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The spent neodymium-iron-boron (NdFeB) magnet is a highly valuable secondary resource of rare earth elements (REEs). Hydrometallurgical processes are widely used in recovering REEs from spent NdFeB magnets, but they will consume large amounts of organic chemicals, leading to severe environmental pollution. This work developed an alternative green route to selectively recover REEs from spent NdFeB permanent magnets using a purely inorganic zinc salt. The Hammett acidity measurement showed that concentrated ZnCl 2 solutions could be regarded as a strong Brønsted acid. Concentrated ZnCl 2 solutions achieved a high separation factor (>1 × 10 5 ) between neodymium and iron through simple dissolution of their corresponding oxide mixture. In the simulated recovery process of spent NdFeB magnets, the Nd 2 O 3 product was successfully recovered with a purity close to 100% after selective leaching by ZnCl 2 solution, sulfate double-salt precipitation, and oxalic acid precipitation. The separation performance of the ZnCl 2 solution for Nd 2 O 3 and Fe 2 O 3 remained almost unchanged after four cycles. The energy consumption and chemical inputs of this process are about 1 / 10 and half of the traditional hydrometallurgy process separately. This work provides a promising approach for the green recovery of secondary REE resources.

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. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]

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]

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]

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]

• 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 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]

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]

In this work, the eutectic Tb 70 Cu 20 Ga 10 alloy was applied to high magnetic performance NdFeB magnet. The coercivity of magnets effectively improved of 60.61% without reduction in maximum energy product and remanence after diffusion. The magnetic vector potential of magnet was analyzed by general finite element method. The diffusion mechanism of eutectic had been discussed at various diffusion depth. The Tb diffuses into the magnet formation continuous Tb-rich shells and thin grain boundary phase, which strongly enhance coercivity. The Cu, Ga and O enrich into grain boundary form thin RE 2 (Fe, CuGaO) 3 phases, which increase diffusion channel and recover microcrack near surface of magnet. This Tb 70 Cu 20 Ga 10 diffusion alloys has a promising potential to develop high magnetic performance and low cost sintered NdFeB magnet. • This study provides a coat method in NdFeB magnet. • The Tb 70 Cu 20 Ga 10 alloys is the first time used to improve coercivity. [ABSTRACT FROM AUTHOR]

We present the results of a systematic investigation into how the coercivity and maximum energy product of NdFeB permanent magnets are affected by magnetic and geometric microscopic properties. The results are based on numerical micromagnetic simulations carried out with the open source numerical framework MagTense. We considered artificially generated realistic microstructures for which we can control the number of crystal grains as well as the thickness of the intergrain region. Based on variations of the exchange constant, easy axis orientation, grain boundary width and intergrain material properties, the results indicate that while all of these can contribute to a reduction of coercivity, the easy axis orientation has the largest influence. For this, if the easy axis orientation is distributed within a cone with an opening angle of 15°, that is enough to reduce the coercivity by 1 T. Regarding the maximum energy product, the width of the grain boundary layer as well as the easy axis orientation were seen to have the largest influence, with the exchange constant only very weakly influencing the maximum energy product. Our analysis thus methodically clarifies the different factors contributing to the reduction of the value of the coercivity and maximum energy product when compared to the theoretical limit, a discrepancy known as Brown's paradox. • We systematically investigate coercivity and maximum energy product of NdFeB magnets. • We use the open-source numerical framework MagTense to simulate the NdFeB magnets. • The easy axis orientation is shown to have the largest influence on coercivity. • The grain boundary width has the largest influence on the maximum energy product. • The study methodically clarifies the different factors contributing to Brown's paradox. [ABSTRACT FROM AUTHOR]

An organic-inorganic composite passivation of Zn coated NdFeB magnets was carried out using Ce-containing compound and organosilane as source materials. Effects of organosilane content on the microstructure of composite passivation layer were analyzed, and the corrosion resistance and corrosion mechanism of the passivated Zn/NdFeB specimens were deeply studied. Composition, elemental distribution, phase structure and morphology of the specimens were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. The corrosion resistance of the specimens was studied by polarization curves, electrochemical impedance spectroscopy, neutral salt spray text and mass gain test. Results show that adding an appropriate amount of organosilane during the passivating process can form a passivation layer composed of Ce, Si, and O. The optimized Zn(CS-1)/NdFeB achieves the longest NSS time of 840 h, which is twice that of Zn(Ce-5)/NdFeB specimens. Organosilane can build a framework for the passivation layer and make the passivation layer more compact. During the corrosion process, the corrosion medium invasion path is long due to the support of the organosilane frame on the surface, so the corrosion resistance of Zn(CS)/NdFeB is greatly enhanced. • Organic-inorganic composite passivation layer was prepared on Zn-coated NdFeB by liquid phase method. • Corrosion potential of Zn(CS-1)/NdFeB shifts positively and the corrosion current decreases by 1 orders of magnitude. • NSS time of Zn(CS-1)/NdFeB increases from 432 h to 840 h. • Formation of composite passivation layer apparently contributes to the enhancement of corrosion resistance. [ABSTRACT FROM AUTHOR]

