Papers by Keyword: NdFeB Magnet

Abstract: NdFeB magnets were first developed in 1984 and are the most powerful permanent magnets that may possess energy products up to 60 MGOe. However, their working temperature and corrosion resistance are lower as compared to that of Alnico and SmCo magnets. Demand of NdFeB magnets recently has increased due to rapid growth of electrical vehicles. In this research work, NdFeB magnets developed through powder metallurgical technique are investigated for thermal effect on magnetic characteristics. The effect of increase in temperature on remanence, coercivity and energy product were measured using pulsed field magnetizer. Samples for testing were prepared from sintered bricks using wire cut machine. Demagnetization curves for the samples were measured at temperatures in the range of 20-110°C, and the results were analyzed. Decline in magnetic characteristics with temperatures is noted. Performance of the magnets with increase in temperature is essential to be analyzed specially for their use in high-speed motors.

Abstract: This paper proposed a recycling process for neodymium-iron-boron (NdFeB) magnet scrap from the end-of-life (EOL) of hard disk drives by using hydrometallurgical process. Initial chemical composition of NdFeB magnet scrap was consisted of 25.37%Nd, 6.53%Pr, 0.90%Co, 3.63%B and 63.57%Fe. After de-magnetization and crushing into proper size, magnet scraps were directly leached by H₂SO₄ solution. More than 90% dissolved into acid solution with remaining small amount of residuals and Ni-coated metal. Neodymium precipitated from leached solution by pH-control to the optimum condition at pH 0.6 using NaOH solution. Solid Nd-precipitates XRD pattern was observed in form of NaNd (SO₄)₂.(H₂O) and FeSO₄.(H₂O). Elemental analysis of Nd-precipitates by WD-XRF. The precipitates contained 26.50%Nd, 8.46%Pr and 1.19%Fe. In order to elimination of Fe, Nd-precipitates was leached by using H₂SO₄ solution to dissolve FeSO₄.(H₂O) into acid solution to obtain high concentration of Nd and rare-earth metals (REMs) compound. As a result, XRD pattern of Nd-compound after Fe-removal confirmed that the high purity NaNd (SO₄)₂.(H₂O) compound was obtained. The final composition of precipitates analyzed by WD-XRF was 26.36%Nd, 8.13%Pr with Fe as low as 0.14%Fe.

Abstract: Hybrid bonded magnet Ba-Ferrite/NdFeB with 5% wt Epoxy Resin (ER) as polymer binder hsa been developed with variations in BaFe₁₂O₁₉ to NdFeB weight ratio. The variation of the BaO6Fe₂O₃ : Nd-Fe-B weight ratio are 90%:10%; 80%:20%; 70%:30% and 60%:40%. The magnetic particle consist of Ba-Ferrite and NdFeB were mixed until homogenize and compacted by using hydraulic press machine with 8 Tonf force to form a disc shape sample. The disc sample was dried using vacuum dryer with 10 mm bar pressure at 80°C for one hour before being magnetized using impulse magnetizer. The best %wt composition ratio of Ba-Ferrite/NdFeB is 70%/30% and 60%/40%. The hybrid bonded magnetic properties at the best %wt composition ratio are: bulk density = 4.28-4.43 g/cm³, FM = 1057-1121 Gauss, Br = 3.46-3.70 kG, Hc = 3.25-3.70 kOe, and BHmax = 1.60-1.70 MGOe.

Abstract: VIM-HMS method is a novel process to extract REEs (rare earth elements) from NdFeB based permanent magnets. The NdFeB materials were melted in graphite crucible by VIM (vacuum induction melting) process, and the carbon saturated NdFeBC_sat alloy was obtained. The NdFeBC_sat alloy was mechanically pulverized and hydrolyzed in deionized water. In the HMS (Hydrolysis and magnetic separation) process, the neodymium carbide phase in the alloy reacted with water easily, and the rare earth hydroxides and the iron residues were separated by magnetic separation. The purity of the rare earth hydroxides was more than 99%, and the extraction ratio of the REEs is about 93%.

