催化剂MnCe（y）Ox/TiO2的制备及其催化燃烧甲苯的活性

以TiO2为载体,采用浸渍法制备了不同配比的MnCe复合型催化剂,并采用X射线衍射(XRD)、氧气的程序升温脱附(O2-TPD)和氢气的程序升温还原(H2-TPR)对制备的催化剂进行表征,比较了催化剂催化氧化(燃烧)甲苯的活性。研究结果表明,所制备的催化剂MnCe(y)Ox/TiO2对甲苯有明显的催化活性。当Ce/(Mn+Ce)的摩尔比为0.1时,催化剂MnCe(0.1)Ox/TiO2的催化活性最高,甲苯的转化率达到90%时的温度为254℃。在催化剂MnOx/TiO2中掺杂少量的Ce元素,有利于活性组分Mn物种在载体表面上以更小颗粒而且更高的分散度存在,从而提高催化剂的催化活性。     

As-cast microstructures in U–Pu–Zr alloy fuel pins with 5–8 wt.% minor actinides and 0–1.5 wt% rare-earth elements

The Idaho National Laboratory (INL) is investigating U–Pu–Zr alloys with low concentrations of minor actinides (Np and Am) and rare-earth elements (La, Ce, Pr, and Nd) as possible nuclear fuels to be used to transmute minor actinides. Alloys with compositions 60U–20Pu–3Am–2Np–15Zr, 42U–30Pu–5Am–3Np–20Zr, 59U–20Pu–3Am–2Np–1RE–15Zr, 58.5U–20Pu–3Am–2Np–1.5RE–15Zr, 41U–30Pu–5Am–3Np–1RE–20Zr, and 40.5U–30Pu–5Am–3Np–1.5RE–20Zr (where numbers represent weight percents of each element and RE is a rare-earth alloy consisting of 6% La, 16% Pr, 25% Ce, and 53% Nd by weight) were arc-melted and vacuum cast as fuel pins approximately 4 mm in diameter. The as-cast pins were sectioned, polished, and examined by scanning electron microscopy. Each alloy contains high-Zr inclusions surrounded by a high-actinide matrix. Alloys with rare-earth elements also contain inclusions that are high in these elements. Within the matrix, concentrations of U and Zr vary inversely, while concentrations of Np and Pu appear approximately constant. Am occurs in the matrix and with some high-rare-earth inclusions, and occasionally as high-Am inclusions in samples without rare-earth elements.     

Energy transfers in the potential laser materials LMA:Ce,Nd and LMA:Cr,Ce, Nd (LMA = LaMgAl11O19)

Single crystals of LaMgAl₁₁O₁₉ (LMA) coactivated with Ce³⁺, Nd³⁺ or Ce³⁺, Cr³⁺, Nd³⁺, have been grown by the Verneuil (flame-fusion) method. In LMA:Ce, Nd the Ce → Nd energy transfer occurs both radiatively and non-radiatively. The efficiency of the non-radiative Ce → Nd transfer reaches ∼47%, as deduced from Ce³⁺ fluorescence lifetime measurements. In LMA:Ce, Cr, Nd, besides the Ce → Nd energy transfer, Ce → Cr and Cr → Nd transfers occur. The Ce → Cr energy transfer is highly efficient. This results from the good resonance between Ce emission and Cr absorption, and also from the short Ce-Cr distance compared to the longer Ce-Nd one.     

Behavior of fission products in the course of dissolution of simulated spent nuclear fuel in iron nitrate solutions and of recovery of uranium and plutonium from the resulting solutions

Experiments aimed to examine the spent nuclear fuel dissolution in iron(III) nitrate solutions and to elucidate the behavior of fission products in the process were performed with simulated fuel corresponding to spent nuclear fuel of a WWER-1000 reactor. In Fe(III) nitrate solutions, U is quantitatively transferred from the fuel together with Cs, Sr, Ba, Y, La, and Ce, whereas Mo, Tc, and Ru remain in the insoluble precipitate and do not pass into the solution, and Nd, Zr, and Pd pass into the solution to approximately 50%. The recovery of U or jointly U + Pu from the solution after the dissolution of oxide nuclear fuel is performed by precipitation of their peroxides, which allows efficient separation of actinides from residues of fission products and iron.     

