Synthesis mechanism of Sm2Fe17 alloy produced in reduction-diffusion process

Sm₂Fe₁₇ alloy was the precursor of Sm₂Fe₁₇N_x magnetic materials. Reduction-diffusion (R/D) method was a new preparation process for the Sm₂Fe₁₇ alloy, and had been widely employed as a new preparation method for rare earth-transition metal intermetallic compounds. In this text, thermodynamics and kinetics for the synthesis of the Sm₂Fe₁₇ alloy by reduction-diffusion (R/D) method in the Ca-Sm₂O₃-Fe system were analyzed. The related synthesis mechanism of this reaction was investigated in detail by means of scanning electron microscope (SEM). The results showed that the thickness of the Sm₂Fe₁₇ alloy layer versus the reaction time could be fit by the parabola law, and its growth model was determined to be: (L₀-L)²=43.848 t, the diffusion of Sm into Fe proceeded with the formation of the Sm₂Fe₁₇ phase from the very beginning of the reaction, and rich samarium phases, such as SmFe₂ and SmFe₃, were not formed, and the rate-determining step of the R/D reaction was found to be the peritectic reaction between liquid samarium and solid iron.     

Research on microstructure and magnetostriction of Fe₈₃Ga₁₇Dy_x alloys

The crystal structure,microstructure and the magnetostriction of Fe83Ga17Dyx(x=0,0.2,0.4,0.6) series alloys were studied.The results showed that the influence of the Dy on the crystal structure of the alloy was very small but the effect on the microstructure was significant when different contents of Dy were added into the Fe83Ga17 alloy,respectively.Meanwhile,the magnetostriction of Fe83Ga17Dy0.2 alloy was greatly enhanced,the magnetostriction λ value reached 300×10-6 at 400(kA/m) magnetic field.     

Mechanical properties of UHMWPE/Sm₂O₃ composite shielding material

UHMWPE have good effect to slow down fast neutrons and Sm2O3 can absorb the thermal neutrons.A new style UHMWPE/ Sm2O3 composite shielding material was manufractured by hot-press moulding method.The microstructure and mechanical properties were characterized by IR and SEM.The results indicate that Sm2O3 distributed continuously,evenly in UHMWPE,and the interface was combined closely.Hardness of UHMWPE/Sm2O3 composites increased at first and decreased and tensile strength decreased with the increasing of Sm2O3 mass fraction.     

Anomalous thermal expansion of Gd₂Fe_15.5Cr_1.5 compound

The structure and magnetic properties of Gd2Fe15.5Cr1.5 compound were investigated by means of X-ray diffraction and magnetization measurements.The Gd2Fe15.5Cr1.5 compound had a rhombohedral Th2Zn17-type structure.The Curie temperature of Gd2Fe15.5Cr1.5 compound was about 570 K.This value was about 60 K higher than that of the mother compound Gd2Fe17.Negative thermal expansion was found in Gd2Fe15.5Cr1.5 compound in a broad temperature range 294-572 K by X-ray dilatometry.The coefficient of the average thermal expansion was =-3.87×10-6 K-1 in 294-512 K,and-1.58×10-5 in 512-572 K.The magnetostriction deformations from 294 to 532 K were calculated by means of the differences between the experimental values of the lattice parameters and corresponding values extrapolated from the paramagnetic range.The result showed that the spontaneous volume magnetostrictive deformation ωS decreased linearly from 4.73×10-3 to 0.11×10-3 with the temperature increasing from 294 to 532 K.The analysis showed that the ωS mainly came from the contribution of the spontaneous linear magnetostrictive λc along the c axis.     

