Showing papers on "Lanthanum published in 1996"
TL;DR: In this article, thin films of yttrium and lanthanum with a layer of palladium through which hydrogen can diffuse are used to simulate metal-to-insulator transitions.
Abstract: IN many substances, changes in chemical composition, pressure or temperature can induce metal-to-insulator transitions1. Although dramatic changes in optical and electrical properties accompany such transitions, their interpretation is often complicated by attendant changes in crystallographic structure2. Yttrium, lanthanum and the trivalent rare-earth elements form hydrides that also exhibit metal–insulator transitions3–5, but the extreme reactivity and fragility of these materials hinder experimental studies5,6. To overcome these difficulties, we have coated thin films of yttrium and lanthanum with a layer of palladium through which hydrogen can diffuse. Real-time transitions from metallic (YH2 or LaH2) to semiconducting (YH3 or LaH3) behaviour occur in these films during continuous absorption of hydrogen, accompanied by pronounced changes in their optical properties. Although the timescale on which this transition occurs is at present rather slow (a few seconds), there appears to be considerable scope for improvement through the choice of rare-earth element and by adopting electrochemical means for driving the transition. In view of the spectacular changes in optical properties—yttrium hydride, for example, changes from a shiny mirror to a yellow, transparent window—metal hydrides might find important technological applications.
791 citations
TL;DR: A lanthanum-impregnated silica gel has been developed for the removal of fluoride, phosphate, and arsenate ions by adsorption as discussed by the authors, which was applied for removing these anions from synthetic and high-tech industrial wastewaters.
Abstract: A lanthanum-impregnated silica gel has been developed for the removal of fluoride, phosphate, and arsenate ions by adsorption The interaction between silica gel and lanthanum ion was maximum at a final pH of 6 The removal of fluoride and arsenate ions by adsorption on the lanthanum-impregnated silica gel was more than 99 9% at neutral pH from initial concentration of 055 and 02 mmol/L, respectively The removal of phosphate ion was 95% at an initial concentration of 05 mmol/L at neutral pH Arsenite ion was not adsorbed on the material The rate of adsorption of the anions followed the first-order reaction and fit in the Lagergren equation The adsorption of each anion followed the Langmuir isotherm Other anions such as Cl{sup -}, BR{sup -}, I{sup -}, NO{sub 3}{sup -}, and SO{sub 4}{sup 2-} did not interfere with the adsorption A column study was conducted for the removal of these anions at a fixed flow rate of 05 mL/min at pH approximately 7 These anions were removed by more than 999% at initial first or second fraction, and the column was regenerated at pH 85 The method was applied for the removal of these anions from synthetic and high-tech industrial wastewatersmore » 30 refs, 8 figs, 1 tab« less
217 citations
TL;DR: In this article, the luminescence of Eu3+ in two monazite-type orthophosphates: La0.98Eu0.02PO4 and EuPO4 is investigated by site-selective time-resolved spectroscopy.
137 citations
TL;DR: In this article, the authors measured the tracer diffusion coefficient of strontium-doped lanthanum manganites, La 1 − xSrxMnO3 ± δ (x = 0.05, 0.10,0.15 and 0.20) as a function of composition, temperature and oxygen partial pressure.
119 citations
TL;DR: In this paper, single cells with doped lanthanum gallate electrolyte material were constructed and tested from 600 to 800°C, and the results clearly indicate that anode overpotential is the dominant factor in the power loss of the cells.
114 citations
TL;DR: In this paper, the lattice expansion phase stability, and dimensional stability of doped lanthanum chromites have been examined over a wide range of temperatures and oxygen partial pressures, and it was shown that additional doping with aliovalent B-site additives significantly reduced lattice expand in reducing environments.
Abstract: Lattice expansion phase stability, and dimensional stability of doped lanthanum chromites have been examined over a wide range of temperatures and oxygen partial pressures. Reduction of doped lanthanum chromite resulted in a linear expansion of the sample that was dependent on the acceptor (Sr, Ca) concentration, temperature, oxygen partial pressure, and oxygen content within the sample. Additional doping with aliovalent B-site additives significantly reduced lattice expansion in reducing environments. The lattice expansion in reducing environments was directly related to the loss of lattice oxygen and the simultaneous reduction of Cr{sup 4+} to Cr{sup 3+} to maintain electroneutrality.
109 citations
TL;DR: In this article, modified zeolites were found to be active catalysts in the Friedel-Crafts acylation of anisole by acetyl chloride and acetic anhydride.
