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1.
采用一种高效、绿色的物理方法对NdFeB废旧磁体表面进行清理并回收利用。通过晶界添加低熔点Ho63.3Fe36.7合金制备NdFeB再生磁体。在未添加Ho63.3Fe36.7的磁体中,没有足够的富Nd相隔离Nd2Fe14B相,从而导致磁体性能较差;随着Ho63.3Fe36.7合金的加入,晶界相变得清晰且连续。在质量分数2%Ho63.3Fe36.7添加量下,钕铁硼再生磁体获得最佳磁性能[(BH)max+Hcj=1756.07]。此时矫顽力增加123 kA/m(约提高9.1%),磁体的最大能积由290.94 kJ/m3下降到281.07 kJ/m3,而剩磁少量下降。通过对再生磁体显微组织和成分的分析可知,磁体晶界处形成了(Nd, Pr, Ho)2Fe14B壳层,这能够提高磁体的矫顽力。而X射线衍射分析表明,磁体I(006)/I(105)的衍射峰强度比从0.92提高到1.32。这说明磁体取向度提高,可以减弱对剩磁的影响,从而使得再生磁体在保持剩磁的同时提高磁体的矫顽力。  相似文献   

2.
Abstract

Static state immersion experiments, polarisation curve and electrochemical impedance spectroscopy tests have been applied to investigate the corrosion kinetics for both spark plasma sintered (SPS) and conventional sintered Nd–Fe–B magnets in NaCl electrolyte. Effect of microstructure modification on their chemical stability of the magnets was discussed. The electrochemical reactions of both magnets are controlled by the step of active substances adsorption process at the open circuit potential and the anodic potential, which turn to diffusion process at the cathodal potential. Although both magnets are susceptible to corrosion in saline electrolytes, SPS magnets are more corrosion resistant than conventional sintered magnets due to their special microstructure that is different from those of conventional sintered magnets. In SPS magnets, the grain size of the Nd2Fe14B main phase is fine and uniform, only a few Nd rich phase form along the grain boundaries of Nd2Fe14B phase, while most of them agglomerate into triple junctions as small particles. Such microstructure effectively restrains the aggressive intergranular corrosion along Nd rich phases. As a result, the SPS magnet possesses excellent corrosion resistance in NaCl electrolyte.  相似文献   

3.
A novel anisotropic Nd-Fe-B flexible bonded magnet with epoxy resin lubricant was prepared by the two-step method to enhance its performance. Temperature characteristics of epoxy resin and its effect on magnetic properties and preparation of anisotropic Nd-Fe-B flexible bonded magnets were investigated and optimized. DOA of aligned flexible bonded magnets with epoxy resin lubricant increases significantly due to epoxy resin lower viscosity and subsequent better powder particles lubrication at a certain aligning temperature. Meanwhile, Hirr decreases sharply due to improved oxidation resistance of epoxy resin fully encapsulating magnetic powder during magnetic alignment process. Utilizing 1 wt% optimized encapsulating epoxy resin and heating unaligned flexible bonded magnets to 80 °C for 30 min during magnetic alignment resulted in the largest Δ(BH)max and ΔDOA. Δ(BH)max increased to over 126% along with ΔDOA increase to over 75%, much higher compared with unaligned flexible bonded magnets prepared exclusively by calendering.  相似文献   

4.
The absorption of hydrogen by NdFeB magnet has been investigated by using the electrochemical charging technique at constant cathodic current density Ic ranging from 0 to 4 mA/cm2. Open circuit potential measurements (OCP) and polarization curves were carried out to study the corrosion behavior of the charged NdFeB magnet in 0.01 mol/L NaCl solution. The results showed that hydrogen had a strong influence on the corrosion of NdFeB magnet. The open circuit potential became gradually negative due to the hydrogen incorporation into the NdFeB magnet. The corrosion resistance was reduced gradually with the increasing cathodic current density Ic. The surface structure and the morphology of the charged NdFeB magnet were examined by XRD and SEM. The results revealed that the effect of the absorbed hydrogen focused mostly on accelerating the exfoliation corrosion of Nd2Fe14B matrix grain.  相似文献   

5.
粘结剂作为粘结NdFeB磁体制备过程中的重要组成部分,其作用是提高磁粉颗粒的流动性和粘结强度,保证产品的力学性能和磁性能的稳定。采用理论与实验相结合的方法,研究了粘结剂含量对粘结NdFeB磁体力学性能和磁性能的影响。在此基础上,制备了高性能粘结NdFeB磁体。利用扫描电子显微镜(SEM)对磁体的结构和形貌进行了表征。在NIM-200C磁滞回线仪和电子万能试验机(AG-X plus)上分别测定了环形粘结NdFeB磁体(RSM)的磁性能和力学性能。结果表明,当粘结剂含量为3%(质量分数)时,粘结NdFeB磁体密度最高(5.59 g/cm3),抗压强度最高(159 MPa),磁性能最佳。  相似文献   

6.
The grain boundary diffusion process using an Nd70Cu30 eutectic alloy has been applied to hot-deformed anisotropic Nd–Fe–B magnets, resulting in a substantial enhancement of coercivity, from 1.5 T to 2.3 T, at the expense of remanence. Scanning electron microscopy showed that the areal fraction of an Nd-rich intergranular phase increased from 10% to 37%. The intergranular phase of the hot-deformed magnet initially contained ~55 at.% ferromagnetic element, while it diminished to an undetectable level after the process. Microscale eutectic solidification of Nd/NdCu as well as a fine lamellae structure of Nd70(Co,Cu)30/Nd were observed in the intergranular phase. Micromagnetic simulations indicated that the reduction of the magnetization in the intergranular phases leads to the enhancement of coercivity in agreement with the experimental observation.  相似文献   

7.
Strontium hexaferrite nanoparticles were synthesized by chemical coprecipitation method in the presence of polyvinylpyrrolidone (PVP) as a protective agent. A mixture of the deionized water/ethanol (50/50) was used as the solvent. The effects of PVP, pH of the solution, Fe3+/Sr2+ molar ratio and calcination temperature of the precipitates on the synthesis of strontium hexaferrite samples were studied. X-ray diffraction (XRD), scanning electron microscope (SEM), thermal analysis (DTA-TGA), dynamic light scattering particle size analyzer (PSA) and vibrating sample magnetometer (VSM) were used to investigate the properties of the obtained samples. The results showed that increasing the pH from 9 to 13 or decreasing Fe3+/Sr2+ molar ratio from 12 to 9 promoted SrFe12O19 formation and decreased the size of nanoparticles. The minimum coercivity of 4733 Oe and maximum saturation magnetization of 51 emu/g were obtained by increasing the pH from 9 to 13. It was also concluded that PVP could be effective in decreasing the size of SrFe12O19 nanoparticles and resulted to decrease the calcination temperature from 800 to 700 °C.  相似文献   

8.
High-energy NdFeB magnets and their applications   总被引:3,自引:0,他引:3  
In sintered NdFeB magnets, additive elements for increasing coercivity decrease residual magnetization. Also, fine magnetic powder oxidization prevents identification of the stoichiometry composition (Nd 2Fei14B).To improve the magnetic properties of a sintered NdFeB magnet, the authors have developed a method involving two alloys. Magnetic Nd 2Fei14Balloy and a rare- earth- rich alloy (including richer dysprosium content) are melted individually and mixed together after coarse pulverization. After the sintering process, dysprosium in the sintered body is enriched in each grain region near the grain boundary. The two- alloy method minimizes the liquid phase necessary to keep the coercive force at a useful level, and thus results in compositions closer to stoichiometry. The energy product of magnets having an inhomogeneous dysprosium distribution is typically 360 kj - m - 3 (45 MG.Oe) at production level. The corrosion characteristics of cobalt- substituted NdFeB magnets also were investigated. These magnets are now used in voice coil motors for hard disk drives and contribute to shortening access time and hard- drive downsizing.  相似文献   

