SmCo Magnets Research Articles

Alteration of flux density of highly coercive SmCo magnets used in prosthodontics and epithetics in 1.5 T and 3 T MRI

The opposing field stability of highly coercive dental magnets in external magnetic fields of 1.5 and 3 T magnetic resonance imaging (MRI) was investigated. It was further assessed if remagnetizing can reverse the flux density in the magnets. Using an adjustable fixture, 20SmCo magnets were exposed and 6 positions of prosthodontics and epithetics were simulated: P : in the lower jaw parallel to the main field B0, A: in the upper jaw antiparallel to B0 in a straight position, Ad: antiparallel, reclined by 45°, Av: antiparallel, inclined by 45°, G: glabellar region 90° to B0 and M: mastoid region 90° to B0. The effects of exposure in the exterior field directly at the opening for the parallel (Pex), antiparallel (Aex), glabellar (Gex) and mastoid (Mex) positions were also investigated. After each exposure the magnets were remagnetized. The flux density was determined as an equivalent of the adhesive force. With 1.5 T clinically relevant loss of flux density between 7% and 10% occurred only in the angled positions Ad and Av and the external position Aex. In the antiparallel positionsA and Aex the strong external field of 3 T caused very high losses of 72% and 33%, respectively. In the inclined and reclined antiparallel positions Ad and Av the magnets lost 96% of their flux density and were almost fully demagnetized. All of the magnets could be fully remagnetized regardless of the degree of damage. Highly coercive SmCo magnets can remain in situ during a 1.5 T MRI scan unless the resulting artifacts are diagnostically relevant. Exposure to the 3 T main field in antiparallel position may result in acomplete loss of the adhesive force. In this case the magnets should be remagnetized by the manufacturer. Inclination or reclination of the head reinforces the effect of the main field.

Effect of grain boundary on magnetization behaviors in 2:17 type SmCo magnet

Abstract The effect of grain boundary area on the magnetization behaviors in Sm25Co48Fe20Cu5Zr2 magnet was investigated. Grain boundary area with deficiency of Cu and incomplete cellular microstructure was clearly observed. In-situ Kerr observation revealed that the magnetization reversals firstly occurred in the grain boundary areas and then propagated into the interiors of grain. The grain boundary areas with weakened pinning force of magnetic domain walls could undermine the coercivity and induce inferior squareness of the magnet. The investigation using Fresnel LTEM demonstrated that the grain boundary area was magnetized more easily than the grain interior, which agreed with the multi-stage phenomenon of the initial magnetization curve of the magnet.

RARE-EARTH PERMANENT MAGNET IN MAGNETIC SYSTEM OF ELECTRON ACCELERATOR WITH THE ENERGY OF 10 MеV

The radiation resistance of Sm-Co and Nd-Fe-B magnets under 10 MeV electron beam was studied. The simula-tion and design of a magnetic system for electron beam analysis of a technological accelerator for energy up to 10 MeV was carried out. The key component of magnetic system was Sm2Co17 magnets with the size of 30х24х12 mm. The maximum magnetic field in the magnetic system was 0.3 T.

Solvometallurgical route for the recovery of Sm, Co, Cu and Fe from SmCo permanent magnets

A solvometallurgical recycling route for the recovery of samarium, cobalt, copper and iron from SmCo magnets was developed. The SmCo magnets were first crushed and milled to powder size and then leached in a 2 mol L−1 hydrochloric acid solution in ethylene glycol. Afterwards, cobalt, copper and iron were extracted from the leachate with 50 wt% Aliquat 336® in toluene, which was pre-saturated with 37 wt% HCl. The non-aqueous solvent extraction system improved the extraction efficiency of cobalt. The extraction was optimized by evaluating the extraction rates, the effects of temperature, feed/solvent ratio and the hydrochloric acid concentration. Through the construction of a McCabe-Thiele diagram it was possible to calculate the number of stages required for continuous extraction. Cobalt was recovered from the loaded solvent by stripping with a 0.5 mol L−1 aqueous hydrochloric acid solution. Copper was recovered by stripping with a 5 vol% aqueous ammonia solution, whereas iron precipitated under these conditions. The solvent could be reused after regeneration, i.e. evaporation of water and ammonia and reintegration of toluene and HCl. The samarium left in the raffinate was extracted by 20 vol% Cyanex 272 in n-dodecane. Finally, samarium was recovered from the loaded Cyanex 272 by precipitation stripping with a 0.2 mol L−1 aqueous oxalic acid solution. The purity of the recovered cobalt chloride was 98.3 wt% and that of samarium oxalate was 99.4 wt%.