• The coercivity of the magnet was obviously increased from 14.16 kOe to 20.43 kOe after the optimal Dy diffusion process by using a homemade Dy coating. • The work provides an insight on the Dy evolution process during the diffusing process. • The diffusion coefficients of Dy diffusing along the grain boundary and into the grain were systematically analyzed by Fick's second law, which is significant for understanding the mechanism of coercivity improvement. Heavy rare earth (such as Dy) thermal diffusion process is a promising method to increase the coercivity of sintered NdFeB magnets and optimize s their thermal performance. However, the Dy evolution process and the mechanism of coercivity improvement still require further clarification. In this work, commercial 30 M magnets were employed as the initial magnet, and a homemade DyF 3 coating was prepared for thermal diffusion treatment. The optimal Dy diffusion process was obtained at 900 ℃ for 8 h. The coercivity of the magnet was increased from 14.16 kOe to 20.43 kOe with a negligible decrease in remanence. The Dy evolution process was systematically analyzed for understanding the mechanism of coercivity improvement. The diffusion coefficient was calculated based on Fick's second law. The diffusivity of Dy along the grain boundaries (5.16 × 10−8 cm2·s−1) is much higher than that in the grains (2.33 × 10−11 cm2·s−1). Therefore, the Dy diffused into the magnet along the grain boundaries with a faster diffusivity, forming uniform and continuous grain boundaries of the Dy-rich phases around the grains, which plays a decoupling effect and significantly increases the coercivity of the magnet. Simultaneously, the Dy in the grain boundaries diffused into the main phase with a slower diffusivity to form a (Nd, Dy) 2 Fe 14 B thin layer with higher magnetocrystalline anisotropic, which can inhibit the nucleation of reversed magnetic domains and further improve intrinsic coercivity. However, over diffusion process led to the excess Dy diffused into the grain, which will decrease the performance of the magnet. This work provides an insight of Dy evolution process during the diffusing period, and is significant to understand the improvement mechanism of coercivity for preparing NdFeB magnets with high-performance and low cost. [ABSTRACT FROM AUTHOR]

Rare earth element (REE) containing neodymium-iron-boron (NdFeB) magnets play a major role in green technologies, including motor and generator applications. Recycling of REE from NdFeB magnets is expected to be beneficial from an environmental point of view compared to the production of magnets using primary REE currently practiced. This study gives a broad overview of global recycling potentials from end-of-life magnets from eleven different application groups and industrial scrap, quantified through dynamic material flow analysis. Data was obtained through a review of the literature, complemented by expert estimations. Recycling potentials achievable for REEs used in NdFeB magnets, namely neodymium (Nd), praseodymium (Pr), terbium (Tb) and dysprosium (Dy), were calculated for years 2020–2030, derived from two demand scenarios to reflect uncertainties in historic NdFeB demand figures and future demand development, taking into account the recent success in heavy REE reduction efforts. The most important NdFeB application groups in terms of recycling potentials are identified. The modelled scenarios show that between 18 and 22 percent of global light REE (Nd and Pr) and 20–23 percent of heavy (Dy and Tb) REE demand for use in NdFeB magnet production can be met by supply from secondary sources from end-of-life magnets and industrial scrap in years 2020, 25 and 30 (ranges of values for individual years and scenarios). [ABSTRACT FROM AUTHOR]

NdFeB bulk magnets were synthesized by spark plasma sintering (SPS) using the precursors of melt spun nanocrystalline Nd10.15Pr1.86Fe80.41Al1.67B5.91 ribbons mixed with Zn and/or Dy2O3 powders. The addition of 0.6 wt.% Zn or 2 wt.% Dy2O3 is effective in improving the magnetic properties of the magnets, and their coercivities are about 11% or 15%, respectively, higher than that of the additive free magnet. Both additives can suppress the grain growth of Nd2Fe14B phase. Dy2O3 is not beneficial to the densification during SPS, but Dy is considered to partly diffuse into the grains near particle boundaries and to form (Nd, Dy)2Fe14B phase. NdZn and NdZn5 phases were observed in the SPSed magnets with Zn additions more than 1 wt.%, which leads to coarse grains and porosities between the particles. The magnet with combined additions of 2 wt.% Dy2O3 and 0.6 wt.% Zn showed good thermal stability with small temperature coefficients and optimal magnetic properties with high coercivity and maximum energy product. [ABSTRACT FROM AUTHOR]

NdFeB powders were consolidated into nanocrystalline bulk magnets by a near-net-shape process of high-velocity compaction (HVC) at room temperature with no binder employed. The nanostructure can be maintained after compaction. The compacted magnets with relatively high density can inherit the coercivity of the starting powders. The mechanical strength of the HVCed magnet after heat treatment is comparable to that of the conventional bonded NdFeB magnets. The anisotropic magnet has also been prepared by hot deformation using HVCed magnet as the precursor. The remanence value along the pressing direction increased from 0.64 to 0.95 T and maximum energy product (BH) max increased from 65 to 120 kJ/m 3 after hot deformation. The processing–structure–properties relationships for both isotropic and anisotropic magnets are discussed. [ABSTRACT FROM AUTHOR]