Abstract: Modified zeolites were found to be active catalysts in the Friedel-Crafts acylation of anisole by acetyl chloride and acetic anhydride. The effect of two different modifications of the zeolites were tested; lanthanum-exchange and varying the Si Al ratio. For the rare-earth modified zeolites, the activity was found to be dependent on the lanthanum content, and the yield increased with the level of lanthanum even up to 93% exchange. Dealuminated Y-zeolites were also found to be very active, and an almost linear increase in the yield with decreasing aluminium fraction was found. This has been attributed to the increased hydrophobicity of dealuminated zeolites. Zeolite Beta was also found to be very active in the reaction.
78 citations
TL;DR: In this paper, the activity coefficients of neodymium and neptunium were estimated as 10−12.85 and 10−7.43 respectively from the standard potentials in LiCl-KCl eutectic molten salt and the distribution coefficients in the LiClKCl/bismuth system.
73 citations
TL;DR: In this paper, it was shown that Gd(BO 2 ) 2 is an excellent host lattice to obtain efficient VUV excited photoluminescent materials at room temperature.
Abstract: It is shown that Gd(BO 2 ) 2 is an excellent host lattice to obtain efficient VUV excited photoluminescent materials at room temperature. The introduction of Gd 3+ ions in the lanthanum metaborate host lattice increases both the ionicity of the metal-ligand bonding and the energy transfer rate between the host and the activator.
67 citations
TL;DR: In this article, the thermal properties of tetragonal oxide nitrate have been reconsidered using temperature-dependent X-ray powder diffraction and thermogravimetric analysis.
64 citations
TL;DR: Under optimised experimental conditions solvent extraction investigations showed the calix[4]arene ligand L exhibited generally very high percentage extractabilities of lanthanide cations into dichloromethane, presumably on account of the ligand's unique lower rim oxygen containing coordination sphere and its lipophilic exterior.
Abstract: The synthesis and structure determinations of lanthanum, samarium, ytterbium, and lutetium complexes of 5,11,17,23-tetra-tert-butyl-25,27-bis((diethylcarbamoyl)methoxy)-26,28-dihydroxycalix[4]arene (L) are described. The four structures display similar characteristics with the trivalent lanthanide cation being encapsulated in an eight-coordinate oxygen environment, consisting of six oxygens from the calixarene, a water molecule, and unidentate picrate for lanthanum [La(L-2H)(picrate)(H(2)O)]; and bidentate chelating picrate for the other lanthanides [Ln(L-2H)(picrate)]Ln = Sm, Yb, Lu. Under optimised experimental conditions solvent extraction investigations showed the calix[4]arene ligand L exhibited generally very high percentage extractabilities of lanthanide cations into dichloromethane, presumably on account of the ligand's unique lower rim oxygen containing coordination sphere and its lipophilic exterior.
TL;DR: The complexes examined in this study have advantages over those used in prior studies since they do not require surfactants to achieve low limits of detection, and they exhibit longer linear dynamic ranges than other columinescent systems.
Abstract: The luminescence intensity of trivalent lanthanides, especially terbium(III) and europium(III), is shown to be enhanced by coordination with the ligand 2,6-pyridinedicarboxylic acid (DPA). Further enhancement can be obtained by forming a columinescent complex aggregate with ions such as gadolinium(III), terbium(III), lanthanum(III), or yttrium(III), where the Y(III) complex shows the greatest enhancement. A surfactant, sodium dodecyl sulfate (SDS), can be added to the solution to enhance the luminescence intensity of many lanthanide−ligand complexes by segregating the complex from quenchers. In this study, SDS has little effect on the limit of detection, but it does act to extend the linear dynamic range to include higher concentrations. The combination of columinescent complex with surfactant resulted in decreased luminescence intensity coupled with an increase in the background due to the light scattered by the surfactant micelles. A mechanism for the enhancement of the lanthanide luminescent intensity ...
TL;DR: In this article, the perovskite structure of Lanthanum strontium cobalt iron oxides was synthesized using citrate and glycine complexation methods, and the cubic phase was identified as a perovsite, La 0.6 Sr 0.4 − x Co 0.2 Fe 0.8 O 3 − δ, with a large degree of Strontium deficiency ( x = 0.20 to 0.25).
