NdFeB Powder Research Articles

Additive Manufactured Polymer-Bonded Isotropic NdFeB Magnets by Stereolithography and Their Comparison to Fused Filament Fabricated and Selective Laser Sintered Magnets.

Magnetic isotropic NdFeB powder with a spherical morphology is used to 3D print magnets by stereolithography (SLA). Complex magnets with small feature sizes in a superior surface quality can be printed with SLA. The magnetic properties of the 3D printed bonded magnets are investigated and compared with magnets manufactured by fused filament fabrication (FFF), and selective laser sintering (SLS). All methods use the same hard magnetic isotropic NdFeB powder material. FFF and SLA use a polymer matrix material as binder, SLS sinters the powder directly. SLA can print magnets with a remanence of 388 mT and a coercivity of T. A complex magnetic design for speed wheel sensing applications is presented and printed with all methods.

Chemical synthesis and coercivity enhancement of Nd2Fe14B nanostructures mediated by non-magnetic layer

High-performance Nd2Fe14B magnets have been widely required in various fields recently due to the lightweight and miniaturization of devices. In this work, we synthesize Nd2Fe14B nanostructures with tunable magnetic properties through surfactant-assisted high energy ball milling (SAHEBM) process, achieving prominently enhanced coercivity by forming non-magnetic layers as grain boundary phase. When the reduction annealing process was carried out as pellet with Ca, the coercivity increased from 0.8 kOe to ver 3 kOe as Nd2Fe14B powder, which is proved to be the contribution of the chemical diffusion of Nd elements and the formation f Nd-rich layer as magnetic insulating medium. In addition, two-dimensional graphene oxide (GO) was employed to build extra grain boundary, by which the coercivity of the core@dual-shell structure can achieve up to 8 kOe, tenfold of the original sample. The intrinsic mechanism indicated that the Nd-diffusion induced Nd-rich phase along with the reduced GO in the system could form non-magnetic layer as grain boundary and magnetically isolate the adjacent grains, significantly enhancing the exchange coupling effect. This work markedly opens up an effective approach for the chemical preparation of high-performance Nd2Fe14B nanostructured magnets, especially after post treatment, and gives an insight on the interactions at nanoscale.

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.

Effect of contact alignment on shrinkage anisotropy during sintering: Stereological model, discrete element model and experiments on NdFeB compacts.

This works aims at analysing the effect of alignment of particle contacts on the shrinkage anisotropy during sintering. A stereological model is proposed which relates the shrinkage anisotropy factor to the distribution of contact area orientations. The shrinkage anisotropy is further analysed by using a discrete element method (DEM) to simulate the sintering of isostatically compacted packings of aligned particle chains. Finally, the analysis is performed on experimental magnetically oriented NdFeB powder compacts. The stereological model predicts a higher shrinkage in the direction of preferentially aligned contacts, in agreement with DEM simulations and experimental results, where a shrinkage anisotropy factor close to 2 is observed.

Oxidative Roasting–Selective Pressure Leaching Process for Rare Earth Recovery from NdFeB Magnet Scrap

To recover rare earths (RE) with low acid consumption and low environmental pollution, selective pressure leaching with hydrochloric acid from roasted NdFeB scrap was explored. The phase evolution of NdFeB scrap during roasting at 800 °C as a function of time was confirmed, and after complete oxidation, its phase components consisted of Fe2O3, NdFeO3, and NdBO3. In the selective pressure leaching procedure, the optimal leaching was achieved at 110 °C for 30 min, in which the leaching rate of rare earth was 96.27% along with 13.33% of Fe. Subsequently, the effects of the hydrochloric acid dosage, the hydrochloric acid concentration and the particle size of the roasted NdFeB powder on the leaching rate of rare earth were investigated. For leaching at 110 °C for 30 min, the leaching of 13.33% Fe2O3 was derived from the Fe2O3 and NdFeO3 phases in the fully oxidized NdFeB scrap. This phenomenon was verified by the leaching of Fe from Fe2O3 of analytical purity and synthetic NdFeO3. Moreover, the leaching of Nd and Fe from the NdFeO3 phase was found to occur simultaneously. The advantages of the selective pressure leaching process using hydrochloric acid for the oxidized NdFeB scrap were comprehensively evaluated.

