dumped in landfills.

It contains hollow particles that, when added to a molten metal such as aluminum, create a porous metal foam that is lighter than solid metal yet absorbs a higher amount of energy under compression.

Researchers tested aluminum and magnesium alloys filled with fly ash at high compression rates—similar to those experienced in high-speed auto accidents—and found that the lightweight foams absorb more energy than the solid metals.

The research is reported in the Journal of Metals.

“Composite metal foams made with fly ash could be seamlessly incorporated into vehicle manufacture with no compromise in performance,” says Nikhil Gupta, associate professor of mechanical and aerospace engineering at Polytechnic Institute of New York University.

“As a starting point, these materials are ideal replacements in automotive parts that aren’t load-bearing—for example, engine and wheel covers and intake manifolds, where the weight and strength of solid metal doesn’t provide any benefit—in fact, it just costs more and weighs more.”

Diverting fly ash for use in metal foams will have significant environmental and cost-saving benefits, Gupta says.

Keeping it out of landfills will preserving the $1 billion spent annually to dispose of it and manufacturers will be able to reduce costs by purchasing smaller quantities of expensive metals that take a high environmental toll in mining and production.

Because additions of fly ash make automotive parts lighter in weight, the finished vehicle will require less fuel to operate, leading to further energy and cost-savings for consumers.

Reduction in vehicle weight by 10 percent can lead to an improvement of about 5 percent in fuel economy. With 137 billion gallons of gasoline consumed each year in the U.S., this can translate into more than $22 billion in savings at the current gas prices.

Replacing 10 percent of solid aluminum with fly ash in a manufacturing application would result in approximately 8 percent overall weight-savings.

While fly ash itself is available at no cost, companies would need to bear the cost of transporting the material and preparing it for use.

Composite foams made from fly ash could be widely useful outside the automotive industry in everyday items including highway and runway signs, park benches, lamp posts, sliding tracks for windows and home accessories like doorknobs could all be made lighter and less expensive through the incorporation of metal foams, Gupta says.

Fly ash could be used to create lightweight composites while keeping millions of tons of waste out of landfills. (Credit: NYU)

“Look around you—anywhere you see aluminum or steel, there’s an opportunity for these materials.”

Researchers from the University of Wisconsin-Milwaukee contributed to the study, funded was provided by the U.S. Office of Naval Research and the National Science Foundation.

More news from NYU: