NdFeB Permanent Magnets Research Articles

Controllable hydrophobicity of magnetoactive elastomer coatings

A series of magnetoactive elastomer (MAE) coatings consisting of a silicone matrix and carbonyl iron particles (3–5 μm in diameter) have been synthesized and their hydrophobic properties have been investigated in various magnetic fields of disk-shaped permanent NdFeB magnets. Concentration of magnetic filler in MAEs has been varied in the range of 63–76 mass%. Both isotropic samples and structured samples synthesized in the magnetic field of 80 mT have been obtained. It has been shown that application of a magnetic field induces structuring of the filler on the surface of MAE coatings, resulting in formation of mountain-like microstructures. Microstructure relief on coating surfaces leads to an increase of a water contact angle which could be varied from 110° ± 10° at zero field up to 163° ± 2° at 600 mT. The contact angle at the maximum field increases with iron filler content and with softening of the polymer matrix.

Recovery of neodymium and dysprosium from NdFeB magnet swarf

The rare earth elements neodymium and dysprosium were separated and recovered from NdFeB permanent magnet swarf by hydrometallurgical route. The magnet swarf was leached with HCl after crushing and grinding, and from the leach liquor, Nd and Dy were separated by solvent extraction using NaCyanex 302. The separation factor (β) of Dy/Nd with NaCyanex 302 was high at low equilibrium pH. So Dy was first separated from the leach liquor at pH0.5 (equilibrium pH1.2). After separation of Dy, the separation of Nd was also carried out with the same extractant. The effect of equilibrium pH and extractant concentration on the extraction of Nd and Dy with NaCyanex 302 was studied. The McCabe-Thiele plots for extraction of both Dy and Nd with NaCyanex 302 were constructed and the number of stages for quantitative extraction was determined. The stripping of loaded organic was carried out with three different mineral acids and it was observed that the stripping efficiency followed the order HCl<HNO3<H2SO4. The McCabe-Thiele plots for stripping of loaded organic were also constructed. The reaction mechanism of both Nd and Dy was determined from the slope analysis method and the extracted species was found to be MA3.5HA.

First report on soapnut extract-mediated synthesis of sulphur-substituted nanoscale NdFeB permanent magnets and their characterization

Biosynthesis of nanoscale materials has its own advantages over other physical and chemical methods. Using soapnut extract as reducing and stabilizing agent for the synthesis of inorganic nanoscale materials is novel and has not been exploited to its potential so far. Herein, we report for the first time on the effects of sulphur substitution on soapnut extract-mediated synthesis of nanoscale NdFeB (S-NdFeB) permanent magnetic powders (Nd 15%, Fe 77.5%, B 7.5% and S with molar ratios: 0.1, 0.2, 0.3, 0.4, and 0.5). To synthesize, a 10 ml of 10% soapnut extract was added to 90 ml of respective chemical composition and heated to 60 °C for 30 min and aged for 24 h. The dried powder was sintered at 500 °C for 1 h. The characterization of the as-prepared nanoscale S-NdFeB magnetic materials was done using the techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersion spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS for size and zeta potential measurements) and vibrating sample magnetometer (VSM)–hysteresis loop studies. The results revealed that particles were highly stable (with a negative zeta potential of 25.7 mV) with irregular and spherical shape (with measured hydrodynamic diameter 6.7 and 63.5 nm). The tetragonal structures of the formed powders were revealed by XRD micrographs. Hysteresis loop studies clearly indicate the effect of S concentration on the enhanced magnetization of the materials.

Octagonal Halbach Magnet Array Design for a Magnetic Refrigerator

ABSTRACTAn effective magnet array design for magnetic refrigeration systems is crucial given the space limitations and need for maintaining the required cooling capacity. Here, Halbach permanent magnet arrays (HPMA) in an octagonal orientation are studied using NdFeB permanent magnets. Gadolinium is selected as the magnetocaloric material (MCM) for the aperture inside the octagonal HPMA. The optimum outer-to-inner radii ratio for the octagonal HPMA and MCM system is found to be 2, at which the cooling energy per volume of magnet has a peak. For this ratio, the effect of using soft magnetic material, which in this study is FeVCo, inside and outside the HPMA is evaluated over a range of material thicknesses. The optimum soft magnetic material thickness outside the HPMA is obtained to be 3% of the external radius. At this thickness, soft magnetic material is also placed inside the array as a concentrator. It is found that although using soft magnetic material inside the magnet array increases the average flux, cooling energy is decreased due to using less MCM inside the aperture because of the space occupied by the soft magnetic material.

