NdFeB Magnets Research Articles

Study on Magnetic Properties of High Performance NdFeB Magnets for NEVs under Extreme Working Conditions

Study on Magnetic Properties of High Performance NdFeB Magnets for NEVs under Extreme Working Conditions

Processability and Separability of Commercial Anti-Corrosion Coatings Produced by In Situ Hydrogen-Processing of Magnetic Scrap (HPMS) Recycling of NdFeB.

The recycling of NdFeB magnets is necessary to ensure a reliable and ethical supply of rare earth elements as critical raw materials. This has been recognized internationally, prompting the implementation of large-scale legislative measured aimed at its resolution; for example, an ambitious recycling quote has been established in the Critical Raw Materials Act Successful recycling in sufficient quantities is challenged by product designs that do not allow the extraction and recycling of these high-performance permanent magnets without excessive effort and cost. This is particularly true for smaller motors using NdFeB magnets. Therefore, methods of recycling such arrangements with little or no dismantling are being researched. They are tested for the hydrogen-processing of magnetic scrap (HPMS) method, a short-loop mechanical recycling process. As contamination of the recycled material with residues of anti-corrosion coatings, adhesives, etc., may lead to downcycling, the separability of such residues from bulk magnets and magnet powder is explored. It is found that the hydrogen permeability, expansion volume, and the chosen coating affect the viable preparation and separation methods as recyclability-relevant design features.

Recent Advances in Corrosion Inhibition of Bonded NdFeB Magnets.

Bonded permanent NdFeB magnets are useful in numerous applications, including electric vehicles, and the demand is steadily increasing. A major drawback is corrosion due to inadequate wetting of the magnetic particles by liquid polymers such as polyphenylene sulfide or polyamide. Recently reported methods for corrosion inhibition are summarized, and their applicability is critically evaluated. The phosphorylation of magnetic particles inhibits corrosion but does not enable appropriate properties in harsh environments. The same applies to metallic coatings, which usually contain aluminum and zinc. Advanced epoxy adhesives are a promising solution, although some authors have reported inadequate corrosion resistance. The application of composite coatings seems like an appropriate solution, but the exact mechanisms are yet to be studied.

Production of High-Coercive nanostructured Nd-Fe-B alloy by chemical method

For the first time, a nanostructured alloy powder with high coercive force was obtained by a chemical method without the addition of Dy, which can compete with physical methods of production. The work carried out a study of the influence of stoichiometric composition on the magnetic properties of nanostructured Nd-Fe-B alloys. Alloys with different contents of Nd, Fe, and B were synthesized: Nd12Fe84B6, Nd14Fe80B6, Nd16Fe76B8, and Nd16Fe72B8. With a decrease in the iron content in the first two compositions, a decrease in the iron content in the soft magnetic phase α-Fe was observed, which led to an increase in the coercive force Hc and a decrease in the values of Ms and Mr. Experiments have shown that an increase in the content of Nd and B promotes the formation of the hard magnetic phase Nd2Fe14B and an increase in the coercive force. For example, the nanostructured Nd16Fe76B8 alloy demonstrated a maximum coercive force of Hc = 8439 Oe, while compensating for the values of Ms (109 emu*g−1) and Mr (78 emu*g−1). A comprehensive study of the nanostructured Nd16Fe76B8 alloy was carried out, including structural analysis. XRD using FullProff and Vesta software revealed the tetragonal crystal structure of the Nd2Fe14B phase, providing details of the atomic arrangement. The unit cell contains four layers with Nd and Fe atoms, and boron atoms are embedded in the center of the octahedron of Nd and Fe atoms, playing an important role in the magnetic exchange interaction. The results of Mössbauer spectroscopy confirmed the presence of the Nd2Fe14B phase and revealed details of the state of Fe atoms in the structure of six sextets.

An experimental investigation and predictive modeling using machine learning technique for reclamation of metal values from scrap NdFeB magnets

Neodymium-Iron-Boron (NdFeB) magnets are widely used in various industries due to their exceptional magnetic properties, such as high coercivity, remanence, and maximum energy product. These magnets consist of rare earth elements (REEs) viz., neodymium (Nd), praseodymium (Pr), and Dysprosium (Dy), along with other metals. With the ever increasing demand for REEs and the need to bridge the supply gap, it is crucial to develop alternative methods for their extraction. Recycling metal from scrap magnets is a promising approach to address the pressure on the supply chain and work towards sustainable development. The primary goal of this study is to generate a predictive model based on machine learning to determine the optimal conditions for metal recovery from scrap NdFeB magnets through water leaching after chloridizing roasting. Bench-scale leaching experiments were carried out to generate a dataset for statistical process optimization and machine learning analysis. The leaching kinetics of neodymium was also explored, and mixed-controlled shrinking core model was found to be most suitable, with an activation energy of 58.11 kJ/mol in the temperature range of 25– 95 °C. This study is the first to utilize a machine learning approach to analyze the potential process variables and their impact on metal recovery from calcined NdFeB magnet powder. A comparative analysis between experimental and machine learning approaches is presented to predict the optimal conditions for selective recovery of metal values from scrap NdFeB magnets. The maximum efficiency of extraction of metal ions was found to occur at a temperature of 95 °C, solid to liquid ratio of 125 g/l, and leaching duration of 60 min.

The effect of Dy-Cu co-deposition and grain boundary diffusion on the microstructure and magnetic properties of sintered NdFeB magnets

In this paper, Dy-Cu coating was electrodeposited on the surface of commercial sintered NdFeB magnet as a diffusion source and the grain boundary diffusion was carried out on the sintered NdFeB magnet. The experimental results show that the coercivity of the diffusion magnet is increased from 993 kA/m to 1241 kA/m, an increase of 24.95 %, and the remanence is only reduced to 1.366 T, a decrease of 0.44 % compared with the original magnet. The electrochemical behavior analysis shows that with the addition of Cu2+, the reduction potential of Dy3+ appears a large positive shift, and the Dy-Cu co-deposition process is a three-dimensional instantaneous nucleation process. The SEM images show that the Dy-Cu deposition layer has a dense and flat surface with small grain size. The energy spectrum analysis shows that the Dy-Cu elements obtained by electrodeposition are uniformly distributed, and there is no massive agglomeration phenomenon. SEM-EDS line scan observation shows that the Dy elements diffused along the grain boundary phase mainly accumulate in the grain boundary phase and the epitaxial layer of the main grain. EPMA shows that Cu and Dy elements are evenly distributed in the grain boundary phase after grain boundary diffusion. SEM-BSE shows that the near-surface grain boundary phase structure is significantly optimized after grain boundary diffusion. XRD shows that Dy partially replaces the NdFeB main phase, leading to the migration of the main peak to the large angle direction. At the same time, due to the existence of low melting point metal, Dy preferentially enters the magnet internal, resulting in the decrease of the content of (Dy, Nd)2Fe14B phase. The optimization of the microstructure and grain boundary phase composition and the formation of (Dy, Nd)2Fe14B structure are the main reasons for the significant enhancement of the coercivity According to Kronmüller plots, the coercivity mechanism of diffusion magnet is still the magnetic domain nucleation inversion mechanism. After the Tafel test, it is found that the diffusion Dy magnet has a relatively positive corrosion voltage Ecorr and a relatively low corrosion current density Icorr, and its corrosion resistance is greatly improved.

Ex-ante LCA of magnet recycling: Progressing towards sustainable industrial-scale technology

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.

Improvement of thermal stability by co-introducing Dy and Co with dual-alloy method in NdFeB magnets

A dual-main-phase magnet with excellent thermal stability was prepared by co-mixing two types of magnetic powders, which was the conventional N55-grade powder without Dy elements, while the Co and Dy contents reached 50 wt% and 6 wt% respectively in another Co-rich powder. Studies showed that the magnetic properties along with the thermal stabilities of the magnets exhibited significant differences with the changes in the mixing ratio of the two powders. Especially, when mixing the two powders in equal proportions, a great remanence temperature coefficient of −0.0725 %/°C at 20–100 °C was obtained with a rather high Curie temperature of 581 °C, possessing its magnetic properties with Br = 12.58 kGs, Hcj = 15.9 kOe, and (BH)max = 36.88 MGOe. Note that as the proportion of Co-rich powder increased to 2/3, although the Curie temperature of the prepared magnets further increased to 622 °C, both the remanence temperature coefficient and the magnetic properties deteriorated significantly. The phase composition and microstructure analyses revealed that when the proportion of added Co-rich component exceeded 1/2, the RE(Fe,Co)2B phase transformed into the RE(Fe,Co)4B phase, and a significant amount of RE(Fe,Co)1.8B0.2 phase precipitated at the grain boundaries, leading to a deterioration in magnetic performance. In addition, dynamic domain evolution analyses under variable temperature conditions demonstrated the positive effect of the appropriate introduction of Co/Dy on the anti-demagnetization in high temperatures. This work provides insights and an experimental foundation for the development of high-performance magnets with high thermal stability, used in high-temperature environments.

Laser powder bed fusion of NdFeB and influence of powder bed heating on density and magnetic properties

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.

