New Alloy Can Convert Heat Directly Into Electricity

[T]he new alloy — Ni45Co5Mn40Sn10 — undergoes a reversible phase transformation, in which one type of solid turns into another type of solid when the temperature changes, according to a news release from the University of Minnesota. Specifically, the alloy goes from being non-magnetic to highly magnetized. The temperature only needs to be raised a small amount for this to happen.

But if it’s a phase transformation, it should be happening at a specific temperature. Once the material has heated up and you get your magnetic field, what then? The article and press release on which it was based don’t go into that.

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.

Faraday’s law tells us this should happen upon the creation of the magnetic field, but once it has happened — nada. You would need to cycle between states to maintain a changing field needed to continually produce electricity, so after heating you would need to then cool the substance.

The paper confirms this requirement

The design of the coil is to give a maximal component of E parallel to the wire, thereby driving a current. A potential difference across the coil of opposite polarity is obtained on the reverse phase transformation upon cooling.

So here “directly” doesn’t mean “directly” in the sense that you slap it on a car engine and produce electricity. You need a temperature gradient, just like always, and in this case, you need to bracket a specific temperature. Promising, but these headlines always seem to outnumber new products by a fair margin.