查看更多>>摘要：In this paper,the effects of rare earth oxides on the microstructure and mechanical properties of nickel-based superalloys prepared by high-energy beam processing technology were critically studied.The focus is on the optimal amount of rare earth oxides that can produce ideal results.Special attention was paid to their main strengthening mechanisms,including solid solution strengthening mainly in the form of solid solution dissolved in the nickel-based alloy and improving the microstructure of the alloy by grain refinement or fine grain strengthening produced by homogenizing the distribution phase.Y2O3,La2O3 and CeO2 rare earth oxides can also improve the fluidity of the alloy molten pool and reduce the segregation of alloying elements.These advantages can significantly improve the mechanical properties of the alloy.Thereafter,this paper outlines the future research directions of rare earth oxides,aiming to expand their application potential.
查看更多>>摘要：Metal halide perovskites exhibit promising prospect in light-emitting diodes,solar cells,photodetectors and bioimaging.However,the workhorse of metal halide perovskites relies on toxicity lead element,which severely damages human body and environment.Among lead-free perovskites,Cs2NaInCl6 double perovskite is one of the most promising candidates because of its great stability and easy synthesis,but suffers inadequate optical performance.Here,we doped Sb3+and Sm3+into Cs2NaInCl6 nanocrystals by a hot injection method.Cs2NaInCl6∶Sb3+exhibits blue emission at 447 nm.Cs2NaInCl6∶Sm3+,Sb3+nano-crystals simultaneously generate the blue emission of Sb3+and the multiple emissions of Sm3+at 565,602,650 and 710 nm.With the increase of Sm3+feed ratio,the emission color of Cs2NaInCl6∶Sm3+,Sb3+gradually moves to cold white region at(0.27,0.28)in CIE chromaticity diagram and correlated color temperature of 11840 K.This work shows the potential application of Cs2NaInCl6∶Sm3+,Sb3+nanocrystals as a single-component cold white emitter.
查看更多>>摘要：In this work,a group of Bi3+/Eu3+-doped SiO2-Al2O3-MCO3(M=Ca,Sr,Ba)glasses were fabricated through melt-quenching method.Their structure and photoluminescence characters were studied via X-ray diffraction(XRD),UV-Vis transmission spectra(TRS),excitation spectra,emission spectra and decay lifetimes.The XRD results show that no nano-crystal phase forms in glass matrix with different doping concentrations of Bi3+and Eu3+ions.Through regulating optical alkalinity value,the intensity of Bi3+ions increases and the peak position shifts to red wavelength.The Bi3+/Eu3+co-doped glasses show a blue-white-yellow-red luminescence by changing concentration of Eu3+ions.Energy transfer efficiency from Bi3+to Eu3+can reach as high as 10.54％.At 423 K,the emission intensity of 55SiO2-10Al2O3-35BaO-0.25Bi2O3(GBE0.5)is 31.1％of that at 308 K.Meanwhile,the activation energy of the glass matrix is 0.251 eV.All results suggest that these Bi3+/Eu3+co-doped glass samples possess potential application in LED field.
Ivan V.NikiforovEkaterina V.IliinaBogdan I.LazoryakSergey M.Aksenov...
1658-1668页
查看更多>>摘要：Novel Ca8CuRE(PO4)7 where RE3+=Eu3+,Tb3+,Dy3+,Ho3+and Er3+were synthesized by a solid-state method in air.The structures of the samples were characterized by powder X-ray diffraction using Rietveld refinement to determine the occupation of crystal sites.The samples are found to have a centrosymmetric structure with space group R3c,as shown by dielectric measurements.These synthe-sized Ca8CuRE(PO4)7 samples have multifunctional properties.The Cu2+ions provide antibacterial properties,while the rare earth elements ions exhibit luminescence properties,and the β-Ca3(PO4)2-type host is biocompatible.The photoluminescence properties of RE3+ions were studied and compared with other simmilar Ca8MRE(PO4)7 phosphates,where M is a divalent metal.The photoluminescence intensity quenching in terms of energy transfer from RE3+to Cu2+is disscused.The bioactive properties were studied in relation to antibacterial activity against E.coli and S.aureus.All syntesized Ca8CuRE(PO4)7 samples demonstrate very high and stable inhibition of bacteria growth.The correlation between crystal structure and properties is discussed.By combining multiple approaches to the directional design of such materials,several important properties within a single chemical compound to achieve biovisualization and bioactive properties simultaneously can be combined.
