Search

Rare earth elements (REEs) are fundamental for various modern technologies and industrial applications. One significant application of REEs is in the production of neodymium-iron-boron (NdFeB) magnets, which are key components in electric vehicles (EVs), wind turbines, and electronic devices. These applications play a crucial role in driving the ecological and digital transition, highlighting the significance of REEs as strategic materials. With the dominance of very few countries in the REEs global supply and the rising of EVs demand, several concerns regarding resource availability, supply chain security, and price volatility have heightened the importance of efficient NdFeB magnet recycling, especially in Europe. This study assessed the elemental recycling potential of REEs from EV components through collaboration with authorized treatment facilities and metal recyclers in Italy. The study focused on three representative electric vehicles: a compact car, a van, and a hybrid vehicle. NdFeB magnets were found in various components, including the electric drive motor, air conditioning system, electric power steering, alternator, and electric gear box. The content of NdFeB magnets and REEs inside these components has been determined and economic feasibility of their recycling has been estimated by considering the intrinsic value of the raw materials contained. Despite being preliminary results, the economic value of REEs and Cu recoverable attested a promising potential for recycling, while the direct dismantling of magnets from the engine proves economically unviable for the studied components. Therefore, the study emphasizes the need for the development of specific recycling processes such as demagnetization and mechanical processing of the motors. The study also analysed the dismantling times of the target components from the vehicle and their relative economic impact on the potential for recovery. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) is an additive manufacturing technique that provides an opportunity to create complex NdFeB magnets, potentially enhancing their performance. L-PBF possesses its own processing challenges, such as porosity/cracks and thermal stresses due to rapid cooling. This study focused on optimizing the parameters and the use of elevated temperature (300–550 °C) powder bed heating to reduce defect generation. This paper includes a detailed process parameter investigation, which revealed samples with a maximum energy product, (BH)max, of 81 kJ/m3 (remanence, Br 0.72 T; coercivity, Hci 891 kA/m) without post/pretreatment, which are the highest (BH)max and Br for L-PBF-processed NdFeB commercial powder. It was observed that all the high-magnetism samples possessed high density, but not all the high-density samples possessed high magnetism. The SEM images and discussions are academically valuable since they clearly illustrate grain formation and morphology in the melt pool, areas where the literature provides limited discussion. Furthermore, this paper incorporates quantitative phase analyses, revealing that the magnetic properties increase with increasing volume fraction of the strong magnetic phase Nd2Fe14B. Another significant contribution of this paper is that it is the first study to investigate the effect of heated bed on L-PBF-NdFeB alloys. The density of the samples and Br can be improved with the use of elevated powder bed heating, while the Hc decreases. The (BH)max can also be improved from 55 to 84 kJ/m3 through elevated powder bed heating. The maximum magnetic properties obtained with the heated bed (400 °C) were as follows: Br, 0.76 T; Hci, 750 kA/m; and (BH)max, 84 kJ/m3. [ABSTRACT FROM AUTHOR]

The oxidation behavior of spent NdFeB magnets was investigated when exposed to the selective oxidation conditions as a prerequisite method to achieve Nd2O3–Fe2O3 system. XRD results confirmed that the selective oxidation heat treatment successfully formed the Nd2O3 particles in the α-Fe phase as a result of the selective oxidation of Nd. The oxidation degree calculated from the weight gain became faster with temperature so the 100% oxidation degree could be achieved when heat treated at 950 °C for 60 min. The SEM analysis revealed that grain boundaries were the main path for oxygen diffusion at the initial stage of the selective oxidation and then, oxidation spread into grains through α-Fe lattice diffusion. TEM analysis confirmed that the Nd2O3 formed at the early oxidation had hcp structure and further oxidation led to only coarsening of the Nd2O3 particles, without any phase change. Due to no existence of Fe2O3 under the selective oxidation condition, facile oxygen diffusion through the grain boundary and α-Fe lattice was possible, leading to the activation energy for oxygen diffusion as low as 28 kJ/mol. Except for the microstructural changes related to the Nd oxidation, the specific oxidation condition maintained the fast-path for oxygen diffusion, grain boundaries and α-Fe lattice of the α-Fe matrix containing submicron Nd2O3 particles. [ABSTRACT FROM AUTHOR]

Recent advances in electrochemical methods promise a more sustainable recycling of rare earth elements (REEs) from discarded NdFeB permanent magnets. The demand for NdFeB magnets for clean energy applications is rapidly increasing, motivating recycling efforts to diversify REE supply. The main electrochemical steps include the selective dissolution of REE-rich phases at the anode and the reduction of REE ions at the cathode. Pretreatment with demagnetization, mechanical size reduction, and leaching contributes to the release and concentration of REEs. Thermal demagnetization and mechanical crushing make the magnets brittle and improve the penetration of leaching agents. Acid leaching dissolves the REEs, but also dissolves the iron. To facilitate the extraction of REEs at high temperatures, molten salt electrolytes such as chlorides are used, while ionic liquids allow extraction under milder conditions, but with the caveat of possible decomposition during the process. Aqueous solutions have been most thoroughly investigated due to their versatility and affordability. Fluoride-based molten salt electrolytes effectively dissolve RREs and provide a stable environment for hightemperature electrodeposition, improving the efficiency and sustainability of rare earth element recovery. To isolate highpurity REE oxides and metals, additional processing is required using techniques such as solvent extraction, selective precipitation, and electroseparation. Key factors for optimal electrochemical recycling are maximizing selectivity for REEs, minimizing energy consumption and waste generation, and simplifying integration. Although technical challenges remain, recent advances show that electrochemical technologies can improve the sustainability of recycling critical REEs from permanent magnets.

Detailed investigations of the properties essential for the interaction of permanent NdFeB magnets were performed at T=300 and 77 K. Axial and radial magnetic field distribution, attracting force, and work are well described using a single-turn substitutional coil model. Strain resulting from the interaction of magnets was calculated and measured for the first time. Unexpected radial strain and additional negative change in the magnet volume were revealed in the experiment performed at T=77 K. This additional change in the volume was proportional to the diminishing of the magnet free energy. A similar dependence was observed for the magnetostriction. It was concluded that any change in the magnetic free energy Fm is accompanied by the change in the elastic free energy ΔFe ≈ 0.1ΔFm at T=77 K. At room temperature, ΔFe is much smaller than ΔFm. [ABSTRACT FROM AUTHOR]

A significant enhancement in the coercivity and grain refinement was revealed for the spark plasma sintered NdFeB magnets by doping eutectic alloy (Nd0.75Pr0.25)70Cu30 powders. The commercially available NdFeB powders were mixed with (Nd0.75Pr0.25)70Cu30 powders (0, 2 and 5 wt.%) and then consolidated by spark plasma sintering at 700°C under 50 MPa. Microstructure analysis shows that the addition of (Nd0.75Pr0.25)70Cu30 alloy reduces the formation of coarse grain zone and decreases the average Nd2Fe14B grain size by intergranular phase modification. The RE-rich phase containing Nd, Pr at the Nd2Fe14B grain boundary caused the magnetic isolation effect. Hence, the coercivity increased from 18.3 kOe for un-doped NdFeB to 20.3 and 21.6 kOe with doping content of 2 and 5 wt.%, respectively. This study provides an economic way to fabricate sintered NdFeB magnets with enhanced coercivity and homogeneous nanostructure. [ABSTRACT FROM AUTHOR]

A significant enhancement in the coercivity and grain refinement was revealed for the spark plasma sintered NdFeB magnets by doping eutectic alloy (Nd0.75Pr0.25)70Cu30 powders. The commercially available NdFeB powders were mixed with (Nd0.75Pr0.25)70Cu30 powders (0, 2 and 5 wt.%) and then consolidated by spark plasma sintering at 700°C under 50 MPa. Microstructure analysis shows that the addition of (Nd0.75Pr0.25)70Cu30 alloy reduces the formation of coarse grain zone and decreases the average Nd2Fe14B grain size by intergranular phase modification. The RE-rich phase containing Nd, Pr at the Nd2Fe14B grain boundary caused the magnetic isolation effect. Hence, the coercivity increased from 18.3 kOe for un-doped NdFeB to 20.3 and 21.6 kOe with doping content of 2 and 5 wt.%, respectively. This study provides an economic way to fabricate sintered NdFeB magnets with enhanced coercivity and homogeneous nanostructure. [ABSTRACT FROM AUTHOR]

After mechanical pre-treatment, the typical hydrometallurgical route of NdFeB magnet recycling starts with leaching in acidic solutions. However, due to the high concentration of iron ions in the leaching solution, the selective recovery of rare earths from the solution is challenging. In our work, the selective precipitation of rare earth oxalates as a potential separation method was proposed. The precipitation of neodymium oxalate was first tested on model solutions, which was then followed by experimental tests carried out on real solutions after the leaching of NdFeB magnets. The recovery of rare earths in the form of oxalates was investigated with the use of different amounts of oxalic acid in relation to its stoichiometric amount. The most efficient separation of rare earths was observed in the case where sulfuric acid was used for leaching. The use of oxalic acid in stoichiometric amounts resulted in the precipitation of about 93% of all rare earths present in the solution, whereas the concentration of Fe and other elements (Ni, Co, and B) practically did not change. An increase in oxalic acid of 20% and 40% more than the stoichiometric amount (100%) led to the increase in the precipitation efficiency of rare earths to 96.7% and 98.1%, respectively. However, the use of oxalic acid in a 1.4 ratio caused a 7% decrease in Fe concentration, which suggests Fe co-precipitation. In order to investigate a possibility of further increasing the separation of rare earths from iron, an additional method was tested, in which iron was first oxidized from Fe2+ to Fe3+ before the precipitation of rare earth oxalates. [ABSTRACT FROM AUTHOR]

Nowadays, the circular economy is gaining more and more attention in sectors where the raw material supply is critical for both cost and geo-political reasons. Moreover, the environmental impact issue calls for recycling. From this perspective, the recovery of rare earth elements represents a strategic point. On the other hand, the high cost and the dangerous standard recovery methods that apply to NdFeB magnets limits options for traditional recycling. A new mechanical method is proposed, not requiring hydrogen, high temperature, or chemical processes, but instead using an impact mill designed to operate in vacuum. A traditional impact mill operating in a glove box filled with Ar atmosphere has also been used for comparison. The obtained NdFeB powders were analyzed in terms of magnetic properties and chemical composition, particularly in terms of the oxygen content. [ABSTRACT FROM AUTHOR]

Brushless Direct Current (BLDC) motors are known as synchronous motors and used in industrial areas due to their advantageous features. NdFeB magnets used in BLDC motors and produced at different power levels of rare earth elements are preferred due to their excellent magnetic properties. Although physical factors and environmental conditions have an effect on permanent magnets, the performance values are determined by the maximum energy efficiency (BHmax), residual flux density (Br,) and intrinsic coercive force (Hei) parameters. In this study, Alnico, Ceramic, SmCo and NdFeB magnets used in BLDC motors with permanent magnet rotor structure and the effects of these magnets on motor performance parameters are analyzed. For motor performance, magnet types are compared by considering speed, efficiency and torque values. The magnetic properties of the NdFeB are determined by analysis comparisons. Therefore, the effects of the types of these magnets obtained at different power degrees (N28-N38-N42-N52) on the engine performance are included in the study by considering the operating conditions at different temperatures (20°C, 60°C, 80°C). In the study, the effects of NdFeB on motor heat transfer are determined by an inner mounted rotor IPMBLDC motor with 2.45 kW power, the analysis made with finite element method (FEM). [ABSTRACT FROM AUTHOR]

Sol-gel alumina coatings have been deposited on neodymium-iron-boron magnets for corrosion protection. The coatings present a compact amorphous structure due to the low thermal treatment (500 °C) with a thickness ranging from 0.8 to 2 microns, a Vickers hardness of 10 GPa and good adhesion to the substrate, measured by scratch test, with a failure mode of tensile cracking and chipping. The coatings are effective in protecting the NdFeB magnets from corrosion with reduction of current density (i.e. 2.07 × 10−6 A/cm2 for 2dip sample) of one order of magnitude with respect to the neat sample (1.15 × 10−5 A/cm2). [ABSTRACT FROM AUTHOR]

A sustainable separation concept for large-scale recycling of NdFeB magnets under atmospheric pressure was developed by utilizing a combination of two separation concepts known from the literature: (I) selective pre-separation by in situ chlorination and evaporation of ground oxidized NdFeB material and (II) subsequent distillation for high-purity recovery of all recyclable chlorinated material components, especially its Rare Earth Elements (REEs). Theoretically, simplified estimations of the time conversion curves at 1173 K, 1273 K, and 2000 K of a single particle resulted in the idea of realizing chlorination in some kind of combustion chamber, fluidized bed, or continuous combustion chamber. After chlorination, all non-volatile components, such as REE chlorides, are condensed out of the vapor phase in a single-stage phase separator. For subsequent fine separation by distillation (1292–1982 K for Rare Earth Chlorides and 418–867 K at 2500 kPa for boron and zirconium chloride recovery), simplified simulations were performed in a total-reflux column under ideal phase equilibrium conditions to show the estimated minimum separation effort. Using two composition examples from the literature, high-purity separation of the major Rare Earth Chlorides within a twelve-stage distillation column as a residual heavy boiling product has been demonstrated to be potentially technically feasible. [ABSTRACT FROM AUTHOR]

High-performance permanent magnets play an indispensable role in manufacturing highly efficient motors and generators, ultimately contributing to the sustainability of our planet. Achieving high coercivity ( μ _0 H _c ) in hard magnetic materials at or above room temperature without relying on heavy rare-earth elements remains a challenge. Effective strategies for augmenting μ _0 H _c utilizing low-cost materials involve inter-granular addition and the grain-boundary diffusion (GBD) processes. This review provides a comprehensive overview of selected techniques for developing grain-boundary (GB) modification through a specific focus on the reduction of using heavy rare earth (HRE) elements and utilizing cost-effective non-rare earth and light rare earth (LRE) sources for GBD. To date, the successful application of HRE based metals and compounds, and LRE based alloys as diffusion sources has significantly contributed to μ _0 H _c enhancement. Drawing upon global advancements and findings from various research groups, this comprehensive review offers a critical analysis of the fundamentals and progress in GBD processes (GBDPs). Considering the different types of permanent magnets, the GBDPs, based on the diverse diffusion sources and diffusion processes, are thoroughly compared and summarized. This encapsulates the current state of knowledge in the field, providing valuable insights into the ongoing developments in GB modification to improve permanent magnet performance.

Electric current‐assisted sintering (ECAS) technologies are highly promising for processing of NdFeB magnets. Due to the combination of direct Joule heating and application of external load, even powders, whose particle size distribution and morphology are not optimum for conventional powder processing like melt‐spun powders or magnet scrap, can be easily sintered to high densities. A systematic study is done to demonstrate the potential of field‐assisted sintering technique/spark plasma sintering (FAST/SPS) and flash spark plasma sintering (flash SPS) for sintering of NdFeB powders. Melt‐spun, commercial NdFeB powder (Magnequench MQU‐F) is used as starting material. Its platelet‐like shape makes this powder extremely difficult to sinter by conventional methods. This study clearly reveals that especially in the case of flash SPS application of external pressure in combination with short cycle times enables to achieve well‐pronounced anisotropic magnetic properties without the need of subsequent upset forging. Optimized flash SPS parameters are applied to NdFeB magnet scrap with broad particle size distribution, demonstrating the general potential of ECAS technologies for recycling of waste magnet materials. Finally, the results are benchmarked with respect to established NdFeB processing technologies and electrodischarge sintering (EDS), another promising ECAS technology with very short cycling time. [ABSTRACT FROM AUTHOR]

This article presents and evaluates a dual rotor axial flux permanent magnet motor for electric aircraft applications. Several features, including grain-oriented electrical steel, Halbach arrays, and wires with rectangular cross sections, are used to improve torque density and efficiency. A novel winding arrangement is used to mitigate interturn short-circuit faults. Rather than simply optimizing the motor by itself, this article evaluates the tradeoffs between motor performance and its interfaces with the drive, thermal management system (TMS), and mechanical structure. This information can be used along with similar analyses of these subsystems to select the design with the system-level optimal performance. This article uses finite-element simulations to characterize tradeoffs among active mass, efficiency, fundamental frequency, power factor, axial forces on the rotors, and cooling surface area. Several designs exceed 95% efficiency at takeoff with less than 8 kg of active mass. While high pole counts, a large outer radius, and short stator teeth tend to optimize the magnetic performance at takeoff, this can reduce cruise efficiency, reduce the surface area through which the TMS can extract heat, increase the fundamental frequency the drive must supply, increase the structural mass required to support the rotors, and introduce complexity to the manufacturing process. Further analysis for a selected design reveals that the power factor can be significantly improved with a minimal torque penalty via field weakening due to significant saturation in the stator teeth. [ABSTRACT FROM AUTHOR]

Selective leaching behavior of the spent NdFeB magnets was investigated to find out how controlled phase system through the roasting conditions gave an impact on the performance of the selective leaching. The pre-formed Nd 2 O 3 by the selective oxidation made it possible to prevent the formation of NdFeO 3 at high roasting temperature. This resulted in the ideal Nd 2 O 3 and Fe 2 O 3 phase system, which was obtained by roasting at 660 °C, suitable for the selective leaching of Nd. While the roasting at 600 °C was still not enough to get full oxidation, the roasting at 720 °C made the NdFeO 3 formed. These characteristics with the roasting conditions affected leaching behavior. The NdFeB powder sample of 32 μm particle diameter, roasted at 600 °C showed the highest Nd leaching efficiency as well as the highest Fe leaching efficiency, which seemed to be ascribed to the existence of the metallic Fe. The poor leaching efficiency for the large powder size after roasting was ascribed to the poor diffusion characteristic of the H 2 SO 4 solution. With the controlled phase system, the 100% leaching efficiency of Nd could be obtained by reducing the particle size to 16 μm. The formation of NdFeO 3 as a co-product, which had resistance to the reaction with the leaching agent, could prevent the dissolution of Nd 2 O 3 around the NdFeO 3 layer. Thus, the 720 °C roasting condition showed the lowest leaching efficiency. The co-product Fe 2 O 3 also showed good resistance to leaching so its leaching efficiency was just 5–6% after the leaching time of 3–4 h. • Roasting over 500 °C could be applicable in manipulating phases for selective leaching in case Nd was oxidized in advance through selective oxidation. • Good controlled phase system enabled to achieve the improved leaching efficiency as well as selectivity. • The powder size played an important role in determining the rate constant and finally, leaded to the improved leaching efficiency. [ABSTRACT FROM AUTHOR]

In this work, tannic acid (TA) was employed to modify the surface of multiwall carbon nanotubes (CNTs) to form TCNTs hybrids via noncovalent functionalization to enhance its dispersibility in water. Then, the TCNTs enhanced epoxy coatings were applied on sintered NdFeB magnets by cathodic electrophoretic deposition method for corrosion test. The corrosion resistance of prepared specimens was assessed by electrochemical experiments. The results show that TCNTs hybrids present a more homogeneous distribution in epoxy resin than pristine CNTs and could obviously promote anticorrosion properties of prepared specimens. Within 36-day soaking in 3.5 wt.% NaCl solution, the specimens maintain a high value of |Z|0.01Hz (108 Ω cm2) when the concentration of TCNTs is 2 g/L. When immersed in 3.5 wt.% NaCl solution for 40 days, the Ecorr of specimens shifts to − 0.207 V and Jcorr is about 5.281 × 10−11 A cm−2, which demonstrates superior corrosion resistance. [ABSTRACT FROM AUTHOR]

In the existing friction brakes there are several problems such as squealing, judder, thermal and mechanical failures, disc distortions etc. Hence, in the current work an effort is made to develop contactless braking system using eddy current principles. Aluminum disc along with Neodymium – Iron – Boron (NdFeB) permanent magnets are used for investigations. Thickness of discs considered are 4, 6 and 8 mm. Speeds of disc rotation are equivalent of 75.39 Km/hr, 113 Km/hr, 150.8 Km/hr and 188.5 Km/hr. Considered brake parameters are percentage of reduction in speed, negative acceleration and time consumed. In lone magnet situation with gradual application, higher percentage of reduction in speed, good negative acceleration and less time consumed were observed in 4 mm disc thickness. Hence is suitable for faster train applications. In lone magnet with rapid application situation, superior negative acceleration and lesser time consumed were found in 4 mm disc thickness. This situation is beneficial for high speed automobile applications. [ABSTRACT FROM AUTHOR]

Nowadays, the circular economy is gaining more and more attention in sectors where the raw material supply is critical for both cost and geo-political reasons. Moreover, the environmental impact issue calls for recycling. From this perspective, the recovery of rare earth elements represents a strategic point. On the other hand, the high cost and the dangerous standard recovery methods that apply to NdFeB magnets limits options for traditional recycling. A new mechanical method is proposed, not requiring hydrogen, high temperature, or chemical processes, but instead using an impact mill designed to operate in vacuum. A traditional impact mill operating in a glove box filled with Ar atmosphere has also been used for comparison. The obtained NdFeB powders were analyzed in terms of magnetic properties and chemical composition, particularly in terms of the oxygen content.

Currently, the recovery of materials from secondary sources is increasingly necessary because of the scarcity of materials. Significant amounts of rare earth elements (REE) are found in permanent neodymium-iron-boron (NdFeB) magnets, used in various electrical and electronic equipments, such as mobile phones. However, the estimated recycling rate for REEs is only 1%. Hydrometallurgical routes are the most commonly used for REE recovery from secondary sources. This route usually uses inorganic acids, which are expensive and toxic. Thus, in this work the leaching efficiency of organic acids (acetic and citric) in leaching the REE (neodymium and praseodymium) present in magnets of obsolete or defective mobile phones was evaluated. Different concentrations of acids, solid/liquid relations, times and leaching techniques (microwave, ultrasound and conventional) are also evaluated. The results indicate that acetic and citric acids have the potential to leach Nd and Pr. Microwave leaching was the most effective method, compared to ultrasound and conventional methods. In microwaves, citric acid at 0.5 M (ratio s/l 1/100) leached 57% of Nd and 58% of Pr. Acetic acid at 0.5 M (s/l ratio—1/100) leached 48% of Nd and 65% of Pr, in 15 min. Furthermore, both citric acid and acetic acid also leached high percentages of iron (51% and 72%, respectively). [ABSTRACT FROM AUTHOR]

• The efficiency of the extraction of REEs from an acetic acid leachate of NdFeB powder is investigated. • Effective separation of REEs, particularly towards iron, is established using a TODGA extractant phase and a salting-out agent. • The recyclability of the extraction phase is demonstrated, highlighting the sustainability of the recovery process. Due to their indispensable role in a wide range of advanced technologies, rare earth elements (REEs) are becoming increasingly essential. As a result, there is a growing need to develop optimised processes for the recovery of these elements, whether from primary or secondary sources. This need extends to the recovery of REEs from a variety of sources, including mine tailings, the recycling of end-of-life products and the management of urban and industrial waste. The recovery of REEs from NdFeB permanent magnets from end-of-life computers hard disk drives (HDDs) is a great opportunity if separation from iron is effective. For this purpose N , N , N ′, N ′-tetraoctyldiglycolamide (TODGA) has been used for the selective extraction of REEs from a real leachate, obtained by NdFeB magnet powder dissolution in acetic acid. Process parameters such as TODGA concentration, ionic strength, time, and temperature have been investigated highlighting the complete selective recovery of REEs from the acetic acid leachate. The results show that TODGA at a concentration of 0.25 mol/L in aliphatic diluents allows the selective extraction of rare earths from an acetic acid feed solution at 1.6 mol/L, when NaNO 3 is added, with high separation coefficients for REEs in regards to iron, boron and nickel respectively. After a stripping step, the recyclability of the extractant phase was also demonstrated for at least 9 cycles. The complete process allows the recovery of the REEs from the NdFeB leachate with efficiencies of approximately 92 %, 88 % and 99 % for Nd, Pr and Dy respectively. [ABSTRACT FROM AUTHOR]

To alleviate the pressure on the rare earth supply chain, new technologies are under development for recovering, recycling and remanufacturing NdFeB magnets. In this study, the anticipated environmental performance of large-scale recycling is investigated and compared to the production of primary magnets. To do so, this ex-ante life cycle assessment combines input from measurements of pilot processes, expert technology forecasts, thermodynamic modeling, and equipment data from manufacturers. We examined the effect of four technology developments: process changes, size scaling, internal recycling, and optimization. The results show that at pilot scale, recovered NdFeB powders have lower impacts than primary powders for almost all impact categories. This demonstrates that the recovery of NdFeB alloys is environmentally beneficial. Magnets from anticipated large-scale recycling have over 80% lower impacts than primary magnets in most of the impact categories analyzed. All four investigated types of technology development contributed to this improved performance. The final configuration was validated by comparison with an industrial reference and theoretical optimum configuration. Four magnet manufacturing routes (sintering, extrusion, metal injection molding, bonding) have distinct environmental profiles, but all can progress to similarly low levels of impact. The choice among routes should be primarily based on the functional requirements. • Analysis of potential magnet recycling technology developments. • Environmental impacts of recycled and virgin magnets are compared. • All four development types can contribute to significantly lower recycling impacts. • Magnet manufacturing is more influential than the source of waste magnets. • Validation against industrial reference processes and a theoretical optimum. [ABSTRACT FROM AUTHOR]

The commercial 35M magnet prepared from recycled materials was used as the research object, and a self-made new DyF3 coating was used to conduct thermal diffusion treatment on the magnets. The results show that the new coating has the characteristics of quick-drying, good adhesion and uniform coating, which effectively improves the stability of thermal diffusion process. The magnet subjected to thermal diffusion treatment at 920 't: x 10 h, has a good performance on the magnetic properties, where the coercive force of the magnet reaches 1 710. 2 kA/m with an increase of 37. 9% . Microstructure analysis reveals the diffusion process of Dy element and the mechanism of coercive force improvement of the magnet. It is found that Dy element diffuses along the grain boundary and a Dy-rich shell of ( Nd, Dy)2 Fe14 B with a higher anisotropy field can be formed around the grains of main phase, which makes the Nd-rich phase of the grain boundary more continuous and clear, resulting in a substantial increase in the coercive force of the magnet. [ABSTRACT FROM AUTHOR]

NdFeB hot-pressed and hot-deformed magnets were prepared by hot-pressed (HP) sintering and spark plasma sintering (SPS). The effects of sintering mechanisms of SPS and HP on the microstructure of hot deformation magnets were studied. The temperature of the mold surface is much higher than that of the sample in the cavity in HP, but lower than that of the sample in SPS. The Nd-rich phase is uniformly distributed and the grain size is smaller in the hot-deformed magnets prepared by HP, while the Nd-rich phase is excessively enriched and the grain size in the liquid-enriched region is abnormal in the hot-deformed magnets prepared by SPS. The comprehensive magnetic properties of hot deformed magnets prepared by SPS are significantly lower than those prepared by HP. [ABSTRACT FROM AUTHOR]

Currently, the recovery of materials from secondary sources is increasingly necessary because of the scarcity of materials. Significant amounts of rare earth elements (REE) are found in permanent neodymium-iron-boron (NdFeB) magnets, used in various electrical and electronic equipments, such as mobile phones. However, the estimated recycling rate for REEs is only 1%. Hydrometallurgical routes are the most commonly used for REE recovery from secondary sources. This route usually uses inorganic acids, which are expensive and toxic. Thus, in this work the leaching efficiency of organic acids (acetic and citric) in leaching the REE (neodymium and praseodymium) present in magnets of obsolete or defective mobile phones was evaluated. Different concentrations of acids, solid/liquid relations, times and leaching techniques (microwave, ultrasound and conventional) are also evaluated. The results indicate that acetic and citric acids have the potential to leach Nd and Pr. Microwave leaching was the most effective method, compared to ultrasound and conventional methods. In microwaves, citric acid at 0.5 M (ratio s/l 1/100) leached 57% of Nd and 58% of Pr. Acetic acid at 0.5 M (s/l ratio—1/100) leached 48% of Nd and 65% of Pr, in 15 min. Furthermore, both citric acid and acetic acid also leached high percentages of iron (51% and 72%, respectively).