TL;DR: In this article, the development of a solvent-extraction process for the recovery of magnet-grade neodymium oxide (95% Nd 2 O 3 ) from a light rare earth nitrate liquor is described.
TL;DR: The synthesis and X-ray structure of the novel polymeric lanthanum(III) oxydiacetate complex [La2(C4H4O5)3(H2O)3·5H 2O]n (1) is reported in this article.
Abstract: The synthesis and X-ray structure of the novel polymeric lanthanum(III) oxydiacetate complex [La2(C4H4O5)3(H2O)3·5H2O]n (1) is reported. One metal ion is coordinated to three tridentate oxydiacetate ligands, the other, to six outer carboxylate oxygens and three oxygens from metal-bound water molecules. The crystal structure of 1 shows it to be a three-dimensional polymer where the lanthanum centers are bridged by the carboxylate groups of the oxydiacetate ligands. Upon thermolysis 1 is converted into hexagonal La2O3.
TL;DR: The catalytic behavior for styrene hydrogenation of two series of La-promoted nickel/sepiolite catalysts (xLaNi and NixLa) is reported in this paper.
TL;DR: A series of palladium-substituted La2CuO4, corresponding to the formula La 2Cu1 −xPdxO4 (x = 0−0.2) were prepared by metal nitrate decomposition in a polyacrylamide gel as discussed by the authors.
Abstract: A series of palladium-substituted La2CuO4, corresponding to the formula La2Cu1 −xPdxO4 (x = 0−0.2) were prepared by metal nitrate decomposition in a polyacrylamide gel. This method allows an easy incorporation of palladium in the mixed-oxides, which are formed at moderate temperature with rather high specific areas (13–17 m2/g). The partial substitution of copper for palladium allows a strong improvement of the three-way catalytic activity, in particular for NO reduction. The light-off temperatures for the conversions of CO, NO and C3H6 decreased markedly when increasing the palladium content, the activity of catalysts La2Cu0.9Pd0.1O4 and La2Cu0.8Pd0.2O4 being comparable to that of a Pt-Rh/CeO2–Al2O3 catalyst for NO reduction, and higher for CO and C3H6 oxidation.
All the La2Cu1 − x PdxO4 catalysts are activated under reacting conditions. This activation corresponds to the destruction of the mixed-oxide structure, with formation of reduced Pd0 ions atomically dispersed, surrounded by Cu+ and Cu2+ species on a lanthanum oxycarbonate matrix. This high dispersion state of the two transition metals in various oxidation states is supposed to originate from the initial La2Cu1 −xPdxO4 structure.
TL;DR: In this article, the differing marine chemical behaviors of some trivalent elements are compared on the bases of their crustal rock concentrations and of those in various marine compartments, and the rare earth elements, lanthanum, samarium and lutetium show behaviors intermediate between those of rhodium and bismuth.
TL;DR: In this article, the lattice parameters, atom positions and bond lengths determined from X-ray powder diffraction show that Lanthanum chromate (LaCrO4) forms a monazite-type crystal structure.
Abstract: Lanthanum chromate (LaCrO4) was synthesized as a low temperature ( < 700 °C) intermediate to perovskite-type, lanthanum chromite (LaCrO3). The lattice parameters, atom positions and bond lengths determined from X-ray powder diffraction show that LaCrO4 forms a monazite-type crystal structure. Lanthanum chromate forms a solid solution with Ca, having a solubility between 10 and 20 at%. Thermal analysis shows that at ambient oxygen pressure, LaCrO4 transforms to LaCrO3 at a temperature near 700 °C. It also indicates that (La,Ca)CrO4 initially transforms to LaCrO3 and CaCrO4 with the subsequent formation of a (La,Ca)CrO3 solid solution. Evidence of Ca segregation to the surface of (La,Ca) CrO3 particles is given by Auger electron spectroscopy and scanning electron microscopy.[/p]
TL;DR: In this paper, the synthesis conditions for which dispersed spherical particles and plates may be formed of lanthanum, the lightest of the lanthanide elements are given in the form of morphological diagrams and the chemistry and yield of the process is also reported.
