First direct calculation of 4f‘ 4f oscillator strengths for dipolar electric transitions in PrCl3

In two previous papers, we interpreted completely the crystal field splitting and Zeeman data of trivalent praseodymium ions in PrCl₃ taking into account configuration interaction between 4f², 4f5d and 4f6p. The obtained eigenvectors are now used to calculate directly the oscillator strengths originating from dipolar electric processes between opposite parity configurations, giving rise to apparent 4f ‘4f transitions. The calculation reproduces in a satisfactory way the absorption from the ground levels toward the ³P₂ and ¹D₂ multiplets but not toward ³P₀ and ³P₁.     

High-Temperature Strength of High-Purity Aluminum Alloyed with Various Elements

A derivatographic method is used to study the high-temperature strength of aluminum with a purity of 99.9999% and its alloys with magnesium, scandium, gadolinium, holmium, barium, and strontium. The degree of oxidation of high-purity aluminum and its alloys is determined depending on the temperature and the hold time. It is shown that the high-temperature strength of aluminum depends on its purity. The heat fastness threshold of high-purity aluminum is 580°C as compared to 475°C of commercial-purity aluminum.     

过渡元素改善B4C/Al材料界面润湿性的机理研究

B₄C/Al复合材料是目前最理想的中子吸收材料,但工业上常用的液态搅拌法制备过程中存在着界面润湿性差的问题。本文结合实验及第一性原理的方法,通过研究Al(111)/AlB₂(0001)和Al(111)/TiB₂(0001)界面的结构来分析工业上添加过渡元素Ti对B₄C/Al界面润湿性的改善机制。通过计算发现,Al(111)/TiB₂(0001)界面相对Al(111)/AlB₂(0001)界面具有更高的粘附功值,说明其界面结合更强。进一步对比Ti掺杂二硼化物和AlB₂的偏态密度结构,发现Ti掺杂体具有较低的反键态,表明Ti-3d和B-2p轨道电子杂化后,在B、Ti原子间形成了较强的化学键,从而促进了Al(111)/TiB₂(0001)界面处的强结合作用,提高了Al(111)/TiB₂(0001)界面粘附功,故而改善了B₄C/Al界面的润湿性。根据同样的理论依据,V掺杂体也具有较低的反键态,V和B之间的强结合效果或许能够改善B₄C/Al界面的润湿性,成为又一理想的溶体改性掺杂元素。     

XPS spectra of the AFe4Al8 compounds with A=Y, Sc, U and Th

The XPS electronic structures of the AFe₄Al₈ (A=Sc, Y, U, Th) single crystals were measured. The valence band of UFe₄Al₈ exhibits domination of the U 5f states at the Fermi level, while for the other AFe₄Al₈ compounds the valence states are shifted by 0.5 eV toward higher binding energy. The multiplet structure of the U 4f and Th 4f states was analyzed in comparison with the U 4f states of U₃Ge₅ and UNiSb₂.     

A Numerical Model of Nitriding of a Gadolinium Specimen and Its Further Destruction during Storage

A numerical model of nitriding of an isotropic gadolinium specimen and its states during further storage under normal conditions (room temperature and atmospheric pressure) is developed. The model is implemented on the basis of the principles of thermoelasticity and mass transfer. The dynamics of distribution of nitrogen (N) and gadolinium nitride (GdN) in the specimen, which represents an additional phase formed during nitriding of the specimen, is considered. An algorithm of numerical solution of model equations is given.     

Crystalline and electronic structure of Pu–Ce and Pu–Ce–Ga alloys stabilized in the δ phase

In the actinides series (which corresponds to the progressive filling of the 5f sub-shell), plutonium lies at the changeover for the behavior of the 5f electrons between the light actinides (up to Np) with delocalized 5f states, and the heavy actinides (from Am on) with localized 5f states. At this boundary, the expanded δ-phase exhibits an intermediate and thus controversial behavior of its 5f electrons. This high temperature δ-phase can be stabilized at and below room temperature by alloying with so-called deltagen solutes Ga, Al, Ce and Am. In this work, some Pu–Ce and Pu–Ce–Ga alloys were studied using several techniques (dilatometry, X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy (EXAFS), electrical resistivity and magnetic susceptibility). It is found that the mechanism of δ-Pu stabilization is far from straightforward as both Pu 5f and Ce 4f electronic states are involved, inducing complex crystalline organization while no clear localization of the 5f states can be deduced from experimental results. Ternary Pu–Ce–Ga alloys show cooperative deltagen effects of Ce and Ga.     

