NdFeB Magnets Research Articles

Optimizing the grain boundary structure of sintered Nd-Dy-Fe-Co-B magnets by low-melting-point alloys grain boundary addition

To respond to the gradually increasing demand for thermal stability of sintered NdFeB magnets and grasp the evolution rules of their phase structure, research on sintered Nd-Dy-Fe-Co-B magnets was conducted. The magnets used in this study were prepared by the powder metallurgy method (Strip Casting + Hydrogen Decrepitation + Jet Milling). The room temperature magnetic properties of the magnet sample were Br = 11.45 kGs and Hcj = 22.42 kOe, with a low-temperature coefficient of Br (αBr(20 °C∼100 °C) = −0.059 %/°C) and a high Curie temperature (Tc = 460 °C). Based on the microstructure observation, there were planar anisotropic soft magnetic phase Nd2Co17 within grain boundaries and the "Cu-Co Opposite Distribution". Low-melting-point binary alloy Pr80Cu20 was introduced into the magnet by grain boundary addition to eliminate Nd2Co17 phases and improve the coercivity. After the grain boundary addition, the "Cu-Co Opposite Distribution" was used to eliminate the Nd2Co17 phase, the grain boundary structure was optimized, and the coercivity was increased by approximately 2.6 kOe, which was approximately 10 % of the total coercivity. Therefore, Cu-containing low-melting-point binary alloy grain boundary addition is an effective method for optimizing the grain boundary structure of Nd-Dy-Fe-Co-B magnets, thereby improving the high-temperature stability and coercivity.

Leveraging available data for efficient exploration of materials space using Machine Learning: A case study for identifying rare earth-free permanent magnets

It is shown that even the relatively small amount of available materials data can be innovatively utilized to explore the materials space in order to identify materials with desired target properties. As an example of this, data from the novomag and Novamag databases are used to train random forest and neural network models which can predict thermodynamic stability, and magnetic properties of materials. Performance of these models are tested thoroughly and are found satisfactory. These models are subsequently used to interpolate within the above databases, and to extrapolate to parts of the materials composition and structure space not covered in these databases, to identify stable, magnetic materials that have large saturation magnetization and large easy-axis anisotropy. Screening 686 materials via the trained models, and subsequently performing first principles calculations, 21 new candidate materials for rare earth free permanent magnet are identified. Some of these materials have anisotropy constants as large as 5 and 6 MJ m−3, larger than that of the most widely used permanent magnet Nd2Fe14B. This simple approach can be used to screen materials with other functionalities in future.

The effect of In-doping on the evolution of microstructure, magnetic properties, and corrosion resistance of NdFeB magnet

Abstract The grain boundary phase affects the magnetic properties and corrosion resistance of sintered NdFeB magnets. In this work, a small amount of Indium (In) was added to the NdFeB magnet by induction melting to systematically investigate its effect on the evolution of the microstructure, magnetic properties, and corrosion resistance of the NdFeB magnet. The microstructural analysis illustrated that minor In-addition generated more grain boundary phases and an abundant amorphous phase at the triple junction grain boundary. While the addition of In element failed to enhance the magnetic isolation effect between adjacent matrix grains, fortuitously, its incorporation elevated the electrochemical potential of the In-containing magnets. Besides, during corrosion, an In-rich precipitate phase formed, hindering the ingress of the corrosive medium into the magnet. Consequently, this significantly bolstered the corrosion resistance of sintered NdFeB magnets. The phase formation, magnetic properties, and corrosion resistance of In-doped NdFeB magnets are detailed in this work, which provides a new prospect for the preparation of high-performance sintered NdFeB magnets.

