Turning Toxic Fly Ash into Automotive Metal Foams

25 March 2011 Experiments into recycling toxic 'fly ash' as an additive to create lightweight composite metal foams for use in the automotive industry have been taking place at the Polytechnic Institute of New York University (NYU-Poly). Researchers at the university claim to have demonstrated the potential to keep millions of tons of toxic waste out of landfills, while simultaneously improving the performance and lowering the cost of some of expensive raw materials such as aluminium and magnesium. Nikhil Gupta, associate professor of mechanical and aerospace engineering at NYU-Poly's Composites Materials and Mechanics Laboratory, and collaborators from the University of Wisconsin-Milwaukee published their findings in a recent issue of Journal of Metals (JOM), a publication of The Minerals, Metals & Materials Society. More than 70 million tons (63.5 million tonnes) of fly ash is produced by coal power plants every year in the United States alone, and more than half that amount is dumped in landfills. Fly ash contains hollow particles, that when added to a molten metal such as aluminium, create a porous metal foam that is lighter than solid metal yet absorbs a higher amount of energy under compression. The researchers says they tested aluminium and magnesium alloys filled with fly ash at high compression rates - similar to those experience in a high-speed car crash - and found that the lightweight foams absorb more energy than the solid metals. "Composite metal foams made with fly ash could be seamlessly incorporated into vehicle manufacture with no compromise in performance," said Gupta. "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," he added. The researchers say that diverting fly ash for use in metal foams has significant environmental and cost-saving benefits. First, it keeps toxic ash out of landfills and preserves the $1 billion spent annually disposing of this waste. Second, manufacturers can reduce their costs by purchasing smaller quantities of expensive metals that take a high environmental toll in mining and production. Lastly, because additions of fly ash make automotive parts lighter in weight, the finished vehicle requires less fuel to operate, leading to further energy and cost-savings for consumers. According to Gupta, a reduction in vehicle weight by 10% can lead to an improvement of about 5% in fuel economy. With 137 billion gallons of gasoline consumed each year in the United States, this can translate into more than $22 billion in savings at the current gas prices. The JOM reports estimate that replacing 10% of solid aluminum with fly ash in a manufacturing application would result in an approximate 8% 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. In addition to the potential automotive uses, Gupta claims that everyday items such as 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. "Look around you - anywhere you see aluminum or steel, there's an opportunity for these materials." Gupta concluded. Research funding was provided by the U.S. Office of Naval Research and the National Science Foundation.