As part of the MSCA PF OCARINA project (https://cordis.europa.eu/project/id/101024046) we provided guidelines for developing new permanent magnets of the Nd-Fe-B type by tailoring the magnetic properties at the level of individual grains. The strategy involves the preparation of an input material on which a new microstructure of the magnet is built by adding novel phases. The input material must, therefore, be monocrystalline or single-grain and be based solely on the Nd2Fe14B matrix phase. The monocrystalline Nd2Fe14B was obtained by environmentally friendly chemical etching with an organic acid. The latter is selective and preserves the magnetic properties of the Nd2Fe14B matrix phase while successfully removing the Nd-rich intergranular phase, proven on fresh and recycled materials.
The work was published in MDPI Materials in two manuscripts: “Environmentally friendly approach for Nd2Fe14B magnetic phase extraction by selective chemical leaching: a proof-of-concept study (https://doi.org/10.3390/ma16145181) and in “Short-loop recycling of Nd-Fe-B permanent magnets: a sustainable solution for the Nd2Fe14B matrix phase recovery” (https://doi.org/10.3390/ma16196565).
Figure 2: A schematic flow of the selective leaching process of Nd-Fe-B permanent magnets
Our work within the Horizon EU project 101058598 – REEsilience (https://reesilience.eu/) continues the research for the development of new permanent magnets of the Nd-Fe-B type by tailoring the magnetic properties at the level of individual grains. The latter was obtained through selective chemical leaching based on recycled feedstocks. Adding a low-eutectic Nd-Cu alloy in the range between 0-30 wt. % to the single crystal matrix phase Nd2Fe14B, we introduced a new metallic phase source at the grain boundary. The bulk Nd-Fe-B magnets prepared with SPS furnace had a high coercivity Hci=826 kA/m and remanent magnetization Br=1 T. The developed method, which uses Nd70Cu30 instead of pure Nd, supports the development of efficient recycled permanent magnets with a reduced content of critical elements and significant performance. Furthermore, by applying an electrochemical approach to the Nd2Fe14B monocrystalline phase, we successfully deposited 1 µm layer of Cu on the powder particles via chemical reduction. By introducing Cu as a non-critical element into the Nd-Fe-B microstructure, we can further tailor the magnetic properties of Nd-Fe-B magnets at the level of individual grains.