Recycling NdFeB Magnets and Rare Earth Fluorescent Materials from Electronic Waste

Recycling NdFeB Magnets and Rare Earth Fluorescent Materials from Electronic Waste

Effect of Graphene-Based Coating 3D Printing Process on the Remanence and Corrosion of Sintered NdFeB Magnets

Effect of Graphene-Based Coating 3D Printing Process on the Remanence and Corrosion of Sintered NdFeB Magnets

NdFeB magnet scrap valorization by leaching and recovery of rare earth metals by sorption on low-cost expanded clay

The search for new sources of rare earth metals (REM), such as neodymium and dysprosium, has ensued globally due to their strategic value for the sustainability of the energy sector. In this context, this work explored the potential of vermiculite as a sorbent for recovering rare earth cations from the leachate of end-of-life NdFeB magnets by kinetic, equilibrium, and desorption investigations. In which the REM uptake on vermiculite occurred by fast kinetics, and the significant sorbate-sorbate interactions at the equilibrium indicated that the REM sorption was a cooperative process; vermiculite sorbed the metals from the acid leachate in the following order: Fe(III) > Nd(III) > Zn(II) > Pr(III) > Co(II) > Dy(III) > Ni(II) > Al(III) > Mn(II); and the chelating agent ethylenediaminetetraacetic acid desorbed Nd(III) preferably over other metals, indicating the potential for further selective recovery processes. The characterization analyses indicated that the loaded vermiculite preserved the original structure, composition, functional groups, and thermal stability. Also, X-ray photoelectron spectroscopy corroborated the cation exchange mechanism between interlayer magnesium in the REM sorption. Thus, the experimental findings and a cost analysis compared to the literature demonstrated the cost-effectiveness and potential of vermiculite for the valorization of NdFeB magnet leachates.

Facile and mass-producible Ni-added iron nanowires with excellent microwave absorbing performance

The application of magnetic nanocrystalline powders as radar absorption materials is increasingly attracting R&D interest. Severe agglomeration and mass production, however, are critical issues for practical application of magnetic nanoparticles. In the present study, iron nanowires with varying amounts of nickel addition (0, 1, 10, 30, and 50 wt%) were synthesized via direct reduction of iron salts with the aid of strong NdFeB magnets. The yield rate of these Ni-added iron nanowires (NiFe NWs) exceeded 1 g/min, making them suitable and was feasible for mass production. The characteristics of the so-obtained NiFe NWs were confirmed using field emission scanning electron microscopy, X-ray diffraction, and high-resolution transmission electron microscopy. Composite resins with NiFe NWs additions (3, 5, and 10 wt%) were prepared and examined using the coaxial line method to reveal their microwave absorption characteristics. Experimental results showed that composite resins with 10 wt% NiFe NWs additions possessed superior microwave absorbing properties, with the Ni1Fe99 NWs-added product exhibiting the best performance. When produced with a thickness of 1.7 mm, the reflection loss of the composites reached −39.28 dB at 12.53 GHz. Additionally, the efficient maximum absorption bandwidth was 3.33 GHz, ranging from 14.27 to 17.60 GHz.

Finite Element Analysis Results and Analysis of Attraction Cases Between Like Poles of NdFeB Magnets

A novel phenomenon of attraction between unequally sized magnet like poles with different permeance coefficients ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_c</i> ) has been experimentally discovered. This attraction occurs only when a localized region of the low | <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_c</i> | magnet reverses its polarity, forming an unlike pole region with respect to the high | <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_c</i> | magnet. The attraction of like pole magnets is caused by the localized demagnetization ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LD</i> ) and is influenced by the factors, including the linearity of the BH curve, magnets’ geometries, and alignment. This paper reports more detailed finite element analysis (FEA) simulation and verification of the experimental results. Additionally, FEA simulation results for other untested unequally sized magnet pairs with various geometries are presented. The factors affecting the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LD</i> level, based on the field/force map from FEA results, are demonstrated. The potential of FEA simulation results for developing novel devices with unequally sized like poles in various applications is emphasized. The results have significant implications for the development of novel magnetic devices with enhanced performance and efficiency.

