## Ames Lab team replaces Dysprosium in permanent magnets with Cerium for lower-cost, high performance solution

##### 24 April 2015

Researchers led by a team at the US Department of Energy’s Ames Laboratory have created a new lower-cost magnetic alloy that is an alternative to conventional NdFeB-based permanent magnets. The new alloy—a potential replacement for high-performance permanent magnets found in EV motors and wind turbines—replaces dysprosium (Dy), one of the scarcest and costliest rare earth elements.

The new alloy of neodymium, iron and boron co-doped with cerium and cobalt is a less expensive material with properties that are competitive with traditional sintered magnets containing dysprosium. As reported in a paper in the journal Advanced Materials, the Ce, Co co-doped alloys have excellent high-temperature magnetic properties with an intrinsic coercivity being the highest known for T ≥ 453 K (180 ˚C).

Permanent magnets are critical components for numerous devices ranging from electric motors to miniature speakers to disk drives to traction motors for hybrid vehicles to wind generators. The strongest permanent magnets that exist today are based on Nd2Fe14B, which is a complex metallic system. … Nd2Fe14B has excellent magnetic properties at room temperature, but poor high temperature performance, and the addition of Dy—a highly critical element—is required for above room temperature applications. Rapidly increasing demand for permanent magnets coupled with supply restrictions and the potential for the ever rising costs of critical elements makes a strong economic case for developing competitive magnets that do not rely on critical elements like Dy.

Here we report the results of an experimental study performed on Ce (the most abundant and low cost rare-earth element) based (Nd1-x Cex)2Fe14-yCoyB nanostructured magnets.

—Pathak et al.

Experiments performed at Ames Laboratory by post-doctoral researcher Arjun Pathak, and Mahmud Khan (now at Miami University) demonstrated that the cerium-containing alloy’s intrinsic coercivity—the ability of a magnetic material to resist demagnetization—far exceeds that of dysprosium-containing magnets at high temperatures. The materials are at least 20 to 40% less expensive than the dysprosium-containing magnets.

This is quite exciting result; we found that this material works better than anything out there at temperatures above 150° C. It’s an important consideration for high-temperature applications.

—Karl A. Gschneidner

Previous attempts to use cerium in rare-earth magnets failed because it reduces the Curie temperature—the temperature above which an alloy loses its permanent magnet properties. But the research team discovered that co-doping with cobalt allowed them to substitute cerium for dysprosium without losing desired magnetic properties.

Finding a comparable substitute material is key to reducing manufacturing reliance on dysprosium; the current demand for it far outpaces mining and recycling sources for it.

The research was supported by the U.S. Department of Energy’s ARPA-E REACT program (Advanced Research Projects Agency-Energy–Rare Earth Alternatives in Critical Technologies) which develops cost-effective alternatives to rare earths. (Earlier post.) The REACT projects identify low-cost and abundant replacement materials for rare earths while encouraging existing technologies to use them more efficiently.

Resources

• Pathak, A. K., Khan, M., Gschneidner, K. A., McCallum, R. W., Zhou, L., Sun, K., Dennis, K. W., Zhou, C., Pinkerton, F. E., Kramer, M. J. and Pecharsky, V. K. (2015) “Cerium: An Unlikely Replacement of Dysprosium in High Performance Nd–Fe–B Permanent Magnets” Adv. Mater. 27: 2663–2667 doi: 10.1002/adma.201404892

I am starting to understand why Tesla appears to be one of the few EV OEMs using induction motors with no rare earth elements. The small loss of efficiency is made up for by a more sustainable technology as the market scales.

Both switched reluctance motors and the new ABB synchronous motors can be more efficient and weigh less than even inductance motors. The Tesla ones have copper in the rotor for higher efficiency already. Silver conductor rotors could easily pay for themselves in Tesla automobiles. Die casting of silver should not be much more difficult than the copper now used. Modern locomotives are using a high percentage of induction motors. Tesla could use ABB synchronous reluctance rotor designs in their motors with a slight change in the programming of the electronics probably and get better efficiency. ..HG..

HG, spot price silver $16/oz spot price copper$2.76/lb
says it all, assuming 40oz in an axial rotor.

Even so it was interesting to find out silver has a conductivity / specific density product ratio which is not as favourable as copper due to the overwhelming greater density of silver.

Regarding motor type, Musk has been adamant in favour of asynchronous working from the start. Both types require digital tach feedback for field oriented design but the synchronous motor requires stator sensors which must be accurately phased to the absolute rotor position.

While it is true that asynchronous motor software is a little more difficult and there is the additional requirement for realtime modelling of the rotor temperature since a 100 deg C rise in temperature will increase the rotor resistance by about 30%, the robust nature of the 4-pole induction machine makes it a good choice for automotive powertrains.

I am with Henry on this matter. ABB motors with more sophisticated control would be an excellent choice for automotive industry. I have not seen liquid cooled design yet (of these motors) but when it happens it would produce one of the most power dense machines. Torque ripple can be addressed via smart motor drive system even at low RPM. Permanent magnet machines paved the way but no more required.

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