We describes a controllable synthesis procedure for growing a-Ee2O3 and Ee3O4 nanowires. High magnetic hematite a-Fe2O3 nanowires are successfully grown on Fe0.5Ni0.5 alloy substrates via an oxide assisted vapor-solid...We describes a controllable synthesis procedure for growing a-Ee2O3 and Ee3O4 nanowires. High magnetic hematite a-Fe2O3 nanowires are successfully grown on Fe0.5Ni0.5 alloy substrates via an oxide assisted vapor-solid process. Experimental results also indicate that previous immersion of the substrates in a solution of oxalic acid causes the grown nanowires to convert gradually into magnetite （Fe3O4） nanowires. Additionally, the saturated state of Fe3O4 nanowires is achieved as the oxalic acid concentration reaches 0.75 mol/L. The average diameter and length of nanowires expands with an increasing operation temperature and the growth density of nanowires accumulates with an increasing gas flux in the vapor-solid process. The growth mechanism of a-Fe2O3 and Fe3O4 nanowires is also discussed. The results demonstrate that the entire synthesis of nanowires can be completed within 2 h.展开更多
The structure of a-Fe metal magnetic recording particles coated with silane coupling agents have been studied by TEM, FT-IR, EXAFS, Mossbauer. The results show that a close, uniform, firm and ultra thin layer, which i...The structure of a-Fe metal magnetic recording particles coated with silane coupling agents have been studied by TEM, FT-IR, EXAFS, Mossbauer. The results show that a close, uniform, firm and ultra thin layer, which is beneficial to the magnetic and chemical stability, has been formed by the cross-linked chemical bond Si-O-Si. And the organic molecule has chemically bonded to the particle surface, which has greatly affected the surface Fe atom electronic structure. Furthermore, the covalent bond between metal particle surface and organic molecule has obvious effect on the near edge structure of the surface Fe atoms.展开更多
The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau-Lifshitz-Gilbert equation. The evolutions of the magnetic d...The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau-Lifshitz-Gilbert equation. The evolutions of the magnetic domain morphology are studied, and our analyses show that the magnetization reversal process is affected by the interaction between the moving domain wall and the existing nonmagnetic particles. This interaction strongly depends on the size of the particles, and it is found that particles with a particular size contribute the most to magnetic hardening.展开更多
In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-...In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-rich phases and within Nd-rich phases.The misfits between 2:14:1 and Nd-rich phases were quantitatively determined,reflecting the concentration of interface stresses in magnet.Grain boundaries of magnet were reconstructed by diffusing Tb-containing and Tb-free sources,respectively.The Tb-rich shells at extensive layers of 2:14:1 grains caused lattice distortion,i.e.,internal stresses,resulting in the crack mode changing from intergranular to transgranular in near surfaces of Tb-containing diffused magnets.Therefore,the bending strengths were deteriorated although the coercivities were apparently enhanced.In the case of Tb-free Pr-Cu diffused magnet,the Pr and Cu elements were enriched at grain boundaries,and the misfits between 2:14:1 and Nd-rich phases were declined,lowering interface stresses and strengthening grain boundaries.The mechanical and magnetic properties of Pr-Cu diffused magnet were simultaneously improved.展开更多
The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modi...The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modification treatment resulted in the formation of a smooth and continuous weakly magnetic grain boundary layer and the(Nd,Pr,Dy)_(2)Fe_(14)B main phase with a high magnetocrystalline anisotropy field,leading to an increased coercivity of 23 kOe.MOKE observations revealed that the dynamic evolution of the maze domain area under an external magnetic field varied significantly between the original and modified magnets.Compared with the original magnets,the modified magnets exhibited a slower decrease in maze domain area during magnetization and a slower increase during reverse magnetization,contributing to the observed coercivity enhancement.展开更多
In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step ann...In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step annealed magnet exhibits the highest intrinsic coercivity of 19.72 kOe,which is a 58.5%enhancement relative to the as-sintered magnet,and has the best temperature stability of coercivity.The best continuity of grain boundary(GB)phase and the highest content of RE6Fe13Ga phase can be observed in the triple-step annealed magnet,along with relatively small grain size.After triple-step annealing process,the phase separation occurs at the triple-junction(TJ)region of the magnet,which is the Fe-rich phase identified as RE6Fe13Ga and the Fe-poor phase identified as Ia-RE_(2)O_(3).The Ia-RE_(2)O_(3)phase located at the corner of the TJ region can extend between the grains of(Nd,Pr)_(2)Fe_(14)B main phase to form the GB phase with a Fe content of less than 15 at%,thereby enhancing the magnetic isolation effect.The lattice misfit between the Ia-RE_(2)O_(3)phase and the adjacent main phase is less than 5%,which is helpful to reduce defects at the edges of the main phase grains,thus reducing the nucleation of reverse domains.展开更多
