Effect of Rare Earth Elements on Exchange Performances of Cesium Ion-Sieve

The exchange performances and the distribution coefficient of Cesium Ion-Sieve (Cs-IS) for cesium and for some rare earth elements were compared. In particular, the effects of neodymium on the cesium ion exchange and the Cs^ selectivity variation on Cs-IS owing to introduction of rare earth elements into HLLW were studied. Though rare earth elements exhibit a small influence on the distribution coefficient for Cs^ ,they impair Cs-exchange capacity of Cs-IS to some extent. This interruption on the selectivity to Cs^ can be significantly eliminated provided an appropriate ratio of liquid to solid V: m is used.     

STUDY ON THE EXCITATION BEHAVIOUR OF RARE EARTH ELEMENTS IN DC ARC BY AXIAL-INTRODUCTION OF AEROSOL

In order to eliminate influence of the carriers on the evaporation of rare earth elements in DC arc,a de-vice which introduces axially the sample aerosol has been designed to study the effects of controlled-atmos-phere,discharge current,electrode polarity and introduction direction of aerosol on the emission of rare earthelements in DC arc discharge.The influence of various matrices and carriers on the line density and excitationcondition of rare earth elements have also been studied,then the related excitation mechnism is proposed.     

Effects of Heavy Rare Earth Elements on Properties ofAmorphous NiB Alloy Catalyst

Gas-phase hydrogenation of benzene was selected as probe reaction to study the effects of heavy rare earth ele-ments on the catalytic activity and sulfur resistance of amorphous NiB alloy. XRD, DSC, CO chemical adsorption, TPR and TPD were used to characterize the bulk and the surface properties of the alloys, respectively. The results indicate that the addition of a small amount of heavy rare earth (HRE) elements obviously improves the activity, thermal stability and sulfur resistance of amorphous NiB alloy. The HRE can alter H2 adsorption bond strength, increase the surface area of ac-tive nickel and the number of active centers over the surface of NiB alloy and it also can decrease the activation energy of NiB alloy for benzene hydrogenation. There are four kinds of adsorbing sites over the surface of NiB and NiBRE, only three kinds of them have concerned with the reaction.     

Mechanism of Thermal Decomposition of Rare Earth Acetate Hydrates

The mechanism of thermal decomposition of rare earth acetate hydrates(Ln(Ac)_3·nH_2O,n=5,forLn=La;n=4,for Ln=Pr→Lu,Y,except Pm)has been studied by TG-DTG,DSC,infrared spectra,X-raydiffraction and chemical analysis.The thermal decomposition reaction consists of two stages,one is dehydrationand the other one is decompostion.The final product is oxide.It has been found that the temperature of pro-ducing anhydrous acetates decreases with increasing atomic number of rare earth elements.The activation ener-gies for dehydration and decomposition reaction of rare earth acetate hydrates have been calculated byFreeman-Carroll and Kissinger method.The dependence of activation energy Jor dehydration reaction on theatomic number of rare earth elements shows“inclined‘W’effect”.The enthalpy changes for dehydration anddecomposition reaction have been determined.     

Influence of Rare Earth Elements on Luminescent Properties of Y2SiO5 ： Tb

Photoluminescent （PL） and cathodoluminescent （CL） properties of rare earths （Sc^3＋ , La^3＋ , Gd^3＋ and Lu^3＋ ） doped （Y0.97Tb0.03）2SiO5 were studied. Rare earth doping clearly influences PL and CL properties of Y2SiO5 ： Tb. For La^3＋ doped system, PL intensity increases nearly 10 % at x = 0.05 whereas for Lu^3＋ doped system, the intensity increases about 20% at x = 0.20. Gd^3 ＋ doping and Sc^3＋ doping reduce the intensity; at x = 0.3, it is reduced about 30% for Gd^3＋ doped system and about 15 % for Sc^3＋ doped system, respectively. Quenching concentration of activator became higher in rare earth doped samples, which may be understood by that the rare earth dopants might dilute the concentration of the activator. Additionally, doping also influences the color saturation of Y2SiO5 ： Tb. Sc^3＋ , La^3＋ , and Gd^3 doping improve the color saturation, whereas Lu^3＋ doping decreases the color saturation. CL measurements show that CL intensity increases for all rare earths doped systems. The energy transfer from Gd^3＋ to Tb^3＋ was discussed.     