9.
Rapid solidification of stoichiometric Nd2Fe14B alloy in drop tube processing (DTP) is studied experimentally and theoretically. All relevant physical processes, including fluid flow, heat transfer, nucleation and crystal growth, are modeled at different scales. Transient nucleation is described using an extension of the classical nucleation model in terms of Poisson statistics and accounting for the geometrical factors of heterogeneous nuclei. Analysis of phase selection allows prediction of the appropriate processing conditions to optimize the magnetic properties of the as-solidified Nd-Fe-B samples by reducing the amount of α-Fe that forms during solidification. Comparison with experimental microstructural data confirms the modeling results.  相似文献   

10.
The quenching, fracture and aging treatment of radially oriented Sm2Co17 ring magnets were investigated. The results indicate that the ring magnets have obvious anisotropy of thermal expansion, which easily leads to the splits of the magnets during quenching. The fracture is brittle cleavage fracture. The difference (Aa) of the expansion coefficient reaches the maximum value at 800-850 ℃. So, various quenching processes at different steps are adopted in order to reduce the splits. When the magnets are aged, 1:5 phase precipitates from the 2:17 matrix phase and forms a cellular microstructure with 2:17 phase. BHmax and JHc reach the maximum value 226 kJ/m^3 and 2 170 kA/m after being aged at 850 ℃ for 4 h and 8 h, respectively. The aging treatment at 850 ℃ has little influence on remanence(Br), which can always keep a high value (≥1.0 T). Through appropriate heat treatment, the ring magnets have uniform cellular microstructure and excellent magnetic properties: Br ≥ 1.0T, JHc ≥2 100 kA/m, BHmax ≥ 220 kJ/m^3.  相似文献   

11.
The Oxidation of NdFeB Magnets   总被引:10,自引:0,他引:10  
Li  Y.  Evans  H.E.  Harris  I.R.  Jones  I.P. 《Oxidation of Metals》2003,59(1-2):167-182
The oxidation kinetics in air of a commercial NdFeB magnet have been investigated over the temperature range 335–500°C. The oxide microstructure has been characterized by SEM, XRD and cross-sectional TEM. The results show that the external scale formed consists of an outer layer of Fe2O3 and an inner layer of Fe3O4 but that the principal degradation process is the formation of an extensive zone of internal oxidation. HREM has been used to show that this zone contains NdO particles embedded in an -Fe matrix. These particles are discrete and very small, approximately 2 nm in diameter, and have an amorphous structure. The -Fe matrix has a columnar grain structure with a grain width of approximately 100 nm. It is argued that the high rates of internal oxidation arise because the external-oxide layers are not protective at the oxidation temperature, and oxygen penetrates to the zone front by fast diffusion along the columnar -Fe grain boundaries.  相似文献   

12.
Sintered NdFeB magnets possess excellent magnetic properties. However, the corrosion resistance property of NdFeB is very poor due to its multiphase microstructure consisting of matrix phase Nd2Fe14B, Nd‐rich phase, and B‐rich phase. The corrosion behavior of NdFeB magnets in sodium hydroxide (NaOH), sodium chloride (NaCl), nitric acid (HNO3), and oxalic acid (H2C2O4) solutions was investigated by immersion and electrochemical tests. HNO3is the strongest corrosive electrolyte compared with the other three solutions. The increase in HNO3concentration can accelerate the corrosion of NdFeB magnets. NaCl belongs to medium corrosion electrolyte. A NaCl concentration of 0.5 M shows the severest corrosive feature in comparison with other concentrations of NaCl solution. NdFeB hardly suffers corrosion in NaOH and H2C2O4solutions owing to the formation of passivation films on the surface of magnets. Based on the corrosion behavior of NdFeB in different electrolytes, the possible corrosion mechanisms are discussed.  相似文献   