Optimized process for the fabrication of PDMS membranes integrating permanent micro-magnet arrays

Here we report on the fabrication of micro-magnet arrays by powder agglomeration in a polymer matrix. The NdFeB@polydimethylsiloxane (PDMS) inner microstructure and the generated magnetic forces were studied, when prepared under two different magnetic field configurations. The initial process uses the classical crosslinking of PDMS mixed with NdFeB powder under a low magnetic field gradient provided by a permanent magnet (LG set-up for low gradient). In contrast, the optimized process uses an intermediate layer, composed of iron microstructures in a PDMS matrix that amplifies and focuses the magnetic field gradient given by the permanent magnet (HG set-up for high gradient). Both processes result in a heterogeneous material that can be described as an array of permanent micro-magnets diluted in a non-magnetic host matrix. The NdFeB@PDMS microstructure was characterized by X-ray tomography and optical microscopy. The magnetic properties were also measured by magnetometry and colloidal probe AFM. Results showed that the HG set-up leads to an array of micro-magnets localized at the surface, with higher compactness and density, resulting in stronger magnetic performances compared to the LG set-up. This technology only implies easy-to-handle and cheap fabrication processes, paving the way for the development of low-cost lab-on-chip devices integrating magnetophoretic trapping functionality.

Synthesis and Characterization of Nd2Fe14B Powder by using Mechanical Milling of Flakes NdFeB

Flakes NdFeB is one of type NdFeB alloy made and it was produced by strip casting method. Flakes NdFeB can be used as a raw material to produce sintered permanent magnet and it has about 0.2 – 0.3 mm in thickness. The flakes of NdFeB was milled by using High Energy Milling (HEM) machine and used a liquid toluene as milling media. The milling time was varried such as : 15, 30, 60 and 90 minutes. After milling, the samples were dried by using vacuum dryer at temperature 80°C under vacuum (10 mmbar) for 2 hours. The fine powder samples were analyzed crystall structure by using XRD, measured magnetic properties by using VSM and also measured particle size distribution (PSA). The characterization result show that the milling time gives an effect on the crystal structure and magnetic properties, where samples with milling time 60 dan 90 minutes has Fe phase as dominant phase and the Nd2Fe14B phase does not existing also the coercivity value tends to decrease until lower than 900 Oe. Samples with milling time about 15 and 30 minutes have Fe phase and Nd2Fe14B phase also they have corecivity value about 2000 – 2250 Oe. The means of particle size is achieved about 43.59 µm at sample with milling time 15 minutes.

Influence of Melt-Pool Stability in 3D Printing of NdFeB Magnets on Density and Magnetic Properties.

The current work presents the results of an investigation focused on the influence of process parameters on the melt-track stability and its consequence to the sample density printed out of NdFeB powder. Commercially available powder of Nd7.5Pr0.7Fe75.4Co2.5B8.8Zr2.6Ti2.5 alloy was investigated at the angle of application in selective laser melting of permanent magnets. Using single track printing the stability of the melt pool was investigated under changing process parameters. The influence of changing laser power, scanning speed, and powder layer thickness on density, porosity structure, microstructure, phase composition, and magnetic properties were investigated. The results showed that energy density coupled with powder layer thickness plays a crucial role in melt-track stability. It was possible to manufacture magnets of both high relative density and high magnetic properties. Magnetization tests showed a significant correlation between the shape of the demagnetization curve and the layer height. While small layer heights are beneficial for sufficient magnetic properties, the remaining main parameters tend to affect the magnetic properties less. A quasi-linear correlation between the layer height and the magnetic properties remanence (Jr), coercivity (HcJ) and maximum energy product ((BH)max) was found.

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.

Systematic study of the dependence of magnetic and structural properties of Nd2Fe14B powders on the average particle size

A systematic study of the magnetic and structural properties dependence on the particle size was realized. For this, commercial NdFeB powder was separated into five different mean particle sizes using sieves. Besides, from the original powder, eleven samples were also produced by mechanical milling assisted by surfactant, using various milling times. A total of sixteen samples were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and Mössbauer spectrometry (MS). The particle sizes of the samples vary from the micrometer to the nanometer scale. The crystallite size decreases with decreasing particle size. XRD result indicates that the Nd2Fe14B phase is found in all the samples, and the presence of this phase is also corroborated by MS using six sextets for fitting their spectra, with an additional singlet corresponding to the Nd1.1Fe4B4 phase. The mean hyperfine magnetic field increases with increasing particle size because the magnetic dipolar interaction between the magnetic moment of the particles increases with particle size. From the VSM measurements the magnetic energy density (BH)max values were calculated for different particle sizes, and their maximum value of 34.45 MGOe is obtained for the sample with the particle size of 60 μm.

Effect of High Energy Ball Milling Washing Process on Properties of Nd<sub>2</sub>Fe<sub>14</sub>B Particles Obtained by Reduction-Diffusion

Nd2Fe14B particles were obtained from mixture of neodymium oxide, iron oxide, boric acid and CaH2 by reduction-diffusion process. Two different washing processes were used for the separation of magnetic particles from Ca and CaO matrix: usual washing with water and planetary ball milling process in ethanol media. Nd2Fe14BHx hydrogenated state was formed after usual washing with water. Ethanol planetary ball milling washing procedure prevented the formation of Nd2Fe14B hydrides during washing. Variation of milling parameters allowed producing particles with different morphology such as spherical or flakes after planetary ball milling washing process. Influence of milling parameters on magnetic properties of Nd2Fe14B powder was investigated.

