In this work,we proposed a method to enhance the magnetic properties of(Nd,Ce)-Fe-B magnets with Ce/TRE ratios below 25 wt%by introducing a moderate amount of La elements.The segregation behavior of La elements toward...In this work,we proposed a method to enhance the magnetic properties of(Nd,Ce)-Fe-B magnets with Ce/TRE ratios below 25 wt%by introducing a moderate amount of La elements.The segregation behavior of La elements towards grain boundaries(GBs)was utilized to optimize the GB phase structure.Incorporation of La atoms into the main phase induces lattice expansion,leading to an increased formation of Ce^(3+)ions with enhanced magnetic moments.Comparative analysis with the original magnet(La/Ce=0 wt%)demonstrates that the magnet with a La/Ce ratio of 10 wt%exhibits improvements of 0.3%in remanence,12.6%in coercivity,and 0.6%in maximum energy produ ct.These results underscore that the moderate addition of La elements enhances the fluidity of the rare earth-rich phase and optimizes the distribution of lamellar GB,consequently reinforcing the magnetic isolation effect.Furthermore,the promotion of the transformation from Ce^(4+)to Ce^(3+)ons contributes to the comprehensive enhancement of the magnetic properties.This research offers a novel strategy for fabricating high-performance and resource-e fficient sintered magnets based on LaCe alloys.展开更多
The microstructure of(Nd,Ce)-Fe-B sintered magnets with different diffusion depths was characterized by a magnetic force microscope,and the relationship between the magnetic properties and the local structure of grain...The microstructure of(Nd,Ce)-Fe-B sintered magnets with different diffusion depths was characterized by a magnetic force microscope,and the relationship between the magnetic properties and the local structure of grain boundary diffused magnets is discussed.The domains perpendicular to the c-axis(easy magnetization direction)show a typical maze-like pattern,while those parallel to the c-axis show the characte ristics of plate domains.The significant gradient change is shown in the concentration of Dy with the direction of diffusion from the surface to the interior.Dy diffuses along grain boundaries and(Dy,Nd)_(2)Fe_(14)B layer with a high anisotropy field formed around the grains.Through in-situ electron probe micro-analysis/magnetic force microscopy(EPMA/MFM),it is found that the average domain width decreases,and the proportion of single domain grains increases as diffusion depth increases.This is caused by both the change of concentration and distribution of Dy.The grain boundary diffusion process changes the microstructure and microchemistry inside the magnet,and these local magnetism differences can be reflected by the configuration of the magnetic domain structure.展开更多
The combination of dual-main-phase(DMP)(Nd,Ce)-Fe-B magnets and grain boundary diffusion process(GBDP)is currently a research topic for obtaining high-cost performance materials in rare earth permanent magnet fields.T...The combination of dual-main-phase(DMP)(Nd,Ce)-Fe-B magnets and grain boundary diffusion process(GBDP)is currently a research topic for obtaining high-cost performance materials in rare earth permanent magnet fields.The novel structural features of GBDP(Nd,Ce)-Fe-B magnets give a version of different domain reversal processes from those of non-diffused magnets.In this work,the in-situ magnetic domain evolution of the DMP magnets was observed at elevated temperatures,and the temperature demagnetization and coercivity mechanism of the GBDP dual-main-phase(Nd,Ce)-Fe-B magnets are discussed.The results show that the shell composition of different types of grains in DMP magnets is similar,while the magnetic microstructure results indicate the Ce-rich grains tend to demagnetize first.Dy-rich shell with a high anisotropic field caused by GBDP leads to an increase in the nucleation field,which enhances the coercivity.It is found that much more grains exhibit single domain characteristics in the remanent state for GBDP dual-main-phase(Nd,Ce)-Fe-B magnets.In addition,the grains that undergo demagnetization first are Ce-rich or Nd-rich grains,which is different from that of non-diffused magnets.These results were not found in previous studies but can be intuitively characterized from the perspective of magnetic domains in this work,providing a new perspective and understanding of the performance improvement of magnetic materials.展开更多