Preparation and performance of electrodeposited Ni-TiB₂-Sm₂O₃ composite coatings

Sm2O3 and TiB2 were used as codeposited particles in electrodeposition Ni-TiB2-Sm2O3 composite coatings to improve its performance. Ni-TiB2-Sm2O3 composite coatings were electrodeposited in the nickel sulfate,hexadecylpyridinium bromide and cetyltrimethylammonium bromide solution containing TiB2 and Sm2O3 particles. The content of codeposited Sm2O3 in the composite coating was controlled by changing the concentrations of Sm2O3 particles in the solution. The composite coatings were characterized with X-ray diffraction(XRD) and inductively coupled plasma-atomic emission spectrometer(ICP-AES) . The effects of Sm2O3 content on microhardness,wear weight loss and friction coefficient of composite coatings were investigated,respectively. The microhardness of the Ni-TiB2-Sm2O3 composite coatings was 19.35%,16.58%,2.03% higher than that of the Ni coating,Ni-Sm2O3 and Ni-TiB2 composite coatings,respectively. The wear weight loss of the Ni-TiB2-Sm2O3 composite coatings was 7,2.33,1.22 times lower than that of the Ni coating,Ni-Sm2O3 and Ni-TiB2 composite coatings,respectively. The friction coefficient of the Ni coating,Ni-Sm2O3,Ni-TiB2 and Ni-TiB2-Sm2O3 composite coatings were 0.712,0.649,0.850 and 0.788,respectively. The loading-bearing capacity and the wear-reducing effect of the Sm2O3 particles were closely related to the content of Sm2O3 particles in the composite coatings.     

Preparation of Sm_2Fe_(17)Alloys in Ca-Sm_2O_3-Fe System

Sm2Fe17alloyisanimportantprecursorforthe preparationofSm2Fe17Nxmagnet.Sincethenitrogen containedSm2Fe17(Sm2Fe17Nx)alloy,asapermanent magnetmaterial,possessesahigherCurietempera ture,largeranisotropyfield,betterresistancetooxi dationandthermalstability,and…     

水溶液中电沉积Sm-Fe合金

Sm2Fe17是一种性能优异的永磁材料(SmFeN)的前驱体。用循环伏安法研究了三价钐(Sm(Ⅲ))和二价铁(Fe(Ⅱ))在含甘氨酸的水溶液中的电化学行为,在Pt电极上,Fe(Ⅱ)一步还原为Fe,Sm(Ⅲ)能被Fe(Ⅱ)诱导共沉积。在水溶液中成功电沉积出Sm-Fe合金。研究了pH和电流密度对镀层组分的影响,在电流密度为40mA.cm-2时,随着pH升高,镀层中Sm含量增加,在pH=4.5时,随着电流密度的增加,镀层中Sm含量增加。电子显微镜(SEM)显示镀层表面是紧密一致的。镀层在热处理前是非晶态Sm-Fe合金和微晶Fe的混合相,经750℃热处理后,镀层转化为Fe和Sm-Fe合金的混合相。     

Magnetic properties and magnetocaloric effects of manganite (La_0.8Ho_0.2)_2/3Ca_1/3MnO₃ and (La_0.5Ho_0.5)_2/3Ca_1/3MnO₃

We reported the magnetic properties and magnetocaloric effects(MCE) of(La0.8Ho0.2)2/3Ca1/3MnO3 and(La0.5Ho0.5)2/3Ca1/3MnO3 nanoparticles by sol-gel technique.With this method,we were able to obtain the samples with particle diameters ranging from 50 to 200 nm.In the(La1-xHox)2/3Ca1/3MnO3 compound,an external magnetic field induced a magnetic transition from an paramagnetic phase to a ferromagnetic phase above Ts=105-135 K,leading to magnetocaloric effects.The maximum value of ΔSM was 1.19 J/(kg·K) at 100 K and 2.03 J/(kg·K) at 152 K for a magnetic field change of 5 T.Because both samples had large relative cooling power(RCP) and wide δTFWHM,the study on systems with the(La1-xHox)2/3Ca1/3MnO3-related magnetic transitions may open an important field in searching good magnetic materials.     