Promoting the La solution in 2:14:1-type compound:Resultant chemical deviation and microstructural nanoheterogeneity

RE₂Fe₁₄B-based(RE,rare earth)permanent magnets containing abundant and cheap La/Ce have attracted intense attention recently.In comparison with Ce that can fully replace Nd in the 2:14:1 lattice,La substitution for Nd has long been limited at a low level.Here we present that through doping La35 Ce65 alloy with the La/Ce ratio in natural mineral,stable 2:14:1 phase can be maintained at 1273 K within the entire substitution range of[(La₃₅Ce₆₅)、(Pr₂₀Nd₈₀)_1-x]_2.14Fe₁₄B(0.6≤x≤1.0,at.%),as verified by composition analysis,microstructural characterization and magnetic measurements.Interestingly,the promoted La solution in 2:14:1 phase induces two unique findings upon coexisting La-Ce-Pr-Nd:i)Compared to Ce that fits well with the nominal concentration,La deviates noticeably from the nominal one;ii)Nanoscale spinodal-decomposition-like phase separation is observed due to different solubilities of La-Ce-Pr-Nd elements in 2:14:1 phase.Above joint effects induce higher Curie temperature than estimation based on the rule of mixture,which delights the prospect of La₃₅Ce₆₅alloy in developing low-cost permanent materials.     

The comparison of effects of four rare earth elements additions on structures and grain sizes of Ti-44Al alloy

By vacuum arc melting, four kinds of rare earth (RE) elements, Ce, La, Nd and Gd, were added in the range from 0.05% to 0.5% (mole fraction) to binary Ti-44% Al alloy to refine its grains of structures for high ductility. Effects of RE elements on structures and grain sizes of the alloy were investigated and compared. It was observed that Ce had the strongest effect on promoting growth of columnar colonies and Gd had the weakest one, while the other RE elements obviously promoted this growth in as-cast structures of the ingots. It was seen that the four RE elements initially reacted with oxygen to form oxides in the melt, the RE aluminides occur at boundaries during heat treatment, and sometimes the aluminide co-existed with oxide at boundaries or in grains. Results of measurement of grain sizes showed that the grains in the ingots heat-treated were effectively refined by properly adding the four RE elements, and the average grain size in the ingot with 0.15% Gd is finer and more uniform than that with Ce, La and Nd. The results of comparison verified that the sequence of effects of the four RE elements is Ce, La, Nd and Gd from strong to weak, which means that the alloy is sensitive to a small amount of Ce addition and is comparatively dull to a larger amount of Gd.     

Effect of Heat Treatment on Microstructure and Magnetic Properties of Ce-Doped NdFeB Ribbons

The substitution for Nd by abundant element cerium (Ce) is a practical way for the comprehensive utilization of rare earth resources in NdFeB permanent magnets. In this letter, we have prepared the Ce-doped NdFeB ribbons and conventional NdFeB ribbons by melt quenching method and investigated the effects of heat treatment on the crystallization behavior, microstructure, and magnetic properties of the alloy. The results show that: (1) The crystallization behavior and the microstructural changes of the (Nd,Ce)FeB magnets are similar to the conventional NdFeB magnet when heat treatment. In addition, the Ce₂Fe₁₄B phase has a significant effect on the properties of the whole magnets. (2)The NdFeB phase and CeFeB phase are relatively close to each other after being precipitated from the amorphous phase. The coupling effect between the two phases is strong enough to weaken the effect of the addition of Ce and making the properties of the NdFeB magnets to not reduce too much after adding Ce.     