To obtain lightweight multicomponent magnesium alloys with high tensile strength,ductility,and stiffness,two extruded Mg_(92−5x)Al_(1.5+3x)Zn_(3)Cu_(3.5+x)Ce_(x)(x=0.5 and 1,labeled as C0.5 and C1)alloys were designed...To obtain lightweight multicomponent magnesium alloys with high tensile strength,ductility,and stiffness,two extruded Mg_(92−5x)Al_(1.5+3x)Zn_(3)Cu_(3.5+x)Ce_(x)(x=0.5 and 1,labeled as C0.5 and C1)alloys were designed.The results reveal that the ultimate tensile strength,yield strength(YS),and fracture strain of the C0.5 alloy are simultaneously improved compared to those of the C1 alloy,with values of 346 MPa,312 MPa,and 11.7%,respectively.This enhancement is primarily attributed to the refinement of numerous secondary phases(micron scale Al_(3)CuCe,micron scale MgZnCu,and nanoscale MgZnCu phases).The calculation of YS shows that the Orowan strengthening and coefficient of thermal expansion mismatch strengthening are the main strengthening mechanisms,and the contribution values of both to the YS are 28 and 70 MPa for C0.5 alloy.In addition,the C0.5 alloy has a greater plasticity than the C1 alloy because the<c+a>slip system is initiated.展开更多
The large and dense rare earth (RE)-oxide inclusions in high-oxygen RE metal increase the risk of producing variable properties in RE steel. Consequently, a self-developed electrolysis cell was utilized for the produc...The large and dense rare earth (RE)-oxide inclusions in high-oxygen RE metal increase the risk of producing variable properties in RE steel. Consequently, a self-developed electrolysis cell was utilized for the production of low-oxygen La/Ce mischmetal. The electrolysis process and the origin of oxygen in mischmetal were comprehensively investigated. The results indicate that the reaction between La/Ce oxide and fluoride molten salt results in the formation of La/Ce oxy-fluoride. The deposition of oxy-fluoride at the bottom of the electrolysis cell is the primary factor contributing to the increased oxygen content in mischmetal. The comprehensive influence of oxide addition quantity, feeding interval, and electrolysis temperature on oxygen content, purity, and current efficiency using the response surface methodology model is revealed. The results for industrial experiment show that the purity of mishcmetal reaches higher than 99.78 wt.%, the oxygen content of mischmetal is only 0.0047 wt.% and the current efficiency of the electrolysis process achieves 80.79% under the optimized parameters of 225 kg/d, 30 s and 1069 ℃. The findings offer valuable insights into the application of molten salt electrolysis for the production of low-oxygen mischmetal.展开更多
Defect engineering in metal organic frameworks(MOFs)has captured significant attention in the field of photocatalysis.A series of UiO-66(Ce)(UiO=University of Oslo)MOFs with different contents of missing-linker defect...Defect engineering in metal organic frameworks(MOFs)has captured significant attention in the field of photocatalysis.A series of UiO-66(Ce)(UiO=University of Oslo)MOFs with different contents of missing-linker defects have been developed for the photocatalytic selective oxidation of benzylamine(BA)and thioanisole(TA)under visible light.The introduction of missing-linker defects promotes the formation of unsaturated Ce sites with a high Ce3+content.It also generates a high concentration of oxygen vacancies.In situ Fourier transform infrared spectroscopy(FTIR)results revealed that BA and TA molecules were activated on coordinatively unsaturated Ce sites via the H-N…Ce and the C-S…Ce interactions,respectively.Simulated in situ electron paramagnetic resonance(EPR)data indicate that O_(2) activation and reduction occur at coordinatively unsaturated Ce^(3+)sites to form·O_(2)^(-).This is accelerated by the Ce^(3+)/Ce^(4+)redox cycle associated with the photogenerated electrons.The corresponding photogenerated holes are involved in the deprotonation of the activated BA and TA.The most active sample exhibits 98.4%and 95.5%conversion rates for BA and TA oxidation.Mechanisms for the molecular activation are proposed at the molecular level.展开更多
生态系统文化服务(CES)作为生态系统服务的重要组成部分之一,具有连接人类、社会文化与自然,尤其是与特定区域自然环境相互联系的纽带作用,对保护生态环境和增进人类福祉具有十分重要的意义。本文使用CiteSpace软件,对Web of Science网...生态系统文化服务(CES)作为生态系统服务的重要组成部分之一,具有连接人类、社会文化与自然,尤其是与特定区域自然环境相互联系的纽带作用,对保护生态环境和增进人类福祉具有十分重要的意义。本文使用CiteSpace软件,对Web of Science网站2010—2023年369条文献数据进行主题词网络、高频和中心主题词、主题词聚类等分析,归纳了主要的CES研究类别及其主要开展的视角。结果表明,2010—2023年CES研究获得快速发展,研究对象主要为(1)位于城市内部、具有较高进入性、重视个体身心情感体验的城市公园绿地,(2)提供游憩娱乐价值、美学价值、部分精神/宗教价值的旅游地,(3)关注土地利用、景观管理和人地关系等领域的保护地;整体呈现由货币化方法向非货币化方法转向,由微观尺度向宏观微观相结合转向,由关注价值评估向关注人类感知体验转向,由单一视角研究向多学科多视角研究转向等特点。未来研究需加强多学科交叉,尤其是与人文社会科学领域的交叉研究,重视人地关系与CES的相互影响,探索CES价值实现的多元机制和模式,助力人、自然与社会的和谐统一。展开更多
