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Steel
Monday | 26 August, 2013 | 1:38 pm

Pursuing metal purity

By Gretchen Salois

One MIT professor is spearheading efforts to make carbon emission-free metals

August 2013 - As recently as the 1980s and early 1990s, being eco-friendly and environmentally conscious wasn’t as mainstream as it is today. Professor Donald Sadoway at MIT experienced this sentiment first-hand when he tried to acquire funding for his research into how to create aluminum and steel with few carbon emissions. “Environmentalism wasn’t fashionable,” he says. “But I started thinking about new chemistries for the production of metals and just got drawn into the pursuit of reducing the carbon footprint of conventional steel and other metal making.”

Upon arriving at MIT in 1978, Sadoway first looked into how aluminum is made and along the way, became interested in reducing the carbon footprint in aluminum smelting. Then he started thinking about the electrolysis of the cell itself. This segued into looking at steel. “The carbon footprint of conventional steel making is so heavy, steel has overtaken cement in terms of CO2 emissions,” Sadoway says. “At that time, people thought I was crazy since carbon is so abundant and cheap while electricity is precious and expensive.”

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His persistence prevailed, and recently Sadoway uncovered an affordable way to create an oxygen evolving anode to work in concert with the production of liquid iron at the cathode. The new anode material was inspired by the properties of aluminum, which forms a thin surface film of aluminum oxide. “Aluminum is very reactive but it forms a very thin skin of aluminum oxide. At 4 nanometers thick, it self-limits—if you take a nail and scratch a piece of aluminum, as fast as that aluminum is exposed, it reacts to oxygen and self-seals again,” he explains. “It’s self-repairing and so thin that you don’t get any resistance, but it does protect the aluminum from catastrophic oxidation.” 

He then looked into the properties of the molten oxide electrolyte to produce iron and conceived a material that would allow the sustainable production of oxygen. “We came across an alloy of chromium and iron that works,” he explains. “We feed in iron oxide and by the passage of electric current we make liquid iron and oxygen gas, so now you have two products and for every a ton of iron you make 2/3 ton of oxygen. That’s two product streams coming out of that cell. You don’t make CO2 as is the case with conventional blast furnace technology. Instead, that noxious oxide is turned into a valuable product.”

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Sensible viability

Funding his environmentally friendly metal-making process was proving to be problematic, but Sadoway managed to get NASA interested in his idea. NASA was in the process of going to the moon, and transporting water and oxygen was an expensive component to a space mission. Sadoway was charged with trying to figure out a way to make oxygen from “moon rocks.” “Bringing water and oxygen to the moon from earth is very expensive. NASA wanted to be able to take soil from the moon and create oxygen while in space,” Sadoway says. 

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NASA provided Sadoway with a sample from a meteor crater in Arizona. The material is similar to the soil found on the moon. He successfully produced oxygen with liquid iron and silicon as byproducts. Subsequently, he received funding from the American Iron and Steel Institute with matching funds from the U.S. Department of Energy. However, once the recession hit in 2008, funding fizzled and Sadoway’s research slowed.

He continued pursuing interest in his efforts. Sadoway kept in mind that steel is a mass-produced commodity,  and realized he could create purer, albeit smaller, amounts of steel for high-technology applications. “This high-quality steel is not something for use in reenforcing bar or plain base plate that is used on roads. With high-purity nickel and ferrochromium, I imagined producing high-quality stainless steel,” he says. 

Moving from the lab to real-world applications often is a big hurdle because of the difficulty finding funding after a recession and producing the material in an economical manner. Sadoway’s recently formed Boston Electrometallurgical Corp., located outside of Boston, currently is working on the design and construction of an industrial prototype cell that Sadoway believes will be ready in two years.

Going forward, Sadoway imagines interest will come from companies in need of certain types of high-purity stainless steel or some iron alloy. Instead of relying on big producers, it might be feasible to integrate upward and become producers of the metal they need. “Imagine someone who makes aluminum beverage containers decides they don’t want to be at the mercy of the open market, so they decide to build their own smelter,” Sadoway says. “Or a supplier who would rather produce high-quality ferroalloys from ore at 100,000 tons a year instead of mass-production amounts of two million tons per year.”

He knows his efforts will only be successful if they are economically practical. “No one will pay us out of charity, even if it is created in a green manner,” he says. “It has to be better than the other guy’s or you’re not going to win that business.” 

The key is finding harmony between the chemistry of turning ore into metal and the design of alloys. “[It’s about] finding the relationship between alloy design and the performance of the material,” he says. “Whether for higher strength, toughness or corrosion resistance, or some combination of various properties.

“People are constantly trying to invent superior metals that will give us more performance with less mass,” he continues. “Look at lightweighting efforts for cars—you can’t just replace all the steel with aluminum, that’s way too pricey. With steel, the energy needed to make one unit of steel using electrolysis versus the furnace must be approached by looking at cost and metal performance, which starts to look really tempting.” MM

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