Waste electrical and electronic equipments (WEEE or e-waste) are an important source for rare earth elements (REEs). Among various type of WEEE, NdFeB magnets are known for their high content of neodymium (Nd) and dysprosium (Dy). Recovery of REEs from NdFeB magnets is of prime interest for the industry to meet the ever-growing demand for REEs. In this study, some physical and hydrometallurgical approaches including demagnetization, grinding, screening, leaching, precipitation and extraction have been adopted to study the Nd and Dy recovery from spent NdFeB magnets. Various inorganic (HCl, HNO₃, H₂SO₄ and aqua regia) and organic reagents (acetic acid and oxalic acid) were tested as lixiviants for leaching of the magnets. As a new approach, the recovery of Nd and Dy in the leaching solution was tested by eliminating the iron by a solution purification process involving precipitation of ferric iron in solution as hydroxide and solvent extraction with ionic liquids (ILs). The comparative studies demonstrated that the extraction efficiency of di-2-ethylhexyl phosphoric acid (D2EHPA) was higher than trihexyltetradecylphosphonium chloride (CYPHOS® IL101) after leaching stage. Nd and Dy were successfully extracted with complete recovery from the optimized system. [ABSTRACT FROM AUTHOR]

Phosphate coating is a commonly used anti-corrosion coating for NdFeB magnets, but its application is hindered by the intrinsic porosity and adverse impact on magnetic performance during the conventional chemical conversion process. Here, a compact magnesium phosphate coating with high protective efficiency has been successfully fabricated on the surface of NdFeB magnets. The surface properties, corrosion resistance and magnetic performance were investigated in detail. It is found that the quality of magnesium phosphate coating significantly depends on the deposition temperature. The coated sample deposited at 60 °C possesses the highest impedance value and protective efficiency (94.25%), because this temperature is appropriate for sufficient deposition of magnesium phosphate crystals (MgHPO4·3H2O) and can avoid defects induced by the excess growth of (021) plane. In addition, the magnesium phosphate coatings fabricated by electrochemical cathodic method exhibits no prejudice to the magnetic performance of NdFeB magnets. The superiority in corrosion resistance and magnetic performance of electrodeposited magnesium phosphate coating provides tremendous application prospect for developing protective coating of sintered NdFeB magnets. [ABSTRACT FROM AUTHOR]

With the introduction of rare earth magnets like neodymium-iron-boron (NdFeB), it has become possible to produce small magnets with high forces, necessary for its usage in the field of dentistry, such as for orthodontic tooth movement. The ultimate goal of this project is to establish magnetic force-driven orthodontic treatment as a future treatment modality for comprehensive orthodontic treatment.In order to utilize magnets for orthodontic treatment, we must first understand the characteristics of tooth movement created by magnetic forces. In this study, we aimed to digitally assess the efficacy of magnetic attraction and repulsion forces by means of a 3D digital analysis of movement (distance, direction, angulation and duration) and rotation (yaw, pitch and roll) of the crown and root of teeth in an ex vivo typodont model. We performed space closure and space gain treatment of maxillary central incisors (n = 30) and analyzed the movement and rotation of the teeth and root apex with 3D digital analysis. The results of the typodont model indicated significant differences on amount, speed and rotation of tooth and root movement created by magnetic attraction and repulsion forces.We also mimicked a moderate crowding typodont case and successfully treated it with a combination of attraction and repulsion magnetic forces. The moderate crowding case utilized magnets and a titanium archwire to guide the planned tooth movements and prevent undesired or unexpected movement. Further ex vivo experiments and considerations for biosafety will be necessary to investigate magnet force-driven orthodontics as a future modality of orthodontic treatment.

In this work, the structural, magnetic and mechanical properties of Nd16Fe76−xCoxB8 alloys with a varying Co content of x = 0, 10, 20 and 25 were experimentally investigated by X-ray diffraction (XRD), Mössbauer spectrometry (MS) and vibrating sample magnetometry (VSM) at room temperature (RT), and microhardness tests were performed. The system presented hard Nd2Fe14B and the Nd1.1Fe4B4 phases for samples with x = 0; when the concentration increased to x = 20 and 25, the CoO phase appeared. All MS data showed ferromagnetic behavior (eight sextets: sites 16k1, 16k2, 8j1, 8j2, 4c, 4e, sb) associated with the hard and soft magnetic phases, and one paramagnetic component (doublet: site d) associated with the minority Nd1.1Fe4B4 phase, which was not identified by XRD. All samples were magnetically hard and presented hard magnetic behavior. The increase of Co content in these samples did not improve the hard magnetic properties but increased the critical temperature of the system and decreased the crystallite size of the hard phase. There was a general tendency towards increased microhardness with cobalt content that was attributable to cobalt doping, which reduces the lattice parameters and porosities within the sample, improving its hardness. [ABSTRACT FROM AUTHOR]

