NdFeB Magnets Research Articles

Grain boundary infiltration in HDDR processed Nd2Fe14B magnets

We investigate the grain boundary infiltration process of various low melting eutectic alloys for the coercivity enhancement of hydrogenation disproportionation desorption recombination (HDDR) processed Nd-Fe-B powders. Nd-based as well as heavy rare earth (Tb) and light rare earth (La, Ce) containing alloys were systematically studied: Nd70Cu30, Nd90Al10, Nd80Ga15Cu5, Nd62Fe14Ga20Cu4, Nd60Tb10Cu30, La71Cu29 and Ce72Cu28. Moreover, the Fe content in the quaternary Nd-Fe-Ga-Cu system was varied to investigate the effect of grain boundary phase magnetism on the resultant coercivity.The largest coercivity enhancement, from 0.42 T in the as-HDDR powder to 1.88 T after infiltration was observed in the case of ternary Nd80Ga15Cu5 composition. Furthermore, it also shows the best temperature stability with the infiltrated sample still exhibiting a coercivity of 0.58 T at 200 °C. Infiltration of light rare earth (La, Ce) based alloy did not increase coercivities due to poor wetting at the grain boundaries. Adding Fe to the grain boundary alloys was shown to enhance magnetization up to a certain extent without significant loss in coercivity. These findings demonstrate the effectiveness of grain boundary infiltration in HDDR-processed magnets without using heavy rare earths. The infiltration with non-magnetic material strongly decreases the intergranular interaction, reflected in a different magnetic domain evolution during the magnetization reversal process.

Recovery of Rare Earth Elements from Spent NdFeB-Magnets: Separation of Iron through Reductive Smelting of the Oxidized Material (Second Part)

This paper proposes a pyrometallurgical recycling method for end-of-life NdFeB magnets by oxidizing them in air and subsequently smelting them. The smelting process enabled the recovery of rare earth elements (REEs), producing a new reach concentrate separating the iron as a metallic phase. From the products of smelting, the metallic phase showed a maximum Fe content of 92.3 wt.%, while the slag phase showed a maximum total REE (Nd, Pr, and Dy) content of 47.47 wt.%, both at a smelting temperature of 1500 °C. ICE-OES and XRD analysis were conducted on both phases, and results showed that the metal phase consists mainly of Fe and Fe3C while the slag phase consists of the RE-oxides, leftover Fe2O3, and a mixture of Fe6Nd4. The obtained slag concentrate based on the oxides of rare earth elements is suitable for further pyrometallurgical or hydrometallurgical treatment in order to obtain rare earth elements.

Comparative Study of Manufacturing NdFeB Magnet Wastes Recycling: Oxidative Roasting-Selective Leaching and Whole Leaching Routes

This research investigated recycling of manufacturing NdFeB magnet wastes in as-sintered and powder forms which contained high carbon via pyro-hydro metallurgy process. Effects of oxidative roasting on selective leaching of the magnet wastes were the main focus in comparison to recycling via whole leaching without oxidative roasting. The process started from oxidative roasting at 600 °C, sulfuric leaching, drying, roasting at 750 °C for powder and 800 °C for sintered wastes, water leaching, oxalic acid precipitation and calcination at 1000 °C to obtain neodymium oxides. Oxidative roasting was found to reduce carbon and resulted in neodymium and iron oxide formation with a minimum amount of neodymium iron oxide. This provided effective selective leaching of neodymium. For whole leaching, a significant loss of neodymium into leached residue was observed. Oxidative roasting-selective leaching provided significant recovery in the amount of 75.46% while whole leaching resulted in only 31.62 wt.% in the case of sintered waste. The final composition via oxidative roasting-selective leaching consisted of 68.11 wt.% neodymium, 19.83 wt.% praseodymium and 0.31 wt.% iron, while whole leaching resulted in a higher amount of iron at 1.20 wt.%. Similar results were obtained for powder magnet waste.

