Replacing Critical Rare Earth Materials in High Energy Density Magnets
Not a "rare-earth free" magnet but a "free" (relatively $ wise) rare-earth magnet.
This project will develop Cerium transition-metal (Ce–TM) based permanent magnets for vehicle and wind energy applications. The abundance of Ce (~50% of the rare-earth (RE) content of Molycorp Bastnasite concentrate) is three times that of Nd and Pr combined. Due to an excess of Ce on the market, the development of a Ce–TM permanent magnet would facilitate an increase of the supply of high-energy rare-earth magnets by a factor of 2 to 3 without requiring additional mining or an increase in the amount of separated RE produced. The feature that sets RE elements apart from other elements is the fact that the 4f electron shell is being filled in the series from 1 electron in Ce to 2 in Pr, and so on to 14 for Lu, the last rare earth element. This electron shell has unique magnetic and optical properties. The RE in a permanent magnet plays a key role due to its 4f electrons; unfortunately, in many intermetallic compounds with Fe and Co, Ce atoms lose their local magnetic properties, significantly decreasing the magnetic ordering (Curie) temperature and the saturation magnetization i.e. the strength of the magnet. This project will avoid such effects by controlling the intrinsic ferromagnetic properties through intelligent materials design. The performance goal is to develop a Ce-TM based permanent magnet with a Curie temperature in excess of 300°C, a remnant magnetization in excess of 10 kG, and coercivity in excess of 10 kOe. The project is a combined theoretical and experimental effort to study the potential of Ce intermetallic compounds for use in permanent magnets.
Exploiting the intrinsic ferromagnetic properties Ce-TM based permanent magnets; we will develop a Ce-TM based permanent magnet for use in automotive electric drive motors and wind turbines. Using a combined experimental and theoretical approach, we will develop an understanding of the role of valence and hybridization in determining the Curie temperature, magnetization, and anisotropy of Ce-TM alloys. This will allow us to design nanostructured and aligned hard/semi-hard magnetic alloys with properties suitable for permanent magnet applications and to produce magnets based on those alloys.
A critical benefit of the alternative Ce-TM-based materials will be to provide a market for Ce that is currently under utilized. The development of a high magnetic energy density Ce–TM – based permanent magnet would facilitate an increase of the supply of high-energy rare-earth magnets by a factor of 2 to 3 without requiring additional mining or an increase of RE processing. The effective utilization of the available Ce will drastically alter the economics of rare earth production by effectively doubling the marketable product without incurring additional costs.
This project targets proposes to reduce the content of critical rare earth elements in traction motors to <0.33g/kW. The collaborations with General Motors and NovTorque provide the evaluation of the material for traction motors with a specific power greater than 1.9 kW/Kg. Molycorp, LLC will provide the important materials supply chain and development path for commercialization of these materials.
Alam A; Khan M; McCallum R W; Johnson D D . 2013. Site-preference and valency for rare-earth sites in (R-Ce)(2)Fe14B magnets. Applied Physics Letters. 102:042402.