Experimental evidence for the suitability of the hydrogen decomposition process for the recycling of Nd-Fe-B sintered magnets

Michalski, B.; Szymański, Mateusz; Gola, Katarzyna; Zygmuntowicz, Justyna; Leonowicz, M.

doi:10.1016/j.jmmm.2021.168979

Cited by 17 publications

(17 citation statements)

References 24 publications

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“…More exposure to the hydrogen gas completes the hydrogenation of the bulk until no further absorption of hydrogen is observed. The change in volume (Δ V ) of the grain boundary is 3 times the change in the grains, resulting in a strain that decrepitates the magnets . As can be seen in a single Nd 2 Fe 14 B grain in Figure , a trans-granular crack confirms the brittleness of the hydrogenation product.…”

Section: Hydrogen Processing Mechanism and Thermodynamicsmentioning

confidence: 87%

“…The stoichiometric coefficients of the reactions were simplified in Figure , and they can vary depending on the temperature and pressure of the hydrogenation process. ,− For example, the stoichiometric coefficient of H 2 might be higher. There are three neodymium hydrides, the most stable of which is NdH 2 , but under certain circumstances, such as high H 2 concentration, other neodymium hydrides also occur, including Nd 2 H 5 and NdH 3 . , The presence of NdH 3 after hydrogenation has also been confirmed by Michalski et al Since NdH 3 forms at a much higher pressure than NdH 2 , the possibility of detecting neodymium hydride with an index greater than two decreases with decreasing hydrogenation pressure . Therefore, the more accurate form of eqs 1 and 2 in Figure is as follows: x and y depend on pressure and temperature …”

Section: Hydrogen Processing Mechanism and Thermodynamicsmentioning

confidence: 99%

“…The better magnetic properties of the mediumsized particles (200−450 μm) compared to the large-sized particles (450−600 μm) are attributed to the fact that the medium-sized particles contain fewer grains and therefore have better crystallographic alignment. 63 The particle size distribution was determined by Michalski et al 52 after a hydrogenation process at 200 °C and 200 kPa for temperature and pressure, respectively, and dehydrogenation at 780 °C, as shown in Table 2. These data show that the final magnetic properties will be more similar to those of the fine fractions with a particle size below 200 μm due to their weight percentage.…”

Section: Characteristics Of Hpms Productsmentioning

confidence: 99%

“…This degree of damage to the coating is sufficient to initiate hydrogenation at low temperatures. After hydrogenation, the coating layer remains as a coarse fraction up to a few centimeters long and can be easily separated by suitable sieving and even with the hands, since it does not interact with the hydrogen gas. , …”

Section: Hydrogen Processing Parametersmentioning

confidence: 99%

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Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

2023

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Regarding the restrictions recently imposed by China on the export of rare-earth elements (REEs), the world may face a serious challenge in supplying some REEs such as neodymium and dysprosium soon. Recycling secondary sources is strongly recommended to mitigate the supply risk of REEs. Hydrogen processing of magnetic scrap (HPMS) as one of the best approaches for magnet-to-magnet recycling is thoroughly reviewed in this study in terms of parameters and properties. The processes of hydrogen decrepitation (HD) and hydrogenation–disproportionation–desorption–recombination (HDDR) are two common methods for HPMS. Employing a hydrogenation process can shorten the production route of new magnets from the discarded magnets compared to other recycling routes such as the hydrometallurgical route. However, determining the optimal pressure and temperature for the process is challenging due to the sensitivity to the initial chemical composition and the interaction of temperature and pressure. Pressure, temperature, initial chemical composition, gas flow rate, particle size distribution, grain size, and oxygen content are the effective parameters for the final magnetic properties. All these influencing parameters are discussed in detail in this review. The recovery rate of magnetic properties has been the concern of most research in this field and can be achieved up to 90% by employing a low hydrogenation temperature and pressure and using additives such as REE hydrides after hydrogenation and before sintering.

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Section: Hydrogen Processing Mechanism and Thermodynamicsmentioning

confidence: 87%

Section: Hydrogen Processing Mechanism and Thermodynamicsmentioning

confidence: 99%

Section: Characteristics Of Hpms Productsmentioning

confidence: 99%

Section: Hydrogen Processing Parametersmentioning

confidence: 99%

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Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

2023

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“…These magnetic properties are high remanence (Br), high coercivity (Hc) [4], and these properties also enable them to have a high maximu m energy product, (BH)max [1,5]. Their superior magnetic properties; make it possible for them to be widely used in many fields such as hybrid electric vehicles [9] and energy storage systems [10], as well as in fields such as electronics [6], aviation [7], and medical [8]. In the production of NdFeB-based permanent magnets, methods such as rapid solidification (for example, melt spinning), atomization, HDDR process, mechanical alloying, severe plastic deformation, powder metallurgy are used [11].…”

Section: Introductionmentioning

confidence: 99%

Effects of Heat Treatment and on Magnetic Properties of NdFeB Based Permanent Magnet Alloys

Yılmaz¹,

Akgül²

2022

EJOSAT

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In this study, the effect of flash annealing heat treatment applied at 680 oC for 5 minutes on the magnetic properties of NdFeB-based permanent magnet alloys produced by melt spinning method, which is one of the fast solidification methods, was investigated by using a very fast heating and cooling rate of 300 K/s. The obtained results showed that there was a remarkable improvement in the magnetic properties of the alloys with the applied heat treatment. Mainly, the hard magnetic properties were optimized by enhancing magnetic remanence from 21.64 emu/g to 55.76 emu/g, magnetic coercivity from 1184.15 Oe to 9146.30 Oe, and maximum energy product from 4.06 kJ/m3 to 62.02 kJ/m3 respectively.

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Toward the Improvement of the Short‐Loop Recycling of Dy‐Rich Nd–Fe–B Permanent Magnets: Experimental and Numerical Approaches

Bacchetta,

Luca,

Rado

et al. 2024

Adv Eng Mater

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The method of short‐loop recycling of Nd‐Fe‐B magnets is implemented, with End of Life (EoL) magnets used as a source of Heavy Rare Earths (HRE). Partially recycled magnets are fabricated by co‐sintering of HRE‐free powders obtained from strip casted alloys, blended with HRE‐rich powders obtained from EoL magnets. The impact of several process parameters (blending ratio, sintering cycle and HRE‐rich recycled particle sizes) on the microstructure and magnetic properties are discussed. A coercivity gain up to 160 kA m‐1 per wt. % of Dy with respect to the HRE‐free magnets is reported, even though impurities are incorporated. Microstructural characterizations show a heterogeneous Dy localization in core‐shell/anti‐core‐shell structures, and thus a non‐optimal use of HRE. The experimental results are compared with finite elements simulations performed using existing data of bulk Dy diffusion coefficients. The simulation model consists of a network of square grains separated by a liquid phase, whose fraction is based on the ternary Nd‐Fe‐B phase diagram. Results show similarities with the observed microstructures, and point to the interest of reducing the Dy‐rich particle size with respect to the main powder. This study provides new insights into the Dy transport mechanisms at stake in an efficient short‐loop recycling of HRE.This article is protected by copyright. All rights reserved.

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Experimental evidence for the suitability of the hydrogen decomposition process for the recycling of Nd-Fe-B sintered magnets

Cited by 17 publications

References 24 publications

Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

Effects of Heat Treatment and on Magnetic Properties of NdFeB Based Permanent Magnet Alloys

Toward the Improvement of the Short‐Loop Recycling of Dy‐Rich Nd–Fe–B Permanent Magnets: Experimental and Numerical Approaches

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