Recovery of neodymium from the magnets of hard disk drives using organic acids

This work investigates the use of leaching with malic and citric acids for the recovery of neodymium (Nd) from the NdFeB permanent magnets of discarded hard disk drives (HDDs). Evaluation was made of the effect of previous roasting of NdFeB powder on the recovery of Nd. The HDDs were manually disassembled and the magnets were removed, demagnetized, and comminuted. The roasted NdFeB powder was produced by heating in a muffle furnace at 900 °C for 480 min, resulting in complete transformation of the metals into their oxides. Evaluation was made of the effects of the following leaching parameters: temperature (30–90 °C), acid concentration (0.2–1.2 M), solid:liquid ratio (1:10–1:50), and leaching time (10–900 min). For both organic acids, the best values for the first three parameters were 90 °C, 1.0 M, and 1:20. Using malic acid, the best leaching time for the unroasted NdFeB powder was 360 min, which resulted in 99% recovery of Nd. Leaching with citric acid showed good efficiency up to 60 min, with 72.8% recovery of Nd. However, for longer times, complexation between Fe and citrate led to the formation of a thick sludge, which prevented continuation of the leach. Leaching of the unroasted NdFeB powder resulted in low selectivity between Nd and Fe. In the case of the roasted NdFeB powder, the Nd recovery efficiencies achieved using malic acid and citric acid were 22% and 32.1%, respectively. However, high selectivity was obtained, with 86.0% and 98.0% Nd, relative to Fe, using malic acid and citric acid, respectively.

Synthesis and Characterization of Nd<sub>2</sub>Fe<sub>14</sub>B Powder Prepared by Using Milling and Heat Treatment

The Nd2Fe14B powder has been made by using High Energy Milling (HEM) from mixed metal powders Iron (Fe), Neodymium (Nd) and Boron (B). The Nd, Fe and B powders were mixed according stoichiometric composition (atomic ratio Nd:Fe:B = 2 : 14 : 1) and milled with milling time 40 hours by using HEM. Toluene liquid was used as milling media to protect of metal powders from oxygen. The sample after milling was heated at temperature 600, 700 and 800 °C in vacuum condition (10-3 Pa) for one hour. The measurement result of x-ray diffraction show that the Nd2Fe14B phase already formed as dominant phase and Fe-phase after milling 40 hours, with magnetic remanence (mr) = 4.10 emu/g and coercivity = 1,5 kOe. After heat treatment at temperature 700°C , the sample has magnetic remanence (mr) = 78 emu/g and coercivity (Hc)= 2,0 kOe. But sample after heat tgreatment at 800°C became soft magnet with lower mr and Hc value.

Analysis mechanical, magnetic and micro structure on composite hybrid magnet NdFeB-BaO6Fe2O3 prepared by using silicon rubber

Composite hybrid magnet NdFeB-BaO6Fe2O3 was made from a mixture of NdFeB and BaO6Fe2O3 magnetic powders by using silicon rubber (SR) as a binder. The magnetic powder mixture comprises 90% by weight of NdFeB (MQP-B +) and 10% by weight of BaO.6Fe2O3, while the SR-binder composition was 20, 40, 60 and 80% by weight. All raw materials were weighed according to the composition and mixed until homogeneous, then poured into the mold and dried at room temperature for 1 hour. All samples obtained were characterized including: measurement of tensile strength with elongation, hardness, magnetic properties and micro structure. The composition of SR binder gives a significant effect on the value of tensile strength and elongation as well as hardness and magnetic properties. But based on xrd analysis does not show any crystal structure change. Based on performance as a magnetic material, the appropriate SR composition for magnetic hybrid composite is sample with 40% SR, and in this composition it still has good flexibility properties with a remanence value of 40 emu/g and a coercivity of 1.55 kOe.

Squareness factors of demagnetization curves for multi-main-phase Nd-Ce-Fe-B magnets with different Ce contents

Abstract Multi-main-phase (MMP) magnets prepared by co-sintering Nd2Fe14B and (Nd,Ce)2Fe14B powders have shown better magnetic properties than the single-main-phase (SMP) magnets with the same average composition, enabling the preparation of high cost-performance permanent magnets with high Ce content. The present work focuses on the squareness factor (Q) of demagnetization curve for MMP Nd-Ce-Fe-B magnets, which represents the magnetic stability in practical applications. It is found that the MMP magnets prepared with larger fraction of (Nd,Ce)2Fe14B components possess higher Q value than those with lower fraction, which highlights the importance of relative fraction between the magnetically softer Ce-rich and the magnetically harder Nd-rich 2:14:1 grains on the squareness for the MMP magnets. Besides, the reduced Ce/Nd gradients within 2:14:1 grains and the formation of continuous RE-rich (RE, rare earth) grain boundaries also make contributions to the recovered squareness factor as well as the sustained coercivity.