Improving the performance of room temperature rotary magnetic refrigerators via magnet shape optimization

A magnetic structure intended for use in a room-temperature rotary active magnetic regenerator (AMR) is presented, under construction at the University of Genoa. Given the overall size of the regenerator and the thickness of the gap, the magnet design is optimized to produce the highest possible magnetic field difference between two adjacent regions. Magnet shape optimization is obtained by introducing a geometry with four degrees of freedom corresponding to the position of the edges of each magnet, plus the remanence angle. This approach serves two main purposes: the primary is to increase the magnetic induction and, to follow, some effort is made to minimize the volume and weight of the expensive NdFeB magnets, while preserving the cooling performance. So, a balance between these two goals must be achieved. After a rough preliminary sizing, a parametric investigation is performed toward these targets and some shapes are presented. The magnetic flux density in the gap, and other consolidated and novel performance indices, are evaluated and compared to those found in the literature for similar devices. The final design achieves, in the air gap, a maximum induction value of 1.045 T, and an average flux density of 0.83 T in a volume per unit length of 0.00268 m3/m in the high induction region. This is accomplished by using 0.00606 m3/m of magnetic material (N50, NdFeB). The magnet designs presented here exhibit a well-balanced performance (in terms of greater cooling for the same magnet weight) compared to earlier designs for similar AMR devices.

PEDOT-functionalized carbon nanotubes for anticorrosive reinforcement of epoxy coatings on sintered NdFeB magnets

PEDOT-functionalized carbon nanotubes for anticorrosive reinforcement of epoxy coatings on sintered NdFeB magnets

Selective leaching behavior of Nd from spent NdFeB magnets treated with combination of selective oxidation and roasting processes

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 Nd2O3 by the selective oxidation made it possible to prevent the formation of NdFeO3 at high roasting temperature. This resulted in the ideal Nd2O3 and Fe2O3 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 NdFeO3 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 H2SO4 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 NdFeO3 as a co-product, which had resistance to the reaction with the leaching agent, could prevent the dissolution of Nd2O3 around the NdFeO3 layer. Thus, the 720 °C roasting condition showed the lowest leaching efficiency. The co-product Fe2O3 also showed good resistance to leaching so its leaching efficiency was just 5–6% after the leaching time of 3–4 h.

Production of Permanent Magnets from Recycled NdFeB Powder with Powder Extrusion Moulding

In the last fifteen years, several groups have investigated metal injection moulding (MIM) of NdFeB powder to produce isotropic or anisotropic rare earth magnets of greater geometric complexity than that achieved by the conventional pressing and sintering approach. However, due to the powder’s high affinity for oxygen and carbon uptake, sufficient remanence and coercivity remains difficult. This article presents a novel approach to producing NdFeB magnets from recycled material using Powder Extrusion Moulding (PEM) in a continuous process. The process route uses powder obtained from recycling rare earth magnets through Hydrogen Processing of Magnetic Scrap (HPMS). This article presents the results of tailored powder processing, the production of mouldable feedstock based on a special binder system, and moulding with PEM to produce green and sintered parts. The magnetic properties and microstructures of debinded and sintered samples are presented and discussed, focusing on the influence of filling ratio and challenging processing conditions on interstitial content as well as density and magnetic properties.

Exploring mass and economic potentials of rare earth elements recycling from electric vehicles at end-of-life

AbstractRare 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.

Constraint free physics-informed machine learning for micromagnetic energy minimization

We introduce a novel method for micromagnetic energy minimization which uses physics-informed neural networks to find a magnetic configuration which minimizes the Gibbs Free energy functional without the need of any constraint optimization framework. The Cayley transform is applied to a neural network to assure that the model output lives on the Lie group of rotation matrices SO(3). For the stray field computation we use the splitting ansatz of Garcia-Cervera and Roma together with a hard constraint extreme learning machine in combination with a Taylor series approximation for very accurate evaluation of the single layer potential which only requires a very coarse discretization of the surface. Further, we present a modeling framework for constructive solid geometry which uses R-functions to exactly satisfy essential boundary conditions arising in the course of stray field computation. This framework can be applied to many other areas of interest. Our method shows promising results on the NIST μMAG Standard Problem #3, and is also applied to compute the demagnetization process of a hard magnetic Nd2Fe14B cube.

