Terra Magnetica

Recently I came across a May 2009 presentation published by the US Department of Energy’s [DoE] Ames Lab, on a new mixed rare earth-based [MRE-Fe-B] permanent magnet [PM] alloy, for high temperature applications.

The work forms part of the DoE’s multi-year FreedomCAR project, with a number of specific goals:

• Production of magnet materials for PM motors, capable of operating at 150-200 °C [300-390 °F]  and for up to 15 years;
• Increasing the specific power of PM motors to over 1.2 kW / kg, leading to a reduced cost of less than $12 / kW, through increases in the PM energy density;
• Production of interior permanent magnet [IPM] motor type designs, to obtain efficiencies greater than 93%.

The material is based on a (Nd_0.45(Y_xDy_y)_0.55)₂Fe₁₄B composition.

The project partners include Ames Lab, Oak Ridge National Lab, Arnold Magnetic Technologies, Magnequench, General Motors and industry consultant Dr. Peter Campbell.

The team worked to develop fully sintered anisotropic permanent magnets from this material family. They also worked on powders with special nanocrystalline microstructures, for use in blending with polymers in order to produce isotropic bonded magnets. such bonded magnets lend themselves very well to use in PM motor.

In addition, and of most interest to me, was their work to substitute dysprosium [Dy] with more readily-available yttrium [Y], and by minimizing cobalt [Co] content. In addition to potentially bringing the cost of high temperature magnets down, successful use of Y as a substitute for the rarer, and more difficult to procure Dy, would mean that the implementation of electrical machines using neodymium-based magnets becomes that much easier – and a little less prone to the geo-political fun and games inherent in the rare earth elements business.

Figure 1 shows a set of hysteresis loops for one version of the material composition. While the current maximum energy density of 25 MGOe [200 kJ/m³] is a long way from currently available commercial high temperature grades, it does show considerable promise and no doubt the team will be working on improving the magnetic properties through a variety of means.

Future work on this project includes the inclusion of aluminum powder as a sintering aid, the production of MRE-Fe-B materials via melt spinning, and various methods of coating individual flakes and particles in order to magnetically isolate the grains.

The presentation can be downloaded here.