Microstructure and magnetic properties of SmCo5 sintered magnets

SmCo5 sintered magnets with good thermal stability are mainly used in high-temperature field. In this study, two types of SmCoz powders with different nominal z values were mixed and synthesized into SmCo5 magnets by the traditional powder metallurgy method. The magnetic properties of the SmCo5 sintered magnet are maximum energy product of (BH)max = 172.29 kJ·m−3, remanence of Br = 7.47 × 105 A·m−1 and coercivity of Hci = 2.42 T. The results show that there are three coexisting phases in the magnet, which are SmCo5 phase, Sm2Co7 phase and Sm2O3 phase. The microstructural observation indicates that the average grain size in the magnet is about 8 μm, and the high coercivity of this magnet is attributed to these fine grains. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) results indicate that the magnet has a well-aligned (00l) orientation texture.

Magnetic Domain Structures and Magnetic Properties of Lightly Nd-Doped Sm–Co Magnets With High Squareness and High Heat Resistance

The relationship between magnetic domain structures and magnetic properties of Nd-doped Sm(Fe, Cu, Zr, Co)7.5 was investigated. In the preparation process, slow cooling between sintering and solution treatment was employed to promote homogenization of microstructures. The developed magnet achieved a maximum energy product, [BH]m, of 33.8 MGOe and coercivity, Hcb, of 11.2 kOe at 25 °C, respectively. Moreover, B-H line at 150 °C was linear, which means that irreversible demagnetization does not occur even at 150 °C. Temperature coefficients of remanent magnetic flux density, Br, and intrinsic coercivity, Hcj, were 0.035%/K and 0.24%/K, respectively, as usual the conventional Sm-Co magnet. Magnetic domain structures were observed with a Kerr effect microscope with a magnetic field applied from 0 to -20 kOe, and then reverse magnetic domains were generated evenly from grain boundaries. Microstructures referred to as “cell structures” were observed with a scanning transmission electron microscope. Fe and Cu were separated to 2-17 and 1-5 phases, respectively. Moreover, without producing impurity phases, Nd showed the same composition behavior with Sm in a cell structure.

A novel high temperature eddy current damper with enhanced performance by means of impedance matching

When an electrically conductive material is exposed to time-varying magnetic fields, eddy currents are generated inside the conductor which oppose the change in the magnetic field. When eddy currents circulate through the conductor they are dissipated in form of heat due to the resistivity of the material. For low frequency vibrations, eddy current damping force is proportional to the vibration speed. Therefore, damping of vibrations at low frequencies or displacement amplitudes becomes increasingly difficult using this technology. Typical damping densities of eddy current dampers range between 0.1 for most devices and 2 MN s m−4 for best-in-class prototypes. Those values are relatively low compared with, for examples, hydraulic dampers that can reach up to 4 MN s m−4. This low density limits potential applications of the technology. In addition, certain applications like vibration isolation of aircraft engines may require the damper to operate at high temperatures. However, most of current damping solutions are rarely effective at temperature higher than 100 °C because they frequently use NdFe magnets. In this paper, a passive eddy current damper with enhanced performance for use in high temperatures is presented. The Z-Damper takes advantage from impedance matching inside a magnetic linear gear to amplify the input vibration motion, maximizing the effectiveness of an integrated eddy current damper. SmCo magnets and high temperature components are used in the Z-Damper, potentially enabling operation in a wide temperature range. A theoretical model describing the dynamic behavior of the Z-Damper is presented and a set of experiments were conducted to evaluate its performance. A prototype of the Z-Damper has been designed, manufactured and experimentally demonstrated in a temperature range from 25 °C to 200 °C under low frequency (up to 60 Hz) harmonic excitations. A maximum equivalent viscous damping coefficient of 35 Ns mm−1, measured at 200 °C, has been achieved. A damping density of 8.4 MN s m−4 is calculated.

Grain boundary modification induced magnetization reversal process and giant coercivity enhancement in 2:17 type SmCo magnets

Grain boundary modification induced giant coercivity enhancement from 945 kA/m to 1904 kA/m was achieved in Sm25Co48Fe20Cu5Zr2 magnets by doping 0.4 wt% CuO. Different magnetization reversal behaviors were clearly observed between un-doped and doped magnets. Compared with un-doped magnets, Cu enrichment along grain boundary promoting regular cellular structure was obviously found in doped magnet. The in-situ Kerr observation indicated that complete cellular structure could strengthen the pinning field of grain boundary regions and the propagations of magnetization reversals into interiors of grains were restrained by the modified grain boundaries, which resulted in the remarkable coercivity increment.

