New low-cost cerium alloy magnets developed for motors and turbines

Author：John Hewitt  Published：2015-5-5

Permanent magnets based on neodymium-iron-boron are about the strongest money can buy. The main problem with them is that in order to work above room temperature you need to add significant amounts of the rare element dysprosium. With prices soaring, this situation will likely have to change. Researchers at the Energy Department’s Ames Laboratory have just found that the most abundant rare earth we have, cerium, can substitute for dysprosium when properly co-alloyed with cobalt.

Previously, attempts to use cerium in magnets failed because it actually lowered the Curie temperature. That’s the point above which magnetic properties for the alloy or metal are lost. However, when cobalt is added to the mix, you get an alloy that performs better than anything else above 150° C. Several important variables come into play when spec’ing out a magnet, but its intrinsic coercivity at elevated temperatures is key for many common applications. This is the ability of the material to resist the evil forces of demagnetization.

In addition to the magnet-busting effects of elevated temperature, the forces that degrade motor magnet lifetime and performance include vibration and even radiation. For mining companies that can hardly give cerium away, the robustness of these new cerium alloys to these forces is great news. Compared with the standard dysprosium based magnets now used in many turbine, electric car, and servomotor applications, cerium should chop 20 to 40 percent off the sticker price.

Magnetmotor

That may not sound like a huge deal, but as demand for larger permanent magnet motors increases, manufacturers may be able to meet it using cerium. Some electric vehicles still use induction-style or other motor designs that lack permanent magnets. But above a certain size, manufacturing big magnets gets progressively more uneconomical. On the other hand, winding the coils of all-electromagnetic motors gets easier when everything gets bigger. For applications like 10 degree-of-freedom robotic arms, you are never going to beat the compactness and power density of permanent magnet motors.

It is estimated that the drive motor in a hybrid typically delivers around 80 horsepower per kilogram of neodymium. With more elite applications like all-electric airplanes now looming, motors will likely be pushed to their extreme. The high temperature capabilitiesof cerium magnets would let motors made from them run at correspondingly higher temperatures. That means that the currents pushed through their coils can be higher, longer, and stronger.

In a time when China tightly regulates more than 90 percent of the world’s production of rare earth metals, being a little more strategic with our strategic materials would seem like a wise move. Moving to more abundant cerium would certainly be one way to do this.