A Novel Hybrid Saturated Core Fault Current Limiter Topology Considering Permanent Magnet Stability and Performance

The saturated core fault current limiter (SFCL) is one of the most effective methods for limiting fault current. A permanent magnet (PM)-biased SFCL (PFCL) can reduce dc bias current and additional energy consumption. However, the thermal stability of NdFeB PMs in PFCL poses a major challenge. This paper proposes a novel hybrid-type SFCL (HSFCL) topology that can reduce this risk. In the HSFCL, a hybrid PM/dc coil is designed to saturate the core, and a fault-limiting reactor is used to guarantee fault-clipping performance. The new structure provides air-gap branches for the time-varying magnetic field produced by alternating current, which reduces the eddy current in the PMs and enhances their stability. Electromagnetic coupling is used to analyze the operating principles and characteristics of HSFCL. Finite-element analysis simulations were performed using Maxwell and compared with verification experiments, proving that HSFCL is efficient in fault clipping and PM reliability enhancement.

A Coupled Method for Evaluating Eddy Current Loss of NdFeB Permanent Magnets in a Saturated Core Fault Current Limiter

Eddy-current loss of NdFeB permanent magnets (PMs) is widely analyzed in PM motors. This paper proposes a coupled 2-D transient finite-element analysis (FEA) of the saturated core fault current limiter (SCFCL) and 3-D analytical model of PMs to evaluate eddy-current loss in SCFCL. The comparison between the result from coupled method and that from 3-D FEA verifies the applicability of the coupled method in analyzing eddy current loss of PMs in SCFCL. The 3-D analytical model of PM is applied to analyze the effect of segmentation on the reduction of PM's eddy-current loss. And the results show that segmentation along width has a better performance, which is also verified by 3-D FEA.

Retracted: Morphology and electrochemical comparison of ceramic and composite anti‐corrosion barriers for sintered NdFeB permanent magnets

AbstractThis article has been retracted due to a substantial overlap with a previously published article in another journal.

Relating atomic local structures and Curie temperature of NdFeB permanent magnets: an X-ray absorption spectroscopic study

Relationship between atomic local structures and Curie temperature of NdFeB permanent magnets was investigated semi-quantitatively using synchrotron radiation technique. Fe K-edge X-ray absorption spectroscopy (XAS) was employed to study the local structure of Fe atoms for samples before and after doping Dy, Tb or Gd. It is found that the bond lengths and coordination numbers are changed. Thus, the exchange interaction between Fe atoms increases with Dy, Tb or Gd doping, resulting in the improvement of Curie temperature of NdFeB permanent magnets. The doping effect is proven by experimental measurement of the magnetic properties. Microstructural characterization using scanning electron microscopy (SEM) was also used to further analyze the effect of different rare earth elements doping on Curie temperature of NdFeB permanent magnets.

Development of rare earth free permanent magnet generator using Halbach cylinder rotor design

Direct-drive permanent magnet generators (DDPMGs) offer increased reliability and efficiency for wind turbine application over the more commonly used geared doubly-fed induction generators. However, deployment of DDPMGs is limited in the U.S. wind industry due to reliance on NdFeB permanent magnets, which contain critical rare earth elements Nd and Dy. To allow for the use of lower energy density, rare earth free permanent magnets, Halbach cylinders are employed as the rotor in a 3.5 kW PMG to concentrate magnetic flux over the rotor surface and increase magnetic loading. By varying the slot-to-pole ratio in Halbach PMGs (HPMGs), designs are developed, which allow for the use of ceramic, or hard ferrite, strontium iron oxide permanent magnets. At the 3.5 kW scale, the ceramic HPMGs are able to achieve rated performance at reduced average efficiency of between 82 and 87%, which is due to the difference in permanent magnet material properties. For scaling of the ceramic HPMGs to 3 MW, rated performance and high efficiency were achieved on average at rated speed, demonstrating the potential for a rare earth free PMG in commercial scale wind turbines.