Influence of Light Rare Earth on Toughness of Welded Seam of LAHS Steel

The influence mechanism of light rare earth elements, which are transited to the welding seam of low-alloy high strength (LAHS) steel through the covering of the electrode, on the toughness of the welding seam was studied. The experimental results show that proper amount of rare earth elements can desulfurate, dehydrogenate, reduce inclusions and purify the structure of the welding seam. Rare earth element additions have .the effect on welding seam and, at the same time, the transformation of side-batten ferrite is resisted while the pin-ferrite structure is promoted. The improvement of the toughness of the welding seam is due to the purifying action of rare earth elements as well as their refining effect on the structure. However, the toughness of the welding seam can decrease when the amount of light rare earth elements are added excessively because the crystal grains become coarser, porosities appear and the inclusions increase as well. The experimental results show that the suitable amount of light rare earth element additions is about 2%.     

Effect of Rare Earth Elements on Isothermal Transformation and Microstructures in 20Mn Steel

The effect of rare earth elements on the isothermal transformation and microstructures in 20Mn steel is in-vestigated by means of metallography and dilatometry.Rare earth elements decrease both the incubation periodof pro-eutectoid ferrite and the rate of pearlitic transformation.In addition,rare earth elements play a role ofreducing needle-like ferrite and the amount of pearlite,densifing the lamellar space of pearlite and enhcingsegregation of carbide in granular bainite.It is suggested that rare earth elements may decrease the interfacialenergy of grain boundary and interphase,hinder the diffusion of carbon atoms and form rare earth carbides withhigh melting point which reduce the carbon content in austenite.     

Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Cast High-Speed Steel Rolls

The influence of rare earth （RE） elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry （DSC） and scanning electron microscopy energy dispersive spectrometry （SEM-EDS）. The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing longpole M C carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.     

Effect of Rare Earth Metals on Structure and Properties of Electroless Co-B Alloy Coating

The effect of rare earth metals cerium, lanthanum and yttrium on chemical composition, structure and properties of electroless Co-B alloy coating was studied. By plasma transmitting spectrograph, electron energy spectrometer, X-ray diffractometter, miero-hardometer and vibratory- sample magnetometer the chemical constitution,structure and properties of the alloy coatings were analyzed and inspected. The results show that with a tiny quantity of rare earth metal added into Co-B alloy coating, the content of boron is decreased in the alloy coatings, and the kinds of rare earth metal have enormous effect on the structure and properties of electroless Co-B alloy coating. At the same time electroless Co-B alloy with amorphous structure is transformed to electroless Co-B-RE alloy with microcrystalline or crystalline structure. In this way microhardness of the coatings is increased remarkably. Cerium and lanthanum would also increase the saturated magnetic intensity and decrease coercitive force of the coating. So soft magnetization of the coatings would be improved.     

STUDY ON THE SEPARATION AND EXTRACTION MECHANISM OF RARE EARTH ELEMENTS BY MEANS OF REVERSED-PHASE PAPER CHROMATOGRAPHY

Reversed-phase paper chromatography technique is used for study on the extraction mechanism and sep-aration of rare earth elements.As the stationary phase,chromatographic paper strips are impregnated with asolution of monomyristyl phosphoric acid (MPA) in chloroform.Mineral acids are used as developers.The effect of concentration of acids and/or salts upon R_f has been investigated.According to the re-sults of R_f values for a given rare earth element in various acids,the order of extraction ability isHCl>HNO_3>H_2SO_4.A tetrad effect is clearly observed.for the R_f value of rare earth elements.Theeffects of other parameters on the R_f value,such as the quantities of extractant retained by the paper and thetemperature are also examined.Based on the determination of the molar ratio of MPA to rare earth elementsand the number of H~ ions released in extraction reaction,a reasonable mechanism is proposed.The mutualseparation of heavy rare earth elements will be better than that of the light rare earth group because of thelarger separation coefficient of the former.A mixture of Ho-Er-Tm-Lu is successfully separated by thepresent method.     