This work analyses the effects of segmentation followed by parallel magnetization of ring-shaped NdFeB permanent magnets used in slotless cylindrical linear actuators. The main purpose of the work is to evaluate the effects of that segmentation on the performance of the actuator and to present a general overview of the influence of parallel magnetization by varying the number of segments and comparing the results with ideal radially magnetized rings. The analysis is first performed by modelling mathematically the radial and circumferential components of magnetization for both radial and parallel magnetizations, followed by an analysis carried out by means of the 3D finite element method. Results obtained from the models are validated by measuring radial and tangential components of magnetic flux distribution in the air gap on a prototype which employs magnet rings with eight segments each with parallel magnetization. The axial force produced by the actuator was also measured and compared with the results obtained from numerical models. Although this analysis focused on a specific topology of cylindrical actuator, the observed effects on the topology could be extended to others in which surface-mounted permanent magnets are employed, including rotating electrical machines. [ABSTRACT FROM AUTHOR]

Herein, we investigated the effects of Ce on the corrosion behavior of NdFeB magnets in 3.5% NaCl solutions using electrochemical tests, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) mapping, and scanning Kelvin probe force microscopy (SKPFM). We demonstrated that Ce markedly enhances the corrosion resistance of NdFeB magnets. Ce primarily replaces Nd in the Nd-rich phase instead of matrix phase, increasing the surface potential of the Nd-rich phase. An increase in the Ce content from 0 to 5.21 wt%, decreased the potential difference between the main phase and (Nd, Ce)-rich phase from 350.2 mV to 97.7 mV; therefore, the corrosion resistance of the magnetic materials increased. The corrosion resistance constituted the Nd-rich phase < the void < metal matrix. Moreover, based on the results of the study, we discussed the impact mechanism of additions of Ce on the corrosion resistance of the magnets. [ABSTRACT FROM AUTHOR]

This work reports the grain boundary character distribution (GBCD) on a statistical meaning of phase boundaries that are between Nd2Fe14B and thin‐layer‐like Nd‐rich phases in a sintered NdFeB magnet. In the low‐textured sample, the phase boundaries are divided into preferred phase boundaries (with a preferred misorientation of 31°/[001] across the boundary plane) and random phase boundaries. By the five parameter analysis (FPA) method, the orientations of phase boundaries as well as the subsets are textured. The correlation between the GBCDs and magnetic properties is suggested via the illustrated anisotropic features at phase boundary positions. [ABSTRACT FROM AUTHOR]

End-of-life NdFeB magnets are an important secondary source of rare-earth elements (REEs) and cobalt. Recycling of these magnets can also mitigate the supply problems of its constituent critical REEs (mainly neodymium and dysprosium). The recycling of bonded NdFeB magnets has received much less attention than that of sintered NdFeB magnets. In this study, a novel flow sheet is presented for recycling of bonded NdFeB magnets that is applicable to sintered magnets as well. Demagnetized magnet powder was mixed with 25 or 40 wt./vol% NaOH solution and baked at 150 to 200 °C for 30 to 540 min. In this way, REE metals were transformed into their corresponding hydroxides, whereas iron metal formed NaFeO 2. By washing the reaction mixture with water, 96.5% of Na was recovered as NaOH and Na 2 CO 3 , whereas 90.3% of B was recovered as borax. The calcine containing REE hydroxides and iron oxide was then leached at 60 or 90 °C with 20 vol% Versatic Acid 10 diluted in an aliphatic diluent. >95% of the REEs were dissolved, with <1% co-dissolution of iron and <10% co-dissolution of cobalt. Precipitation stripping with an oxalic acid solution quantitatively regenerated the organic solvent with virtually the same composition of fresh solvent. After calcination of the oxalate precipitate, a mixed rare-earth oxide with 98.4 wt% purity was produced. The waste oxalic acid solution (pH ≤1) containing co-dissolved sodium and minor amounts of iron and cobalt could be used as a leaching agent for Co in the maghemite-dominated residue. • A novel flow sheet is presented with alkali baking and Versatic Acid 10 leaching. • ≥ 95% REEs with <1% Fe and <10% Co co-dissolution was achieved. • 90.3% B and 96.5% of Na were recovered as borax, NaOH and Na 2 CO 3. • By stripping precipitation, a mixed REO was formed with 98.4 wt% purity. • Almost all consumed Versatic Acid 10 was regenerated. [ABSTRACT FROM AUTHOR]

In recent years, China's dominant role in the rare earth market and the associated impacts have strengthened the interest in the recovery of rare earth elements (REE) from secondary resources. Therefore, numerous research activities have been initiated aiming at the recovery of REEs from different types of waste streams, which includes, inter alia, neodymium-iron-boron (NdFeB) magnets. Although several research projects have successfully been completed, most experts do not expect an industrial implementation in Europe within the next years. This article analyses the reasons for this situation, addressing the availability of sufficient amounts of NdFeB wastes, the technology readiness level of the developed processes in Europe, as well as the economic aspects. Based on these analyses, an estimation of a realistic timeframe for the industrial implementation of NdFeB recycling in Europe is deduced and critically discussed. [ABSTRACT FROM AUTHOR]