Simulation and Characterisation of Planar Spring Based on PCB-FR4 in Electromechanical System for Energy Harvesting

This paper presents comparison study of simulation and fabrication characterized two type planar springs at micro–fabricated electromagnetic power generator for an ambient vibration energy harvesting system. The power generator utilized a LASER–machined FR4-PCB planar spring, a copper coil, and NdFeB magnet. In order to change resonant frequency, we developed a gimbal suspension structure for the fabrication of spring. The NdFeB permanent magnet was applied as inertial mass. The system was specially designed to harvest low ambient vibrations from 20 to several hundred hertz and low acceleration. The dimension of fabricated energy harvester had 2.5 x 2.5 cm2 in size. In this study we present two different design of cantilever, which is has two and four cantilever, respectively. The different designed given different resonance frequency to the system. The result of simulation giving resonance frequency of two cantilever membrane 22.6 Hz and four cantilever membrane 110.3 Hz. The measurements result has generated 0.135 V with resonance frequency 39 Hz of two cantilever membrane appropriate for human motions, four cantilever membrane has generated 0.174 V with resonance frequency106 Hz appropriate for machine industries.

Design Synthesis of Switched Flux Hybrid-Permanent Magnet Memory Machines

This paper develops a design methodology for switched flux (SF) hybrid permanent magnet memory machines (HPMMMs). The memorable flux is achieved due to the variable magnetization level of low coercive force (LCF) permanent magnets (PMs) Thus, the associated excitation loss is negligible, resulting in high efficiency operation over a wide speed range. A general hybrid PM magnetic circuit is modeled, which is characterized by spoke-array NdFeB PMs and LCF PMs sandwiched between an outer stator ring and an inner stator pole. Based on the magnetic circuit, the design conflicts within the stationary side are unveiled. Thereafter, the machine configuration is introduced, followed by a description of the design procedure. First, the optimal stator pole number is determined based on one-phase machine models. In addition, a simplified permeance function is utilized to analytically optimize the rotor number, accounting for different ratios of the slot opening to NdFeB PM thickness. The electromagnetic performance of the machines with alternate stator/rotor pole combinations are compared. The design guidelines for LCF PMs are presented. Finally, the theoretical analysis is verified experimentally on the prototype machine.

Characterization of Electromagnetic Valveless Micropump

This paper presents an electromagnetically-actuated micropump for microfluidic application. The system comprises two modules; an electromagnetic actuator module and a diffuser module. Fabrication of the diffuser module can be achieved using photolithography process with a master template and a PDMS prepolymer as the structural material. The actuator module consists of two power inductors and two NdFeB permanent magnets placed between the diffuser elements. The choice of this actuation principle merits from low operating voltage (1.5 V dc ) and the flow direction can be controlled by changing the orientation of the magnet vibration. Maximum volumetric flow rate of the fabricated device at zero backpressure is 0.9756 µLs -1 and 0.4659 µLs -1 at the hydrostatic backpressure of 10 mmH 2 O at 9 Hz of switching speed.

Characteristic analysis of a less-rare-earth hybrid PM-assisted synchronous reluctance motor for EVs application

Low-energy permanent magnet (PM) such as ferrite is usually adopted in a PM-assisted reluctance (PMAREL) motor to enhance the output torque and reduce costs. However, the relatively low magnetic energy product and remanence in such PMs may lead to the risk of demagnetization. By using two types of materials of rare-earth NdFeB and non-rare-earth ferrite PM, a new less-rare-earth hybrid PMAREL motor is proposed in this paper, where the output torque and the power factor can be improved obviously, and meanwhile the risk of irreversible demagnetization in ferrite PMs can be reduced significantly due to the existence of NdFeB PMs. To verify the validity of the proposed motor, the operating principles of the motor and the positive interaction influences between the two involved types of PMs are analyzed. Moreover, by using the finite element method, the torque characteristics and anti-demagnetization capabilities are also investigated in details. Both the theoretical analysis and simulated results confirm the advantages of the proposed motor.