EDTA-柠檬酸络合法制备(Ce0.8Y0.2-xNdxO1.9)0.99（ZnO）0.01电解质材料及其性能研究

采用EDTA-柠檬酸联合络合法制备了(Ce0.8Y0.2-xNdxO1.9)0.99(ZnO)0.01(0≤x≤0.2)系列电解质试样.通过热重、X射线衍射、扫描电镜、热膨胀测试和交流阻抗谱等方法对试样进行分析,着重研究了Y/Nd掺杂配比对CeO2基电解质材料电性能的影响.结果表明:采用EDTA-柠檬酸联合络合法制备的试样均为单一的立方萤石型结构;添加1mol%的ZnO,在1350℃下能得到较为致密的(Ce0.8Y0.2-xNdxO1.9)0.99(ZnO)0.01系列电解质陶瓷片,其中(Ce0.8Y0.05Nd0.15O1.9)0.99(ZnO)0.01电解质试样表现出最高的离子电导率,其在750℃测试时的离子电导率为58.79 mS/cm;所有试样的热膨胀系数在(11.83~12.30)×10 6/K之间.     

Research and development of Ce-containing Nd_2Fe_(14)B-type alloys and permanent magnetic materials

Much demanded and overused are the critical rare-earth elements such as Pr, Nd, Dy, and Tb with increasing need of Nd Fe B-type rare-earth permanent magnets in the enlarging application areas, developing new high-tech industries, and emerging cutting-age frontiers. The balance and efficient use of rare-earth resources comes into being the national strategy, national defense, and border safety for many major countries and regions in the world.(Nd,Ce)Fe B-based permanent magnetic materials, which can not only reduce cost but also offer a feasible way for integrated and effective utilization of rare earth resources,have received much attention in recent years. The existence of CeFe_2 and the mixed valence state of Ce in Ce Fe B compound, the different metallurgy behavior and the particular processing as well as potential various magnetic-hardening mechanisms, however, make it quite different from Nd-based alloys.For instance, the coercivity of Ce-containing magnets in some certain composition range, is even higher than that of the counterpart pure Nd-based magnets though the Ce-containing magnets possess inferior intrinsic properties. Consequently, it is very important to design proper composition and structure, optimize processing, and analyze the mechanisms in depth for this kind of magnet. High performance and cost-effective magnets can be fabricated if we can make full use of the composition's inhomogeneous and abnormal coercivity variation of the Ce-containing permanent magnets. In this paper, we have summarized the phase structures, magnetic properties and microstructures of(Nd,Ce)Fe B-based permanent magnetic materials to shed light on further research and development of this type of so-called "gap magnet".     

Leaching of Radioactive Waste Surrogates from a Glassy Matrix and Migration of the Leaching Products in Gneisses

Changes in the glassy matrix containing high-level waste surrogates after 24-h heating in an autoclave at 300°С with steam at 66% relative humidity were studied. Experiments were performed with an Na–Al–P glass sample containing Cs, Sr, Ce, Nd, and U. The effect of crystallization on the leaching of the elements from the glassy matrix and the form in which the waste surrogates are released into water were determined. The transport of the leaching products in a gneiss sample taken from the core of a borehole of the Yeniseiskii site of the Nizhnekansky massif was studied. REE and U occur in the solution after leaching mainly in the colloidal form. Colloidal particles of elements exhibit high mobility in migration in the rock.     

Effect of addition of elements on two-glass-forming ability of Zr–Ce–Co–Cu immiscible alloys

The effects of Al element addition and partial substitution of Ce with La, Pr, and Nd on the two-glass-forming ability of the phase-separating Zr–Ce–Co–Cu alloy system have been studied. The distribution of the additions in the two coexistent immiscible liquids was analysed thermodynamically. The results indicate that Al almost equally distributes in the two liquids, whereas the elements La, Pr, and Nd are predominantly found in the Ce–Cu-rich liquid. X-ray diffraction analysis reveals that these additions obviously enhance the two-glass-forming ability of the coexisting liquids. This work presents a strategy for improving the two-glass-forming ability of immiscible alloys to obtain phase-separated bulk metallic glasses.     

