回收利用是稀土资源高效利用的可持续方案.氢化破碎技术因其高效环保特性被广泛采用,但氢破过程中产生的混合相会显著降低回收效率,这对工艺的优化提出了新的挑战.本文采用基于第一性原理计算结合机器学习方法,通过德拜模型系统地探究...回收利用是稀土资源高效利用的可持续方案.氢化破碎技术因其高效环保特性被广泛采用,但氢破过程中产生的混合相会显著降低回收效率,这对工艺的优化提出了新的挑战.本文采用基于第一性原理计算结合机器学习方法,通过德拜模型系统地探究了氢化破碎过程中关键稀土氢化物(如NdH_(2),NdH_(3),Nd_(2)H_(5))的热力学行为.研究结果表明,在600 k Pa压强下,630 K左右的温度区间有望为氢化破碎工艺提供一个较为理想的操作条件.在此条件下,NdH_(2)能够实现自发氢化,且能够有效抑制非稳定相的形成,有助于提高稀土回收效率.本研究还揭示了过高温度对NdH_(2)热力学性质可能产生的不利影响,进一步强调了在特定温度区间操作的重要性.这些发现不仅为理解钕铁硼氢化过程的热力学机理提供了新的视角,而且为工业应用中氢化破碎工艺参数的优化提供了理论参考.展开更多
A single-phase Nd_(2)Fe_(14)B powder was prepared from end-of-life(EOL)wind turbine magnets by a combination of hydrogen processing of magnetic scrap(HPMS)and selective leaching with citric acid.The impact of leaching...A single-phase Nd_(2)Fe_(14)B powder was prepared from end-of-life(EOL)wind turbine magnets by a combination of hydrogen processing of magnetic scrap(HPMS)and selective leaching with citric acid.The impact of leaching time on chemical composition,particle size and magnetic properties was investigated.Due to the low reduction potential of rare earth element(REE),the Nd-rich phase was preferentially leached.The use of an acid concentration of 0.5 mol/L,a solid to liquid ratio of 1/10 and a leaching time of 30 min was sufficient to leach the Nd-rich phase.Atomic resolution transmission electron microscopy was employed to examine the surface structure and chemistry of the leached Nd_(2)Fe_(14)B powder.It is revealed that the leaching process affects not only the Nd-rich phase but also the matrix grains,resulting in the formation of a predominant oxygen-rich amorphous reaction layer,25 nm thick.However,the oxygen content is reduced from 3500 to 2500 ppm and the magnetic saturation is increased by 8%.This method is a promising addition to the HPMS process,as the powder can be mixed with fresh,unoxidized grain boundary phase to produce recycled magnets with high remanence.展开更多
To analyze the magnetic properties of Nd_(2)Fe_(14)B compound under high pressure,an improved two-sublattice molecular field model coupled with equivalent stress field was applied to study the effect of pressure on ma...To analyze the magnetic properties of Nd_(2)Fe_(14)B compound under high pressure,an improved two-sublattice molecular field model coupled with equivalent stress field was applied to study the effect of pressure on magnetization,magnetostriction coefficient,susceptibility and Curie temperature.The calculation results show that the pressure has a stronger effect on the magnetization of Fe sublattice compared to that of Nd sublattice at varied temperatures when the external magnetic field is parallel to the alignment direction.Saturated magnetization,initial susceptibility and magnetic moment of Nd_(2)Fe_(14)B compound are found to decrease gradually with pressure increasing,and the Curie temperature of Nd_(2)Fe_(14)B decreases to about 298 K under an applied pressure of 1.15 GPa.The results suggest that the pressure-induced magnetic phase transition of Nd2Fe14B occurs under 1.15 GPa at room temperature.展开更多
Texture evolution in nanocomposite Nd_2Fe_ 14B/α-Fe magnets prepared by direct melt spinning was investigated. The free surface and wheel-contacted surface exhibit different texture direction. Modification of composi...Texture evolution in nanocomposite Nd_2Fe_ 14B/α-Fe magnets prepared by direct melt spinning was investigated. The free surface and wheel-contacted surface exhibit different texture direction. Modification of composition not only enhances magnetic properties, but also changes texture direction of the ribbon. Low temperature heat treatment can increase the magnetic properties to some extent, and high temperature annealing decreases the magnetic properties. Both low and high temperature heat treatment have effects on grain orientation, but the difference still exists between the two surfaces of the ribbon. So it is infeasibility to prepare anisotropic Nd_2Fe_ 14B/α-Fe nanocomposite magnets by direct melt spinning.展开更多
This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine st...This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine structures of the Ce_(2)Fe_(14)B,(Ce,Nd)_(2)Fe_(14)B and MM_(2)Fe_(14)B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystal structure. The results show that the isomer shift δ and the quadrupole splitting öEQ of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field Bhfincreases monotonically with increasing Nd content and its value is influenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the low fraction secondary phases are determined by the ^(57)Fe Mössbauer spectrometry due to its high sensitivity. On this basis,the content, magnetic behavior, and magnetization of the REFe_(2) phase, the amorphous grain boundary(GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.展开更多
Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for...Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for 4 min, which enhanced the interaction coupling between grains and improved the magnetic properties. The results of three-dimensional atom probe (3DAP) revealed that V-enriched intergranular phase existed at the grain boundaries, suppressing the grain growth during crystallization process. The remanence and coercivity for annealed ribbons reached to 80 emu·g-1 and 567 kA·m-1, respectively.展开更多
Based on the observation of temperature variation of both domain structure and magnetic con- trast.the thermal demagnetization and randomness of domain nucleation was discussed.
