查看更多>>摘要：In this work,a series of self-activated KYb(MoO4)2 phosphors with various x at％Er3+doping concen-trations(x=0.5,1,3,5,8,10,15)was synthesized by the solid-state reaction method.The phase structure of the as-prepared samples was analyzed by X-ray diffraction(XRD),XRD Rietveld refinement and Fourier transform infrared(FT-IR)spectroscopy.The as-prepared samples retain the orthorhombic structure with space group of Pbcn even Er3+doping concentration up to 15 at％.High-purity upcon-version(UC)green emission with green to red intensity ratio of 55 is observed from the as-prepared samples upon the excitation of 980 nm semiconductor laser and the optimum doping concentration of Er3+ions in the self-activated KYb(MoO4)2 host is revealed as 3 at％.The strong green UC emission is confirmed as a two-photon process based on the power-dependent UC spectra.In addition,the fluo-rescence intensity ratios(FIRs)of the two thermally-coupled energy levels,namely 2H11/2 and 4S3/2,of Er3+ions were investigated in the temperature region 300-570 K to evaluate the optical temperature sensor behavior of the sample.The maximum relative sensitivity(SR)is determined to be 0.0069 K-1 at 300 K and the absolute sensitivity(SA)is determined to be 0.0126 K-1 at 300 K.The SA of self-activated KYb(MoO4)2∶Er3+is almost twice that of traditional KY(MoO4)2∶Er3+/Yb3+codoping phosphor.The re-sults demonstrate that Er3+ions doped self-activated KYb(MoO4)2 phosphor has promising application in visible display,trademark security and optical temperature sensors.
查看更多>>摘要：Phenol-containing wastewater is typical organic wastewater,and its treatment is arduous.An advanced method to treat this type of wastewater is persulfate activation.Environmentally friendly cerium-manganese composite oxide materials were synthesized by hydrothermal method and applied to the phenol degradation process.Various ratios of cerium and manganese,as well as the amount of sodium hydroxide,were investigated.The solid solutions of cerium and manganese were formed and confirmed by X-ray diffraction(XRD)and transmission electron microscopy(TEM).H2-temperature programmed reduction(H2-TPR)and X-ray photoelectron spectroscopy(XPS)were utilized to analyze the synergistic effect of cerium and manganese.It is found that there is a transformation between Ce4+/Ce3+and Mn2+/Mn3+,which makes the material more trivalent manganese and thereby increases the catalytic activity.The effect of materials in catalyzing phenol degradation by peroxodisulfate(PDS)under various prepa-ration conditions is discussed and high-efficiency removal of phenol can be achieved and the removal rate at 180 min is close to 100％.The kinetic of this process was investigated and activation energy of phenol degradation is 62.35 kJ/mol.The degradation pathway of phenol was studied and it is found that PDS can be activated by low metal ions and the OH and SO4--radicals play crucial roles according to the quenching experiments.
查看更多>>摘要：Ce/BEA has the potential to be applied as a novel passive NOx absorber(PNA)in the after-treatment of vehicles due to its considerable NOx storage capacity.However,as a vehicle exhaust after-treatment material,it must withstand the test of long-term hydrothermal aging.This work examined the deacti-vation mechanism of Ce/BEA during hydrothermal aging.3.0 wt％Ce/BEA was prepared using the ion-exchange method,and then subjected to hydrothermal treatment at 650 ℃ with 10％H2O for 1-12 h to obtain samples with different aging extent.For comparison,the H-BEA support was aged under the same conditions.Brunauer-Emmett-Teller(BET)method,X-ray diffraction(XRD),NH3 temperature programmed reduction(NH3-TPD),27Al MAS nuclear magnetic resonance(27Al MAS NMR),H2 temper-ature programmed reduction(H2-TPR),and high resolution-transmission electron microscopy(HR-TEM)were performed to characterize the changes in PNA performance,structure,Ce species,and acidity.The HR-TEM and H2-TPR results show that CeOx particles appear after hydrothermal aging,which results from the detachment and aggregation of active Ce species.Based on the 27Al MAS NMR results,we conclude that BEA zeolite dealumination leads to the loss of acidic sites and the transformation of active Ce species on the acidic sites into the less active CeOx.This is the primary reason for the hydrothermal aging deactivation of Ce/BEA.