Additive manufacturing and numerical modeling of injection mold for fabricating NdFeB magnets

Additive manufacturing and numerical modeling of injection mold for fabricating NdFeB magnets

A new strategy for improving the Tb utilization efficiency in sintered NdFeB magnets through pressure-assisted grain boundary diffusion

Improving the utilization efficiency of heavy rare earth is currently a research hotspot in the field of rare earth permanent magnets. In this article, the effect and mechanism of pressure-assisted grain boundary diffusion (PGBD) on improving Tb utilization efficiency was investigated. The magnetic properties, microstructure, and magnetic domain morphology of the PGBD magnets were compared and analyzed in relation to conventional grain boundary diffusion (CGBD) magnets. The results shows that the PGBD process promoted Tb diffusion into the magnets. The residual layer thickness of the PGBD magnets was thinner than that of the CGBD magnets, demonstrating that the PGBD process could allow more Tb to diffuse into the magnets. The formation of a more complete and deeper core-shell structure in the PGBD magnets significantly enhances their resistance to demagnetization fields, thereby resulting in an increased coercivity. The PGBD process exhibits a reduction in TbH3 usage by approximately 0.2 wt% compared to the CGBD process, while maintaining an equivalent level of coercivity increment. These findings highlight the efficacy of the PGBD process in enhancing Tb utilization efficiency and conserving Tb resources.

Supply and demand conflicts of critical heavy rare earth element: Lessons from gadolinium

Our understanding of supply and demand conflicts of critical minerals is quite limited, which may inhibit strategies in their criticality mitigation. This is particularly severe for gadolinium (Gd), as a heavy rare earth element, given its small amounts in supply and wide applications ranging from glass to NdFeB magnets. This study (1) developed a sophisticated accounting framework to measure the supply and demand trends of Gd within China from 1990 to 2018 and (2) provided a qualitative review and discussions on Gd supply-demand balance in a holistic perspective. Our findings suggest that the balance of Gd supply and demand shows a cyclical trend, termed as periodic "scarcity-abundance" pattern, influenced by changes in environmental regulations, trade structures, and technological applications. This highlights the importance of the joint measurement of both supply and demand of critical minerals for their criticality mitigation.

THE EFFECT OF BAKELITE BINDERS ON MAGNETIC PROPERTIES AND HARDNESS VALUES OF MQP-TYPE BONDED NdFeB MAGNETS

Permanent magnets are important in modern society as components in various devices used by many industries and consumers, especially in generators and electric motors. Bonded magnet technology allows combining powdered magnetic materials with polymers as a binder to produce magnetic components that can be applied to certain applications, such as SynRM (synchronous reluctance) motors. Bonded magnets are easy to form without sacrificing their magnetic properties, which are too large, and also reduce costs, making them more effective and efficient. This paper reports the results of a study on the manufacture of bonded magnets NdFeB using bakelite binder on MQP-type NdFeB magnets with a bakelite variation of 0.5 - 2 wt.%. The characterization included testing magnetic properties with Permagraph, morphology with SEM (scanning electron microscope), and hardness values with micro Vickers hardness tester. The results of this study obtained remanence values in the range 5.53 - 6.44 kG and hardness values in the range 341.8 - 507.9 HV for NdFeB bonded magnets. According to SEM observations, the bakelite polymer matrix has successfully bound NdFeB grains, and no porosity is visible.

Composite Resins Impregnated by Phosphorus Organic Extractants for Separation of Rare Earth Elements from Nitrate-Based Leachate of Permanent Magnets.

Composite resins impregnated by different organophosphorus extractants were developed and used for the extraction chromatography recovery of rare earth elements from nitrate-based leachate of NdFeB permanent magnets. The influence of different factors on recovery of Nd(III) and Fe(III), as the most difficult to separate elements, by developed resins was studied. The influence of extractant structure, the composition of feed solutions, and concentrations of HNO3 and NH4NO3 on the recovery of Fe(III) and Nd(III) by prepared resins were considered. The best recovery of Nd(III) was shown by resin impregnated with N,N-dioctyl (diphenylphosphoryl) acetamide. For this material, sorption characteristics (values of the distribution coefficient, capacity, and the Nd(III)/Fe(III) separation factor) were obtained, and the reproducibility of the loading-stripping process was evaluated. This resin and its precursors were characterized by IR spectroscopy. It was found that the developed resin is more efficient for Nd(III) recovery than resin impregnated with TODGA. An effective approach to the Nd(III)/Fe(III) separation with developed resin in nitrate solution was proposed. This approach was used for recovery of Pr(III), Nd(III), and Dy(III) from the nitrate-based leachate of NdFeB magnets by the developed resin. The final product contained 99.6% of rare earths.