文摘回收利用是稀土资源高效利用的可持续方案.氢化破碎技术因其高效环保特性被广泛采用,但氢破过程中产生的混合相会显著降低回收效率,这对工艺的优化提出了新的挑战.本文采用基于第一性原理计算结合机器学习方法,通过德拜模型系统地探究了氢化破碎过程中关键稀土氢化物(如NdH_(2),NdH_(3),Nd_(2)H_(5))的热力学行为.研究结果表明,在600 k Pa压强下,630 K左右的温度区间有望为氢化破碎工艺提供一个较为理想的操作条件.在此条件下,NdH_(2)能够实现自发氢化,且能够有效抑制非稳定相的形成,有助于提高稀土回收效率.本研究还揭示了过高温度对NdH_(2)热力学性质可能产生的不利影响,进一步强调了在特定温度区间操作的重要性.这些发现不仅为理解钕铁硼氢化过程的热力学机理提供了新的视角,而且为工业应用中氢化破碎工艺参数的优化提供了理论参考.
基金Project supported by the German Federal Ministry of Education and Research as part of the program"FH-Kooperativ"the European Commission under the Horizon Europe Research and Innovation Program(101058598)。
文摘A single-phase Nd_(2)Fe_(14)B powder was prepared from end-of-life(EOL)wind turbine magnets by a combination of hydrogen processing of magnetic scrap(HPMS)and selective leaching with citric acid.The impact of leaching time on chemical composition,particle size and magnetic properties was investigated.Due to the low reduction potential of rare earth element(REE),the Nd-rich phase was preferentially leached.The use of an acid concentration of 0.5 mol/L,a solid to liquid ratio of 1/10 and a leaching time of 30 min was sufficient to leach the Nd-rich phase.Atomic resolution transmission electron microscopy was employed to examine the surface structure and chemistry of the leached Nd_(2)Fe_(14)B powder.It is revealed that the leaching process affects not only the Nd-rich phase but also the matrix grains,resulting in the formation of a predominant oxygen-rich amorphous reaction layer,25 nm thick.However,the oxygen content is reduced from 3500 to 2500 ppm and the magnetic saturation is increased by 8%.This method is a promising addition to the HPMS process,as the powder can be mixed with fresh,unoxidized grain boundary phase to produce recycled magnets with high remanence.
基金This study was financially supported by the National Natural Science Foundation of China(No.11072036).
文摘To analyze the magnetic properties of Nd_(2)Fe_(14)B compound under high pressure,an improved two-sublattice molecular field model coupled with equivalent stress field was applied to study the effect of pressure on magnetization,magnetostriction coefficient,susceptibility and Curie temperature.The calculation results show that the pressure has a stronger effect on the magnetization of Fe sublattice compared to that of Nd sublattice at varied temperatures when the external magnetic field is parallel to the alignment direction.Saturated magnetization,initial susceptibility and magnetic moment of Nd_(2)Fe_(14)B compound are found to decrease gradually with pressure increasing,and the Curie temperature of Nd_(2)Fe_(14)B decreases to about 298 K under an applied pressure of 1.15 GPa.The results suggest that the pressure-induced magnetic phase transition of Nd2Fe14B occurs under 1.15 GPa at room temperature.
文摘Texture evolution in nanocomposite Nd_2Fe_ 14B/α-Fe magnets prepared by direct melt spinning was investigated. The free surface and wheel-contacted surface exhibit different texture direction. Modification of composition not only enhances magnetic properties, but also changes texture direction of the ribbon. Low temperature heat treatment can increase the magnetic properties to some extent, and high temperature annealing decreases the magnetic properties. Both low and high temperature heat treatment have effects on grain orientation, but the difference still exists between the two surfaces of the ribbon. So it is infeasibility to prepare anisotropic Nd_2Fe_ 14B/α-Fe nanocomposite magnets by direct melt spinning.
基金Project supported by the Zhejiang Provincial Natural Science Foundation of China(Grant Nos.LY20E010002,LR18E010001,and LD19E010001)the National Natural Science Foundation of China(Grant Nos.U1704253 and 51801047)+2 种基金Liaoning Revitalization Talents Program(Grant No.XLYC1807177)the Key Research and Development plan of Zhejiang Province,China(Grant No.2020C05014)Ten Thousand Talents Plan of Zhejiang Province,China(Grant No.2018R52003)。
文摘This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine structures of the Ce_(2)Fe_(14)B,(Ce,Nd)_(2)Fe_(14)B and MM_(2)Fe_(14)B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystal structure. The results show that the isomer shift δ and the quadrupole splitting öEQ of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field Bhfincreases monotonically with increasing Nd content and its value is influenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the low fraction secondary phases are determined by the ^(57)Fe Mössbauer spectrometry due to its high sensitivity. On this basis,the content, magnetic behavior, and magnetization of the REFe_(2) phase, the amorphous grain boundary(GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.
基金the National Advanced Technology Research and Development Committee of China (2002AA302602-2) Shanghai Municipal Development Foundation of Science and Technology (0552nm049)+1 种基金Shanghai institute of Technolo-gy (YJ-2006-16)Project (P1502) Supported by Shanghai Leading Academic Discipline
文摘Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for 4 min, which enhanced the interaction coupling between grains and improved the magnetic properties. The results of three-dimensional atom probe (3DAP) revealed that V-enriched intergranular phase existed at the grain boundaries, suppressing the grain growth during crystallization process. The remanence and coercivity for annealed ribbons reached to 80 emu·g-1 and 567 kA·m-1, respectively.
文摘Based on the observation of temperature variation of both domain structure and magnetic con- trast.the thermal demagnetization and randomness of domain nucleation was discussed.