Photoluminescence study of SiO₂ coated Eu³⁺:Y₂O₃ core-shells under high pressure

Uniform core-shell Eu3+:Y2O3/SiO2 spheres were synthesized via precipitation and the Stber method.The structural transition of core-shell Eu3+:Y2O3/SiO2 was studied by using high pressure photoluminescence spectra.With pressure increasing,the emission intensities of 5D0→7F0,1,2 transitions of Eu3+ ions decreased and the transition lines showed a red shift.The relative luminescence intensity ratio of 5D0→7F2 to 5D0→7F1 transitions decreased with increasing pressure,indicating lowering asymmetry around Eu3+ ions.During compression,structural transformation for cores in the present core-shell Eu3+:Y2O3/SiO2 sample from cubic to monoclinic took place at 7.5 GPa,and then the monoclinic structure turned into hexagonal above 15.2 GPa.After the pressure was released,the hexagonal structure transformed back to monoclinic and the monoclinic structure was kept stable to ambient pressure.     

Re-determination of the crystal structure of Ca₂Y₈Si₆O₂₆ and study on the luminescent properties of Ca₂Y₈Si₆O₂₆:Tb³⁺

The crystal structure of silicate oxyapatite Ca2Y8Si6O26 was indexed as hexagonal,space group P63/m,a=0.93515 nm,c=0.67872 nm,α=β=90°,γ=120°,V=0.5138692 nm3.Three strong peaks located at 32.079o,32.595o,and 50.104o with d=2.7903,2.74649,1.8194 was in accordance with,(112),and(213) planes.The optimum concentration of Tb3+ in Ca2Y8Si6O26 to yield highest photoluminescence intensity was 10 mol.% of Y3+.The corresponding excitation spectrum consisted of an intense broad band from 220 to 260 nm.The photoluminescence measurements showed that the green emission originated from 5D4-7F5 was predominant in the measured range with strong doublet lines at 543 and 549 nm.     

Intense blue-emitting Ca₂PO₄Cl:Eu²⁺ phosphor for near-ultraviolet converting white light-emitting diodes

A blue phosphor Ca2PO4Cl:Eu2+(CAP:Eu2+) was synthesized by solid state reaction.The Ca2PO4Cl:Eu2+ exhibited high quantum efficiency and excellent thermal stability.The luminescent intensity of Ca2PO4Cl:Eu2+ was found to be 128% under excitation at 380 nm,149% under 400 nm,and 247% under 420 nm as high as that of BaMgAl10O17:Eu2+.The optimal doping concentration was observed to 11 mol.% of CAP:Eu2+.The energy transfer between Eu2+ ions in CAP were occurred via electric multipolar interaction,and the critical transfer distance was estimated to be 1.26 nm.A mixture of blue-emitting Ca2PO4Cl:Eu2+,green-emitting(Ba,Sr)2SiO4:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors were selected in conjunction with 400 nm chip to fabricate white LED devices.The average color-rendering index Ra and correlated color temperature(Tc) of the white LEDs were found to be 93.4 and 4590 K,respectively.The results indicated that it was a promising candidate as a blue-emitting phosphor for the near-UV white light-emitting diodes.     

Optimization of BaMgAl₁₀O₁₇:Eu²⁺ phosphors by the substitution of Si-N bonds for Al-O bonds

We proposed a simple method to improve the thermal stability of BaMgAl10O17:Eu2+(BAM) phosphors by the substitution of Si-N bonds for Al-O bonds in the host lattice.Both photoluminescence properties and thermal stability under ultraviolet(UV) and vacuum ultraviolet(VUV) excitation could be significantly improved through Si-N incorporation.After thermal degradation at 600 °C for 1 h in air atmosphere,the Si-N doped sample(Ba0.88Eu0.12MgAl9.97Si0.03O16.97N0.03) had the highest emission intensity which was 22% and 40% stronger than that of as-received sample under UV and VUV excitation,respectively.This could be attributed to the stable local structure surrounding the Eu2+ ions and the lower electronegativity of nitrogen.     