查看更多>>摘要：In this work,several ceria-zirconia based catalysts with very low(and equimolar)metal contents were prepared,characterised and tested for the CO oxidation reaction(under lean and stoichiometric condi-tions),trying to emulate those conditions found in a diesel oxidation catalyst(DOC)system from a diesel engine and those encountered under gasoline exhaust(λ=1).The metals chosen are Cu,Co,Ag and Pt(as a reliable benchmark).The results reveal enormous differences among reducibility and catalytic activity despite quite similar structural and textural properties of the catalysts,showing differences among dispersion(Ag-catalyst seems to present a low level of dispersion).This catalyst seems to be characterised,as well,by a strong electronic interaction between Ce and Ag centres which is suggested to yield an improved reducibility under H2-TPR conditions.Nevertheless,the order in catalytic activity(Cu＞Ag＞Co ≈ Pt》support)seems not to follow the order found in reducibility and the Cu-catalyst seems to be the most active independently on the reaction conditions,yielding nearly overlapped CO oxidation catalytic curves.Interestingly,a strong correlation between the catalytic activity under the two conditions tested and the OSC values of the Ce0.8Zr0.2O2-supported metal catalysts is found.Therefore,OSC parameter measured at 150 ℃ can be used as a relevant descriptor to evaluate the CO oxidation activity at low and medium conversions for the investigated catalysts,much better than the H2-TPR measurements.
查看更多>>摘要：Improving the alkali resistance of catalysts for selective catalytic reduction of NOx with NH3 is still a challenge.In this work,the co-modification with Fe,Ce and sulfates on V2O5-WO3/TiO2 catalysts(denoted as xSFeCeVWTi)significantly enhances its alkali resistance with K element as a representative.A series of xSFeCeVWTi catalysts was synthesized by wet impregnation with designed 0.05Fe/V,1.5Ce/V and different S/V molar ratios x.The NOx conversion and K resistance of xSFeCeVWTi catalysts increase with the increase of loading amounts of sulfates but no longer further increase as the sulfates load is excessive to block the pores of catalysts and hinder the adsorption of reactants.The optimal modified catalyst in about 2.2S/V actual loading ratio,corresponding to 10.5SFeCeVWTi sample,shows over 99.0％NOx conversion and N2 selectivity at 300-400 ° C after K-poisoning.The interaction between Fe,Ce and V improves its redox ability but slightly weakens surface acidity,while the proper amount of sulfate species enriches surface Brønsted acid sites but attenuates its redox capability.However,a balance of redox capacity and surface acidity,caused by Fe,Ce and sulfate co-modification,contributes to the excellent K resistance of 10.5SFeCeVWTi catalyst.Finally,the change of physicochemical properties influences the reaction mechanism which follows the Eley-Rideal mechanism on 10.5SFeCeVWTi catalyst.These results show that the co-modification with Fe,Ce and sulfates is a good way to improve the alkali tolerance of V2O5-WO3/TiO2 catalyst in industrial applications.
查看更多>>摘要：Pt-HSiW/CeO2 catalysts were prepared for chlorobenzene(CB)catalytic combustion by hydrothermal method at different calcination temperatures,and the effects of the surface acidity and chemical valence on the catalytic activity were investigated.The results show that the catalyst calcined at 450 ℃(Cat-B)exhibits the outstanding catalytic performance,and the Cat-B catalyst possesses 90％conversion of CB at 148 ℃.The excellent catalytic activity of Cat-B is attributed to more Ce3+/(Ce3++Ce4+),Pt0/(Pt0+Pt2+),Oads/(Olatt+Oads)and Lewis acid sites.The degradation mechanism is proposed based on the analysis of the intermediates with the following reaction pathway:chlorobenzene → phenates/benzoquinone →acetate → maleate → CO2+H2O.