Solid state reactions in highly dispersed praseodymium oxide–SiO2 system

This paper reports results of studies on the interaction of praseodymium oxide nanocrystals with an amorphous silica. Nano-sized (3–4 nm) amorphous precursor of praseodymium oxide synthesized using a microemulsion technique were supported onto a high surface SiO₂ or occluded into SiO₂ matrix. Solid state reactions occurring in these binary systems upon heat treatment in air, argon or hydrogen at 800–1100 °C were studied by TEM, XRD, FT-IR and UV–vis spectroscopy. It has been found that morphology of the sample as well as annealing atmosphere influence greatly the phase evolution. At temperatures above 900 °C, nanocrystalline praseodymium silicates of various morphology and crystal structure were obtained. In particular, a new polymorph of Pr₂Si₂O₇, isostructural with I-type Ln₂Si₂O₇ (Ln₆[Si₄O₁₃][SiO₄]₂) Ln = Ce, La, has been identified.     

不同冷速Ag-5Sc合金的凝固组织

采用感应熔炼钢模凝固、慢速平衡凝固、液态快速凝固制备Ag-5Sc二元合金。借助差示扫描量热仪(DSC)、金相显微镜、电子探针(EMPA)和X射线衍射仪(XRD)研究合金在不同冷速条件下的组织结构、钪的分布和形成的化合物相。结果表明,钢模凝固形成环状Ag4Sc相与共晶组织交替的环形层状组织结构,其它组织为致密细小的共晶组织。慢冷凝固是粗大的胞状共晶组织,胞状间存在块状Ag4Sc相。液态快冷凝固为呈细小蜂窝状结构,组织为等轴晶粒。钢模凝固环形和慢冷凝固块状Ag4Sc相中钪元素分布密度比共晶中的Ag4Sc相高,液态快冷合金中钪元素分布均匀。     

Extraction of scandium from red mud by modified activated carbon and kinetics study

Activated carbon （AC） was modified by tri-butyl phosphate （TBP） for selectively extracting scandium from red mud and characterized by BET （Brunauer-Emmett-Teller） surface area. The modified AC had a preferential adsorption to scandium. The influences of adsorbent dos- age, adsorption temperature, and time on adsorption capacity and selectivity to scandium were examined. An optimum adsorbent dosage （-6.25 g/L）, adsorption temperature （308 K）, and adsorption time （40 min） were figured out. A pseudo-second-order kinetics model was employed for describing the adsorption process of scandium.     

Effects of scandium and zirconium combination alloying on as-cast microstructure and mechanical properties of Al-4Cu-1.5Mg alloy

The influences of minor scandium and zirconium combination alloying on the as-cast microstructure and mechanical properties of Al-4Cu-1.5Mg alloy have been experimentally investigated.The experimental results show that when the minor elements of scandium and zirconium are simultaneously added into the Al-4Cu-1.5Mg alloy,the as-cast microstructure of the alloy is effectively modified and the grains of the alloy are greatly refined.The coarse dendrites in the microstructure of the alloy without Sc and Zr additions are refined to the uniform and fine equiaxed grains.As the additions of Sc and Zr are 0.4% and 0.2%,respectively,the tensile strength,yield strength and elongation of the alloy are relatively better,which are 275.0 MPa,176.0 MPa and 8.0% respectively.The tensile strength is increased by 55.3%,and the elongation is nearly raised three times,compared with those of the alloy without Sc and Zr additions.     