Recovery of rare earth elements(REEs)from bulk Nd-Fe-B scrap by chlorination with NH_(4)Cl as a chlorinating agent has been reported to be an energy efficient and environmentally friendly method.However,the reaction m...Recovery of rare earth elements(REEs)from bulk Nd-Fe-B scrap by chlorination with NH_(4)Cl as a chlorinating agent has been reported to be an energy efficient and environmentally friendly method.However,the reaction mechanism and phase evolution of the low-temperature selective chlorination process of Nd-Fe-B sludge are not clear.In this paper,we systematically investigated the lowtemperature selective chlorination process of Nd-Fe-B sludge with NH4Cl by combining thermokinetic theoretical calculations and experiments,and revealed its reaction mechanism.The phase evolution during chlorination was determined by X-ray diffraction(XRD),scanning electron microscopy(SEM)and ene rgy-dispersive X-ray spectroscopy(EDS)characterization as well as co mputational analysis of the phase stability diagram of the M-O-Cl system.To determine the optimum chlorination conditions,the effects of chlorinating agent dosage,reaction temperature and reaction time on the reaction were investigated.The results show that the rare earth components in Nd-Fe-B sludge are selectively chlorinated to RECl3and the formation of REOCl is avoided in the temperature range of 300-420℃,while the iron components are preferentially oxidized to Fe2O3.The selective chlorination reaction is consistent with the unreacted shrinking core model,and the rate-controlling step of the reaction is the internal diffusion process of NH4Cl through the transition layer of the reactant product to the surface of the Nd-Fe-B sludge.The complete chlorination of REEs is successfully achieved and 99.8%of REEs are selectively extracted into the leaching solution under optimal chlorination conditions(300℃,2.5 times of stoichiometric amount,4 h).展开更多
Neodymium-iron-boron(Nd-Fe-B)sludge is an important secondary resource of rare-earth elements(REEs).However,the state-of-the-art recycling method,i.e.,HCl-preferential dissolution faces challenges such as slow leachin...Neodymium-iron-boron(Nd-Fe-B)sludge is an important secondary resource of rare-earth elements(REEs).However,the state-of-the-art recycling method,i.e.,HCl-preferential dissolution faces challenges such as slow leaching kinetics,excessive chemical consumption and wastewater generation.In this work,the in situ anodic leaching of Nd-Fe-B sludge was developed to selectively recover REEs with high efficiency.The leaching rates of the REEs are 2.4-9.0 times higher using the in situ anodic leaching at the current density from 10 to 40 mA/cm^(2)than using conventional chemical leaching under the maintained pH of 3.7.Mechanism studies reveal that the anode-generated H~+plays the key role during the in situ anodic leaching process that locally increases the H^(+)concentration at the interface of sludge particles,accele rating the leaching kinetics.By achieving a total leaching efficiency of Nd-Fe-B sludge close to 100%and the Fe deposition efficiency in the range of 70.9%-74.3%,selective leaching of REEs is successfully realized and thus largely reduces chemical consumption.Additionally,a two-step recycling route involving electrolysis-selective precipitation was proposed that enables a stable REEs recovery of 92.2%with recyclable electrolyte.This study provides a novel and environmentally-friendly strategy for the efficient recovery of REEs from secondary resources.展开更多
文摘We describes a controllable synthesis procedure for growing a-Ee2O3 and Ee3O4 nanowires. High magnetic hematite a-Fe2O3 nanowires are successfully grown on Fe0.5Ni0.5 alloy substrates via an oxide assisted vapor-solid process. Experimental results also indicate that previous immersion of the substrates in a solution of oxalic acid causes the grown nanowires to convert gradually into magnetite （Fe3O4） nanowires. Additionally, the saturated state of Fe3O4 nanowires is achieved as the oxalic acid concentration reaches 0.75 mol/L. The average diameter and length of nanowires expands with an increasing operation temperature and the growth density of nanowires accumulates with an increasing gas flux in the vapor-solid process. The growth mechanism of a-Fe2O3 and Fe3O4 nanowires is also discussed. The results demonstrate that the entire synthesis of nanowires can be completed within 2 h.