Extraction Equilibrium of Valuable Metals from NdFeB Permanent Magnet Using Carboxylic Acid as Extractant

Extraction Equilibrium of Valuable Metals from NdFeB Permanent Magnet Using Carboxylic Acid as Extractant

Microstructure, corrosion resistance and formation mechanism of alumina micro-arc oxidation coatings on sintered NdFeB permanent magnets

Alumina ceramic coatings were prepared on the sintered NdFeB magnets by micro-arc oxidation (MAO) in aluminate solution. The effects of anodic voltages on the microstructure and corrosion resistance of the coatings were investigated and the formation mechanism of the coating was also detailedly discussed. The microstructure and composition of the MAO coatings were characterized by SEM, XRD, EDS, XPS and surface roughness, respectively. The MAO coatings on NdFeB magnets were mainly composed of Al2O3 crystal phase, and Fe2O3 and Nd2O3 amorphous phase with some absorbed H2O and –OH. With increasing the voltages, the crystallinity of Al2O3 phase enhanced, while the surface roughness of the coatings also increased. At the same time, the pore sizes of MAO coatings increased, while the amount of the pores decreased. The corrosion resistance of NdFeB samples was improved due to the existence of the MAO coatings. With increasing the voltages, the corrosion resistance of the coated NdFeB samples increased first, reaching the optimum at 420V, and then decreased. The corrosion protection efficiency of the coatings could be up to 94.3%. At the initial stage of MAO process, the compact barrier layer of NdFeB magnets was formed through the deposition of the electrolyte, which was the critical procedure for the MAO treatment of NdFeB magnets and the biggest difference from the valve metals through the conventional anodizing.

Publisher's Note: Monte Carlo analysis for finite-temperature magnetism of Nd2Fe14B permanent magnet [Phys. Rev. B 94 , 174433 (2016)

Publisher's Note: Monte Carlo analysis for finite-temperature magnetism of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Nd</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Fe</mml:mi><mml:mn>14</mml:mn></mml:msub><mml:mi mathvariant="normal">B</mml:mi></mml:mrow></mml:math> permanent magnet [Phys. Rev. B <b>94</b> , 174433 (2016)

Quantum Hall effect in epitaxial graphene with permanent magnets.

We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications.

Preparation and characterization of amorphous SiO2 coatings deposited by mirco-arc oxidation on sintered NdFeB permanent magnets

Amorphous SiO2 coatings were prepared on sintered NdFeB magnets by micro-arc oxidation (MAO) in silicate solution. The surface and cross-sectional morphologies, element and phase composition, corrosion resistance and magnetic properties of the coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), potentiodynamic polarization test and physical properties measurements system (PPMS). The results showed that the surface morphologies of the coatings exhibited the “coral reef” like structure, different from the typical MAO porous structure. With increasing the voltages, the thickness of the coatings increased from 12.72 to 19.90µm, the content of Si element increased, while the contents of Fe, Nd and P elements decreased. The coatings were mainly composed of amorphous SiO2 and a few amorphous Fe2O3 and Nd2O3. The amorphous SiO2 coatings presented excellent thermal shock resistance, while the thermal shock resistance decreased with increasing the voltages. The corrosion resistance of the coatings increased with increasing the voltages, and it could be enhanced by one order of magnitude compared to the uncoated NdFeB magnets. The MAO coatings slightly decreased the magnetic properties of the NdFeB samples in different degrees.

Site preferences for La and Pr in Nd2Fe14B permanent magnet: A first principles study

Using the first principles method, we studied the site preference and the magnetic ground state of rare-earth elements La and Pr doped Nd2Fe14B permanent magnet. It was found that the La preferred the f-site doping at low doping ratio (12.5 %) while the g-site was more favorable at high doping (25 %). For the Pr impurity, we observed the opposite behavior because the site preference was switched. In addition, the spin configuration also depended on the impurity type and concentration. An antiferromagnetic (AFM) type spin configuration was found at both lower and higher doping ratios of La. For the Pr impurity, at a lower doping ratio, the AFM spin configuration was still preserved. However, the ferromagnetic spin configuration was more stable at a high doping ratio. Through impurity-substitution energy calculations, we found that the La impurity preferred to enter into the 2:14:1 phase at low doping, but it favored the grain-boundary phase at high (25 %) doping ratio. On the other hand, we observed that the Pr always preferred the main phase for both low and high doping concentrations.

Magnetic field simulation of wiggler on LUCX accelerator facility using Radia

A flat wiggler consisting of NdFeB permanent magnets was installed on a compact linear electron accelerator LUCX (KEK) in Japan. After installing the wiggler on LUCX, the experiments on the generation of undulator radiation (UR) in the terahertz wavelength range is planned. To perform the detailed calculations and optimization of UR characteristics, it is necessary to know the parameters of the magnetic field generated in the wiggler. In this paper extended simulation results of wiggler magnetic field over the entire volume between the poles are presented. The obtained in the Radia simulation magnetic field is compared with the field calculated by another code, which is based on the finite element method.