13.
Substantial progress has been made in fabricating long lengths of flexible silver-clad high-critical-temperature superconductor tapes by the powder-in-tube method. Tapes with high critical current density (Jc) that are attractive for electrical power and high-field magnet applications have been produced. At liquid helium (4.2 K) and liquid neon (27 K) temperatures, tapes made by this improved processing method yielded Jc values greater than 100 kA/cm2 at zero field; at liquid nitrogen temperatures (77 K), the Jc values exceeded 40 kA/cm2. This article discusses the processing and properties of short-length tapes and of pancake coils made from long-length tapes via “wind and react.”  相似文献   

14.
提出了一种新的雾化喷涂沉积(SCD)方法,在Nd-Fe-B磁体表面均匀沉积TbF3粉末,同时通过晶界扩散过程(GBDP)将Tb元素引入到磁体中。用这种方法(SCD+GBDP)处理厚度达5 mm的钕铁硼磁体。研究了TbF3涂层增重比、扩散时间和扩散温度对烧结磁体组织和磁性能的影响。样品扩散温度和时间为940 ℃和10 h,退火温度和时间为480 ℃和5 h。TbF3增重比(w)从0%增加到0.8%时,磁体的矫顽力从1201 kA/m 提高到1930 kA/m,剩磁下降约0.01 T。研究发现,随着TbF3增重比的增加,磁体的矫顽力先增大后减小。SEM结果表明,在Nd2Fe14B晶粒边界区域,Tb取代Nd形成(Nd, Tb)2Fe14B核壳相。晶界相和核壳相中较高的磁晶各向异性对矫顽力的增强有积极的促进作用。核壳相的分布和浓度对矫顽力有密切的影响。当TbF3增重比大于2.4%时,靠近磁体表面区域的晶界扩散明显增强。元素的SEM图像显示,进入磁体的Tb越多,晶核内的Tb浓度就越高。此外,大量Nd-F/Nd-O-F相的形成导致晶界相不像w=0.8% 时的样品那样连续,这可能是导致矫顽力下降的主要原因。  相似文献   

15.
In this study, finite element analysis based on an Ansoft Maxwell software was used to reveal the temperature stability of a magnet ring and the equivalent structural periodic permanent-magnet(PPM) focusing system. It is found that with the temperature increasing, the decrease rate of magnetic induction peak(Bz)maxof single magnet ring is greater than that of remanence Brof magnet in the range from room temperature to 200 °C, however,the PPM focusing system do have the same temperature characteristics of permanent-magnet materials. It indicates that the magnetic temperature properties of the PPM system can be effectively controlled by adjusting the temperature properties of the magnets. Moreover, the higher permeability of the magnets indicates the less Hcb, giving rise to lower magnetic induction peak (Bz)′max: Finally, it should be noted that the magnetic orientation deviation angle θ(\15°) of permanent magnets has little effect on the focusing magnetic field of the PPM system at different temperatures and the temperature stability. The obtained results are beneficial to the design and selection of permanent magnets for PPM focusing system.  相似文献   

16.
Multifunctional Fe@C@Y2O3:Eu3+ nanocomposites were prepared by the solvo thermal method, and their structure, magnetic and luminescent properties were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and scanning electron microscope (SEM). Results show that the nanocomposites are spherical with a mean diameter of 700 nm and there are high special saturation magnetization (47.4 emu/g) and strong red emission under UV-light. Even dispersed in water solution, the nanocomposites also exhibit a strong red emission under ultraviolet light radiation, and it could be manipulated using an external magnet. Thus it looks promising for application in biomedicine field, especially in drug targeting and fluorescence label. And we also discussed the effect of the electron transfer process between the Fe magnetic core and Y2O3:Eu3+ shell.  相似文献   