基金The authors gratefully acknowledge the support of the National Natural Science Foundation of China (NO.50071057), and the support of the National Synchrotron Radiation Laboratory and Center Foundation (Hefei), China.
文摘The structure of a-Fe metal magnetic recording particles coated with silane coupling agents have been studied by TEM, FT-IR, EXAFS, Mossbauer. The results show that a close, uniform, firm and ultra thin layer, which is beneficial to the magnetic and chemical stability, has been formed by the cross-linked chemical bond Si-O-Si. And the organic molecule has chemically bonded to the particle surface, which has greatly affected the surface Fe atom electronic structure. Furthermore, the covalent bond between metal particle surface and organic molecule has obvious effect on the near edge structure of the surface Fe atoms.
文摘The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau-Lifshitz-Gilbert equation. The evolutions of the magnetic domain morphology are studied, and our analyses show that the magnetization reversal process is affected by the interaction between the moving domain wall and the existing nonmagnetic particles. This interaction strongly depends on the size of the particles, and it is found that particles with a particular size contribute the most to magnetic hardening.
基金supported by the National Natural Science Foundation of China(No.52271165)the National Key R&D Program of China(No.2022YFB3505501).
文摘In this paper,the fracture behaviors and interface stresses of sintered Nd-Fe-B magnets were investigated.It was revealed that cracks propagated along the interfaces of Nd_(2)Fe_(14)B/Nd_(2)Fe_(14)B,Nd_(2)Fe_(14)B/Nd-rich phases and within Nd-rich phases.The misfits between 2:14:1 and Nd-rich phases were quantitatively determined,reflecting the concentration of interface stresses in magnet.Grain boundaries of magnet were reconstructed by diffusing Tb-containing and Tb-free sources,respectively.The Tb-rich shells at extensive layers of 2:14:1 grains caused lattice distortion,i.e.,internal stresses,resulting in the crack mode changing from intergranular to transgranular in near surfaces of Tb-containing diffused magnets.Therefore,the bending strengths were deteriorated although the coercivities were apparently enhanced.In the case of Tb-free Pr-Cu diffused magnet,the Pr and Cu elements were enriched at grain boundaries,and the misfits between 2:14:1 and Nd-rich phases were declined,lowering interface stresses and strengthening grain boundaries.The mechanical and magnetic properties of Pr-Cu diffused magnet were simultaneously improved.
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFB3500300,2023YFB3507000,and 2023XYJG0001-01-03)the National Natural Science Foundation of China(Grant No.52171167)Inner Mongolia Northern Rare Earth Advanced Materials Technology Innovation Co.,Ltd.Project(Grant No.CXZX-B-202304-0004).
文摘The enhancement of coercivity in Nd-Fe-B sintered magnets modified by Pr_(58)Dy_(10)Cu_(32)alloy was investigated through scanning electron microscope(SEM)and in-situ magneto-optic Kerr effect(MOKE)microscopy.The modification treatment resulted in the formation of a smooth and continuous weakly magnetic grain boundary layer and the(Nd,Pr,Dy)_(2)Fe_(14)B main phase with a high magnetocrystalline anisotropy field,leading to an increased coercivity of 23 kOe.MOKE observations revealed that the dynamic evolution of the maze domain area under an external magnetic field varied significantly between the original and modified magnets.Compared with the original magnets,the modified magnets exhibited a slower decrease in maze domain area during magnetization and a slower increase during reverse magnetization,contributing to the observed coercivity enhancement.
基金Project supported by the Major Special Project of Fujian Province(2023HZ021005)the Guiding Project of Fujian Province(2023H0006)+2 种基金the Major Project of Science and Technology of Fuzhou(2022-ZD-010)the Young and Middle-aged Teachers Education Scientific Research Project of Fujian Province(JAT200594,JAT231008)the Natural Science Foundation of Fujian Province(2022J011151)。
文摘In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step annealed magnet exhibits the highest intrinsic coercivity of 19.72 kOe,which is a 58.5%enhancement relative to the as-sintered magnet,and has the best temperature stability of coercivity.The best continuity of grain boundary(GB)phase and the highest content of RE6Fe13Ga phase can be observed in the triple-step annealed magnet,along with relatively small grain size.After triple-step annealing process,the phase separation occurs at the triple-junction(TJ)region of the magnet,which is the Fe-rich phase identified as RE6Fe13Ga and the Fe-poor phase identified as Ia-RE_(2)O_(3).The Ia-RE_(2)O_(3)phase located at the corner of the TJ region can extend between the grains of(Nd,Pr)_(2)Fe_(14)B main phase to form the GB phase with a Fe content of less than 15 at%,thereby enhancing the magnetic isolation effect.The lattice misfit between the Ia-RE_(2)O_(3)phase and the adjacent main phase is less than 5%,which is helpful to reduce defects at the edges of the main phase grains,thus reducing the nucleation of reverse domains.