Abstract: The synthesis of lanthanide oxide precursor particles through urea decomposition has received considerable attention over the past few years It was previously reported by several different workers that the synthesis of spherical, monodispersed light lanthanide ceramic precursor particles was consideably more difficult than the precipitation of spherical particles from the heavy lanthanide elements These difficulties have been overcome to a large extent by proper choice of processing conditions This paper describes the synthesis conditions for which dispersed spherical particles and plates may be formed of lanthanum, the lightest of the lanthanide elements The experimental conditions for the synthesis of these particles is given in the form of morphological diagrams and the chemistry and yield of the process is also reported The process was also analyzed as a function of time in order to observe the supersaturation and growth regimes The effect of calcining on the morphology of the particles is also discussed
Journal Article•
TL;DR: The role of the lysosome during the intracellular concentration of diverse mineral elements has been evidenced by the electron probe X-ray microanalysis (EPMA), which allows an in situ chemical analysis of any chemical element with an atomic number greater than 11, present in ultra thin tissue sections as mentioned in this paper.
Abstract: The role of the lysosome during the intracellular concentration of diverse mineral elements has been evidenced by the electron probe X-ray microanalysis (EPMA). This highly sensitive technique allows an in situ chemical analysis of any chemical element with an atomic number greater than 11, present in ultra-thin tissue sections. Therefore, it has been demonstrated by using this EPMA that 21 out of the 92 elements of the periodic table, once injected in a soluble form, were selectively concentrated within lysosomes of several types of mammalian cells. Amongst these 21 elements, 15 are concentrated and precipitated in an insoluble from in association with phosphorus whereas the other 6 are precipitated in association with sulphur. Amongst the 15 elements which precipitate with phosphorus in lysosomes, there are: 3 group IIIB elements of the periodic system, (aluminium, gallium and indium); the rare-earth elements (cerium, gadolinium, lanthanum, thulium and samarium); 2 group IVA elements (hafnium and zirconium), two actinides (uranium and thorium) and elements such as chromium and niobium. The 6 elements which precipitate with sulphur comprise the 3 group VIII elements of the classification (nickel, palladium, platinum) and the 3 group IB elements (copper, silver and gold). The mechanisms responsible for this selective concentration involve enzymatic processes and predominantly acid phosphatases for elements precipitating as phosphates and arylsulfatases for elements precipitating with sulphur.
TL;DR: It is proposed that lanthanum, gadolinium and barium can usefully separate these endogenous membrane currents in Xenopus oocytes.
Abstract: 1. The effects of multivalent cations on membrane currents recorded from Xenopus oocytes were studied. 2. The hyperpolarization-activated chloride current was reversibly blocked by lanthanum; half-maximal block occurred at a concentration of 8 microM. Zinc, cadmium, cobalt and nickel were less potent than lanthanum, and gadolinium, manganese, barium and strontium had no effect at a concentration of 100 microM. 3. The calcium-activated chloride current was blocked by gadolinium (50 microM), and lanthanum, cadmium, cobalt, nickel and manganese were equally effective. The actions of gadolinium and lanthanum were almost irreversible, while partial (30-80%) recovery was observed with the other cations. Zinc (100 microM) had no effect. 4. In lanthanum (100 microM), membrane depolarizations from -70 mV activated an outward potassium current that was partially blocked by barium (0.1-2 mM). The barium-sensitive current was confined to potentials less negative than -70 mV. The current consisted of a time-independent as well as a time-dependent component, the latter of which had voltage dependence similar to the M-current. 5. It is proposed that lanthanum, gadolinium and barium can usefully separate these endogenous membrane currents in Xenopus oocytes.
TL;DR: In this paper, the electrical resistivity measurements in the 1.5-300 K temperature range for the LaXSn phases (X ≡ Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) are reported.
TL;DR: In this article, a simultaneous spectrophotometric method was developed for assay of uranium, thorium and lanthanum in mixed solutions by absorbance measurements of their arsenazo III complexes at appropriate wavelengths in three different solutions.
TL;DR: In this article, the crystal and molecular structure of a lanthanum mellitate, La2C12H22O23, has been determined by X-ray structural analysis using a combination of direct and heavy atom methods.
Abstract: The crystal and molecular structure of a lanthanum(III) mellitate, La2C12H22O23, has been determined by X-ray structural analysis using a combination of direct and heavy atom methods. The complex crystallizes in the monoclinic space group P21/n with unit-cell dimensions of a = 6.723(4), b = 11.368(5), c = 29.813(4) A and β = 95.851(3)°. Block-diagonal least-squares refinement using automated diffractometer-collected data resulted in R = 2.5 and Rw = 3.4. The crystal structure consists of layers perpendicular to the a axis. Each layer is formed by an extended network of lanthanum ions coordinated with mellitate anions and water molecules, and linked through a complex three-dimensional hydrogen-bonding network. Among the six carboxylate groups of the mellitate anion, five form coordination bonds to six lanthanum atoms. The two independent lanthanum ions are both nine-coordinate and the configuration around lanthanum is a tricapped trigonal prism with the La-O bond distances ranging from 2.457 A to ...