基金Project supported by the National Natural Science Foundation of China(52071004,52301228,51971005,52171168)the Program of Top Disciplines Construction in Beijing(PXM2019_014204_500031)the International Research Cooperation Seed Fund of Beijing University of Technology(2021B23)。
文摘In this work,we proposed a method to enhance the magnetic properties of(Nd,Ce)-Fe-B magnets with Ce/TRE ratios below 25 wt%by introducing a moderate amount of La elements.The segregation behavior of La elements towards grain boundaries(GBs)was utilized to optimize the GB phase structure.Incorporation of La atoms into the main phase induces lattice expansion,leading to an increased formation of Ce^(3+)ions with enhanced magnetic moments.Comparative analysis with the original magnet(La/Ce=0 wt%)demonstrates that the magnet with a La/Ce ratio of 10 wt%exhibits improvements of 0.3%in remanence,12.6%in coercivity,and 0.6%in maximum energy produ ct.These results underscore that the moderate addition of La elements enhances the fluidity of the rare earth-rich phase and optimizes the distribution of lamellar GB,consequently reinforcing the magnetic isolation effect.Furthermore,the promotion of the transformation from Ce^(4+)to Ce^(3+)ons contributes to the comprehensive enhancement of the magnetic properties.This research offers a novel strategy for fabricating high-performance and resource-e fficient sintered magnets based on LaCe alloys.
基金Project supported by the National Key Research and Development Program of China(2021YFB3503003,2021YFB3503100,2022YFB3505401)。
文摘The microstructure of(Nd,Ce)-Fe-B sintered magnets with different diffusion depths was characterized by a magnetic force microscope,and the relationship between the magnetic properties and the local structure of grain boundary diffused magnets is discussed.The domains perpendicular to the c-axis(easy magnetization direction)show a typical maze-like pattern,while those parallel to the c-axis show the characte ristics of plate domains.The significant gradient change is shown in the concentration of Dy with the direction of diffusion from the surface to the interior.Dy diffuses along grain boundaries and(Dy,Nd)_(2)Fe_(14)B layer with a high anisotropy field formed around the grains.Through in-situ electron probe micro-analysis/magnetic force microscopy(EPMA/MFM),it is found that the average domain width decreases,and the proportion of single domain grains increases as diffusion depth increases.This is caused by both the change of concentration and distribution of Dy.The grain boundary diffusion process changes the microstructure and microchemistry inside the magnet,and these local magnetism differences can be reflected by the configuration of the magnetic domain structure.
基金supported by the National Key Research and Development Program of China(Nos.2021YFB3503003,2021YFB3503100,and 2022YFB3505401).
文摘The combination of dual-main-phase(DMP)(Nd,Ce)-Fe-B magnets and grain boundary diffusion process(GBDP)is currently a research topic for obtaining high-cost performance materials in rare earth permanent magnet fields.The novel structural features of GBDP(Nd,Ce)-Fe-B magnets give a version of different domain reversal processes from those of non-diffused magnets.In this work,the in-situ magnetic domain evolution of the DMP magnets was observed at elevated temperatures,and the temperature demagnetization and coercivity mechanism of the GBDP dual-main-phase(Nd,Ce)-Fe-B magnets are discussed.The results show that the shell composition of different types of grains in DMP magnets is similar,while the magnetic microstructure results indicate the Ce-rich grains tend to demagnetize first.Dy-rich shell with a high anisotropic field caused by GBDP leads to an increase in the nucleation field,which enhances the coercivity.It is found that much more grains exhibit single domain characteristics in the remanent state for GBDP dual-main-phase(Nd,Ce)-Fe-B magnets.In addition,the grains that undergo demagnetization first are Ce-rich or Nd-rich grains,which is different from that of non-diffused magnets.These results were not found in previous studies but can be intuitively characterized from the perspective of magnetic domains in this work,providing a new perspective and understanding of the performance improvement of magnetic materials.