Electrical conduction in light rare-earth tungstates

This paper reports the results of electrical conductivity (σ) and thermoelectric power (H) of light rare-earth tungstates in the temperature range 600–1200K. Holes are the dominant charge carriers over the whole studied temperature range for Nd, Sm and Gd tungstates. However, in the case of La, Ce and Pr tungstates, the conduction is dominated by electrons at lower temperatures, but above 950K in La, 800K in Ce and 950K in Pr the dominant charge carriers become holes. A sharp break and change in the log σ vs 1/T slope occurs in La, Ce and Pr tungstates around the same temperature at which the dominant charge carrier changes from electrons to holes. In the case of Nd, the conductivity anomaly occurs around 1020K without any change in the nature of the charge carrier. The data have been analysed using band theory.     

Preparation,cristallogenese et caracterisation des bromures mixtes de lanthanide,de sodium et de cesium Cs2 NaLn (III) Br6

Single crystals of the new perovskites Cs₂Na Ln (III) Br₆ (with Ln (III) = Ce, Nd, Gd, Y) have been grown by the Bridgmann-Stockbarger method, using sealed silica-glass ampoules. They have been characterised by analytical and standard X-Ray methods; they crystallised with cubicface centered lattices, the parameters of which are: $\text{a}\text{= 11.508 - 11.421 - 11.370 - 11.304}\text{A}\text{?}$ for Ln = Ce - Nd - Gd - Y.     

Hydrogenation and Anisotropic Expansions in R3Fe29-xTx (R = Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

1.IntroductionIntensiveinvestigatiOnsontheR-Fe-T(R=rareearth,T=transitionmetalasastabilizingelement)phasediagrams,locatedattheironrichcorner,ledtothediscoveryofthenovelR2(Fe,T)l9phase[1l2]duetothegreatinterestinhighperfOrmanceper-manentmagneticmaterials.ItsrealstoichiometriccompOsitionandcrystallographicstructurewerede-terminedasaNd3(Fe,Ti)29-typestructurewithmon-oclinicsymmetry[3]andtheA2/mspacegrOup[4]byX-rnypowderdiffractiOn(XRD)andthenthiswasconfirmedbyneutrOnpOwderdiffraction[5'6…     

Efficient sorption of light rare-earth elements using resorcinol-formaldehyde polymeric resin

The sorption behavior of light rare-earth elements (La, Ce, Nd, Sm) on resorcinol-formaldehyde (RF) resin was studied. The effect of pH, shaking time, and temperature on the metal distribution coefficients was examined. The RF resin affinity for the examined lanthanides increases with a decrease in the ionic radius of the metal ion: Sm > Ce > Nd > La. The capacity of RF resins for the lanthanides shows the same trend. Because of the relatively high capacity of the resin, the presence of interfering ions affects the sorption percentage of the light REEs insignificantly. The thermodynamic functions of the sorption process were determined. They show that the adsorption of the light lanthanides on RF resin occurs spontaneously with the dehydrated metal ion.     

Oscillatory Extraction System with a Liquid Membrane for Separating REEs

A nonstationary oscillating system consisting of two extractors separated by a continuous liquid membrane is examined, including the effects of the pumping rate of the organic phase of the membrane and of the acid concentration. The time dependences of the enrichment factors of the aqueous and organic phases (Pr/Nd) are studied. The enrichment factor depends on the low-frequency oscillations of the redox potential (high-frequency oscillations were low-frequency-modulated). The HNO₃ concentration optimal for Nd - Pr separation is determined. The enrichment factor of the aqueous phase (Pr/Nd) increases with increasing rate of pumping of the liquid membrane between the extractors. The ¹⁴²Ce/¹⁴⁰Ce ratios in the aqueous phase of both extractors are measured.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 355–358.Original Russian Text Copyright © 2005 by Kopyrin, Baulin, Afonin.     