17.
The major applications of high-temperature superconductors have mostly been confined to products in the form of wires and thin films. However, recent developments show that rare-earth REBa2Cu3O7−x and light rare-earth LREBa2Cu3O7−3 superconductors prepared by melt processes have a high critical-current density at 77 K and high magnetic fields. These superconductors will promote the application of bulk high-temperature superconductors in high magnetic fields; the superconducting bulk magnet for the Maglev train is one possible application. Editor’s Note: A hypertext-enhanced version of this article can be found on the TMS web site at www.tms.org/pubs/journals/JOM/9810/Fujimoto-9810.html. Hiroyuki Fujimoto earned his Ph.D. in electrical engineering at Kyushu University, Japan, in 1994. He is currently a manager of the Materials Engineering Laboratory at the Railway Technical Research Institute.  相似文献   

18.
With the rapid growth in the use of NdFeB-type magnets and with the growing environmental need to conserve both energy and raw materials, the recycling of these magnets is becoming an ever important issue. In this paper it is demonstrated that hydrogen could play a vital role in this process. Fully dense sintered NdFeB-type magnets have been subjected to the hydrogen decrepitation (HD) process. The resultant powder has been subsequently processed in one of two ways in order to produce permanent magnets. Firstly, the powder was subjected to a vacuum degassing treatment over a range of temperatures up to 1000 °C in order to produce powder that would be suitable for the production of anisotropic bonded or hot pressed magnets. Secondly, the HD-powder has been used to produce fully dense sintered magnets; in which case optimisation of the milling time, sintering temperature and time was carried out. The optimum degassing temperature for coercive powder was found to be 700 °C, giving powder with a remanence (Br) of 1350 mT (±50 mT) and an intrinsic coercivity (Hcj) of 750 kA m−1 (±50 kA m−1). The best sintered magnet was produced by very lightly milling the powder (30 min, roller ball mill), aligning, pressing and vacuum sintering at 1080 °C for 1 h. The magnetic properties of this magnet were: (BH)max = 290 kJ m−3 (±5 kJ m−3), Br = 1240 mT (±50 mT) and Hcj = 830 kA m−1 (±50 kA m−1); representing decreases of 15%, 10% and 20%, respectively, from the properties of the initial magnet.  相似文献   

19.
The compositions of grain boundaries (GBs) and other interfaces surrounding Nd2Fe14B grains in commercial Nd-Fe-B sintered magnets have been investigated by laser-assisted three-dimensional atom probe to understand the mechanism of the coercivity enhancement by post-sinter annealing. While only a slight segregation of Nd and Pr to the GBs was confirmed in the as-sintered sample, a thin Nd-rich amorphous phase layer was observed along the GBs with Cu segregation to the interfaces in the annealed sample. The segregation of Cu to NdOx/Nd2Fe14B interfaces was also found, suggesting that the Nd2Fe14B grains are enveloped by a Cu-enriched layer after the annealing. The concentration of Fe + Co in the thin GB layer was found to be as high as 65 at.%, and a model amorphous film processed by sputtering with the same composition as the thin GB layer was found to be ferromagnetic. Ferromagnetic behavior of the thin GB layer suggested that Nd2Fe14B grains are magnetically coupled. The coercivity mechanism of the sintered magnets is discussed based on these new findings.  相似文献   

20.
In this paper, an electroless nickel plating and sol-gel combined technique used to prepare the Ni-P/TiO2 composite film on sintered NdFeB permanent magnet is described and the composite film was characterized by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), and energy dispersive X-ray spectrometer (EDX). The corrosion resistance of Ni-P/TiO2 film was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The self-corrosion current density (icorr) of Ni-P/TiO2 composite film is 2.38μA/cm2 in 0.5mol/L H2SO4 solution about 33% of that of Ni-P coating and 0.22μA/cm2 in 0.5mol/L NaCl solution about 14% of that of Ni-P coating, respectively. In 0.5mol/L H2SO4 and 0.5mol/L NaCl solutions, the polarization resistance (Rp) of the composite film is 12.5kΩ cm2 and 120kΩ cm2, about 1.6 and 2 times that of Ni-P coating, respectively. The results indicate that Ni-P/TiO2 composite film has a better corrosion resistance than Ni-P coating.  相似文献   

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