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Rare-earth Elements (rare-earth + element)
Selected AbstractsChemInform Abstract: Reduced Ternary Rare-Earth,Transition Metal Tellurides for the Smaller Rare-Earth Elements.CHEMINFORM, Issue 32 2009An Exploration, an Explanation of the Marked Stability Differentiation among the Rare-Earth Elements in these Phases. Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Thiosilicates of the Rare-Earth Elements.CHEMINFORM, Issue 35 2005Part 3. Abstract For Abstract see ChemInform Abstract in Full Text. [source] Thiosilicates of the Rare-Earth Elements.CHEMINFORM, Issue 25 2003Part 2. Abstract For Abstract see ChemInform Abstract in Full Text. [source] Raman spectroscopic study of the phosphate mineral churchite-(Y) YPO4·2H2OJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2010Ray L. Frost Abstract Raman spectroscopy has been used to study the rare-earth mineral churchite-(Y) of formula (Y,REE)(PO4) ·2H2O, where rare-earth element (REE) is a rare-earth element. The mineral contains yttrium and, depending on the locality, a range of rare-earth metals. The Raman spectra of two churchite-(Y) mineral samples from Jáchymov and Medv,dín in the Czech Republic were compared with the Raman spectra of churchite-(Y) downloaded from the RRUFF data base. The Raman spectra of churchite-(Y) are characterized by an intense sharp band at 975 cm,1 assigned to the ,1 (PO43,) symmetric stretching mode. A lower intensity band observed at around 1065 cm,1 is attributed to the ,3 (PO43,) antisymmetric stretching mode. The (PO43,) bending modes are observed at 497 cm,1 (,2) and 563 cm,1 (,4). Some small differences in the band positions between the four churchite-(Y) samples from four different localities were found. These differences may be ascribed to the different compositions of the churchite-(Y) minerals. Copyright © 2009 John Wiley & Sons, Ltd. [source] Energy transfer from rare-earth element to Mn in (Ca,Sr)Ga2S4 compoundsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009Toshimitsu Obonai Abstract For realizing a red-colour emission using SrGa2S4 compounds, Mn and rare-earth-element (REE) co-doping is tried. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra are measured using samples so prepared. As a result, enhancement of the Mn red emission is observed. Considering the 4f and 5d levels of REE in the host material, it is expected that the energy transfer from REE to Mn is caused by the weak coupling between the d levels of REE and Mn. Moreover, in the Ce co-doping case, another process is expected as a resonant energy transfer between the 4f,5d transition of Ce3+ and a certain transition of Mn2+. To specify the Mn2+ levels related to the resonant transfer, PL spectra of a Mn only doped CaGa2S4 single crystal and an undoped one are measured at low temperatures, though we could not find emission expected to be related to the resonant transfer. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pre-Variscan metagabbro from NW Sardinia, Italy: evidence of an enriched asthenospheric mantle source for continental alkali basaltsGEOLOGICAL JOURNAL, Issue 2 2003Marcello Franceschelli Abstract Small metagabbro bodies are enclosed in the metasedimentary sequence of NW Sardinia. The metagabbros represent the last magmatic episode before the continent,continent collision that built up the Variscan chain of north Sardinia. The metagabbros are composed of variable proportions of plagioclase and pyroxene igneous relics and metamorphic minerals. Major and trace element data, specifically high TiO2 and P2O5 and low K and Rb contents, as well as light rare-earth elements, Nb and Ta enrichment, suggest an alkaline affinity for the gabbro and emplacement in a within-plate tectonic setting. The gabbro was derived from an ocean island alkali basalt-like asthenospheric mantle source enriched with incompatible elements and uncontaminated by crustal or subducted materials. Non-modal modelling indicates a 5,7% partial melting of the asthenospheric mantle. Copyright © 2003 John Wiley & Sons, Ltd. [source] Trace-element distributions in silicates during prograde metamorphic reactions: implications for monazite formationJOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2008S. L. CORRIE Abstract To assess the petrogenetic relationship between monazite and major silicates during prograde metamorphism, REE were measured across coexisting zoned silicates in garnet through kyanite-grade pelitic schists from the Great Smoky Mountains, western Blue Ridge terrane, southern Appalachians, to establish REE concentrations and distributions before and after the monazite-in isograd, and to identify the role major silicates play in the formation of monazite. Results indicate