Better Performance at Higher Temperatures with a Rare Earth Blend

Not so very long ago this blog learned more about the use of neodymium magnets in axial flux, permanent magnet, electric motors. In regards to the use of magnetic powders, to improve the efficiency of electric motor production, Iver Anderson, a senior metallurgist at Ames Laboratory and Iowa State University adjunct professor of materials science and engineering, opines:

The most desirable permanent-magnet materials currently are neodymium-iron-boron magnet materials based on a 2-14-1 crystal structure – Nd2Fe14B. Most of those types of magnets tend to lose a lot of their magnetic energy at fairly modest temperatures and are operating at much less than half of their power by the time they reach 100° C to 125° C,.

[Consequently], researchers at Ames Laboratory have designed a new a high-performance permanent magnet (PM) alloy that operates with good magnetic strength at 200° C (392° F) to help make electric drive motors more efficient and cost-effective.

Purdue News Service photo / David Umberger

Jaeseon Lee, at left, a doctoral student in mechanical engineering at Purdue, and Issam Mudawar, a professor of mechanical engineering, test a “micro-channel heat sink”, a device that circulates coolant through numerous channels about three times the width of a human hair.

All electric machines dissipate power in their windings as well as in their magnetic materials. Since as much as half of the power losses occurred in the stator windings, there is considerable emphasis upon advanced technology for cooling motors. Rather than focus upon new approaches to cooling those electric drive motors that are used in power applications, the Ames Lab researchers focused upon improving how the magnetic materials could operate more efficiently.

According to

Green Car Congress1, the goal for the Ames Lab researchers was good magnetic strength at temperatures up to 200° C, while minimizing cooling needs.

They found it necessary to design an alloy to replace pure neodymium. Anderson and his Ames Lab colleagues Bill McCallum and Matthew Kramer chose a mixture of rare earth metals.

We used a combination of neodymium, yttrium and dysprosium because they all form 2-14-1 crystal structures. Together they have much less degradation of their magnetic properties with temperature due to the influence of the yttrium and dysprosium. Our concept, put forth in our patent application, is that the mixed rare earth 2-14-1 phase would have a lower temperature coefficient.

The DOE’s Energy Efficiency and Renewable Energy Office, Vehicle Technologies Program, Power Electronics and Electrical Machines (PEEM) Program funds the research. Ames Laboratory is operated for the Department of Energy by Iowa State University.

GCC had previously reported on next-generation SiC (Silicon carbide) crystal growth techniques based on Norstel’s High Temperature Chemical Vapor Deposition (HTCVD) method to optimize crystal growth quality. It would seem that the Ames researchers are familiar with such improvements in manufacturing processes, i.e., an atomization process, whereby kinetic energy from supersonic jets of gas cause a stream of liquid metal to break up into droplets. They were able to achieve a fine, spherical powder, and subsequently decided to switch from helium to argon gas since it made the powder-making process a lot cheaper.

In comparing the new powders to spherical commercial powders of larger size, Anderson and his colleagues look at the “crossover in temperature” at which the properties of their magnet powders become better than the commercial powders for higher temperature uses. The crossover temperature initially was 175° C, but is now approximately 75° C.

GCC Suggested Resources

Power Electronics and Electric Machines FY 2006 Progress Report, Development of Improved Powder for Bonded Permanent Magnets (pp 249-263)

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1Ames Lab Researchers Design New Permanent Magnet Alloy for More Efficient and Cost-Effective Electric Drive Motors

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