基金Project supported by the National Natural Science Foundation of China(52261037,52401251)Key Research Project of Jiangxi Province(20203ABC28W006)+2 种基金the Research Fund of Key Laboratory of Rare Earths,Chinese Academy of SciencesKey Laboratory of Ionic Rare Earth Re sources and Environment,Ministry of Natural Resources of the People's Republic of China(2022IRERE302)the Ganzhou Science and Technology Innovation Empowerment Youth"Jie bang Gua shuai"Project。
文摘Recovery of rare earth elements(REEs)from bulk Nd-Fe-B scrap by chlorination with NH_(4)Cl as a chlorinating agent has been reported to be an energy efficient and environmentally friendly method.However,the reaction mechanism and phase evolution of the low-temperature selective chlorination process of Nd-Fe-B sludge are not clear.In this paper,we systematically investigated the lowtemperature selective chlorination process of Nd-Fe-B sludge with NH4Cl by combining thermokinetic theoretical calculations and experiments,and revealed its reaction mechanism.The phase evolution during chlorination was determined by X-ray diffraction(XRD),scanning electron microscopy(SEM)and ene rgy-dispersive X-ray spectroscopy(EDS)characterization as well as co mputational analysis of the phase stability diagram of the M-O-Cl system.To determine the optimum chlorination conditions,the effects of chlorinating agent dosage,reaction temperature and reaction time on the reaction were investigated.The results show that the rare earth components in Nd-Fe-B sludge are selectively chlorinated to RECl3and the formation of REOCl is avoided in the temperature range of 300-420℃,while the iron components are preferentially oxidized to Fe2O3.The selective chlorination reaction is consistent with the unreacted shrinking core model,and the rate-controlling step of the reaction is the internal diffusion process of NH4Cl through the transition layer of the reactant product to the surface of the Nd-Fe-B sludge.The complete chlorination of REEs is successfully achieved and 99.8%of REEs are selectively extracted into the leaching solution under optimal chlorination conditions(300℃,2.5 times of stoichiometric amount,4 h).
基金Project supported by the Natural Science Foundation of Inner Mongolia Autonomous Region of China(2021BS02007,2022MS02014)the"Science and Technology Project of Ordos"Program(2021 CGI 17-9,2021 ZDI11-14)+2 种基金the National Natural Science Foundation of China(21971129,21961022,51903125,21661023)the"Inner Mongolia Autonomous Region 2022 Leading Talent Team of Science and Technology"Program(2022LJRC0008)China Postdoctoral Science Foundation(2018M640043,2019T120038)。
文摘Neodymium-iron-boron(Nd-Fe-B)sludge is an important secondary resource of rare-earth elements(REEs).However,the state-of-the-art recycling method,i.e.,HCl-preferential dissolution faces challenges such as slow leaching kinetics,excessive chemical consumption and wastewater generation.In this work,the in situ anodic leaching of Nd-Fe-B sludge was developed to selectively recover REEs with high efficiency.The leaching rates of the REEs are 2.4-9.0 times higher using the in situ anodic leaching at the current density from 10 to 40 mA/cm^(2)than using conventional chemical leaching under the maintained pH of 3.7.Mechanism studies reveal that the anode-generated H~+plays the key role during the in situ anodic leaching process that locally increases the H^(+)concentration at the interface of sludge particles,accele rating the leaching kinetics.By achieving a total leaching efficiency of Nd-Fe-B sludge close to 100%and the Fe deposition efficiency in the range of 70.9%-74.3%,selective leaching of REEs is successfully realized and thus largely reduces chemical consumption.Additionally,a two-step recycling route involving electrolysis-selective precipitation was proposed that enables a stable REEs recovery of 92.2%with recyclable electrolyte.This study provides a novel and environmentally-friendly strategy for the efficient recovery of REEs from secondary resources.