Properties of NdFeB magnetic cement

Enhanced functional properties of cement pastes were achieved by introducing hard magnetic powders (NdFeB) into cement mixtures. The magnetic cement (cementitious magnet) employed a simple and inexpensive cementitious process to form complex NdFeB magnet shapes. NdFeB particles were distributed uniformly in the cement matrix. The density and compressive strength of the magnetic cement composites increased with the NdFeB concentration. Magnetization (stable up to one year) also increased with NdFeB powder but the coercivity did not change. The saturation magnetization (∼85 emu/g) and coercivity (∼7000 Oe) of the magnetic cement composites were larger than pure Ni, cubic or hard ferrites. The energy product (BH)max was found to be ∼1.0 MGOe, comparable to ferrite bonded magnets. Permanent magnetic behavior was demonstrated by using the magnetic cement for lifting metallic pieces or other magnetic cements. The endurance of the samples was also tested in two artificial environments.

Crystalline orientation control of the platelet Nd2Fe14B phase to produce magnetic anisotropy via electromagnetic vibration processing

Controlled crystalline orientation of the discontinuous phase in a composite enables the production of improved anisotropic properties, e.g., well-aligned Nd2Fe14B platelets by hot pressing and then soaking in a low-melting Nd-Cu eutectic melt to infiltrate to grain boundary. Alternatively, an anisotropic magnet can be fabricated by sintering Nd2Fe14B powder pre-aligned with a static magnetic field. In this study, we used a two-step electromagnetic vibration (EMV) technique to solidify the Nd70Cu30-30wt% Nd2Fe14B alloy, by which the magnetic Nd2Fe14B compound could be segmented into short laths and the easy magnetisation axes of these discontinuous platelets could be highly aligned, as revealed by electron backscatter diffraction (EBSD) patterns. Magnetic properties showed that the alloy exhibited strong anisotropy in its magnetism. Our present results opened a new avenue for the simple production of anisotropic Nd2Fe14B magnets via solidification without the powder metallurgy routine. Moreover, the technique is highly expected to be applied to other systems, e.g., graphene-reinforced metallic and/or polymer composites in which the alignment of graphene can maximise the anisotropy in the thermal or electrical properties of the composites.

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.

Efficient recovery of rare earth elements from discarded NdFeB magnets

Discarded NdFeB magnets are becoming the focus of recycling rare earth metals since the content can reach as high as about 30%. In this study, a novel carbonization/hydrogenation-hydrolysis process was proposed for the recovery of rare earth elements (REEs) from discarded NdFeB magnets by using biochar derived from waste sawdust as an extracting agent. Results showed that NdFeB magnets could react with biochar to form NdFeB-C/H alloy in the carbonization/hydrogenation process. Three factors including material placement mode, temperature and NdFeB powder layer thickness affected the C/H saturation of formed NdFeB-C/H alloy in this process. When NdFeB powder layer with thickness of 1mm was placed above biochar layer (Mode-3) and carbonized/hydrogenated for 90 min at 1400 °C, the C/H saturated NdFeB-C/H alloy subsequently generated 99.43% of rare earth hydroxides purity and 88.4% of the REEs recovery efficiency after hydrolysis and magnetic separation process. All findings indicated that the new carbonization/hydrogenation-hydrolysis process using biochar as an extractant could be an efficient approach for recovering REEs from discarded NdFeB magnets.

An evolving switching surface model for ferromagnetic hysteresis

We propose a thermodynamically consistent rate-independent three-dimensional model of magnetic hysteresis in terms of energetic and dissipation potentials making use of a relatively small number of model parameters that is capable of being implemented in a general incremental numerical setting. The dissipation process occurring during magnetization/demagnetization is described by a power-law potential, which leads to rate-independence at a certain limit of the rate-dependent exponent. The incorporation of isotropic hardening in the model enables us to describe phenomenologically at the macroscopic scale both nucleation and pinning type constitutive responses. We further model the symmetric and asymmetric minor loops by employing the idea of a bounding surface, which was originally introduced in the context of mechanical plasticity. Our model shows a very good agreement with experiments for spark plasma sintered NdFeB magnets, where nucleation is found to be the primary mechanism of coercivity. We also use our model to probe experiments for melt-spun NdFeB ribbons and powders, where both nucleation and pinning mechanisms are experimentally found to be significant. Moreover, we correlate the proposed model parameters with the underlying mechanisms for coercivity. We investigate the predictive capability of the proposed model by first probing an experimental minor loop and then use it to successfully predict the remaining minor loops, obtained from that experiment. We also construct a first-order reversal curve diagram for the floppy disk material and compare it with the corresponding experimental data.