查看更多>>摘要：The substitution of Fe by Co in the 2∶14∶1 phase is an effective method to increase the Curie temperature and enhance the thermal stability of the Nd-Fe-B magnets.However,the accumulation of Co element at the grain boundaries(GBs)changes the GBs from nonmagnetic to ferromagnetic and causes the thin-layer GBs to become rare.In this paper,the method of diffusing Tb element was chosen to improve the microstructure and temperature stability of high-Co magnets.Three original sintered Nd28.5Dy3-CoxFebalM0.6Bi(x=0,6 wt％,12 wt％;M=Cu,Al,Zr)magnets with different Co contents were diffused with Tb by grain boundary diffusion(GBD).After GBD,high-Co magnets exhibit more continuously distributed thin-layer GBs,and their thermal stability is significantly improved.In high-Co magnets(x=6 wt％),the absolute value of the temperature coefficient of coercivity decreases from 0.603％/K to 0.508％/K in the temperature range of 293-413 K,that of remanence decreases from 0.099％/K to 0.091％/K,and the coercivity increases from 18.44 to 25.04 kOe.Transmission electron microscopy(TEM)characterization reveals that there are both the 1∶2 phase and the amorphous phase in the high-Co magnet before and after GBD.EDS elemental analysis shows that Tb element is more likely to prefer-entially replace the rare earth elements in the 2∶14∶1 main phase than in the 1∶2 phase and the amor-phous phase.The concentration of Tb at the edge of the main phase is much higher than that in the 1∶2 phase and amorphous phase,which is beneficial to the improvement of the microstructure.The pref-erential replacement of Tb elements at the edge of the 2∶14∶1 phase and thin-layer GBs with a more continuous distribution are synergistically responsible for improving the thermal stability of high-Co magnets.The study indicates that GBD is an effective method to improve the microstructure and ther-mal stability of high-Co magnets.
查看更多>>摘要：A novel microstructure of magnetically anisotropic SmCo-based magnet with high-performance is re-ported.The magnet consists of SmCo7-H(TbCu7-hexagonal type),Sm2Co17-H(Th2Ni17-hexagonal type)and SmCo3-R(SmCo3-rhombohedral type)phases.The maximum magnetic energy product of the magnet is 231.69 kJ/m3,and the intrinsic coercivity is 1005.47 kA/m.An outstanding intrinsic coercivity temperature coefficient(β)of-0.125％/K between 298 and 773 K is obtained,which is very close to theβof commercial high-temperature Sm2Co17-based sintered magnets.The initial magnetization curve in-dicates that the coercivity mechanism is controlled by a domain wall pinning mechanism.The SmCo3-R lamellar phase may be a potential pinning center or self-pinning center.The microstructure of the magnet is different from that of any previous SmCo-based magnets.These findings provide a new idea for preparing high-performance SmCo-based permanent magnets.
查看更多>>摘要：Lanthanum doped nickel-cobalt nano ferrites with chemical formula Ni0.5Co0.5LaxFe2-xO4(x=0.05,0.10,0.15 and 0.20)were prepared using a simple sol-gel auto combustion method.The basic structural properties were determined by X-ray diffraction method and the formation of single phased spinel ferrite was confirmed.The crystalline size decreased from 25 to 11 nm and lattice parameter a increases with increase of La doping.The surface morphology of these ferrites was observed by field-emission scanning electron microscopy(FESEM)and agglomerated irregular grains are observed with increase of the rare earth element La doping.Energy-dispersive X-ray spectroscopy(EDX)result confirms the presence of the required elements.The Fourier transform infrared spectroscopy(FTIR)spectrum in-dicates the formation of the spinel ferrite structure with M-O bonds.Optical direct band measurements from ultraviolet-visible spectroscopy(UV-Vis)spectroscopy indicate that the direct band gap decreases from 1.39 to 1.19 eV for x=0.05 to x=0.15,then increases to 1.28 eV for x=0.20.The room temperature magnetic properties of these ferrites were studied by a vibrating sample magnetometer(VSM).The enhanced saturation magnetization of 49.73 emu/g is observed for x=0.10 and then saturation mag-netizations are gradually decreased for x=0.15 and x=0.20.Interestingly the remanent magnetization and coercivity also follow the same trend.