Abstract: Traditionally, NdFeB magnets with high remanent flux density or high energy product could only be manufactured through altering the material compounds. In recent years, studies indicated that the magnet properties of NdFeB magnets could be improved through plastic deformation. These studies pointed out that the degree of plastic deformation is a key factor to improve magnetic properties. However, there are still many other process parameters that could affect the magnetic properties either positively or negatively. In this paper, process parameters such as strain, strain rate, and temperature are studied to illustrate their influences on the magnetic properties of NdFeB magnets. The magnetic property could be greatly improved when the preferred orientation appears on the microstructure of deformed NdFeB magnets. One of the experimental results showed that the energy product value had been increased by 76.7% when the effective strain value had reached 0.65. Experimental results also showed that strain rate is a dominating factor with regard to the flow stress of material. Through a proper combination of these parameters, one can obtain NdFeB magnets with their magnetic properties greatly improved.

Abstract: In order to increase the intrinsic coercivity of the Nd-Fe-B magnets, the aging process optimization had been carried out. The results showed that more than 17 kOe intrinsic coercivity could be obtained by the aging process optimization. The microstructures and the fractures of the Nd-Fe-B magnets treated by the optimized aging process were also investigated by optical microscope, thermal field emission scanning electron microscopy and energy disperse spectroscopy. It was showed that the thin, continuous and smooth Nd-rich layer along the boundaries of the main crystal phase Nd₂Fe₁₄B could be formed by the optimized aging treatment and it resulted in the increase of the intrinsic coercivity of the Nd-Fe-B magnets.

Abstract: The new Nd-Fe-B magnets were prepared by powder metallurgical processing. The thermal stability and magnetic properties were found to be remarkably improved after annealing at 680 °C for 2 h. The B_r, and H_c, BH of annealed magnets were improved by-0.04 T, 132 KA·m^-1, 22 KJ·m^-3, from 1.25 T, 882 KA·m^-1, 286 KJ·m^-3 of the as-sintered magnets, respectively. The losses and average temperature coefficients of magnetic properties were very low at 373 K. Compare with the as-sintered magnets, the magnetic property losses of the annealed magnets decreased by half at different temperature. Scanning electron microscopy on magnets did reveal a noticeable difference in phase morphology, and found that the improvements of thermal stability and magnetic properties can be attributed to the change of magnetic domain wall motion, composition, stray demagnetizing fields, and microstructure. The new Nd-Fe-B preferment magnets are promising to use in the all-electric bus hub direct drive motor.

Abstract: In this work, Metal Injection Molding (MIM) process was applied to manufacture Nd-Fe-B magnets, where carbon residues were quantified. In a separated test, controlled additions of carbon were added prior to sintering in the conventional processing of Nd-Fe-B magnets, aiming to simulate the binder residues with more accuracy. The carbon contents in the sintered magnets were related to final magnetic properties such as remanence and coercivity. It was found that the rare-earth content in the alloy influence the threshold where further additions of carbon will degrade coercivity. This study gives directions on developing binder systems and debinding processes, focusing on reaching adequate carbon levels to maximize final magnetic properties.

Abstract: The influence of powder particle size on behaviour of hot plastic deformation, structure and magnetic properties of Nd–Fe–B die-upset magnets have been examined. It was found, that powder particle size strongly affected plastic properties of material during hot deformation process. Precursors made of powder with the smallest particles (d < 32 μm) shown bigger plastic resistance than those made of powder with the larger ones (32 – 88 or 88 – 350 μm). For the same pressing force and temperature, applied within hot plastic deformation process, precursors made of the smallest particle powder allowed to obtain only 56 % deformation, while the another, made of larger particle powder: 65% deformation.

Abstract: The purpose of this study is to develop a micro electro-magnetic actuator manufactured by MEMS-based fabrication and electroplating techniques. This actuator presented a novel technique in the electromagnetic fabrication and smaller physical size than the traditional counterparts for micro actuators and provides a faster response time and lower cost. A micro coil structure is released from FeCl3 etchant and bonded on a thin film (Parafilm”M”, Pechiney Plastic Packaging Inc.) to achieve an actuator-membrane structure. When an external AC power is applied to a micro coil, a magnetic field is created to attract and repel through an NdFeB permanent magnet, and the displacement of the membrane is increased as a current of AC power. The results show the measured magnetic field intensity weakens as the distance between the coil and the Gauss meter probe increases. However, it is observed that the magnetic field intensity does not increase linearly with the number of series coils, which is due to the distance between series coils.