Variety of Characteristic Magnetic Material on Permanent Magnet Synchronous Generator (PMSG)

Wind energy conversion system, one of the main components is a Permanent Magnet Synchronous Generator (PMSG). During the past two decades, many types of per- manent magnet generators for wind power applications have been the research topic. This study focuses primarily on designing a PMSG to create, simulate, and analyze an internal permanent magnet topology with twelve plots and eight poles. We limit with the simulation was carried out at a rotational speed of 1000rpm, and a type of permanent magnet material, Ceramic 11, SmCo 26/26, and NdFeB 48/11. The result of the analysis is that permanent magnets applied in the design of a generator impact its output power and efficiency. At 15 Ω and 60 Ω loads, SmCo 26/26 and NdFeB 48/11 are the only ones that fulfill the specified requirements in this investigation. The permanent magnet type with the most optimal characteristics is Neodymium Iron Boron 48/11 because it has a high flux density, thus causing the electrical energy generated to be greater than other types of permanent magnets. The 48/11 NdFeB permanent magnet generates the most output power, 2110.86 W when loaded with 15 Ω. The best efficiency of 89.38 percent for the PMSG 12 slot eight poles occurs when the load is 15 on the 48/11 NdFeB permanent magnet.

Dy evolution and coercivity improvement mechanism of sintered NdFeB magnets in thermal diffusion process

Heavy rare earth (such as Dy) thermal diffusion process is a promising method to increase the coercivity of sintered NdFeB magnets and optimizes 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 DyF3 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)2Fe14B 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.

Preparation and corrosion resistance of epoxy resin coating for bonded NdFeB magnet

The epoxy resin (ER) coatings were coated on ring-shaped bonded NdFeB magnet (RSM) using air spraying and cathodic electrophoresis deposition processes. The morphologies and microstructures of the bare RSM (B-RSM), sprayed ER/RSM (S-ER/RSM) and electrophoretic ER/RSM (E-ER/RSM) were observed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), 3D laser confocal scanning microscopy (LSCM) and fourier infrared spectrometer (FTIR). The corrosion behaviors of the ER coatings were analyzed by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and neutral salt spray test (NSS). The results showed that ER coatings covered the pores of B-RSM well and played a good sealing role. Moreover, E-ER/RSM had a more uniform film layer and better surface leveling than S-ER/RSM. Compared with B-RSM and S-ER/RSM, the corrosion current density (Icorr) of E-ER/RSM reached 1.904 × 10−5 A/cm2, one order of magnitude lower than that of B-RSM (1.033 × 10−4 A/cm2) and about twice lower than that of S-ER/RSM (4.728 × 10−5 A/cm2). The value of charge transfer resistance (Rct) of E-ER/RSM is 1671.6 Ω·cm2, which is higher than that of both B-RSM (236.96 Ω·cm2) and S-ER/RSM (425.46 Ω·cm2). The NSS time of E-ER/RSM reached 144 h, longer than that of S-ER/RSM (72 h) and B-RSM (24 h). The corrosion resistance of bonded NdFeB magnets was improved due to the good shielding properties and physical barrier effect of the ER coatings. In addition, the corrosion mechanisms of ER coatings were discussed in detail.

Intrinsic hard magnetism and thermal stability of a ThMn12-type permanent magnet

Herein, we theoretically demonstrate that simple metal (Ga and Al) substitutional atoms, rather than the conventional transition metal substitutional elements, not only stabilize the ThMn12-type SmFe12 and Sm(Fe,Co)12 phases thermodynamically but also further improve their intrinsic magnetic properties such that they are superior to those of the widely investigated SmFe11Ti and Sm(Fe,Co)11Ti magnets, and even to the state-of-the-art permanent magnet Nd2Fe14B. More specifically, the quaternary Sm(Fe,Co,Al)12 phase has the highest uniaxial magnetocrystalline anisotropy (MCA) of about 8 MJ m−3, anisotropy field of 18.2 T, and hardness parameter of 2.8 at room temperature and a Curie temperature of 764 K. Simultaneously, the Al and Ga substitutional atoms improve the single-domain size of the Sm(Fe,Co)12 grains by nearly a factor of two. Numerical results of MCA and MCA-driven hard magnetic properties can be described by the strong spin-orbit coupling and orbital angular momentum of the Sm 4f-electron orbitals.