Recycling of rare earth elements from SmCo5-Magnets via solid-state chlorination

Abstract The recycling of rare earths from End-of-Life permanent magnets is a widely studied field of research. However, with rare earth prices falling, recycling processes have become increasingly uneconomical. In this context, solid-state chlorination has been intensively studied as this method has the potential to serve as an alternative to acid leaching. Instead of a mineral acid dissolving the magnets, a chlorination takes place by decomposing NH4Cl at temperatures between 225 and 325 °C. The resulting dry HCl forms water-soluble chlorides from the magnet material. For rare earth recycling from Fe14Nd2B magnets, the method was found to provide significant advantages in terms of consumption of chemicals as well as and chemical costs. The present work sheds light on another obstacle of magnet recycling, which is the inhomogeneous composition of the starting material. Only 2% of the total end-of-life magnet waste material contains SmCo magnets. Fe14Nd2B magnets account for most of the waste material. SmCo magnets are nevertheless the second most important group of rare-earth-based permanent magnets. However, they are not collected separately, and recycling processes have to focus on recovering both magnet alloys within one process. Therefore, the solid-state chlorination of SmCo5 magnets was examined in detail. The present work focusses consequently on three major issues: (i) Adjustment of solid state chlorination so that SmCo alloys can be chlorinated under the same conditions as Fe14Nd2B magnets. This is the most important requirement for a recycling process that utilizes both types of rare earth magnets. (ii) Examination of the reaction of SmCo with NH4Cl. It was found that the chlorination behaviour differs significantly from that of the Fe14Nd2B magnets. The particles arising from SmCo5 disintegrate more rapidly than expected during chlorination, which eventually enables an almost selective chlorination of samarium. (iii) Furthermore, Sm yields were optimised to reach 99.7% by applying a design of experiments.

Experimental study of the transport properties of Nd-Fe-B and Sm-Co magnets

The article adduces new reliable experimental data on the thermal conductivity and the thermal diffusivity of hard magnetic materials of brands N35M, N35H, N35SH, as well as YX18, YX24 and YXG22, YXG30 with main components represented by the crystalline phases of Nd2Fe14B, SmCo5 and Sm2Co17 type, respectively. The temperature range from 293 to 773…1273 K has been investigated by laser flash technique with an error of 3—4%. The reference tables of the thermal diffusivity and thermal conductivity coefficients have been developed. The character of the thermal diffusivity changes near the Curie point has been determined. The critical indices and the critical amplitudes have been defined.

Sm 2Co 7 Nanophase Inducing Low-Temperature Hot Deformation to Fabricate High Performance SmCo 5 Magnet

We report a novel design to fabricate high performance SmCo5 magnet by using Sm2Co7 nanophase inducing low-temperature hot deformation. Our approach can reduce the hot deformation temperature to 650℃ from the previous 900℃ to acquire good texture and nanocrystalline. As a consequence, a giant coercivity of 25.6 kOe is achieved in the anisotropic magnet, 4 times of the value in previous report. Ascribed to the large coercivity, our magnet represents good thermal stability, which possesses a maximum magnetic energy product of 10.6 MGOe at 300 ℃, maintaining 75% of that at room temperature.

Metal Recovery from Spent Samarium-Cobalt Magnets Using a Trichloride Ionic Liquid.

Recycling of samarium–cobalt (SmCo) magnets is essential due to the limited resources of the mentioned metals and their high economic importance. The ionic liquid (IL) trihexyltetradecylphosphonium trichloride, [P666,14][Cl3], which can safely store chlorine gas in the form of the trichloride anion, was used as an oxidizing solvent for the recovery of metals from spent SmCo magnets. The dissolution was studied considering various mixtures of the ILs [P666,14][Cl3] and [P666,14]Cl, solid-to-liquid ratios and different temperatures. The results showed that the maximum capacity of [P666,14][Cl3] for SmCo magnets was 71 ± 1 mg/g of [P666,14][Cl3], in the presence of an extra source of coordinating chloride ions. The maximum loading of the IL could be reached within 3 h at 50 °C. Four stripping steps effectively removed all metals from the loaded IL, where sodium chloride solution (3 mol L–1), twice water and ammonia solution (3 mol L–1) were used consecutively as the stripping solvents. The regenerated IL showed a similar dissolution performance as fresh IL. Oxidative dissolution of metals in trichloride ILs is easily transferable to the recycling of valuable metals from other end-of-life products such as neodymium–iron–boron magnets and nickel metal hydride batteries.