SmFe7金属间化合物--新一代磁体的希望

Sm Fe N的出现 ,再次促使对Sm Fe系进行广泛而深入的研究 ,发现了SmFe7亚稳相的存在。基于其优异的内禀磁性 ,此相有可能作为新型高能积磁体的基材。为引起我国磁体产业界对SmFe7的足够重视 ,特对有关文献作一综述。     

Reduction of SO2 to elemental sulfur over rare earth-iron catalysts

With coal gas as a reducing agent, the catalytic reduction of SO2 to sulfur in the flue gas produced in metallurgical processes was studied over catalysts of rare earth-Fe/Al2O3 (REFe/Al2O3). The catalytic activity of the REFe/Al2O3 catalyst on the reduction of SO2 to sul-fur was investigated based on kinds and the contents of rare earths and different preparation method of the catalyst. Additionally, the mecha-nism of this catalytic reduction reaction was also explored. Results showed that different rare earth imposed different effect on the activity of the Fe/Al2O3 catalyst. Especially, the addition of Sm and Dy greatly improved the catalytic activity of Fe/Al2O3. The yield of sulfur over SmFe/Al2O3was increased to 86.62% at 360 ℃, which was 40.5% higher than that over Fe/Al2O3at the same temperature; and the sulfur yield over DyFe/Al2O3was increased to 91.62% at 400 ℃, 26.4% higher than that over Fe/Al2O3. The catalytic activity of REFe/Al2O3 was somehow dependent on the content of rare earth. For SmFe/Al2O3, the content of Sm was optimized to be about 1.0 wt.%. The rare earth catalyst prepared with different methods also showed varied activity. The sulfur yield over rare-earth transition metal catalysts follows the order: Sm and iron solution mixing impregnationSm first, then iron solution impregnationiron first, then Sm solution impregnation. The reaction mechanism of SO2 reduction to sulfur with coal gas was proposed to be an intermediate mechanism.     

Facile synthesis of visible light excited La_1-xGd_xF₃:Eu³⁺ micro-meter sphere using polyvinylpyrrolidone as a template

Lanthanide fluorides exhibited unique luminescent properties in terms of their low phonon energy can restrict the luminescence quenching and extend luminescent lifetimes.Here,a room-temperature co-precipitation method was used to synthesize europium(III) activated La1-xGdxF3 solid phosphors.X-ray diffraction(XRD) data confirmed the crystalline phases of synthesized sample belongs to orthorhombic system.All the as-derived materials exhibited red luminescence(5D0→7F1) under the excitation at longer wavelengths(394 and 466 nm).The powder with the most intense emission was achieved in terms of 10 mol.% doping concentration(Eu content,La/Gd=1/9) and sample sintered at 700 oC.Scanning electron microscopy(SEM) investigated the morphology and crystalline of the samples,showing that many regular and large balls(5-10 μmol/L) were dispersed within the micro-meter scale composites.We proved that the above crystal growth structures were controllable and predicable based on the surface functionalization by polyvinylpyrrolidone ligand.     

Study on analysis of crystal structure in CeO₂ doped with Er₂O₃ or Gd₂O₃

To simulate the effects of burnable poison doping in nuclear fuel UO2,Er2O3(or Gd2O3)-doped CeO2 pellets were prepared. Changes in lattice constant and atomic disordering for CeO2 due to the Er2O3 and Gd2O3 doping were measured by means of XRD and XAFS. By the Er2O3 doping,the lattice constant decreased,and a disordering of lattice structure was induced in the samples. The doping with Er2O3 also induced the disordering of atomic arrangement around Er atoms,which was observed through the change in XAFS spectra. In contrast,the effect of Gd2O3 doping was smaller than that of Er2O3 doping. The result was discussed in terms of ionic size of dopants in CeO2 crystal.     

铁掺杂对(Na0.5K0.5)NbO3无铅压电陶瓷性能的影响

采用传统陶瓷工艺对(Na0.5K0.5)NbO3进行了铁掺杂改性研究。使用SEM、XRD并结合常规性能测试手段对该体系的显微结构、压电性能进行了表征。研究结果表明:对于(Na0.5K0.5)NbO3无铅压电陶瓷,Fe的掺杂提高了致密性、使晶体颗粒长大、降低了介电性能。     

Phase Equilibrium for the CaO-SiO₂-FeO-P₂O₅ System at 1673K for Dephosphorization With Multi Phase Flux