The use of computational thermodynamic for yttrium recovery from rare earth elements-bearing residue

The rare earth elements are considered critical metals,due to the risk of supply interruption.The recycling of waste electrical and electronic equipment can be an alternative to supply the rare earth market.Several processes have been developed,and by aqueous media is the most prominent,which makes possible the extraction and separation of elements even in low concentration(traces).As an example of thermal processing,the use of thermodynamic simulations might benefit the metal extraction in hydrometallurgical processing.For this reason,the goal of this work is to evaluate the use of FactSage 7.2 software for the leaching of fluorescent lamp powders by sulfuric acid.The effect of concentration and temperature was evaluated.Results comprise that the thermodynamic software wellpredicted the solid phase formed in all residues of leaching experiments-gypsum was predicted by the software and identified in XRD analyses.It demonstrates that FactSage software can be explored for metals extraction in aqueous media,being important for trace-elements extraction.Yttrium extraction reaches up to 95%at 45℃using H₂SO₄2 mol/L.     

Modification Mechanism of Rare Earth Elements in ZA27 Casting Alloys

The model of the liquid-phase ZA27 alloys was set up by molecular dynamics theory. The atomic structure of phase, RE-compounds, and the phase-liquid interface in ZA27 alloys were constructed by computer programming. Electronic structures of phase with rare earth elements dissolved and of phase-liquid interfaces with rare earth elements enrichment in ZA27 casting alloys were investigated by using the Recursion method. The ESE energy of RE elements and the structure energy of RE-compounds, phase, and the liquid-phase ZA27 alloys were calculated. The results show that rare earth elements are more stable to be in the phase interface than in phase, which explains the fact of very small solid solubility of rare earth elements in phase, and the enrichment in the solid-liquid growth front. This makes dendrite melt and break down, dissociate and propagate. RE-compounds can act as heterogeneous nuclei for phase, leading to phase refinement. All above elucidates the modification mechanism of rare earth elements in zinc-aluminum casting alloys, at electronic level.     

Phase Behavior and Crystal Structure of Perovskite-Type Rare Earth Complex Oxides

Several compounds of rare earth complex oxides containing manganese and titanium were synthesized in Ar, and their crystal structures were analyzed by powder X-ray diffraction data and Rietveld method. Structures of A0.67Ln0.33 Mn0.33Ti0.6703（A = Ca or Sr and Ln = rare earth） were found to have orthorhombic symmetry with the space group Pnrna, and their interatomic distances and bond angles were obtained. This space group was also derived from electron microscopic study. Electrical conductivity of Cao.67Ln0.33Mn0.33Ti0.6703 for several rare earth elements showed a semiconducting property with the activation energy of 0.4 eV. Some of these compounds of the strontium system show the antiferromagnetic properties below 10 K.     

A novel blue-purple Ce~(3+) doped whitlockite phosphor:Synthesis,crystal structure,and photoluminescence properties

At present,the rare earth(RE) ions doped phosphors have attracted more and more attention because of their excellent properties.In this paper,a series of novel blue-purple β-Ca_3(PO_4)_2:Ce~(3+) phosphors were synthesized by a high temperature solid phase method.The X-ray diffraction(XRD),infrared spectrum,energy dispersive spectroscopy(EDS),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),photoluminescence excitation and emission spectra were used to investigate the crystal structure,composition and the luminescent properties of the resulting samples.The phosphor shows a strong absorption in the ultraviolet band.Under the excitation of 269 nm,the phosphor emits a strong purple fluorescence ranging from 360 to 520 nm.When Ce~(3+) doping content is 0.07 mol,the strongest luminescence intensity is reached,and the concentration quenching mechanism is dipole-dipole(d-d)interaction for Ce~(3+) based on Dexter theory.     