Partial oxidation of methane over bimetallic nickel–lanthanide oxides

The study of partial oxidation of methane (POM) over bimetallic nickel–lanthanide oxides was undertaken. Binary intermetallic compounds of the type LnNi (Ln = Pr, Gd, Lu) were used as bimetallic nickel–lanthanide oxides precursors and the products (NiO·Pr₂NiO₄, 2NiO·Gd₂O₃ and 2NiO·Lu₂O₃) were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, Raman and temperature programmed reduction. The catalytic activity increases when gadolinium or lutetium replaces praseodymium and the selectivity of the bimetallic nickel–lanthanide oxides is clearly different from that of single metal oxides and/or mechanical mixtures.The existence of an unusual synergism effect between the two metal oxide phases (NiO and Ln₂O₃) that lead to higher conversions of methane and higher selectivities to hydrogen and carbon monoxide correlate also the catalysts stability to deactivation. The activity and selectivity of the gadolinium and lutetium compounds is, under the same conditions, equivalent to that of a platinum commercial catalyst, 5 wt% Pt/Al₂O₃, which stresses the good catalytic performance of this new type of compounds for the production of H₂ and CO (H₂/CO = 2).     

Solvent Extraction off Scandium from Wolframite Residue

The particular properties of scandium make it an attractive candidate for recovery by solvent extraction—one of the most important processes in hydrometallurgy for the separation, purification and concentration of metal ions. Toward this end, an acid leaching and solvent extraction system has been developed and optimized to extract scandium from wolframite residue. With the technique, the scandium oxide content in the resultant scandium hydroxide can reach 70–78 percent. Further, the concentration coefficient and total recovery of scandium oxide from the residue to the product has amounted to (1.9–3.9) × 103 ³ and 76–89 percent, respectively. A mass balance is summarized in Tables I and II.     

Recovery of scandium from bauxite residue——red mud:a review

Red mud is a slimy caustic residue generated from alumina production. Taking into account the relatively considerable content and availability of scandium, red mud can be viewed as an important and promising scandium resource rather than a solid waste. This paper is primarily to review the investigations of scandium recovery from red mud based on the most widely used hydrometallurgical processes including acid leaching, solvent extraction and ion exchange adsorption. It is thought that recovery of scandium from red mud should be considered as a direct objective rather than a by-product in the development of overall flowsheet. In order to achieve environmentally-friendly processes with high scandium recovery and low cost, more attention is required to be paid to optimizing the selective leaching of scandium to decrease mineral acid consumption and alleviate pollution, and developing new solvent extraction systems and novel ion exchange adsorption materials with high selectivity and recognition for scandium.     

Spectroscopic properties of praseodymium-doped YVO4 crystal grown by the Czochralski technique

Optical absorption and emission spectra of YVO₄ crystal containing 1 at.% of praseodymium have been measured at 4.2 and 300 K. Absorption spectra recorded with polarised light at 4.2 K are found to be strongly inhomogeneously broadened but generally consistent with selection rules for D_2d local symmetry except for the ³H₄(1)−³F₂ transition.

Extensive vibronic side-bands of electronic lines corresponding to transitions from the ground ³H₄(1) state to the ³P₀ and ³P₁ states have been observed. Luminescence decay curves have been recorded at several temperatures between 4.2 and 300 K. Strong dependence of the ¹D₂ lifetime on sample temperature and lack of the ³P₀ emission at any temperature between 4.2 and 300 K has been discussed.     

A new model for prediction of dispersoid precipitation in aluminium alloys containing zirconium and scandium

A model has been developed to predict precipitation of ternary Al₃(Sc, Zr) dispersoids in aluminium alloys containing zirconium and scandium. The model is based on the classical numerical method of Kampmann and Wagner, extended to predict precipitation of a ternary phase. The model has been applied to the precipitation of dispersoids in scandium containing AA7050. The dispersoid precipitation kinetics and number density are predicted to be sensitive to the scandium concentration, whilst the dispersoid radius is not. The dispersoids are predicted to enrich in zirconium during precipitation. Coarsening has been investigated in detail and it has been predicted that a steady-state size distribution is only reached once coarsening is well advanced. The addition of scandium is predicted to eliminate the dispersoid free zones observed in scandium free 7050, greatly increasing recrystallization resistance.     

