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September 20, 2011

Thermoelectric materials produced via microwave in minutes instead of days

Rapid Microwave Synthesis of Indium Filled Skutterudites: An energy efficient route to high performance thermoelectric materials

Filled skutterudites are promising thermoelectric materials due to reduced thermal conductivity upon inserting a guest atom or 'rattler' into the CoSb₃ structure. By using an indium rattler dimensionless Figure of Merit (ZT) values over 1 at 650 K have been reported. The conventional synthesis of these compounds typically takes several days (~ 3 days) to obtain the final well-sintered material for property measurements. We report here a microwave-assisted synthesis method that reduces the initial calcination time from two days to two minutes. This route significantly reduces the time needed to produce materials suitable for property and device testing.

Most people are aware you’re not supposed to put metal foil into a microwave, because it will spark. But powdered metals are different, and OSU scientists are tapping into that basic phenomenon to heat materials to 1,800 degrees in just a few minutes – on purpose, and with hugely useful results.



Thermoelectric power generation, researchers say, is a way to produce electricity from waste heat – something as basic as the hot exhaust from an automobile, or the wasted heat given off by a whirring machine. It’s been known of for decades but never really used other than in niche applications, because it’s too inefficient, costly and sometimes the materials needed are toxic. NASA has used some expensive and high-tech thermoelectric generators to produce electricity in outer space.

The problem of wasted energy is huge. A car, for instance, wastes about two-thirds of the energy it produces. Factories, machines and power plants discard enormous amounts of energy.

But the potential is also huge. A hybrid automobile that has both gasoline and electric engines, for instance, would be ideal to take advantage of thermoelectric generation to increase its efficiency. Heat that is now being wasted in the exhaust or vented by the radiator could instead be used to help power the car. Factories could become much more energy efficient, electric utilities could recapture energy from heat that’s now going up a smokestack. Minor applications might even include a wrist watch operated by body heat.

“To address this, we need materials that are low cost, non-toxic and stable, and highly efficient at converting low-grade waste heat into electricity,” Subramanian said. “In material science, that’s almost like being a glass and a metal at the same time. It just isn’t easy. Because of these obstacles almost nothing has been done commercially in large scale thermoelectric power generation.”

Skutterudites have some of the needed properties, researchers say, but historically have been slow and difficult to make. The new findings cut that production time from days to minutes, and should not only speed research on these compounds but ultimately provide a more affordable way to produce them on a mass commercial scale.

OSU researchers have created skutterudites with microwave technology with an indium cobalt antimonite compound, and believe others are possible. They are continuing research, and believe that ultimately a range of different compounds may be needed for different applications of thermoelectric generation.

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