This work follows up on the influence of the processing parameters and a subsequent heat treatment on the resulting properties of magnetizable neodymium-iron-boron (NdFeB) parts produced by Laser Powder Bed Fusion. Highly dense (> 95 %) cubes were built up and an uneven distribution of neodymium- and iron-rich phases was observed. It could be shown that internal stresses leading to crack development represent the main challenge. According to the experimental results, this can be approached more effectively through successive optimization of the processing parameters and therefore adjustment of the energy input rather than heat treatment of the built parts. [ABSTRACT FROM AUTHOR]

Laser based powder bed fusion is a promising manufacturing method that can be used for the fabrication of hard magnets such as NdFeB with nearly any given geometrical shape. However, the weak performance, e.g., low coercivity, of the 3D-printed magnets currently hinder their application. In this work, we demonstrated a proof-of-concept of powder bed additive manufacturing of heavy rare earth free NdFeB magnets with technologically attractive coercivity values. The 3D-printed NdFeB magnets exhibit the highest (up-to-date for the additively manufactured magnets without heavy rare earth metals) coercivity values reaching μ 0 H c = 1.6 T. The magnets were synthesized using a mixture of the NdFeB-based and the low-melting eutectic alloy powders. The essential function of the eutectic alloy, along with binding of the NdFeB-based magnetic particles, is the significant improvement of their coercivity by the in-situ grain boundary (GB) infiltration. The fundamental understanding of the magnetization reversal processes in these 3D-printed magnets leads to the conclusion that the excellent performance of the additively manufactured hard magnets can be achieved through the delicate control of the intergrain exchange interaction between the grains of the Nd 2 Fe 14 B phase. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The daily exposure of humans to artificial magnetic fields has inspired studies of their effects on biological systems. Different views are advocated by many research groups and few studies have clarified the role of magnetic field gradients in observed results. We investigated the effect of strong gradients and continuous magnetic fields in a cellular system. Colonies of Saccharomyces cerevisiae CCMB 355 were grown in solid and liquid media and exposed to the neodymium–iron–boron magnets. Notably, in solid medium, cells exposed to previously demagnetized NdFeB magnets or to the metals contained in magnets exhibited normal activities, but when exposed to the gradient, growth drastically fails near the magnet, even when the intensity of magnetism was near zero. Increasing the distance of the magnet to regions of weak magnetic field gradient caused decreased cellular malaise. When the magnet was removed, the cells were not capable of growing again, indicating that the gradient killed the exposed cells. In liquid medium, we observed a decrease in the absorbance values in the region of 560 nm when the substrate was directly permeated by a strong magnetic field gradient in comparison with a control without the magnet or with a magnet covered with a thin layer of silicone. This study helps to clarify the effect of the magnetic field gradient in biological systems. [ABSTRACT FROM AUTHOR]

• Mo nano-powder as an auxiliary alloy has been added into NdFeB sintered magnets. • Mo nano-powder optimizes the microstructure of the magnet. • The dispersed distribution of the Mo element at the grain boundaries enhances the H cj of the magnet. The Mo doped NdFeB magnets were prepared by the dual alloy method. Through transmission electron microscopy (TEM) and electron probe microanalyzer (EPMA), it is observed that the Mo element is mostly distributed at the grain boundary, which isolates the main phase grains, thus improving the intrinsic coercivity (H cj) of the magnets. When the addition of Mo nano-powder is increased from 0 to1.0 wt%, the H cj of the magnet is significantly improved. Especially, when the addition of Mo nano-powder is 0.8 wt%, the H cj of the magnet is 138 kA/m higher than that of the magnet without Mo addition. The current research work shows that the Mo doped magnet prepared by the dual alloy method effectively improves the H cj of NdFeB magnets, which has practical application value and theoretical significance for the research and development of high-performance NdFeB magnets. [ABSTRACT FROM AUTHOR]

The digestion of neodymium (NdFeB) magnets was investigated in the context of recycling rare earth elements (i.e., Nd, Pr, Dy, and Tb). Among more conventional digestion techniques (microwave digestion, open vessel digestion, and alkaline fusion), focused infrared digestion (FID) was tested as a possible approach to rapidly and efficiently solubilize NdFeB magnets. FID parameters were initially optimized with unmagnetized magnet powder and subsequently used on magnet pieces, demonstrating that the demagnetization and grinding steps are optional.

The circular economy concept and critical resources have recently received significant momentum across the board. However, only little work is done so far to assess the role of circular economy strategies in reducing a system's vulnerability to the increasing supply risk experienced by a number of critical resources. This study is aimed at exploring different resource circularity options (e.g., reuse, refurbishment, remanufacturing, and recycling) for critical resources, such as neodymium (Nd) and dysprosium (Dy) that are two key rare earth elements (REEs) found in the neodymium-iron-boron (NdFeB) magnets, along their value chain. A product classification approach is presented to better understand the circularity potential of critical resources, which in this study is demonstrated by the case study of NdFeB magnets. The proposed approach allows for grouping products considering their most feasible resource circularity pathway. As a next step, the product classification approach leads to developing a theoretical framework for anthropogenic resource classification, inspired from the natural mineral resource classification system of the United States Geological Survey. The key advantage of anthropogenic resource classification is identification and grouping of products with respect to varying degree of economic and technical feasibility of resource recovery from them, under current and future framework conditions. • A number of resource circularity options are explored for NdFeB magnets. • Products are grouped into 3 categories to identify the feasible circularity pathway. • Anthropogenic deposits of magnets bearing products are classified into 3 categories. • Products are grouped based on economic & technical feasibility of resource recovery. [ABSTRACT FROM AUTHOR]