Measurement of Resistivity of NdFeB Magnet with Four-probe Method

Measurement of Resistivity of NdFeB Magnet with Four-probe Method

Deformation behavior and magnetic properties of equiatomic FeNi single crystals

An equiatomic Fe–Ni alloy in its disordered A1 structure is a soft magnetic alloy. On ordering to the L10 ordered phase, it shows significant magneto-crystalline anisotropy and a strong permanent magnet behavior and is of interest as a rare earth-free permanent magnet. However, synthesis of an L10 phase in a bulk form remains a challenge due to its low critical ordering temperature Tc and consequent extremely slow ordering kinetics. This phase is present in asteroids, and how it was formed remains unclear. The likely mechanism is enhanced diffusion kinetics due to extreme dislocation densities and vacancy concentrations produced by deformation during asteroid collisions and the presence of S. Prior to examining extreme deformation in an FeNi alloy comparable to that in asteroid collisions, low strain rate deformation behavior, magnetic properties, and the structure of undoped and S-doped [100]-oriented FeNi single crystals were carried out. Controlled deformation at a strain rate of 1 × 10−5/s showed the yield point to be 89 MPa, and the critical resolved shear stress was 25.7 MPa. The dislocation densities obtained were ∼1017/m2. The saturation magnetization value was ∼147–151 emu/g both before and after deformation, comparable to NdFeB magnets. Coercivity increased slightly from ∼0.04–0.4 to ∼5 Oe after deformation due to an increase in dislocation density. The x-ray diffraction scan of S-doped and deformed single crystals after annealing at 300 °C, just below Tc, showed no evidence of L10 order. These data serve as a baseline for extreme strain rate deformation where much higher dislocation densities and vacancy concentrations can be obtained to facilitate L10 order.

Quantitative analysis of sintered NdFeB backscattered electron images based on a general large model

The macroscopic performance of magnets is determined by their microscopic structure, quantifying the microscopic image of magnets is of great importance for studying its performance. Backscattered electron images of sintered NdFeB magnets contain information about the size, morphology, and distribution of grains and the grain boundary phases. Traditional methods for quantifying images involve labor-intensive manual measurements, digital image processing with complex contour extraction algorithms, and convolutional neural network algorithms that require extensive image data labeling. In this study, we introduced a general vision large model called Segment Anything Model(SAM) for image segmentation. SAM enables rapid and accurate segmentation of grains and grain boundary phases without the need for complex algorithms and tedious data labeling. From the segmented mask images, we extracted various data related to the performance of magnets, including the centroid positions, perimeter, area, sphericity, roughness, and principal axis directions of all grains. We also obtained information on the distances and angles between adjacent grains and the relevant parameters affecting magnet performance, such as the number and volume of grain boundary phases. We conducted comprehensive quantification of the backscattered images for three different magnets and provided reasonable explanations for the differences in magnet performance. This model offers superior speed and accuracy in image quantification compared to traditional algorithms and can be used for the rapid analysis of large datasets. It represents an essential method and trend for the quantification of image data in the future.

Effect of pretreatment methods on the selective leaching of rare earth elements from NdFeB permanent magnets using deep eutectic solvents

In this study, deep eutectic solvents (DESs) were employed as environmentally friendly alternatives of inorganic acid to selectively leach REEs from waste NdFeB magnets. Three DESs were tested, effective for light REE leaching, and preliminary experiments were conducted to study the selective leaching of REEs, using synthetic materials, Nd2O3, Fe, Fe3O4, and Fe2O3. The findings suggest that neodymium and iron should exist as Nd2O3 and Fe2O3, respectively, for selective leaching. To enhance the selective leaching of the NdFeB magnet, three pretreatment methods were applied: oxidative roasting, NaOH digestion, and NaOH digestion-oxidative roasting. During the oxidative roasting, NdFeO3 was formed, and it hindered REE leaching, achieving the highest REE leaching efficiency of 22.5% in the guanidine hydrochloride (GUC)-lactic acid (LA) DES. To counteract NdFeO3 formation, the NaOH digestion was introduced, yielding Nd(OH)3 and Fe3O4. These were then converted to Nd2O3 and Fe2O3 through oxidative roasting. With the NaOH-digested product, selective REE leaching was achieved solely with the ethylene glycol (EG)-maleic acid (MA) DES, while it was feasible in all three DESs with the NaOH digestion-oxidative roasting. The EG-MA DES displayed the highest selectivity, with a leaching efficiency of 97.3% Nd and 0.8% Fe. Additionally, the solvent could be reused at least twice, and the leaching efficiencies of 97% for Nd and 0.7% for Fe were maintained. This selective leaching technique benefits from using environmentally friendly solvents compared to the traditional inorganic acid leaching and demonstrates high REE selectivity and solvent reusability, suggesting a novel method for REE recovery via DESs.

An in-situ magnetising holder achieving 1.5 T in-plane field in 200 kV transmission electron microscope

A strong in-plane magnetic field is required for Lorentz transmission electron microscopy (LTEM) to observe the evolution of the magnetic domain structure of materials with high coercivity, particularly for research on rare-earth permanent magnets. However, the maximum field of the present in-situ magnetising holder applied in 200-kV or 300-kV TEM does not exceed 0.1 T. In this study, the reason for the low field was analysed, and the field strength was significantly elevated by reducing the field application area of the field generator. From finite element method calculations and experimental measurements, a 1.5 T in-plane field was achieved by our new holder in a 200-kV TEM, and images with good quality could still be obtained. Using the newly developed holder, the magnetisation process of hot-pressed NdFeB magnets was observed. The in-situ magnetising holder can be used in research on a wide variety of magnetic materials.