ORALS

SESSION: SISAMThuPM2-R3 C: Processing	Kobe International Symposium on Science of Innovative and Sustainable Alloys and Magnets (5th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM))
Thu Oct, 24 2019 / Room: Dr. Christian Bernard
Session Chairs: Carlo Burkhardt; Session Monitor: TBA

17:10: [SISAMThuPM212]
Effective Eectrochemical and Physical Reprocessing of Nd-Fe-B and Sm-Co Permanent Magnets, Approaching the Zero Waste Economy
Kristina Zuzek Rozman¹ ; Xuan Xu¹ ; Awais Ikram¹ ; Farhan Mehmood¹ ; Richard Sheridan² ; Allan Walton² ; Muhammad Awais² ; Anas Eldosoukey³ ; Spomenka Kobe⁴ ; Saso Sturm⁵ ; ¹Jozef Stefan Institute, Ljubljana, Slovenia; ²University of Birmingham, Birmingham, United Kingdom; ³Magneti LJubljana, d.d., Ljubljana, Slovenia; ⁴Josef Stefan Institute, Ljubljana, Slovenia; ⁵Head of Department for Nanostructured Materials, Ljubljana, Slovenia;
Paper Id: 189 [Abstract]

Currently, less than 1% of the rare-earth elements (REEs) that reach the end of their useful lives are recycled. This is a very small percentage, especially if we consider that the recycling of end-of-life (EoL) (Dy, Nd)-Fe-B magnets is an important strategy for reducing the environmental dangers associated with rare-earth mining, and overcoming the well-documented supply risks associated with the REEs. We report on possibilities of direct electrochemical recycling and electrochemical reprocessing of Nd-Fe(B)-based magnets. Previous attempts to deposit alloys of rare earths from solutions at mild temperatures have met little success. Excitingly, in this investigation, we were able to electrodeposit Nd-Fe from the 1-ethyl-3-methylimidizolium dicyanamide ([EMIM][DCA]) ionic liquid. We observed that Nd(III) cannot be reduced independently, although it can be co-deposited inductively as substrate with the addition of Fe(II), proven by electron-energy-loss spectroscopy. Further, we propose a new concept of recycling the sintered (Dy, Nd)-Fe-B magnets by directly recovering the (Dy, Nd)₂Fe₁₄B matrix phase. Via an electrochemical etching method, we are able to recover pure individual(Dy, Nd)₂Fe₁₄B grains that can be re-used for new types of magnet production. In terms of energy consumption, the proposed electrochemical recycling route is comparable to the established direct re-use methods. These direct methods are considered as the most economical and ecological ways for recycling the sintered (Dy, Nd)-Fe-B magnets. In the frame of physical reprocessing, we have successfully synthesised new magnets out of hydrogen-recycled stocks with contemporary sintering technique of pulsed electric current sintering. The SmCo₅ magnets for recycling were first decrepitated by hydrogen gas to produce the powder. The sample sintered at 900°C showed the best internal coercivity (jHc) of higher than 1500 kA/m with high remanence (Br) value of 0.47 T. The optimal SPS conditions yielded fully dense Nd-Fe-B magnets with the coercivity Hc = 1060 kA/m, which was boosted to 1160 kA/m after the post-SPS thermal treatment. The Br and Hc were tackled further, and increased applied pressures of 100-150 MPa resulted in Br = 1.01 T. Via the addition of DyF₃, 17.5% higher coercivity than the optimally SPS-ed magnet was obtained due to Dy substituting the Nd in the matrix Nd₂Fe₁₄B phase. We showed that with a fine tune of the SPS and post annealing, together with variations in Br and Hc, it is possible to revitalize the recycled Nd-Fe-B and Sm-Co magnets.

SESSION: SISAMFriAM-R3 D: Sustainable resources	Kobe International Symposium on Science of Innovative and Sustainable Alloys and Magnets (5th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM))
Fri Oct, 25 2019 / Room: Dr. Christian Bernard
Session Chairs: George Hadjipanayis; Session Monitor: TBA

11:45: [SISAMFriAM02]
Transmission Electron Microscopy for efficient recycling of Nd-Fe-B permanent magnets
Saso Sturm¹ ; Awais Ikram² ; Xuan Xu² ; Spomenka Kobe³ ; Kristina Zuzek Rozman² ; Farhan Mehmood² ; ¹Head of Department for Nanostructured Materials, Ljubljana, Slovenia; ²Jozef Stefan Institute, Ljubljana, Slovenia; ³Josef Stefan Institute, Ljubljana, Slovenia;
Paper Id: 281 [Abstract]

The transition towards future green and e-mobility technologies, based on permanent magnets, is unavoidably linked to a stable supply of (heavy) rare earth elements. In the recent past, the transition towards green and e-mobility technologies has been hindered due to various geo-political and economic reasons. One promising way to address this problem is to develop strategies for various efficient magnet recycling and reprocessing routes that turn magnet waste into new functional magnets with little or negligible loss of overall magnetic performance [1]. The current recycling techniques, however, such as hydrogenation disproportionation desorption recombination (HDDR) processing, remelting, spark plasma sintering (SPS) and electrochemical deposition, inevitably perturb the desired microstructure. Detecting and understanding the underlying chemical and physical mechanisms is thus the key to optimize the overall magnetic performance of the recycled/reprocessed magnets. These mechanisms are typically associated with the structural/chemical properties of different crystal phases and defects, including dislocations, grains, and interphase boundaries. In recent years, state-of-the-art Transmission Electron Microscopy, which typically includes Scanning Transmission Electron Microscopy (STEM) with different spectroscopy techniques, such as Energy Dispersive X-ray Spectroscopy (EDXS) and Electron Energy-Loss Spectroscopy (EELS), has become an indispensable tool for characterization of rare earth-based permanent magnets. Transmission Electron Microscopy has become indispensable since it provides correlative structural and chemical information along with atomic-scale spatial resolution. In this presentation the above-described analytical techniques will be demonstrated against the most challenging research problems that were encountered during the development of two conceptually different recycling routes. In one approach, end-of-life Nd-Fe-B permanent magnets were first transformed in powder form by a HDDR process. The HDDR process was further used to fabricate initial dense reprocessed bulk magnet by spark plasma sintering (SPS) at different temperatures (ranging from 650⁰C to 850⁰C).Finally, a conventional heat treatment route at 750⁰C for 15 minutes was used on the bulk magnet that was fabricated. By applying advanced TEM, i.e. atomic-scale Z-contrast STEM, combined with EDXS and EELS, the resulting magnetic properties were critically assessed against various types of structural and compositional discontinuities down to the atomic-scale. We believe these discontinuities control the microstructure evolution during the SPS processing route. An alternative reprocessing route for Nd-Fe-based magnets that we have developed is based on electro-co-deposition of Nd and Fe from an ionic-liquid (1-ethyl-3-methylimidizolium dicyanamide) electrolyte. In order to reveal the deposition mechanism, the chemistry and phase composition of the deposit were investigated by means of analytical TEM. This showed that Nd(III) is reduced to Nd(0) during the electrodeposition process. Furthermore, we were able to confirm that the deposition of the Nd–Fe starts with the sole deposition of Fe, followed by the co-deposition of Nd–Fe. These new insights into the electrodeposition process represent an important step closer to efficient recycling of rare earths in metallic form at a mild temperature. This is a sustainable and economically viable route based on the green-chemistry approach, thus providing a genuine alternative to high-temperature molten-salt electrolysis.

References:
[1] This work was supported by the European Union's EU Framework Programme for Research and Innovation Horizon 2020 under Grant Agreement No 674973 (DEMETER).