Attractive-domain-wall-pinning controlled Sm-Co magnets overcome the coercivity-remanence trade-off

Traditional approaches for increasing the intrinsic coercivity of magnets typically come at the expense of remanence, a dilemma known as intrinsic coercivity-remanence trade-off, leading to a substantial reduction of maximum energy product. New metallurgical processing might offer the possibility of overcoming this trade-off. Here, we achieve a combination of an intrinsic coercivity of 26.9 kOe, a remanence of 11.2 kG, and a maximum energy product up to 26.6 MGOe, which surpasses most of conventional Sm-Co based permanent magnets, by manipulating the gradient of domain wall energy landscape of constituent phases to realize the attractive domain wall pinning in Sm(Co,Fe,Cu,Zr)z permanent magnets. Using powerful atomic-scale analysis technique known as atom probe tomography and micromagnetic simulations, we reveal that an enlarged attractive domain wall pinning strength results in the substantial coercivity enhancement with little sacrifice of remanence and maximum energy product in the Cu-particle-alloyed magnet. These results provide atomic-level insights into the coercivity mechanism of rare earth permanent magnets, with the methodology offering exciting possibilities for quantitative analyses and prediction between compositions and magnetic properties of other magnetic materials.

2:17 type SmCo magnets with low temperature coefficients of remanence and coercivity

Spin-reorientation-transition cell boundary phases are used to improve the temperature stability of coercivity in 2:17 type SmCo magnets. A magnet with both low temperature coefficients of remanence (α) and coercivity (β) is developed. In comparison with traditional 2:17 type SmCo magnets with low temperature coefficient of remanence, this magnet exhibits comparable (BH)max and α, meanwhile the β(20–100 °C) is improved by more than two orders of magnitude. The comparative study of reversible magnetization/irreversible magnetizations indicates that the flux losses of this magnet are barely affected by temperature, which is an remarkable improvement in developing temperature-stable magnet.

Fabrication and Characterization of a Magnetized Metal-Encapsulated FBG Sensor for Structural Health Monitoring

A novel means of metal packaging of a fiber Bragg grating (FBG) sensor using stainless steel and tin, together with high temperature resistant samarium cobalt (SmCo) magnet is proposed in this paper. The inclusion of high temperature-capable SmCo magnets enable the metal packaging of the FBG sensor with magnetic capabilities. This packaged sensor can be placed in direct contact with the substrate structures such as iron pipelines and other ferromagnetic components without any adhesives, making them easily detachable and reusable. This is a significant improvement compared with other commercial fiber optic sensors which are, surface attached using epoxies or welded to the substrate. The design parameters and characteristic properties such as load, temperature, and vibration sensitivity of the magnetic metal-packaged FBG sensor are studied numerically and validated experimentally to demonstrate the feasibility of using the encapsulated reusable FBGs for structural health monitoring of compatible structures.

Phase transformation in anisotropic nanocrystalline SmCo5 magnets

SmCo5 nanoflakes with excellent texture have great potential applications in high performance nanocomposite magnets, in which the phase structure of the hard magnetic phase is crucial for obtaining large coercivity. Phase transformation from 1:5H phase to 2:17 R phase is observed in anisotropic nanocrystalline SmCo5 magnets when sintering the nanoflakes at 600–650 °C. The phase transformation is interesting because the 1:5H phase is relatively stable according to the thermodynamic and kinetic analysis. The phase transformation results in much lower coercivity of the wet-milled anisotropic magnets when compared with dry-milled isotropic magnets with 1:5H single phase. Analyses of differential scanning calorimetry, thermogravity and energy dispersive X-ray validate that the phase transformation originates from the oxidation of the nanoflakes with large specific surface area during sintering. The results suggest that controlling oxygen content strictly during sintering is necessary for maintaining 1:5H single phase in anisotropic nanocrystalline SmCo5 magnets prepared by sintering the nanoflakes.