脉冲激光沉积生长单相的Nd_(1.85)Ce_(0.15)CuO_4薄膜及其激光感生热电电压效应

采用脉冲激光沉积(PLD)技术,在SrTiO3单晶衬底表面外延生长单相的1.85 Ce0.15 CuO4(NCCO)薄膜,并首次在斜切衬底上生长的NCCO薄膜中探测到激光感生热电电压(LITV)信号.实验研究表明,在低沉积温度、高沉积氧压和较大的激光脉冲重复频率下生长的NCCO薄膜中存在Nd1-xCexO<<1.75>,(NCO)杂相,是由于衬底表面吸附粒子扩散迁移困难所致;而高温下真空退火导致杂相的产生,则与NCCO的结构相变引起的热分解有关.通过提高沉积温度、降低沉积氧压和激光脉冲重复频率、并采用低温(T≤800℃)真空退火的方式,可以抑制杂相的形成.制备得到的单相的NCCO外延薄膜是一种新型的原子层热电堆材料,能量为1mJ的紫外脉冲激光的辐照,可以在倾斜的NCCO薄膜中诱导产生0.8V的LITV信号.     

Solid-state reactions of sintered commercial radwaste ceramics: I. Purex and magnox wastes without additives

The crystallochemical stabilization achieved in calcined radioactive wastes is dependent upon the elements present in the respective waste compositions. Equilibrium phases obtained by sintering both Purex and Magnox wastes are found to be very dependent on the Ce/Nd ratios. Although oxide additives may be used to stabilize the most leachable waste species, sintering experiments without waste additions demonstrate the relative roles of the lanthanon elements in determining the final equilibrium fluorite solid solution phases. The fluorite structured phases and tetragonal ZrO₂ were found to host U while Cs and Ru preferentially partition into scheelite and spinel structures, respectively. Volatilization experiments at higher temperatures determined the effective maximum fixation temperatures of given crystalline hosts.     

Effect of additions of Mn,Ce, Nd,and Si on rate of dissolution of splat quenched Mg–Al and Mg–Zn alloys in 3%NaCl solution

Abstract

Weight loss resulting from immersion in 3%NaCl solution buffered with Mg(OH)₂ has been determined for Mg alloy splats containing different levels of alloying with Zn or Al with and without ternary additions of Mn, Ce, Nd, and Si. The results show that additions of Zn increase the rate of dissolution, whereas an addition of 15 wt-%Al significantly reduces the dissolution rate. Ternary additions of Mn significantly reduce the dissolution rate of both Mg–Zn and Mg–Al alloys, whereas Ce and Nd reduce the dissolution rate of Mg–Al alloys. Additions of Si to Mg–Zn slightly increase the dissolution rate. These results are discussed in the context of other reported observations on the corrosion behaviour of rapidly solidified Mg alloys.

MST/I098     

Influence of lead oxide addition on LnTiTaO<Subscript>6</Subscript> (Ln = Ce,Pr and Nd) microwave ceramics

The effect of PbO addition on the structural, processing and microwave dielectric properties of LnTiTaO₆ (Ln = Ce, Pr and Nd) ceramics are reported. Conventional solid state ceramic route was used for the preparation of samples. Phase pure LnTiTaO₆ (Ln = Ce, Pr and Nd) ceramics are prepared at a calcination temperature of 1300°C. The samples are sintered at optimized temperatures. Addition of PbO reduces the sintering temperature. The crystal structure of the materials was analysed using X-ray diffraction techniques and the surface morphology of the sintered samples was analysed using scanning electron microscopy. The dielectric constant at microwave frequency range decreases for higher PbO addition for all the samples but the quality factor improves on small PbO addition. The thermal stability of resonant frequency was also improved with PbO addition on all the systems. A number of samples with improved microwave dielectric properties were obtained on all the systems suitable for practical applications.