Investigating the properties of recycled NdFeB magnets

Investigating the properties of recycled NdFeB magnets

Recovery of Rare Earth Elements through Spent NdFeB Magnet Oxidation (First Part)

Due to their remarkable magnetic properties, such as a high maximum energy product, high remanence, and high coercivity, NdFeB magnets are used in a variety of technological applications. Because of their very limited recycling, high numbers of spent NdFeB magnets are widely available in the market. In addition to China’s monopoly on the supply of most rare earth elements, there is a need for the recovery of these critical metals, as their high import price poses an economic and environmental challenge for manufacturers. This paper proposes a pyrometallurgical recycling method for end-of-life NdFeB magnets by oxidizing them in air as first required step. The main goal of this method is to oxidize rare earth elements from NdFeB magnets in order to prepare them for the carbothermic reduction. The experimental conditions, such as the oxidation temperature and time, were studied in order to establish the phase transformation during oxidation using the Factsage Database and experimental conditions. Our thermogravimetric analysis TGA analysis revealed an increased sample mass by 35% between room temperature and 1100 °C, which is very close to the total calculated theoretical value of oxygen (36.8% for all elements, and only 3.6% for rare earth elements REE), confirming the complete oxidation of the material. The obtained quantitative analysis of the oxidation product, in (%), demonstrated values of 53.41 Fe2O3, 10.37 Fe3O4; 16.45 NdFeO3; 0.45 Nd2O3, 1.28 Dy2O3, 1.07 Pr2O3, and 5.22 α-Fe.

Biodegradable ring-shaped implantable device for intravesical therapy of bladder disorders

Intravesical instillation is an efficient drug delivery route for the local treatment of various urological conditions. Nevertheless, intravesical instillation is associated with several challenges, including pain, urological infection, and frequent clinic visits for catheterization; these difficulties support the need for a simple and easy intravesical drug delivery platform. Here, we propose a novel biodegradable intravesical device capable of long-term, local drug delivery without a retrieval procedure. The intravesical device is composed of drug encapsulating biodegradable polycaprolactone (PCL) microcapsules and connected by a bioabsorbable Polydioxanone (PDS) suture with NdFeB magnets in the end. The device is easily inserted into the bladder and forms a ‘ring’ shape optimized for maximal mechanical stability as informed by finite element analysis. In this study, inserted devices were retained in a swine model for 4 weeks. Using this device, we evaluated the system's capacity for delivery of lidocaine and resiquimod and demonstrated prolonged drug release. Moreover, a cost-effectiveness analysis supports device implementation compared to the standard of care. Our data support that this device can be a versatile drug delivery platform for urologic medications.

Enhanced extremely weak-field energy harvesting via magnetic flux and stress concentration effects in ferromagnetic/ferroelectric composite

In this work, we report an enhanced magneto-mechano-electric (MME) coupling in Ni/Pb(Zr,Ti)O3 (PZT) ceramic composited ladder-type cantilever attached with a tip mass of NdFeB magnet, which simultaneously exhibits the magnetic flux concentration effect and the stress concentration effect, and therefore, it shows an enhanced extremely weak-field (EWF) coupling ability. Investigations show that the proposed MME energy harvester (EH) can generate an output power density of 7.16 μW Hz−1 Oe−2 cm−3, which is the highest value compared to the state of the art MME energy harvesters. Under an EWF of even as low as Hac = 0.1 Oe (about half level of the geomagnetic field), the proposed MME-EH can still produce a peak–peak output power of 23.5 μW, which is enough power to light up 4 LEDs in real time. Furthermore, it can drive a wireless sensor communication system in real time under a weak Hac = 0.75 Oe excitation, demonstrating it has potential to serve as a micro-energy source of wireless sensor networks in EWF circumstance. This work is not only beneficial but has also inspired future multi-function-integrated material and smart electronic device designs in Internet of Things in EWF circumstance.

Calculation of Three-dimensional Energy Product for Isotropic Nd2Fe14B Magnet

A conventional energy product calculated by the product of the B-field and the H-field is not sufficient for representing the performance of a magnet because it considers the homogeneous and only the uniaxial magnetic properties of the magnet. The conventional energy product has been compared with another energy product obtained by integrating the scalar product of the B-field and the H-field of each cell composed of the three-dimensional components. We investigated a model system by micromagnetic simulation using finite differential method (FDM) and calculated the full hysteresis of the magnet. The model system of a Nd2Fe14B magnet composed of grains with a diameter of about 100 nm was assumed. In the case of the isotropic multi-grain magnet, the energy product calculated by the integration method was 28% larger than the energy product obtained by the conventional way, although a discrepancy between the distribution of the magnetizations and the demagnetizing fields at the reversal process resulted in the decrease of the energy product.