基金financially supported by the National Key Research and Development Program of China(No.2022YFB3709300)the Guangdong Major Project of Basic and Applied Basic Research,China(No.2020B0301030006)the Chongqing Special Project of Science and Technology Innovation,China(No.cstc2021yszx-jcyjX0007)。
文摘To obtain lightweight multicomponent magnesium alloys with high tensile strength,ductility,and stiffness,two extruded Mg_(92−5x)Al_(1.5+3x)Zn_(3)Cu_(3.5+x)Ce_(x)(x=0.5 and 1,labeled as C0.5 and C1)alloys were designed.The results reveal that the ultimate tensile strength,yield strength(YS),and fracture strain of the C0.5 alloy are simultaneously improved compared to those of the C1 alloy,with values of 346 MPa,312 MPa,and 11.7%,respectively.This enhancement is primarily attributed to the refinement of numerous secondary phases(micron scale Al_(3)CuCe,micron scale MgZnCu,and nanoscale MgZnCu phases).The calculation of YS shows that the Orowan strengthening and coefficient of thermal expansion mismatch strengthening are the main strengthening mechanisms,and the contribution values of both to the YS are 28 and 70 MPa for C0.5 alloy.In addition,the C0.5 alloy has a greater plasticity than the C1 alloy because the<c+a>slip system is initiated.
基金supported by the National Natural Science Foundation of China(No.52101165)the Inner Mongolia Science and Technology Major Project(No.2020ZD0010)the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-CN-2021-3).
文摘The large and dense rare earth (RE)-oxide inclusions in high-oxygen RE metal increase the risk of producing variable properties in RE steel. Consequently, a self-developed electrolysis cell was utilized for the production of low-oxygen La/Ce mischmetal. The electrolysis process and the origin of oxygen in mischmetal were comprehensively investigated. The results indicate that the reaction between La/Ce oxide and fluoride molten salt results in the formation of La/Ce oxy-fluoride. The deposition of oxy-fluoride at the bottom of the electrolysis cell is the primary factor contributing to the increased oxygen content in mischmetal. The comprehensive influence of oxide addition quantity, feeding interval, and electrolysis temperature on oxygen content, purity, and current efficiency using the response surface methodology model is revealed. The results for industrial experiment show that the purity of mishcmetal reaches higher than 99.78 wt.%, the oxygen content of mischmetal is only 0.0047 wt.% and the current efficiency of the electrolysis process achieves 80.79% under the optimized parameters of 225 kg/d, 30 s and 1069 ℃. The findings offer valuable insights into the application of molten salt electrolysis for the production of low-oxygen mischmetal.
基金supported by the National Natural Science Foundation of China(Nos.22272026 and 22272028)the 111 Project(No.D16008)Jinhong Bi thanks the Youth Talent Support Program of Fujian Province(No.00387077).
文摘Defect engineering in metal organic frameworks(MOFs)has captured significant attention in the field of photocatalysis.A series of UiO-66(Ce)(UiO=University of Oslo)MOFs with different contents of missing-linker defects have been developed for the photocatalytic selective oxidation of benzylamine(BA)and thioanisole(TA)under visible light.The introduction of missing-linker defects promotes the formation of unsaturated Ce sites with a high Ce3+content.It also generates a high concentration of oxygen vacancies.In situ Fourier transform infrared spectroscopy(FTIR)results revealed that BA and TA molecules were activated on coordinatively unsaturated Ce sites via the H-N…Ce and the C-S…Ce interactions,respectively.Simulated in situ electron paramagnetic resonance(EPR)data indicate that O_(2) activation and reduction occur at coordinatively unsaturated Ce^(3+)sites to form·O_(2)^(-).This is accelerated by the Ce^(3+)/Ce^(4+)redox cycle associated with the photogenerated electrons.The corresponding photogenerated holes are involved in the deprotonation of the activated BA and TA.The most active sample exhibits 98.4%and 95.5%conversion rates for BA and TA oxidation.Mechanisms for the molecular activation are proposed at the molecular level.
文摘生态系统文化服务(CES)作为生态系统服务的重要组成部分之一,具有连接人类、社会文化与自然,尤其是与特定区域自然环境相互联系的纽带作用,对保护生态环境和增进人类福祉具有十分重要的意义。本文使用CiteSpace软件,对Web of Science网站2010—2023年369条文献数据进行主题词网络、高频和中心主题词、主题词聚类等分析,归纳了主要的CES研究类别及其主要开展的视角。结果表明,2010—2023年CES研究获得快速发展,研究对象主要为(1)位于城市内部、具有较高进入性、重视个体身心情感体验的城市公园绿地,(2)提供游憩娱乐价值、美学价值、部分精神/宗教价值的旅游地,(3)关注土地利用、景观管理和人地关系等领域的保护地;整体呈现由货币化方法向非货币化方法转向,由微观尺度向宏观微观相结合转向,由关注价值评估向关注人类感知体验转向,由单一视角研究向多学科多视角研究转向等特点。未来研究需加强多学科交叉,尤其是与人文社会科学领域的交叉研究,重视人地关系与CES的相互影响,探索CES价值实现的多元机制和模式,助力人、自然与社会的和谐统一。