TL;DR: In this paper, the rate of combustion controlled the growth of the oxide particles, which can be manifested by combustion of the mixture in controlled atmosphere, in order to obtain the desired oxide phase.
Abstract: Fine powder of single and binary mixed oxides can be produced by decomposition of the respective metal nitrates and polyvinyl alcohol (PVA) or, a mixture of PVA and polyacrylic acids. These mixtures, after spray drying, yield a brown fluffy mass, which is spontaneously combustible and the heat liberated is sufficient for the crystallization of the desired oxide phase. The rate of combustion controls the growth of the particles. This can be manifested by combustion of the mixture in controlled atmosphere. The nanoparticles of the oxide system studied are: spinels [MFe2O4 where M = Ni(II), Co(II), Zn(II), Mg(II)]; orthoferrites [MFeO3 where M = Gd(III), Sm(III)]; LaAlO3, NdGaO3, CaO/MgO/Y2O3 stabilized zirconia (ZrO2); lead zirconate titanate (PZT), lanthanum modified lead zirconate titanate (PLZT) and BaTiO3.
TL;DR: In this paper, a theoretical study has been conducted to determine the energy of a variety of neutral and cationic isomeric forms of metal clusters MCx, where M = Y or La and x = 3−6.
Abstract: A theoretical study has been undertaken to determine the energetics of a variety of neutral and cationic isomeric forms of metal clusters MCx, where M = Y or La and x = 3−6. Included in this study are cyclic molecules and linear molecules, as well as recently-proposed “kite” structures. Geometries are optimized by the B3LYP density functional method, and energies are computed with the coupled-cluster method. The major conclusion of this work is that cyclic structures are the most stable, a result which holds for both yttrium and lanthanum and for both cations and neutral molecules.
Patent•
25 Nov 1996
TL;DR: In this article, a general formula of X! a Zr b O c where X is at least one element selected from the group consisting of magnesium, calcium, strontium, barium, yttrium and lanthanum.
Abstract: A catalyst for purifying exhaust gas from an automotive internal combustion engine. The catalyst comprises a monolithic carrier which is coated with a catalyst component carrying layer which includes rhodium and a zirconium oxide. The zirconium oxide contains at least one element selected from the group consisting of magnesium, calcium, strontium, barium, yttrium and lanthanum. The zirconium oxide in the catalyst component carrying layer has a composition represented by a general formula of X! a Zr b O c where X is at least one element selected from the group consisting of magnesium, calcium, strontium, barium, yttrium and lanthanum; and a, b and c indicate ratios in number of atoms, in which a is within a range of from 0.01 to 0.6 on the assumption of b being 1.0, and c is a number of oxygen atom which satisfies valence of respective elements.
TL;DR: In this paper, Lanthanum and cerium oxides have been tested for the title reaction at 623 K and atmospheric pressure in a flow reactor, and the results showed that LanthanUM oxide (prepared from the corresponding nitrate) gives mainly 4-methylpent-1-ene (80% of the products).
Abstract: Lanthanum and cerium oxides have been tested for the title reaction at 623 K and atmospheric pressure in a flow reactor. Lanthanum oxide (prepared from the corresponding nitrate) gives mainly 4-methylpent-1-ene (80% of the products). Similar results are observed with cerium oxide obtained from the corresponding hydroxide, whereas cerium oxide prepared from nitrate is less selective towards alk-1-enes. In addition to dehydration, dehydrogenation to 4-methylpentan-2-one is also observed to a limited extent for all the catalysts. Information on the acid–base properties of the samples was obtained by adsorption microcalorimetry of ammonia and carbon dioxide and correlated to reaction selectivities. Possible changes in the oxidation state of cerium ions due to the reaction atmosphere are considered. The present results are compared with former data for zirconia catalysts. Modification of cerium oxide via immersion in NaOH solution does not appear to be useful for improving alk-1-ene selectivity.
TL;DR: The dimensional stability of calcium-substituted yttrium chromite was evaluated over a wide range of temperatures, oxygen partial pressures, and compositions, and compared to data collected for calcium-doped lanthanum chromite.