Bonded NdFeB Magnets Research Articles

Recent Advances in Corrosion Inhibition of Bonded NdFeB Magnets.

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

Low-temperature manufacturable, recyclable, and reconfigurable liquid-metal bonded NdFeB magnets for sensors and robotics

This work presents a recyclable liquid-metal/NdFeB composite magnet (LM magnet) with a reconfigurable shape and polarity. Taking advantage of the low-temperature phase-transition property of LMs, we can re-orient the NdFeB particles and reshape the LM magnets, to produce complex magnetization profiles or complex structured magnets. The manufacturing of LM magnets was realized at low temperatures by using a template and paired permanent magnets. The microscopic morphology and elemental composition of the LM magnet were analyzed by scanning electron microscopy and energy dispersive spectroscopy, respectively. The magnetic properties and phase-transition properties of the LM magnet were analyzed using a vibrating sample magnetometer (VSM) and a differential scanning calorimeter. The experimental results verified that the LM magnet can be recycled, reconfigured, and welded. The configurable magnetization profile with a resolution of up to 800 µm demonstrates that manufacturing of complex magnetic poles can be achieved through this technique. Finally, three application cases show the application prospects of the LM magnet in robots and sensors.

Preparation and Anticorrosion Performance of Double-Layer Epoxy Resin Coatings on Bonded NdFeB Magnets

Preparation and Anticorrosion Performance of Double-Layer Epoxy Resin Coatings on Bonded NdFeB Magnets

Comparison of phenol formaldehyde with polyvinyl chloride resin as binder bonded NdFeB magnet for axial flux generator

Bonded permanent magnets are made by mixing a magnetic powder material Neodymium Iron Boron (NdFeB) commercial MQP type 16-7 with a polymer material powders phenol formaldehyde (Bakelite) and polyvinyl chloride (PVC) resin. Comparison between the composition of NdFeB powder and the polymer powders were varied at 80:20, 90:10, and 95:5 wt%, respectively. This mixture is then pressed with a hot press system and then carried out magnetic alignment axial flux using a magnetizer machine, Magnet Phisyk-Germany, with an impulse system. Magnetic properties were characterized by permagraph Magnet Phisyk-Germany. The best value obtained for the composition of 95: 5% NdFeB-pvc resin powder to the value of remanence magnet (Br) = 0.604 Tesla (T), the value of coercivity (Hc) = 480 kA/m and maximum energy product (BH)max = 50.05 kJ/m3. Fabrication is done by the size of the magnetic 50 mm diameter, 8 mm thick and was applied to the axial flux generator. The output voltage of the generator has been tested with variations of 50 to 300 rotations per minute (rpm) using a Hantek 6022BE oscilloscope, and the measurement results obtained values of 1.9 to 12.2 Volts.

Structure and Corrosion Resistance Characteristics of ZnAl/EP Coating on Bonded NdFeB Magnet

Structure and Corrosion Resistance Characteristics of ZnAl/EP Coating on Bonded NdFeB Magnet

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.

The Preparation and Properties of ZnAl Coating for Ring-Shaped Bonded NdFeB Magnet with High Corrosion Resistance

The Preparation and Properties of ZnAl Coating for Ring-Shaped Bonded NdFeB Magnet with High Corrosion Resistance

Effect of silane coupling agents on flowability and compressibility of compound for bonded NdFeB magnet

Based on the difference of the Y-terminal functional group of the silane coupling agent (Y–Si(X)3), four different silane coupling agents were employed to pretreat the surface of the NdFeB powders. The effects of silane coupling agents on the flowability and compressibility of compounds for preparing bonded NdFeB magnets were studied. It is indicated that compounds pretreated by silane coupling agents have weaker friction and meshing force. The apparent density is increased by 0.3 g/cm3 compared with the compound without silane coupling agent, and the radial crushing strength is significantly increased by about 3–4 times. In addition, the epoxy resin is more evenly distributed on the surface of the compounds treated by silane coupling agents observed by scanning electron microscopy, and some agglomerated particles are produced. Also, the compressibility of compounds with silane coupling agents is significantly improved due to the fact that hardening exponents are reduced. However, the addition of silane coupling agents has almost no effect on the magnetic properties of bonded magnets. The special energy was used to manifest the flowability of magnetic powder particles representing the macroscopic performance of the force between powder particles, providing a new direction for the study of the interface compatibility of two-phase or multiphase composite materials.

