June 23, 2011 AT 11:35 am

New Alloy Converts Heat Directly into Electricity

Yes, this video is really short, but it’s stunning once you know what’s actually going on:

In the lab, University of Minnesota researchers show how a new multiferroic material they created begins as a non-magnetic material then suddenly becomes strongly magnetic as the piece of copper below is heated a small amount. When this happens, it jumps over to a permanent magnet. This demonstration represents the direct conversion of heat to kinetic energy.

more from ScienceDaily:

Researchers say the material could potentially be used to capture waste heat from a car’s exhaust that would heat the material and produce electricity for charging the battery in a hybrid car. Other possible future uses include capturing rejected heat from industrial and power plants or temperature differences in the ocean to create electricity. The research team is looking into possible commercialization of the technology.

To create the material, the research team combined elements at the atomic level to create a new multiferroic alloy, Ni45Co5Mn40Sn10. Multiferroic materials combine unusual elastic, magnetic and electric properties. The alloy Ni45Co5Mn40Sn10 achieves multiferroism by undergoing a highly reversible phase transformation where one solid turns into another solid. During this phase transformation the alloy undergoes changes in its magnetic properties that are exploited in the energy conversion device.

During a small-scale demonstration in a University of Minnesota lab, the new material created by the researchers begins as a non-magnetic material, then suddenly becomes strongly magnetic when the temperature is raised a small amount. When this happens, the material absorbs heat and spontaneously produces electricity in a surrounding coil. Some of this heat energy is lost in a process called hysteresis. A critical discovery of the team is a systematic way to minimize hysteresis in phase transformations. The team’s research was recently published in the first issue of the new scientific journal Advanced Energy Materials.

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5 Comments

  1. So, how close is the efficiency to the Carnot cycle?

  2. The paper is freely available. The section with efficiency calculations you’re looking for is directly linked here:

    http://onlinelibrary.wiley.com/doi/10.1002/aenm.201000048/full#sec1-5

    The noogie? 0.004%.

  3. wow, pretty cool,…potentially endless possibilities

    nobel prize? lol

  4. So cool! I’ve downloaded the paper, and will read it, but don’t know if I will understand it, not being an engineer. But I have a couple of questions.
    Why are they only proposing limited applications, like car exhaust and power plants? Is there a severe limitation? For example, does it only generate the magnetic field at the transition temp, but not constantly thereafter? Or is it prohibitively expensive to make? Otherwise it seems like this would have far reaching applications. Couldn’t you generate electricity from this by just focusing ambient heat on it, like sunlight? Seems like a fun way for a hobbyist to create a backyard generator w/ a magnifying glass and this metal. People like me who live in hot states like Texas would love to take this heat and turn it into something useful! Or am I missing something and reaching too far?

  5. Kelvin Nishikawa

    @cynichael: The material creates a strong magnetic field once it is heated past the transition temperature. A static magnetic field in and of itself is not enough to generate electricity. You have to vary the field near a coil to generate the electric current (induction).

    To generate electricity with this material, you need to heat it to almost exactly the phase transition temperature (slightly above). The material will then phase-change and create a magnetic field (inducing electricity in the coil), then through hysteresis (and perhaps active cooling) it will lose heat and transition back to its non-magnetic state. With another fixed magnet you can ensure that the field reverses when the material goes non-magnetic. Heat and repeat and you’ve got yourself an alternating current (AC).

    The reason this has limited application (automobile I.C.E.s and such) is that you need to keep the heat very near to the transition temperature if you want to generate electricity. For this material it’s something like 150C, which is conveniently close to the temperatures found in a I.C.E. system. (i.e. Your body heat isn’t high enough to make the system work)

    The main benefit of this new technology is that you can generate a reasonable amount of electricity with a very small temperature differential; you’re not limited by carnot cycle efficiencies like a sterling engine.

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