Alleviation Effects of Rare Earth on Cd Stress to Rape

Using rapes as test materials, the fastness expression and alleviation effect of rapes were studied under Cd stress condition, as the rapeseeds were dipped in the single element( La, Ce, Nd, Pr)and mixed rare earth (RE). The results indicate that, under Cd stress, the dry and fresh weight are increased by both the single element and mixed rare earth treatment, and the fastness of rape is improved. The single element of rare earth decreases the Cd content in rape roots and transmits Cd to the edible parts above the ground in which the alleviation effect of Ce is most significant. La treatment takes the second place, so that the poisonous effect of heavy metal Cd is eased. The mixed rare earth doesnt alleviate the assimilation of Cd in rape roots, but accelerates the transfer of Cd to the parts above the ground. The research puts forward that the alleviation of rare earth on Cd stress has connection with the decrease of Ca content.     

Effects of Polar Organic Solvent on Separation of Y （edta）^-／Nd （edta）^- Complexes on Polyacrylic Anion Exchangers

The use of polar organic solvents for the separations of rare earth elements ( Ⅲ ) is effective especially for their extensive separations despite the solubility limitations.The study shows that polyaerylate anion exchangers, particularly the weakly basic, gel anion exchanger Ambedite IRA 68,can be applied to the separation of rare earth complexes with EDTA in H20-metthanol and H20-ethanol systems.In most cases the determined distribution coefficients of Ln^3 complexes with EDTA in mixed media like water-methanol on polyacrylate anion exchangers are larger than those in pure water media.     

Formation of intermetallic compound at interface between rare earth elements and ferritic-martensitic steel by fuel cladding chemical interaction

The intermetallic compounds formation at interface between rare earth elements and clad material were investigated to demonstrate the effects of rare earth elements on fuel-cladding chemical interaction(FCCI)behavior.Mischmetal(70Ce-30La)and Nd were prepared as rare earth elements.Diffusion couple testing was performed on the rare earth elements and cladding(9Cr2W steel)near the operation temperature of(sodium-cooled fast reactor)SFR fuel.The performance of a diffusion barrier consisting of Zr and V metallic foil against the rare earth elements was also evaluated.Our results showed that Ce and Nd in the rare earth elements and Fe in the clad material interdiffused and reacted to form intermetallic species according to the parabolic rate law,describing the migration of the rare earth element.The diffusion of Fe limited the reaction progress such that the entire process was governed by the cubic rate law.Rare earth materials could be used as a surrogate for high burnup metallic fuels,and the performance of the barrier material was demonstrated to be effective.     

Review on catalytic roles of rare earth elements in ammonia synthesis:Development and perspective

Ammonia(NH3)is mainly produced via the Haber-Bosch process.It was discovered that the performance of a wide variety of catalysts in NH3 synthesis could be considerably enhanced by the addition of rare earth elements(REEs).As a result,catalysts promoted by REEs,especially the Ru-based ones have been extensively investigated.In this review,we summarize the progress of utilizing REEs for ammonia synthesis and outline the prospects of using them in the design and development of highly efficient and stable catalysts for ammonia synthesis.     

Effect of Rare Earth Oxides on Catalysts Mo-Te System

Surface compositions,structures,and acidities of the Mo-Te-Fe-Ni catalysts added with La_2O_3,CeO_2,Pr_6O_(12),Nd_2O_3 and Sm_2O_3 were measured and related with the activities of the catalysts for selective oxidationof olefins.It was found that adding rare earth elements to the Mo-Te catalysts increases obviously theirselectivities to methacrolein(MAL),and the yield percentage of MAL changes periodically with the increase ofatomic numbers of rare earth elements added,and the highest yield was obtained with the catalyst containingCeO_2.The addition of CeO_2 to 9-component Mo-Te catalyst increases not only the activity of the catalyst,but also its thermostability remarkably.The mechanism of rare earth elements in the catalysts was discussed.     

Recent progress in synthesis of lanthanide-based persistent luminescence nanoparticles

Persistent luminescence nanoparticles(PLNPs) are a kind of phosphors that can remain luminescent for seconds to several days after the stoppage of excitation.Lanthanides show the special capability to largely broaden the emission range and enhance the luminescence intensity of PLNPs due to their dense energy structure and unique electronic configurations.In the past decades,various methods have been developed for the synthesis of lanthanide-based PLNPs with excellent pe rsistent luminescence pro...