significant scavenging of light rare-earth elements (LREE) from silicates during the monazite-in isograd reaction; however, the absolute concentration of LREE hosted in the silicates was insufficient to produce monazite in the quantity observed in these schists. Monazite must have formed mainly from either the dissolution of allanite or some other source of concentrated LREE (possibly adsorbed onto grain boundaries), even though direct evidence for allanite is lacking in a majority of the samples. Laser-ablation ICP-MS analyses and theoretical thermodynamic calculations show that monazite may have formed as a result of contributions from both allanite and major silicates. Allanite breakdown initially formed monazite, and monazite production drew LREE liberated from allanite, major silicates and possibly from crystal boundaries. In many rocks the reaction was further promoted by the staurolite-in reaction, allowing for rapid, isogradic monazite growth. [source] Anomalous concentration dependence of the coordination behavior of Cl, ion to Ln3+ ion (Ln3+ = rare-earth ion) in anhydrous LnCl3 alcohol solutionsJOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2007Y. Yoshimura Abstract Raman spectroscopic measurements were carried out for the anhydrous LnCl3·20ROH·XLiCl solutions (Ln3+ = La3+, Lu3+, X = 0,3; ROH = MeOH, EtOH, n -PrOH) in the liquid state. The salt concentration (X) dependence of the wavenumber for the Ln,Cl stretching Raman band (,Ln,Cl) is examined in conjunction with the formation of chloro-rare-earth complexes. We have obtained very intriguing results including the fact that the chloro complexations of the middle rare-earth ions (e.g. gadolinium, holmium ions, etc.) in the MeOH and EtOH solutions show peculiar behavior with regard to the salt concentration dependence: the ,Ln,Cl wavenumber increases with the increasing chloride concentration. However, the ,Ln,Cl wavenumbers of the light and heavy rare-earth (e.g. lanthanum, lutetium, etc.) salt solutions show normal behavior; i.e. ,Ln,Cl decreases with the increasing chloride concentration. On the other hand, in the n -PrOH solutions, the ,Ln,Cl frequency in the solutions of all the rare-earth elements exhibits a normal behavior. We now present a possible mechanism for this anomalous concentration dependence of coordination of Cl, ions to Ln3+ ions in anhydrous LnCl3 alcohol solutions. Copyright © 2007 John Wiley & Sons, Ltd. [source] Use of highly energetic (116,keV) synchrotron radiation for X-ray fluorescence analysis of trace rare-earth and heavy elementsJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2001Izumi Nakai This study has revealed the advantages of the use of 116,keV X-rays as an excitation source of X-ray fluorescence (XRF) analyses. This technique is suitable for nondestructive multielemental analyses of heavy elements such as rare-earth elements. The lowest MDL value evaluated for the bulk analysis of a JG-1 standard reference sample (granite rock) was 0.1 p.p.m. for W for a 500,s measurement. The spectrum of standard glass samples of SRM612 demonstrated clearly resolved K -line peaks of more than 30 elements, including all the existing rare-earth elements, at 50 p.p.m. levels. The calibration curve for the determination of a rare-earth element shows a linear relation between the XRF intensity and concentrations from 10 to 0.03,ng. This powerful technique should be useful for nondestructive analyses of rare-earth and heavy elements in geological, geochemical and archaeological samples as well as industrial materials. [source] Electronic Structure and Bonding of All Crystalline Phases in the Silica,Yttria,Silicon Nitride Phase Equilibrium DiagramJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Wai-Yim Ching This paper reviews the structures and properties of 10 binary, ternary, and quaternary crystals within the equilibrium phase diagram of the SiO2,Y2O3,Si3N4 system. They are binary compounds SiO2, Y2O3, Si3N4; ternary compounds Si2N2O, Y2Si2O7, and YSi2O5; and quaternary crystals Y2Si3N4O3 (M-melilite), Y4Si2O7N2, (N-YAM), YSiO2N (wallastonite), and Y10(SiO4)6N2 (N-apatite, N-APT). Although the binary compounds are well-known and extensively studied, the ternary and the quaternary crystals are not. Most of the ternary and the quaternary crystals simply have been referenced as secondary phases in the processing of nitrogen ceramics. Their crystal structures are complex and not precisely determined. In the quaternary crystals, there exists O/N disorder in that the exact atomic positions of the anions cannot be uniquely determined. It is envisioned that a variety of cation,anion bonding configurations exist in these complex crystals. The electronic structure and bonding in these crystals