Preparation, microstructure and corrosion resistance of Al2O3 coatings by cathodic plasma electrolytic deposition on sintered NdFeB permanent magnet

The Al2O3 ceramic coatings were prepared on the sintered NdFeB magnets by cathodic plasma electrolytic deposition (CPED) method in aluminum nitrate alcohol solution. The surface and cross-sectional morphologies, element and phase composition, corrosion resistance and magnetic properties of the coatings were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermal shock, hydrothermal weight loss, electrochemical corrosion and physical property measurement system (PPMS), respectively. The results show that the coatings mainly consist of γ-Al2O3 and α-Al2O3 phases, and the volume of α-Al2O3 increases with increasing the voltages. The surface of the coatings shows a typical coral reef structure, and the thickness of the coatings increases from 29 µm to 53 µm with increasing the voltages. The Al2O3 coatings have excellent thermal shock resistance as well as the excellent corrosion resistance in hydrothermal conditions. The corrosion resistance of the coatings enhances with increasing the voltages, reaching the strongest at 470 V, and then decreases. This study provides a new method for forming ceramic coatings on the surface of sintered NdFeB magnets to improve its corrosion resistance.

Optimization of grain boundary by Mo nano-powder to enhance the coercivity of NdFeB magnets

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 (Hcj) of the magnets. When the addition of Mo nano-powder is increased from 0 to1.0 wt%, the Hcj of the magnet is significantly improved. Especially, when the addition of Mo nano-powder is 0.8 wt%, the Hcj 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 Hcj of NdFeB magnets, which has practical application value and theoretical significance for the research and development of high-performance NdFeB magnets.

Effect of Nb on microstructure and magnetic decay of sintered NdFeB magnets in NaCl solution

Herein, the influence of Nb on the microstructure and magnetic decay of sintered NdFeB magnets was investigated. The NbFeB and Fe2Nb phases were determined through field emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and selected area electron diffraction. The effects of Nb on the crystal structure of the magnet were studied via electron backscatter diffraction analysis. Laser scanning confocal microscopy, a pulsed field magnetometer, and a fluxmeter were used to measure the changes in the surface roughness and magnetic properties of the magnet during corrosion. Based on the experimental result, Nb can optimize the distribution of the Nd-rich phase inside the magnet, reduce the generation of crystal defects, refine the grains, and promote the crystal orientation along the [001] direction. During magnet corrosion, the Nb compound captured hydrogen atoms, causing internal lattice distortion and stress concentration in the matrix phase thereby leading to crush. The broken matrix phase adhered to the magnet surface, isolating the magnet from contact with the corrosive solution and improving the corrosion resistance of the magnet. Moreover, Nb can reduce the impact of the surface structure damage on the demagnetization of the magnet during corrosion, thereby lowering magnetic decay.

Separation and Recovery of Rare Earths and Iron from NdFeB Magnet Scraps

NdFeB magnet scraps contain large amounts of iron, which poses challenges in recycling and greatly hinders the recovery of rare earths through direct hydrometallurgical treatment. To address this issue, we conducted tests using a flash furnace to explore the low-temperature reduction behavior of NdFeB magnet scraps under an H2 atmosphere based on thermodynamic calculations comparing the reduction properties of rare earth oxides (REOs) and iron oxide (FeOx). The results demonstrated that the reduction rate of FeOx surpassed 95% under optimal conditions including a reduction temperature of 723 K, a particle size (D90) of 0.45 μm, and an H2 flow rate of 2 L/min. X-ray diffraction and electron probe microanalysis of the reduction product revealed that the flash reduction at 723 K facilitated the selective reduction of FeOx, owing to efficient mass and heat transfer. Consequently, a two-step magnetic separation process was employed to separate metallic Fe and REOs from the reduction product. Fe-rich phase, obtained with a remarkable Fe distribution ratio of 90.2%, can serve as an economical raw material for weathering steel. Additionally, the REOs are enriched in REO-rich phase, achieving a distribution ratio of 93.9% and significantly boosting the REO concentration from 30.2 to 82.8 wt%.

