GREENE
research partners have shown
that the answer may be yes. By combining a recycling route that preserves the
original microstructure with in-situ grain-boundary diffusion, they produced
recycled Nd-Fe-B magnets with a coercivity 13% higher than that of the starting
material.
Read the paper: In-situ Grain-Boundary Diffusion in Near-Equilibrium Nd-Fe-B Powders for High-Coercivity Reprocessed Magnets.
When we think about recycling, it is often assumed that there will be a trade-off in quality. For Nd-Fe-B magnets that are widely used in electric vehicles wind turbines because of their high magnetic strength, recycling can indeed lead to performance losses, particularly because the material must be ground into powder and then re-sintered. During this process, the microstructure of the magnet can change, reducing its resistance to demagnetisation (coercivity).
Despite being energy efficient and more environmentally friendly, newer recycling methods, such as those through Hydrogen Processing of Magnetic Scrap (HPMS), often require supplementation with additional Nd-rich material. While this can improve resistance to demagnetisation, it may also reduce other magnetic properties, creating a trade-off between stability and magnetic performance.
Prior research done by the authors showed that recycled magnets can be broken down into powder and re-sintered while largely preserving the original grain structure. The latter is important, because these grains, tiny crystalline regions within the magnet, play a crucial role in determining its magnetic properties. During re-sintering, grains typically grow and merge, which makes magnets demagnetise easily and reduces their coercivity. By limiting this grain growth, the authors were able to retain more of the magnet’s original performance
The approach in the paper relies on preserving the favourable microstructure of the original magnet and then enhancing it through in-situ grain-boundary diffusion. Rather than uniformly modifying the entire magnet, Terbium is transported along the boundaries between individual grains during sintering, where it can most effectively improve resistance to demagnetisation. This allows coercivity to be enhanced while largely preserving the beneficial characteristics of the recycled material.
The authors therefore introduced a small amount of terbium in the form of TbH₃ during sintering. Terbium is a heavy rare earth element known for its ability to increase a magnet’s resistance to demagnetisation. Through this small addition of just 1 wt.% of TbH₃, they achieved a coercivity that exceeded that of the initial magnet by 13%.
Maintaining high coercivity is essential for many applications that rely on strong and reliable permanent magnets, including electric vehicles and wind turbines. By improving the performance of recycled magnets, approaches such as this demonstrate how GREENE aims to reduce reliance on virgin rare-earth materials by recovering and upgrading existing magnetic materials through advanced processing and microstructure engineering.
The recycled magnet wasn’t just restored to its original quality. It became even more resistant to demagnetisation than the original material, demonstrating that recycled magnets can not only retain performance but, under the right conditions, even outperform their starting material.