查看更多>>摘要：The magnetic properties,magnetic phase transition and magnetocaloric effects(MCE)of Er3Si2C2 com-pound were investigated based on theoretical calculations and experimental analysis.Based on the first principles calculations,the antiferromagnetic(AFM)ground state type in Er3Si2C2 compound was pre-dicted and its electronic structure was investigated.The experimental results show that Er3Si2C2 com-pound is an AFM compound with the Néel temperature(TN)of 7 K and undergoes a field-induced first-order magnetic phase transition from AFM to ferromagnetic(FM)under magnetic fields exceeding 0.6 T at 2 K.The magnetic transition process of Er3Si2C2 compound was investigated and discussed.The values of the maximum magnetic entropy change(-ΔSMmax)and the refrigeration capacity(RC)are 17 J/(kg.K)and 193 J/kg under changing magnetic fields of 0-5 T,respectively.As a potential cryogenic magnetic refrigerant,the Er3Si2C2 compound also provides an interesting research medium to study the magnetic phase transition process.
查看更多>>摘要：In perovskite EuTiO3,the magnetic characteristics and magnetocaloric effect(MCE)can be flexibly regulated by converting the magnetism from antiferromagnetic to ferromagnetic.In the present work,a series of Eu(Ti,Nb,Mn)O3 compounds,abbreviated as ETNMO for convenience of description,was fabri-cated and their crystallography,magnetism together with cryogenic magnetocaloric effects were sys-tematically investigated.The crystallographic results demonstrate the cubic perovskite structure for all the compounds,with the space group of Pm3m.Two magnetic phase transitions are observed in these second-order phase transition(SOPT)materials.The joint substitution of elements Mn and Nb can considerably manipulate the magnetic phase transition process and magnetocaloric performance of the ETNMO compounds.As the Mn content increases,gradually widened-ASM-T curves are obtained,and two peaks with a broad shoulder are observed in the-ASM-T curves for △μ0H≤0-1 T.Under a field change of 0-5 T,the values of maximum magnetic entropy change(-ASMmax)and refrigeration capacity(RC)are evaluated to be 34.7 J/(kg·K)and 364.9 J/kg for EuTi0.8625Nb0.0625Mn0.075O3,27.8 J/(kg-K)and 367.6 J/kg for EuTi0.8375Nb0.0625Mn0.1O3,23.2 J/(kg·K)and 369.2 J/kg for EuTi0.8125Nb0.0625Mn0.125O3,17.1 J/(kg·K)and 357.6 J/kg for EuTi0.7875Nb0.0625Mn0.15O3,respectively.The considerable MCE parameters make the ETNMO compounds potential candidates for cryogenic magnetic refrigeration.
查看更多>>摘要：As a kind of non-destructive testing method,magnetic particle inspection is widely used in the fields of aviation and high-speed rail.The properties of magnetic fluorescent bifunctional composites,such as fluorescence intensity and magnetic properties,have increasing demands in magnetic particle inspec-tion.Rare earth compounds offer potential as novel materials for fluorescent magnetic bifunctional composites due to their excellent optical properties and extremely narrow emission spectra.In this work,the rare earth fluorescent material Y2O2S∶Eu3+was synthesized by solid-state reaction method.Fe3O4 nanoparticles prepared by hydrothermal method were uniformly coated on the Y2O2S∶Eu3+particles through physical adsorption of surfactants.The obtained Fe3O4@Y2O2S∶Eu3+exhibits dark red color under the ultraviolet light.In addition,X-ray diffraction,morphology,photoluminescence and hysteresis loop of Fe3O4@Y2O2S∶Eu3+were investigated.The luminescence mechanism of Y2O2S∶Eu3+is described in detail.Fe3O4@Y2O2S∶Eu3+displays good paramagnetism and has a good controllability under a magnetic field.The magnetic particle inspection of Fe3O4@Y2O2S∶Eu3+was performed using a 4-pole electromagnet and a test piece shim.The magnetic fluorescent bifunctional composite presented in this work can be applied for non-destructive testing.
查看更多>>摘要：In current report,the structural,magnetic,and thermoelectric properties of RE doped MgPm2X4(X=S,Se)spinels were investigated.The energy difference in ferromagnetic and antiferromagnetic states re-veals the stability of MgPm2(S/Se)4 in the ferromagnetic states.The computation of enthalpy of formation also ascertains thermodynamic stability of crystal structure.Spin-dependent band structure and density of states analysis reveal ferromagnetic semiconducting character showing different electronic behavior in both spin channels.The room temperature ferromagnetism,spin polarization and Curie temperature are estimated from exchange energies analysis.In addition,exchange constants(N0α and N0β),exchange energy Ax(pd),crystal field energy,and double exchange mechanism were studied to explore the magnetic response.Likewise,the electrical conductivity,thermal conductivity,Seebeck co-efficient,and power factor show effect on electrons spin and their potential for thermoelectric devices.
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