Abstract Acoustic Emission Testing (AT) was applied to monitor the Hydrogen Decrepitation (HD) process for two different NdFeB-type materials: sintered NdFeB magnet and annealed NdFeB ingot alloy. Acoustic signals of clearly different characteristics were acquired for these two materials, indicating different course of the HD process. Acoustic waves of high signal strength and high peak amplitude were generated for the sintered NdFeB magnet whereas acoustic signals of low energy and low intensity were registered for the annealed NdFeB alloy. These findings were supported by real-time visual observation of the HD process. The sintered NdFeB magnet decrepitates rapidly and its particles spatter for a longer distance comparing to the ingot NdFeB alloy. Different behavior of the investigated materials can be explained in relation to their structural properties and manufacturing history. Fine microstructure, homogenously distributed thin layer of the Nd-rich grain boundary phase and stress accumulated after fabrication process can be responsible for more intense characteristic of the HD process in case of the sintered NdFeB magnets. Graphical abstract Image 1 Highlights • Monitoring of the Hydrogen Decrepitation via Acoustic Emission. • Various acoustic waves generated during the HD process. • Waves are influenced by distribution of the Nd-rich phase and accumulated stress. • Incubation time can be determined by AE. [ABSTRACT FROM AUTHOR]

Highlights • Coercivity of NdFeB thin magnet has been significantly enhanced by Pr-Al-Cu diffusion. • A 49% enhancement of coercivity in block magnets is obtained by the diffusion. • Optimized microstructure after grain boundary diffusion is observed and confirmed. • Diffusion behavior and diffusion coefficients of Pr, Al and Cu are investigated. Abstract Low melting point Pr-Al-Cu alloys were employed in grain boundary diffusion for sintered NdFeB magnets. The coercivity of the 7 × 7 × 2 mm magnet was enhanced from 1000 kA/m to 1360, 1615, and 1714 kA/m by diffusing Pr 70 Al 10 Cu 20, Pr 70 Al 15 Cu 15 and Pr 70 Al 20 Cu 10 alloys, respectively, at 800 °C for 2 h followed by 500 °C for 3 h. The optimized microstructure with strip-like grain boundary phase was evident in diffused magnets, which helps to reduce the magnetic exchange interaction between the hard magnetic grains and improve the coercivity. Under the same diffusion process, the coercivity of the diffused magnets decreased with increasing sample thickness, but 27% coercivity enhancement can still be obtained in the magnet with 6 mm in height. A Φ10×10 mm block magnet was diffused by Pr 70 Al 20 Cu 10 alloy at 800 °C for 2–10 h. Up to 49% enhancement in coercivity was achieved, which confirms the diffusion ability of Pr-Al-Cu alloy. The diffusion behavior of Pr, Al and Cu elements has been analyzed by Fick's law. Based on the diffusion coefficients obtained at 800 and 900 °C, Pr diffuses faster than Cu and Al along the grain boundary. The current results demonstrated that Pr-Al-Cu alloys can effectively optimize the grain boundary structure and improve the coercivity of NdFeB magnets. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • 91 components of 4 U.S. top selling vehicles were examined for NdFeB magnet content. • U.S. vehicles had major differences compared to Japanese and European vehicles. • NdFeB magnets were only found in speakers ranging from 16 to 114 g/vehicle. • At least 3.0 tonnes of NdFeB from end-of-life vehicles could be available in 2018. Abstract Research into secondary recovery of rare earth elements (REE) has focused mostly on hard disk drives and automotive applications. While REE content in Japanese and European vehicles is relatively well-known, understanding of U.S. vehicles is mostly based on database analysis. An attempt to pinpoint which components contain the most REEs was conducted on four different vehicle models including the Ford F-150, Chevrolet Silverado, Toyota Corolla and Honda Accord. The disassembly data were combined with 2017 vehicles in operation to estimate stocks and flows of Neodymium-Iron-Boron (NdFeB). Results showed that U.S. vehicles had major differences compared to Japanese and European vehicles. NdFeB magnets were only found in speakers ranging from 16 to 114 g/vehicle. An estimated 3.0–14 tonnes of NdFeB could be available from end-of-life vehicles in 2018 from different cohorts of the four aforementioned models. While opportunities for recycling NdFeB in vehicles exist, challenges are also present. [ABSTRACT FROM AUTHOR]

Co,Al-alloyed NdFeB nanostructures were synthesized by microwave combustion, followed by the reduction–diffusion process. Al and Nd substitution of Fe improved the corrosion resistance of nanostructured Nd20Fe54Co15Al3B8. The corrosion resistance value was comparable to those of sintered NdFeB magnets. X-ray diffraction and TEM revealed a multiphase system and the presence of Nd-rich phase. The $2~\mu \text{m}$ -thick Ni plating improved corrosion potential to −0.77 and −0.74 V, respectively, and current density to 329 and $144~\mu \text{A}$ /cm2, respectively. The $10~\mu \text{m}$ -thick Ni plating provided a high degree of protection against corrosion. [ABSTRACT FROM AUTHOR]

The extrinsic properties of NdFeB-based magnets can be tuned through partial substitution of Nd by another rare-earth element and Fe by Co, as such substitution leads to a modification in the intrinsic properties of the main phase. Optimisation of a magnet's composition through trial and error is time consuming and not straightforward, since the interplay existing between magnetocrystalline anisotropy and coercivity is not completely understood. In this paper we present a model to calculate the intrinsic magnetic properties of pseudo-ternary Nd2Fe14B-based compounds. As concrete examples, which are relevant for the optimisation of NdFeB-based high-performance magnets used in (hybrid) electric vehicles and wind turbines, we consider partial substitution of Nd by Dy or Tb, and Fe by Co.