Development of the efficient hot metal dephosphorization processes during steelmaking process is one of the most essential topics for the production of high grade clean steels. Since the formation of solid solution composed of tricalcium phosphate and dicalcium silicate could obtain a considerable mass transfer of phosphorus from liquid slag into solid phase during hot metal dephosphorization, itcould obviously sustain a high phosphatecapacityof theliquid slag without huge consumption of lime or addition of fluxes, such as fluorite. The above outlines are the main idea of multi phase flux dephosphorization. For the last few decades, many studies have been done towards the scientific principles and the commercial utilization of this technique. However, the reaction mechanism by using multi phase fluxes remains unclear even by now due tolack of evidence. Based on those previous works, providing a reliable and available phase diagram for the fundamental understanding of the reaction mechanism of multi phase flux dephosphorization has become the main purpose of present research. As well known, the CaO-SiO2-FeO-P2O5 slag is the main component of current steelmaking process. Hence the CaO-SiO2-FeO-P2O5 system at equilibrium has been studied at 1673K with low oxygen partial pressure. The solid phase coexisting with liquid flux is approved to be the solid solution composed of CaO, SiO2 and P2O5. Phosphorus distributes mainly in solid solution rather than liquid phase.     

Preparation and characterization of Ce_1-xNi_xO₂ as oxygen carrier for selective oxidation methane to syngas in absence of gaseous oxygen

A citric acid complex method was employed to prepare Ce/Ni mixed oxides with various Ce/Ni ratios useful for selective oxidation methane to syngas in the absence of gaseous oxygen,and the catalytic activity measurement was investigated in a fixed bed reactor at 800 oC.The prepared oxygen carriers were characterized by various characterization techniques such as TG-DSC,XRD and TPR.The results of TG-DSC indicated that the Ce1-xNixO2 precursor generated a stable phase after the heat-treatment at temperatures above 800 oC.The XRD characterization suggested that some Ce-Ni solid solution was formed when Ni2+ ions was incorporated into the lattice of CeO2,and it led to the generation of O-vacancy which could improve the oxygen mobility in the lattice of oxygen carriers.It was found that Ce0.8Ni0.2O2 gave the highest activity in the selective oxidation methane to syngas reaction,and the average methane conversion,CO and H2 selectivity reached to 82.31%,82.41% and 87.64%,respectively.The reason could be not only attributed to the fitting amount of NiO dispersed on the CeO2 surface and bulk but also to actual lattice oxygen amount increased in oxygen carrier.     

Rare earth oxide modified Cu-Mn compounds supported on TiO₂ catalysts for low temperature selective catalytic oxidation of ammonia and in lean oxygen

Selective catalytic oxidation(SCO) of ammonia was carried out over Cu-Mn compounds catalysts modified with trivalent rare earth oxide Ce2O3 and La2O3 respectively.TiO2 was used as support and different ratio of O2 were tested in order to find an appropriate O2 concentration(vol.%),and the results showed that 1%O2(vol.%) was propitious to SCO of ammonia.The effects of the two rare earth oxides modified catalysts Ce2O3-Cu-Mn/TiO2 and La2O3-Cu-Mn/TiO2 on the catalytic activity and selectivity of ammonia oxidation were investigated under the reaction condition of 500 ppm ammonia,1%O2(vol.%),at the temperature from 125 to 250 oC.The results revealed the beneficial role of Ce2O3 and La2O3 in catalytic activity at low temperature and lean oxygen concentration,while the modification with Ce2O3 and La2O3 led to the negative influence on N2 selectivity.For the catalysts modified with Ce showed lower NO and N2O selectivity than the catalysts modified with La,then the effects of different Ce loadings on catalytic activity and selectivity were also considered,in combination with catalysts preparation methods,which include incipient wet impregnation,sol-gel method and co-precipitation.Results revealed that the catalysts prepared by sol-gel method obtained preferable catalytic activity compared with the others,reaching 99% ammonia at 200 oC,whereas 96% NO was detected.It also indicated that different catalyst preparation method significantly determined production distribution.