Improving mechanical properties of 2219 aluminium alloy GTA welds by scandium addition

Abstract

The effect of scandium additions to 2219 aluminium alloy weld metal has been investigated. At low levels (0·16%) of scandium, in spite of grain refinement in the weld metal, improvement in the mechanical properties has been nominal. At higher levels of scandium (0·37%), a substantial improvement in the tensile properties has been obtained. Further improvement in mechanical properties has been achieved by adding small amounts of magnesium. Transmission electron microscopy revealed the presence of fine precipitate particles in the scandium containing weld metals. Electron probe microanalysis (EPMA) and SEM–EDX revealed extensive copper segregation to grain and subgrain boundaries. The presence of scandium reduces the severity of segregation by producing fine equiaxed grains in the weld metals and also by refining the grain substructure. The morphology and size of the high copper eutectic phase at grain boundaries and sub-boundaries have been found to be finer and well distributed in the case of scandium containing weld metals. EPMA linescans and quantitative analyses proved that the depletion of copper in the matrix is minimised as a result of the fine grained structure.     

Scandium-alloyed aluminum alloys

Conclusion The basic principles of alloying of aluminum alloys with scandium are: it is desirable to add scandium to aluminum alloys in a quantity from 0.1 to 0.3% together with zirconium (0.05–0.15%), which strengthens the positive influence of scandium on the structure and properties of alloys;the greatest effect (that is, the positive influence on mechanical properties and other characteristics) from addition of scandium together with zirconium is observed for alloys not containing alloy elements combining scandium in insoluble phases, specifically the Al–Mg, Al–Zn–Mg, and Al–Mg–Li systems;with a limited copper content alloying with scandium together with zirconium of Al–Zn–Mg–Cu and Al–Cu–Li system alloys is possible.At present on the basis of or taking into consideration the principles developed of alloying of aluminum alloys with scandium commercial aluminum alloys based on the Al–Mg–Sc–Sr (01570, 01571, 01523, 01505), Al–Zn–Mg–Sc–Zr (01970, 01975), and Al–Li–Mg–Sc–Zr (10421, 01423) systems have been developed.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 24–28, January, 1992.     

Effect of scandium, transition metals, and admixtures on strengthening of aluminum alloys due to decomposition of the solid solution

Strengthening of aluminum alloys of the Al-Sc system in ingots due to decomposition of the solid solution of scandium in aluminum is studied as a function of the content of scandium (varied from 0.14 to 0.55%), of the presence of Zr, Ti, Hf, V, and Co additives at the same content of scandium (0.2%), of the Sc/Zr proportion at the same total content of Sc + Zr, and as a function of iron and silicon admixtures.     

Ce_(1-x)Pr_xO_2固溶体的低温燃烧合成及表征

以Ce(NO_3)_3·6H_2O和Pr_6O_(11)为主要原料,C_6H_8O_7为燃烧剂,采用低温燃烧法合成了Ce_(1-x)Pr_xO_2(x=0～0.15)系列纳米晶红色颜料.用激光Raman光谱、XPS及色度测试等手段对样品的氧空位浓度、Pr、Ce离子在固溶体中的价态以及样品的红度和色饱和度进行分析.结果表明:随着Pr掺杂量的增加,固溶体的氧空位浓度一致增大;Ce_(1-x)Pr_xO_2固溶体中Ce的价态为+4价,Pr离子以+3价的形式存在;样品的红度、色饱和度随Pr含量的增加呈先增后减趋势,当x=0.05时有最佳的呈色性能.     

Scandium Recovery from Uranium Solutions

The commercial recovery of scandium as a by-product of uranium extraction is described. A flouride strip system was developed to recover scandium from the solvent in concentrated form, and high purity scandium oxide was prepared in multi-pound lots by chemical separation techniques.