are, therefore, of great interest and are indispensable for a fundamental understanding of structural ceramics. We have used ab initio methods to study the structure and bonding properties of these 10 crystals. For crystals with unknown or incomplete structural information, we use an accurate total energy relaxation scheme to obtain the most likely atomic positions. Based on the theoretically modeled structures, the electronic structure and bonding in these crystals are investigated and related to various local cation,anion bonding configurations. These results are presented in the form of atom-resolved partial density of states, Mulliken effective charges, and bond order values. It is shown that Y,O and Y,N bonding are not negligible and should be a part of the discussion of the overall bonding schemes in these crystals. Spectroscopic properties in the form of complex, frequency-dependent dielectric functions, X-ray absorption near-edge structure (XANES), and the electron energy-loss near-edge structure (ELNES) spectra in these crystals also are calculated and compared. These results are discussed in the context of specific bonding configurations between cations (silicon and yttrium) and anions (oxygen and nitrogen) and their implications on intergranular thin films in polycrystalline Si3N4 containing rare-earth elements. [source] Photoconductivity of CaGa2S4 single crystals doped with Eu2+ and Ce3+PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006Kazuma Hiraguri Abstract CaGa2S4 compounds doped with rare-earth elements (REE) exhibit luminescence with various colors. The emission process between the transition levels of REE ions has ever been extensively studied. We have measured the photoconductivity (PC) to confirm the locations of the 4f ground levels of the Eu2+ and Ce3+ ions in the band gap of the host compounds of CaGa2S4 for the first time. The estimated values for Eu2+ and Ce3+ are 1.8 eV and 0.95 eV from the top of the valence band of CaGa2S4, respectively. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Epithermal Gold-Silver Mineralization of the Asachinskoe Deposit in South Kamchatka, RussiaRESOURCE GEOLOGY, Issue 4 2007Ryohei Takahashi Abstract The Asachinskoe epithermal Au-Ag deposit is a representative low-sulfidation type of deposit in Kamchatka, Russia. In the Asachinskoe deposit there are approximately 40 mineralized veins mainly hosted by dacite,andesite stock intrusions of Miocene,Pliocene age. The veins are emplaced in tensional cracks with a north orientation. Wall-rock alteration at the bonanza level (170,200 m a.s.l.) consists of the mineral assemblage of quartz, pyrite, albite, illite and trace amounts of smectite. Mineralized veins are well banded with quartz, adularia and minor illite. Mineralization stages in the main zone are divided into stages I,IV. Stage I is relatively barren quartz,adularia association formed at 4.7 ± 0.2 Ma (K-Ar age). Stage II consists of abundant illite, Cu-bearing cryptomelane and other manganese oxides and hydroxides, electrum, argentite, quartz, adularia and minor rhodochrosite and calcite. Stage III, the main stage of gold mineralization (4.5,4.4 ± 0.1,3.1 ± 0.1 Ma, K-Ar age), consists of a large amount of electrum, naumannite and Se-bearing polybasite with quartz,adularia association. Stage IV is characterized by hydrothermal breccia, where electrum, tetrahedrite and secondary covellite occur with quartz, adularia and illite. The concentration of Au+Ag in ores has a positive correlation with the content of K2O + Al2O3, which is controlled by the presence of adularia and minor illite, and both Hg and Au also have positive correlations with the light rare-earth elements. Fluid inclusion studies indicate a salinity of 1.0,2.6 wt% NaCl equivalent for the whole deposit, and ore-forming temperatures are estimated as approximately 160,190°C in stage III of the present 218 m a.s.l. and 170,180°C in stage IV of 200 m a.s.l. The depth of ore formation is estimated to be 90,400 m from the paleo-water table for stage IV of 200 m a.s.l., if a hydrostatic condition is assumed. An increase of salinity (>CNaCl, 0.2 wt%) and decrease of temperature (>T , 30°C) within a 115-m vertical interval for the ascending hydrothermal solution is calculated, which is interpreted as due to steam loss during fluid boiling. Ranges of selenium and sulfur fugacities are estimated to be logfSe2 = ,17 to ,14.5 and logfS2 = ,15 to ,12 for the ore-forming solution that was responsible for Au-Ag-Se precipitation in stage III of 200 m a.s.l. Separation of Se from S-Se complex in the solution and its partition into selenides could be due to a relatively oxidizing condition. The precipitation of Au-Ag-Se was caused by boiling in stage III, and the precipitation