Effect of Molding Pressure on Structure and Properties of Ring-Shaped Bonded NdFeB Magnet

Ring-shaped polymer-bonded magnets (RSMs) were produced from a mixture of an isotropic NdFeB powder, steel use stainless (SUS) powder, and epoxy resins as binders, using a comprehension-molding technique. Morphology of RSM determined by an SEM indicated that inappropriate molding pressure leads surface defect and brings adverse impact on properties of magnets. The research on mechanical properties shows that the maximum tensile strength of 11.4 N was achieved at optimal pressing pressure of 85 kN. Meanwhile, RSM has excellent stability as the critical component of motor and its amount of unbalance is as low as 0.754 mg. Magnetic property in optimal mechanical conditions was also found to be optimum at H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> = 8.42 kA/m and (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 31.17 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Preparation and characterization of bakelite bonded magnet NdFeB used for electric generator

The permanent magnets based on NdFeB is well known as rare earth alloy magnets made from neodymium, iron and boron elements and has tetragonal crystalline structure Nd2Fe14B which has high coercivity, large energy product (app 50 MGOe) and curie temperature about 312 °C. In this paper will be discussed the preparation of bakelite bonded magnet NdFeB and characterization, also the purpose of this research is to make bonded magnet NdFeB using 3 % bakelite and know the extent to which can be applied in making a small electric generator. The bonded magnet NdFeB was made by mixing a magnetic powder NdFeB with a polymer as binder. The composition of the sample consisted of 97 wt. % of NdFeB powder and 3 wt.% of bakelite. The mixed raw materials were then pressed to form a disc with pressure about 40 MPa at temperature about 160 °C for 20 minutes. It was obtained a disc with size 40 x 18 x 6 mm. The disc samples were magnetized by using impulse magnetizer at 1500 Volt DC, then the samples were measured magnetic properties by using Gauss meter and Permeagraph. The measurements result show that, the bakelite bonded magnet NdFeB has Magnetic Flux = 1100 Gauss, Remanence Br = 5.20 kGauss, Coercivity Hc = 6.14 kOe and Energy product (BH) max = 4.78 MGOe. The bonded magnet NdFeB was applied to the prototype small generator with single rotor and single stator. The results of performance test of generator indicate that it is achieved output power of generator about 9.98 Watt at a maximum speed about 500 rpm.

Study on the Production of Bonded Magnet NdFeB and Polyvinyl Butyral

bonded magnet is composite magnet material made by mixing magnetic powder with non-magnetic binder. The process in manufacturing bonded magnet NdFeB made by mixing powder of neodymium iron boron (NdFeB) commercial type MQP-B with a polyvinyl butyral powder using a glass beaker. The comparisons of variation in composing NdFeB magnets powders with a binder of PVB (% weight) are 98:2, 96:4, 94:6 and 93:7 of 8 grams from total mass of the sample. After mixing the powder, it is molded by using a compression molding method with 8 tons pressure for 20 minutes at curing temperature 1600C. The molded samples are conducted by characterizing the physical properties which include measurement of density, microstructure analysis using SEM-EDX and magnetic properties which include measurement of the magnetic field strength using a Gaussmeter and hysteresis curve using VSM. The result of the study shows that the addition of and binder PVB in bonded magnet NdFeB causes a decrease in the density and magnetic field strength. The best result of density and magnetic field in the manufacture of bonded magnets is obtained by the addition of 2 % binder of 5.66 g/cm3 and strong magnetic field of 1862.4 G. the score of Mr = 72.86 emu/g, Ms = 103 emu/gram, Hc = 8.490 KOe and BHmax = 5.1 MGOe was obtained on the addition of PVB 2 %.

Recycling of bonded NdFeB permanent magnets using ionic liquids

The polymeric binder of bonded NdFeB magnets can be dissolved in ionic liquids with strongly coordinating anions and the magnetic powder can be reused for manufacturing of new magnets.