Diffusion behavior and coercivity enhancement of Tb-containing NdFeB magnet by dip-coating TbH3

There is a growing demand for high coercivity of NdFeB magnets with low heavy rare earth in the emerging applications. In this work, dip-coating 0.02 g and 0.09 g TbH3 on the Tb-containing NdFeB magnet enhance coercivity at room temperature，respectively. The highest coercivity achieve about 30 kOe at room temperature after diffusion, which can apply to traction motors of electric vehicles. The magnetic field intensity distribution of magnet was analyzed by finite element method. Microstructures show TbH3 coat contents and original composition of NdFeB magnet influences the formation of Tb-rich shell and grain boundary phase, and determine finally diffusion depth and Tb concentration. The Tb atoms diffuse into the interior of the magnet, forming a network Tb-rich shell existed around Nd2Fe14B grains, resulting in the coercivity enhancement.

Effects of Magnetizing Yoke Design on the Magnetic Properties of Nd2Fe14B Permanent Magnet for Electric Vehicle Motor Applications

When the uniformity of the magnetization yoke is low, a mismatch occurs between the physical rotation center and the center due to the magnetic force after magnetization. This discrepancy in rotation can cause issues such as vibration and noise during high-speed rotation, which in the long term leads to a decrease in the lifespan of the motor. In addition, in order to minimize the problem of motor lifespan when a vehicle is used for more than 10 years after purchase, the problems caused by magnetization should be solved as far as possible. In this study, magnetization yokes were designed in various ways to optimize the factors that affect the magnetic properties after the magnetization of the Nd2Fe14B permanent magnets used in electric motors. In the case of a 50 µm deviation between the coils wound inside the magnetization yoke, the magnetic property imbalance of the Nd2Fe14B magnets and the motor characteristics are not significantly affected after magnetization. However, when the center of the coil wound inside the yoke is shifted from the center of the yoke, the magnetic field is generated unevenly, which degrades both the magnetic and motor characteristics of the Nd2Fe14B magnet. Therefore, it is very important to control the center of the coil that generates the external magnetic field in the magnetized yoke in order to magnetize the Nd2Fe14B magnet with excellent magnetic properties.

SINTESIS DAN KARAKTERISASI NANOPARTIKEL OKSIDA BESI MENGGUNAKAN METODE BALL MILLING DAN KOPRESIPITASI

This Research has carried out on natural sand originating from the Rokan river, Riau Province by converting it into magnetic iron oxide nanoparticles to determine changes in magnetic properties and particle size. Natural sand samples of the Rokan river were separated between magnetic and non-magnetic particles using an iron sand separator (ISS). ISS products are further synthesized using ball milling and coprecipitation methods. 70-hour ball milling products, coprecipitation without ball milling and coprecipitation with 70-hour ball milling are then given NdFeB (neodymium iron boron) magnets to clean impurities containing non-magnetic elements. The results of this study showed that the highest magnetic acceptability value was obtained in coprecipitation products with ball milling, which was 12.9 × 10 -2 . This is because coprecipitation products have an abundant content of chemicals in the form of magnetic elements. Based on the results of chemical composition testing using X-ray flourescence (XRF) it was found that in coprecipitation products with ball milling there was 64.504% iron (Fe) content, while 70-hour ball milling products and coprecipitation without ball milling the percentage of Fe protection was 15.023% and 54.152%, respectively. Based on the results of the identification of the chemical composition in the sample, coprecipitation products with 70-hour ball milling have high magnetic induction values and magnetic suseptibility caused by the magnetic content in products such as Fe which are very high and non-magnetic content is very low such as Si compared to 70-hour ball milling products and coprecipitation products without ball milling.

PENGARUH DOPING MANGAN TERHADAP KOMPOSISI DAN SIFAT KRISTALINITAS PARTIKEL OKSIDA BESI PASIR ALAM SUNGAI ROKAN DIPREPARASI DENGAN METODE BALL MILLING

The composition, crystallinity and magnetic susceptibility of nanoparticles in natural sand of the Rokan River, Riau Province have been investigated. After the iron sand separator (ISS) process, the natural sand samples were separated using NdFeB magnets to separate iron oxide particles and other non-ferrous oxides. For 70 hours, the NdFeB product was prepared using the ball milling method to produce BM products. The BM products were ball milled for 30 hours with a manganese doping concentration of 0 wt.%; 5 wt.%, and 10 wt.% produced DM 0, DM 5 and DM 10 products. Magnetic susceptibility values increased based on the values of B0 and BT measured using Pasco Magnetic Probe PS-2162. The results of XRD analysis of DM products contain a hematite phase (α-Fe2O3) which has a hexagonal structure. The crystal size increased along with the increasing concentration of Manganese from 25.494 nm; 25,542 nm to 25.669 nm. The results of XRF analysis of DM products on Fe elements decreased in percentage with increasing Manganese concentration from 18.083%; 15.407% to 12.947%. Other chemical elements such as Si, Al, K, P, Ti, Ca, Ti, Cr, Zn, V and Pb also decreased.