NdFeB Permanent Magnet Uses, Projected Growth Rates and Nd Plus Dy Demands across End-Use Sectors through 2050: A Review

Rare earth element (REE) permanent magnets (NdFeB) are a critical element in a vast and growing number of industrial applications. In consumer electronics, a broad category encompassing computer, CD, and DVD hard drives, in addition to the ubiquitous cell phones, the nominal NdFeB magnet content may be small, but the global market share for this sector accounts for almost 30% of NdFeB demand, due to a large and continually increasing consumer base. It is estimated that wind turbines that primarily employ permanent magnets will add roughly 110 GW annually of on- and off-shore capability over the next few years. Electric vehicles (EVs) and E-bicycles (EBs) equipped with permanent magnet motors comprise the transportation contribution. Permanent magnet motors have garnered nearly 100% of the market share among EV manufacturers worldwide. Industrial, professional service, and personal robots, most using permanent magnets, are also included in the projected global need for rare earths, particularly Nd and Dy. The sector projects significant growth of approximately 10% across robotic categories. In this paper, we calculate the future demand for Nd and Dy through 2050 across these sectors using a compounded annual growth rate coupled with magnet weight and rare earth content. Uncertainties in the estimates, such as the true global production of Nd, a range of end-product scales and/or unit types in each sector, varied magnet compositions, and the variety of uses within a sector, are all considered.

System identification and artificial intelligent (AI) modelling of the molten salt electrolysis process for prediction of the anode effect

NdFeB magnets are widely used in various applications including electric and hybrid vehicles, wind turbines, and computer hard drives. They contain approximately 31–32 wt% Rare Earth Elements (REEs), mainly neodymium (Nd) and praseodymium (Pr), and are produced by molten salt electrolysis using fluoride electrolytes. However, anode passivation or anode effect may occur, generating greenhouse gases if insufficient amounts of metal oxides are available in the system. Therefore, in this study, a dynamic model of the electrochemical process was developed to estimate the system variables and predict the anode effect using several system identification methods. The Transfer Function (TF) estimation, Auto-Regressive with Extra inputs (ARX), Hammerstein-Weiner (HW), and Artificial Neural Network (ANN) models were used, and their results were compared based on the occurrence of the anode effect. The best model achieved an average accuracy of 96% in predicting the process output.

Recovery of rare earth metal oxides from NdFeB magnet leachate by hydrophobic deep eutectic solvent extraction, oxalate stripping and calcination

With the scarcity of resources and the growing consumer demand for rare earth elements (RE), it is imperative to develop clean and sustainable methods to recover these valuable elements. This research proposes a novel green process for the selective recovery of RE from spent NdFeB permanent magnet using hydrophobic deep eutectic solvent (HDES). A total of 13 HDES systems composed of trioctylphosphine oxide (TOPO) as hydrogen bond acceptor (HBA) and alcohols as hydrogen bond donor (HBD) were prepared and characterized. Through a simple screening process, it was determined that ternary HDES (DA:MA:TOPO = 5:5:4) exhibited the best extraction and separation performance for REs and Fe. The extraction conditions such as aqueous phase acidity, organic/aqueous phase ratio, the concentration of Fe3+ and equilibration time were further studied and optimized. Under the most suitable conditions, HDES (DA:MA:TOPO = 5:5:4) was used for batch countercurrent extraction, where the concentration of REs in the raffinate was lowered from 4390 mg/L to 34 mg/L, and the recovery reached 99%. The HDES could be stripped by 0.2 mol/L Na2C2O4, which could further separate a small amount of loaded Fe (133 mg/L) and RE, so that the purity of the final product reached >99%. The stripped HDES could be recovered after washing with deionized water. Even after five cycles, HDES still maintained good stability. This innovative process does not require the use of salting-out agents or toxic volatile solvents, providing new possibilities for efficient and clean separation.