Alkali baking and solvometallurgical leaching of NdFeB magnets

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 NaFeO2. By washing the reaction mixture with water, 96.5% of Na was recovered as NaOH and Na2CO3, 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.

Effect of Particle Size Distribution on the Preparation of Bonded NdFeB Permanent Magnet

In this paper, the effect of particle size distribution on the preparation of bonded NdFeB isotropic permanent magnets was investigated. Different particle size distribution of NdFeB powders was prepared by sieving method using standard test sieves of #100, #200, and #325 meshes. Varied distribution of particle size was mixed with 3 wt% of epoxy binder and compacted by uniaxial hydraulic pressing machine to produce bonded isotropic green body. Bonded NdFeB green body was cured by vacuum drying machine under temperature 100 °C for 4 hours with vacuum pressure of 10 mbar. The characterization performed were bulk density measurement, particle size analysis, microhardness Vickers, SEM image and hysteresis curve. We find that the hardness of bonded NdFeB magnets decreased as the particle size decreases. Contrary to common belief that the finer powder with sharply particle size distribution not always give the highest product characteristics. The optimum characteristics of bonded NdFeB was obtained by the mixture of #100+#200 meshes powders with bulk density, hardness, magnetic remanence, coercivity, and energy product of 5.87 g/cm3, 88 HV, 6.5 kG, 11.15 kOe, and 9.4 MGOe, respectively. Therefore, the middle range of particle size distribution is effective to obtain high quality bonded NdFeB permanent magnets.

Selective laser sintering of bonded magnets from flake and spherical powders

The use of additive manufacturing (AM) techniques for low volume production of complex geometries from a wide range of materials has shown to decrease product cost and lead times. This work describes the production of net-shaped bonded NdFeB magnets using selective laser sintering (SLS) from mechanically mixed isotropic powders. Magnets were produced from magnetic powders with both flake and spherical particle morphologies and were shown experimentally to possess magnetic properties comparable to permanent magnets produced using other AM methods (residual induction of 302 and 362 mT, intrinsic coercivity of 661 and 735 kA/m for flake and spherical powders respectively).

Influence of addition Ba-Ferrite on the hardness, magnetic properties and corrosion resistance of hybrid bonded magnet NdFeB.

The preparation of Hybrid Bonded Magnet based of NdFeB with additon of Ba-ferrite has been done with variation of Ba-ferrite (0, 3, 5, 8, and 10 % wt). Preparation process was started by mixing NdFeB (MQP-B+) powder with BaFe12O19, then mixed with binder Exopy Resin (5 %wt.) and compacted with pressure 40 MPa to form a pellet. Then samples pellet was heated by using Vacuum Dryer (10 mmbar) and temperature 90°C for 1 hour. Some parameters were measured such as vickers hardness, magnetic properties (flux magnetic density and hysteresis curve) and corrosion resistance. The best result of hardness test is hybrid bonded magnet NdFeB with compositions of 90 %wt NdFeB, 10 %wt Ba-ferrite and 5 %wt epoxy resin. Hardness value of hybrid bonded magnet NdFeB of this composition is = 265,13 HV. The best result for magnetic properties is hybrid magnet NdFeB with compositions of 95 %wt NdFeB, 5 %wt Ba-ferrite and 5 %wt epoxy resin. Those magnetic properties are Flux Density = 1340 Gauss, Br (remanence) = 3,827 kG, Hcj (coercivity) = 8,924 kOe and BHmax (Energy Product) = 2,847 MGOe. According the corrosion result test is found that sample with higher content Ba-ferrite has better corrosion resistance compare to sample with small content of Ba-ferrite.