Samarium/cobalt separation by solvent extraction with undiluted quaternary ammonium ionic liquids

SmCo permanent magnets are used in the automotive and aircraft industries. They are preferable over NdFeB magnets for applications above 150 °C. End-of-life SmCo magnets are a valuable secondary source of cobalt and samarium. This study presents solvent extraction systems without addition of molecular diluents. Undiluted quaternary ammonium ionic liquids with chloride, thiocyanate and nitrate anions were used to extract metals from aqueous feed solutions with high chloride concentrations in order to separate the main metals (Sm/Co/Cu) present in SmCo magnets. A chloride/chloride extraction was compared with two split-anion extraction systems (i.e. chloride in the aqueous phase and either nitrate or thiocyanate in the organic phase). The advantage of split–anion extraction is that it can be done from a chloride solution, but with the extraction behavior of nitrate or thiocyanate solutions. Split-anion extraction was in this work applied to the separation of rare earth elements/transition metals instead of previous applications to the mixtures of rare earths. For all the systems, the selectivity of extraction, scrubbing and stripping from a multi-element solution were investigated. High separation factors (>7500) were found for Co/Sm separations. Co(II) and Cu(II) extracted in the chloride/chloride and chloride/nitrate systems could be stripped simply by water. However, stripping of the loaded ionic liquid in the chloride/thiocyanate system with water was not feasible. The extraction mechanism for the different ionic liquids was studied by extended X–ray absorption fine structure (EXAFS). A possible explanation on the extraction behavior of samarium ions in the presence of transition metal ions (cobalt and copper) is given.

Recovery of Sm(III), Co(II) and Cu(II) from waste SmCo magnet by ionic liquid-based selective precipitation process

Recovery of secondary resources including waste SmCo magnets contributes to easing the natural resources and environmental issues. For the development of recovery technologies, an ionic liquid (IL)-based precipitation route based on [trihexyl(tetradecyl)phosphonium]2[benzene-1,4-dioxydiacetate] ([P6,6,6,14]2[BDOAC]) is presented. The slow release of [BDOAC]2− from [P6,6,6,14]2[BDOAC] increases the kinetics difference in the formations of precipitates, and makes the precipitates contain less impurity. While cobalt-rich solution is obtained with no loss, precipitation efficiency of Sm(III) and Cu(II) reaches 96.8% and 100% respectively. Afterwards, Cu(II) is removed using aqueous ammonia and pure Cu(II) (96.4% precipitation efficiency) is obtained by adjusting the pH of cuprammonium complex solution. The proposed process without volatile diluent reveals higher separation factors of Sm/Co, Cu/Co and Sm/Cu. Lower acidities are efficient for the complete stripping of Sm(III) and Cu(II) from their precipitates. SmCl3 and CuCl2 solutions are obtained both with the high purities. Moreover, the IL-based precipitant can be regenerative. It is shown that the strategy is efficient for recovering and separating Sm, Co and Cu from the simulated leaching solution of waste SmCo magnets.

Temperature stability of SmCo (2:17) magnets modified by Ni–Cr two-layer coating

The oxidation resistance behavior of SmCo (2:17)-type high-temperature magnets modified with Ni–Cr two-layer coating was studied. The study depicts the mass gain kinetics and magnetic properties of uncoated and Ni–Cr-modified magnets oxidized at high temperature (500 °C) in air for 200 h. The oxidation test results illustrate that the mass gain of uncoated magnet is 6.95 mg·cm−2 which is more than that (0.08 mg·cm−2) of coated magnet after 200 h. For the magnetic properties concerned, there is a great loss for uncoated magnet, while for coated magnet, magnetic properties do not change much. The study of uncoated magnet through X-ray diffraction (XRD) and electron probe microanalysis (EPMA) shows that the invasion of oxygen at high temperature leads to the loss of magnetic properties by changing the microstructure of magnet.

The Programmable Permanent Magnet Actuator: A Paradigm Shift in Efficiency for Low-Speed Torque-Holding Robotic Applications

In this letter, we propose a new type of electromagnetic actuator called the “programmable permanent magnet” (PPM) actuator. The PPM actuator is designed to tackle low-speed high-torque applications where classic electromagnetic actuators are highly inefficient. The PPM actuator is based on the application of pulsed current to magnetize a hard ferromagnetic stator that is made of individual SmCo (custom grade) magnets placed in a Halbach array configuration. The motor creates a springlike torque function that generates up to 0.2 N·m. Unlike electromagnetic actuators, by design, the PPM actuator does not draw current while exerting torque. Instead, the motor's power consumption depends on its rotational speed or torque variations. The PPM actuator is, by consequence, most efficient, whereas classical electromagnetic motors are most inefficient, and is a new alternative to actuators for robotic applications, which tend to operate in low-speed, high-torque conditions. The prototyped PPM actuator measures 47 mm in diameter, with a height of 35 mm and weight of 200 g, and has been successfully integrated in a commercially available 2-finger gripper from Robotiq, Inc.