of Au-Ag-Cu was caused by sudden decompression and boiling in stage IV. [source] Speciation of Rare-Earth Metal Complexes in Ionic Liquids: A Multiple-Technique ApproachCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009Peter Nockemann Dr. Abstract The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu2(bet)8(H2O)4][Tf2N]6, [Eu2(bet)8(H2O)2][Tf2N]6,2H2O, and [Y2(bet)6(H2O)4][Tf2N]6 were found to consist of dimers. These rare-earth complexes are well soluble in the ionic liquids [Hbet][Tf2N] and [C4mim][Tf2N] (C4mim=1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, 1H, 13C, and 89Y,NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry. [source] Bis(amido)cyclodiphosph(III)azane Complexes of Yttrium and the LanthanidesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2009Marcus Rastätter Dr. Abstract The first cyclodiphosph(III)azane complexes of the rare-earth elements have been synthesized. Reactions of the lithium salt cis -[(tBuNP)2(tBuN)2{Li(thf)}2] with anhydrous yttrium trichloride or the heavier lanthanide trichlorides resulted in the corresponding cyclodiphosph(III)azane complexes [Li(thf)4][{(tBuNP)2(tBuN)2}LnCl2] (Ln=Y (1,a), Ho (1,b), Er (1,c)). The single-crystal X-ray structures showed that compounds 1,a,c consisted of ion pairs composed of a [Li(thf)4]+ cation and a C2v symmetric [{(tBuNP)2(tBuN)2}LnCl2], anion. By treating cis -[(tBuNP)2(tBuN)2{Li(thf)}2] with anhydrous SmCl3 in THF, the trimetallic complex [{(tBuNP)2(tBuN)2}SmCl3Li2(thf)4] (2) was obtained. The influence of the ionic radii of the lanthanides can be seen in the single-crystal X-ray structure of compound 2, which forms a six-membered Cl-Li-Cl-Li-Cl-Sm metallacycle. The ring adopts a boat conformation in which one chlorine atom and the samarium atom are displaced from the Cl2Li2 least-square plane. Heating of the metalate complexes in toluene resulted in the extrusion of lithium chloride and the formation of the neutral dimeric metal chloride complexes of the composition [(tBuNP)2(tBuN)2LnCl(thf)]2 (Ln=Y (3,a), La (3,b) Nd (3,c), Sm (3,d)). Furthermore, treating 1,a with KNPh2 resulted in a lithium metalate complex of the composition [Li(thf)4][{(tBuNP)2(tBuN)2}Y(NPh2)2] (4). The coordination mode of the {(tBuNP)2(tBuN)2}2, ligand in 4 is different to that observed in 1,a,c, 2, and 3,a,d; instead of a symmetric ,2 coordination of the ligand, a heterocubane-type structure is observed in the solid state. The complex [(tBuNP)2(tBuN)2NdCl(thf)] (3,c) was used as a Ziegler,Natta catalyst for the polymerization of 1,3-butadiene to poly- cis -1,4-butadiene. The observed activities of the Ziegler,Natta catalyst strongly depended upon the nature of the cocatalyst; in some case very high turnover rates and a cis selectivity of 93,94,% were observed. [source] Microcalorimetric studies on influence of Sm3+, Dy3+ on growth and sporulation of Bacillus thuringiensisCHINESE JOURNAL OF CHEMISTRY, Issue 12 2004Ru-Ming Zhao Abstract By using an LKB-2277 Bioactivity Monitor and cycle-flow method, the thermogenic curves of aerobic growth for Bacillus thuringiensis cry II strain at 28 °C have been obtained. The metabolic thermogenic curves of Bt cry II contain two distinct parts: the first part reflects the changes of bacterial growth phase and the second part corresponds to sporulation phase. From these thermogenic curves in the absence or presence of Sm3+, Dy3+ ions, the thermokinetic parameters such as the growth rate constants k, the interval time ,I, the maximum power PMAX1 and heat-output QLOG for log phase, the maximum power PMAX2 and heat-output QSTAT for stationary phase, the heat-output QSPOR for sporulation phase and total heat effects QT were calculated. Sm3+ and Dy3+ ions have promoting action on the growth of Bt cry II in their lower concentration range, on the other hand, they have inhibitory action on the sporulation of Bt in their higher concentration range. It has also been found that the effects of Sm3+ and Dy3+ ions on Br firing the sporulation phase were far greater than those during the bacterial growth phase. It was concluded that the application of Bt for controlling insecticide could not be affected by the presence of the rare-earth elements in the environmental ecosystem. [source] Preparation of Lanthanide Hydrides of Nanometric Size by the Catalytic MethodCHINESE JOURNAL OF CHEMISTRY, Issue 11 2002Yin-Heng Fan Abstract Rare-earth metals were hydrogenated in the presence of TICI4 catalyst in tetrahydrofuran (THF) at 45 °C under normal pressure. Transmission electron micrographs showed that the resulting lanthanide hydrides were in the form of nanoparticles. The rate of hydrogenation decreased with increasing atomic number of the rare-earth elements. [source] | ||||||||||||||||