Mechanical, magnetic properties and corrosion resistance of hybrid bonded magnet NdFeB - BaFe12O19

The hybrid bonded magnet NdFeB - BaFe12O19 has been made. The composition of BaFe12O19 was varied as 0, 3, 5, 8, and 10 wt%. The preparation process was started by mixing BaFe12O19 powder with NdFeB (MQP-B+), then mixed with exopy resin binder of 8 wt% and subsequently compacted with a pressure of 60 MPa to form a pellet. The pellet samples were heated in 10 mmbar of vacuum dryer at 90°C for 1 hour. Some parameters were measured such as mechanical properties (compressive strength), magnetic properties (magnetic flux density and hysteresis curve) and corrosion resistance. The results show that the hybrid bonded magnet NdFeB with 10 wt% BaFe12O19 exhibits the highest compressive strength of about 268,15 kgf/cm2. While the optimum corrosion resistance of bonded magnet NdFeB - BaFe12O19 is obtained by 5 wt% BaFe12O19 addition. It has a flux magnetic density of 1340 Gauss, remanence Br of 3,827 kG and coercivity Hcj of 8,924 kOe. According to the corrosion test result, it is found that the sample with higher content of Ba-ferrite has a better corrosion resistance compare to the sample with small content of Ba-ferrite.

Optimal Design and Experimental Test of a SPM Motor With Cost-Effective Magnet Utilization to Suppress Torque Pulsations

This paper presents an optimal design for a surface-mounted permanent magnet (SPM) motor to suppress torque pulsations and save the magnet cost, by using multi-grade permanent magnets. Based on a conventional SPM motor with single-grade bonded NdFeB magnets, the proposed SPM motor is designed with two-grade bonded NdFeB and one-grade ferrite magnets, and then optimized by combining the Kriging method with a genetic algorithm, for further minimizing torque pulsations and saving the magnet cost by maintaining the high average torque. As a result, the cogging torque, torque ripple, and magnet cost of the optimized SPM motor are highly reduced compared to those of the conventional SPM motor. Furthermore, the optimized SPM motor is verified to have superior endurance against the magnet's irreversible demagnetization within three times of the rated current excitation. All motor characteristics, including airgap flux density, cogging torque, electromagnetic torque, and demagnetization ratio are first predicted with the aid of a finite-element method. Finally, the optimal design and analysis results are validated by the experimental results.

The effect of dry and wet milling on microstructure and properties of bonded NdFeB magnets

The preparation of NdFeB has been conducted in a dry and wet milling condition using a planetary ball mill (PBM) for ½, 1, 2, 3, 4, and 5 hours. The dry and wet milling was performed in an argon gas and toluent, respectively with ball and powder ratio of 10:1. The milled powder was dried in the vacuum condition of 11 mBar at the temperature of 60°C for 10 hours. 5wt.%Celuna (WE-518) was used as binder, mixed with magnetic powder and anisotropically pressed at 25 kgf/cm2. Curing process was conducted in a vacuum chamber of 11 mBar at temperature of 180°C for 1 hour. The particle diameter and the true density of NdFeB powder were measured by using PSA and Pycnometer, respectively. The morphology and phase composition were characterized using SEM and XRD, respectively. The obtained results show that the optimum milling time of NdFeB powder is 3 hours using wet milling method. The results also concluded that the powder true density of 7.79 g/cm3, the bulk density of 5.98 g/cm3 and the mean particle diameter of 9.59 μm can be achieved. The SEM image confirmed that the milling process has an effect in reducing the particles size. But the milling process lead to a damage in the crystal structure of the material, resulting in decreasing the magnetic flux density. The half hour dry milling is capable to produce a maximum magnetic flux density of 1816 Gauss.

Preparation of parylene-coated bonded NdFeB magnets

The anisotropic parylene-coated bonded NdFeB magnets with parylene C coating on the surface of NdFeB powders are prepared by warm compaction process. The parylene C coating is characterized by focused ion beam-scanning electron microscopy (FIB-SEM) and energy dispersive X-ray Spectroscopy (EDS), revealing a parylene C film of 300–500 nm thickness on the surface of NdFeB powders. The parylene-coated NdFeB magnets show excellent magnetic properties of maximum energy product ((BH)max, 104 kJ/m3), degree of alignment (DOA, 0.476) and density (6.17 g/cm3) than non-coated NdFeB magnets (60 kJ/m3, 0.337, 5.72 g/cm3). And with the increasing thickness of parylene C coating, (BH)max and density increase first, and then decrease while DOA keeps a growing trend all the time. The parylene-coated NdFeB magnets also exhibit better corrosion resistance according electrochemical test. The mechanisms for the improvement of magnetic properties and corrosion resistance are the good lubricating property and super chemical stability of parylene C coating on the surface of NdFeB powders.