Life cycle assessment of regeneration technology routes for sintered NdFeB magnets

Life cycle assessment of regeneration technology routes for sintered NdFeB magnets

Fabrication of Non-Contact Magnetic Screws by Additive Manufacturing

Magnetic screws are characterized by their noncontact features, thus eliminating the disadvantage of friction loss inherent in traditional screws. Some applications require spiral-shaped screws; however, commercially available magnets are rarely spiral in shape. To obtain spiral-shaped screws, manufactures require molds or the magnets are spliced to desired shape. Unfortunately, these two fabrication processes both have drawbacks, which include, discontinuity in the magnetic flux, high cost, and reduced efficiency. This article therefore presents alternative approach that involves the design and fabrication of spiral magnetic screws via 3-D printing with magnetic materials. The prototypes were fabricated using two 3-D printing techniques, pellet deposit melting (PDM) and hybrid soft magnet selective laser melting (SLM). Finite element method is adopted to simulate and validate the fabricated magnetic screw. Experiment results, using the PDM fabricated magnets and the hybrid soft magnet SLM combined with commercial sintered NdFeB magnet are also provided, along with, verification of the design characteristics and the simulation results.

Selective Dissolution of Nd2O3 from the Mixture with Fe2O3 and Ga2O3 by Using Inorganic Acid Solutions Containing Ethylene Glycol

Rare earth elements (REEs) are strategically critical in the manufacture of advanced materials. Red mud and end-of-life NdFeB magnets can be good secondary sources for REEs, but recovery is difficult due to the high iron oxide content and small amount of REEs. Oxide mixtures whose composition of Fe, Nd, and Ga was similar to that in red mud were employed in experiments. In this study, a relatively inexpensive non-aqueous system was used to selectively dissolve Nd2O3 in a mixture with Fe2O3 and Ga2O3. The addition of ethylene glycol (EG) to HCl and H2SO4 solution depressed the dissolution of Fe2O3 and Ga2O3 from the mixtures, and thus selective dissolution of Nd2O3 was possible. The optimum conditions were as follows: (a) 1.0 M HCl in EG, 25 °C ± 1 °C, 50 g/L pulp density, 120 min, 200 rpm; and (b) 0.05 M H2SO4 in EG, 25 °C ± 1 °C, 50 g/L pulp density, 60 min, 300 rpm. Under these conditions, Nd2O3 was completely dissolved, whereas no Fe2O3 or Ga2O3 was dissolved by the H2SO4 system, and the dissolution percentage of these two oxides by the HCl system was less than 1%. Due to the selective dissolution of Nd2O3 from the oxide mixtures, it is simple to recover Nd. An efficient process can be developed for the recovery of REEs from red mud and end-of-life NdFeB magnets by applying our results.

Selective extraction of Nd(III) by novel carboxylic acid based ionic liquids without diluent from waste NdFeB magnets

The development of an environmentally friendly extractant for selective recovery of rare earth elements is critical but still faces significant challenges. Two low viscosity carboxylic acid based ionic liquids [A336][BTA] and [A336][OTA] were synthesized for selective extraction of Nd(III) from waste NdFeB magnets. First, the extraction behaviors of two kinds of ionic liquids were compared under different conditions, such as time, pH value of aqueous phase, dosage of ionic liquids, and concentration of salting-out agent. The optimal extraction condition of [A336][OTA] was optimized by response surface methodology, and the extraction efficiency reached 99.1%. The extraction mechanism was proposed as ion association by UV–Vis spectrum, IR spectrum and 1H NMR, and was supported from that perspective of quantum chemical calculation. The extraction thermodynamics, kinetics and isothermal model were studied in detail. [A336][OTA] maintained an extraction efficiency of 95.6% even after seven cycles. The extractant shows good selective separation performance in waste NdFeB magnets, and is an extractant with good application prospect. This work has provided an environmentally friendly extractant for the recovery of Nd(III) from waste NdFeB magnets.