查看更多>>摘要：Sintered Nd-Ce-Fe-B magnets were grain boundary diffused(GBDed)with PrxTb80-xAl10Ga10(at％)(x=0,20,40,60,80)alloys.The effect of Pr/Tb content in diffusion source on magnetic properties,micro-structure and elements distribution of GBDed magnets was investigated.When Pr is used to substitute for 75％Tb in diffusion source,Tb consumption per unit coercivity improvement of GBDed magnet re-duces by 77％,compared with the Tb80Al10Ga10 diffused magnet.Tb element diffuses into magnets and then forms Tb-rich shell with high magneto-crystalline anisotropy field surrounding main phase grains,resulting in substantial coercivity improvement.Pr with low melting point diffuses deeply along liquid grain boundary phase during GBD process.It can eliminate some sharp defects of main phase grains and make grain boundaries smooth,which provides diffusion channels for further diffusion of Tb element.Therefore,there are more diffusion channels for Tb and less Tb enriched at surface region,making Tb diffuse more deeply and improving Tb utilization efficiency.This method significantly improves the coercivity,and realizes the green,efficient and high-quality utilization of heavy rare earth(HRE)elements.
查看更多>>摘要：The grain boundary diffusion process(GBDP)of Dy and DyAl on sintered NdFeB magnets was conducted via magnetron-sputtering deposition of Dy and DyAl films to enhance coercivity(Hcj).The magnetic properties,microstructure and anti-corrosion properties of Dy-surface-alloying NdFeB magnets obtained via magnetron sputtering and thermal diffusion were evaluated.The Hcj of the Dy95Al5-NdFeB magnet increases by 32.68％,while the remanence declines slightly.Furthermore,X-ray diffraction and micro-structural analysis confirm the formation of Dy-rich shells,the higher-magnetic-anisotropy field of hard(NdxDy1-x)2(FeAl)14B magnetic phases and an optimised grain boundary structure,contributing to the Hcj enhancement of the magnet.The elemental distribution and diffusion mechanism of the magnets are also discussed.Moreover,the corrosion resistance of the Dy95Al5-NdFeB magnet is substantially improved by enhancing the electrochemical stability and optimising the distribution and morphology of the intergranular phases.The findings of this study are of substantial importance in the development of low-heavy rare-earth sintered NdFeB magnets.
Hui LiangSajjad Ur RehmanRuibiao ZhangYongqiang Deng...
1717-1723页
查看更多>>摘要：The potentials of rare earth-based nanocomposite alloys have never been realized due to strict micro-structural constraints.Owing to the easy demagnetization it is challenging to increase the soft magnetic phase content.To avoid the easy demagnetization,Pr-Fe-B/Alnico magnets were fabricated and re-ported in this manuscript.The content of the Alnico phase is increased from 0 to 25 wt％,while the content of Pr element is reduced to below the sub-stoichiometry of the 2:14:1 main phase.The maximum magnetic energy product,which is the figure-of-merit for permanent magnets,is increased from 122 kJ/m3 for the standard alloy to 146 kJ/m3 for the alloy with 15 wt％Alnico which shows a significant improvement considering the fact that the Curie point of the magnet is also increased by～66 K.The special microstructure contains distinctly and heterogeneously distributed 2:14:1 and Alnico phases.The dimensions of neither the 2:14:1 nor the Alnico phases meet the dimensional requirements of the nanocomposite magnets,but still the smooth demagnetization curves are noted for the alloys.The behavior of effective anisotropy,the performance of the magnets in applied magnetic field and the magnetic interactions among the various constituent grains were quantitatively studied by reversible susceptibility,irreversible susceptibility and recoil loop openness.This study may provide some guiding principles for the development of nanocomposite magnetic alloys with excellent magnetic properties by using much less RE elements.
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