Showing papers on "Lanthanum published in 1993"

Electrical Conductivity and Defect Structure of Calcium‐Doped Lanthanum Chromites

Abstract: Electrical conductivity of calcium-doped lanthanum chromites, La 1-x Ca x CrO 3-δ , was determined as a function of composition, temperature, and oxygen partial pressure, P o2 , to determine its defect structure and understand its redox behavior. The conductivity was independent of P o2 and was proportional to the dopant concentration at high P o2 . The activation energy of conductivity was 0.12 to 0.14 eV and the mobility was 0.066 to 0.075 cm 2 /V/s in the temperature range of 900 to 1050 o C, which was ascribable to small-polaron hopping. Under reducing conditions, the conductivity decreased exponentially with decreasing P o2 and asymptotically approached a P 02 1/4 relationship

Adsorption of several actinide (Th, U) and lanthanide (La, Eu, Yb) ions by Mycobacterium smegmatis

Abstract: Adsorption measurements of several actinide [thorium (Th), uranium (U)] and lanthanide [lanthanum (La), europium (Eu), ytterbium (Yb)] cations by Mycobacterium smegmatis showed that sorption kinetics followed a three-phase pattern. For 5% (w/w) bacterial suspensions at pH 1, maximum cation biosorption per gram dry biomass corresponded to 170 μmol Th4+ and 187 μmol UOinf2sup2+. Adsorption of all cations studied obeyed the Brunauer-Emmett-Teller isotherm, which assumes multilayer binding at constant energy. Plots for the Scatchard model showed the existence of at least two types of cation complexation site, with strong and weak affinity and negative cooperation. Th4+ was preferentially adsorbed with respect to the other cations, although all species appeared to compete for the same sites independently of bacterial viability. Adsorption of these cations was accompanied by partial release of magnesium from the cell wall, indicating that exchange reactions occurred at magnesium (Mg)-bonding sites.

Recovery of zinc, cadmium, and lanthanum by biopolymer gel particles of alginic acid

Abstract: Biopolymer gel particles of alginic acid were found to be a useful material for recovering zinc, cadmium, and lanthanum from aqueous solutions. The metals sorbed by the gel particles could be completely eluted by using dilute HCl solution of 0.1 kmol/m3. The distribution ratios of the individual metals between the gel and liquid phases were measured by using a batch method. The equilibrium data were consistent with predictions made assuming that sorption takes place with the ion-exchange reaction between metal ions and alginic acid. The maximum sorption capacity of the gel particles and the distribution equilibrium constants for the metals were determined by comparing the experimental data with the theoretical predictions. The observed effect of temperature on the distribution equilibrium was insignificant in the range from 15 to 35°C.

Liquid‐Phase‐Assisted Sintering of Calcium‐Doped Lanthanum Chromites

Abstract: Investigations have been made on the low-temperature sinterability of calcium-doped lanthanum chromites which are to be used as interconnectors in solid oxide fuel cells (SOFCs). Nominally chromium deficient lanthanum calcium chromites (La[sub 0.7]Ca[sub 0.3]Cr[sub 1[minus]y]O[sub 3], y = 0.02) were found to be sinterable to 94% theoretical density at 1573 K in air, whereas no densification was observed for samples with y = 0. The two-step shrinkage process suggests a liquid-phase sintering mechanism with calcium oxychromates playing an important role as the liquid phase. After sintering at 1573 K, calcium-rich substances remained at grain boundaries.

Catalytic properties of lanthanum strontium transition metal oxides (La1-xSrxBO3; B = manganese, iron, cobalt, nickel) for toluene oxidation

Abstract: The alkaline coprecipitation method was employed to prepare La 1-x Sr x BO 3 (x = 0-1 and B = Mn, Fe, Co, Ni). The activities of the resulting catalysts for oxidizing toluene were measured by a differential flow reactor, and their physical properties were characterized by BET, XRD, AES, SIMS, XPS, SEM, TGA/DTGA, and stepwise oxygen desorption. The results indicate that substitution of La by Sr affects activity due to the oxygen vacancy. Among the Co and Fe series catalysts, those for which x=0.3 demonstrate the highest activity. The catalytic activity of the Mn series catalysts was found to increase not only with the quantity of Mn atoms but also with the sum of Mn and O atoms. In this series, the amount of chemically adsorbed oxygen, instead of the lattice oxygen, plays an important role in the catalytic activity, especially in the temperature range of toluene oxidation, with the catalytic activity for toluene oxidation increasing with the amount of oxygen chemically adsorbed. The activity of the Ni series catalysts does not increase with increasing amounts of NiO and La 2 NiO 4 ; the highest activity occurs at x=0.5. The experimental results are discussed in terms of the role played by various B-site cations, the influence of catalytic surface composition on catalytic activity, and the effect of lattice and chemically adsorbed oxygen. Four influencing factors on the catalytic activity of these four series catalysts were discriminated by analysis of the results of kinetic measurements and by surface characterization

High yield synthesis of lanthanofullerenes via lanthanum carbide

Abstract: A high yield synthesis for lanthanofullerenes has been studied by a newly developed fullerene are generator equipped with an anaerobic sampling apparatus. The yield of the lanthanofullerene La C[sub 82] has increased by a factor of 10 or more, when LaC[sub 2]-enriched composite carbon rods are used for the generation of soot, instead of hydrooxidized or oxidized lanthanum composite rods. The fact is characterized by electron spin resonance and by the powder X-ray diffraction method. Furthermore, the yields of other types of lanthanofullerenes, LaC[sub 2n], have also increased, when the LaC[sub 2]-enriched composite rod is used as an arc-burning material. 21 refs., 4 figs.

Preparation of stabilized copper-rare earth oxide catalysts for the synthesis of methanol from syngas

Abstract: The preparation and the optimization of new copper catalysts for methanol synthesis are described. The catalysts were prepared using a definite La2Zr2O7 support; the preparation of which is also described. In presence of carbon dioxide and water, Cu/La2O3 Catalysts are quickly deactivated by the formation of lanthanum carbonates and hydroxycarbonates. However, the formation of these species can be prevented by incorporating La2O3 in a stable LaZr2O7 pyrochlore. After optimization, up to 600 g methanol gcat−1 h−1 can be produced over the Cu/La2Zr2O7 catalysts. The particular chemical properties of these catalysts allow them to be used with CO-H2, CO-CO2-H2 and CO2-H2 feeds.

Air electrode bodies for solid oxide fuel cells, a process for the production thereof, and a production of solid oxide fuel cells

Abstract: An air electrode body for a solid oxide fuel cell, which is composed of a perovskite-type structure having a chemical composition of (La1-xAx)1-yMnO₃ wherein 0 < x ≦ .5, 0 < y ≦ 0.2, and A is at least one kind of metals selected from strontium, calcium, manganese, barium, yttrium, cerium and ytterbium. The air electrode body has a porosity of 15 to 40 % and an average pore diameter of 1-5 µm. A process for producing the air electrode body, comprises the steps of: mixing lanthanum or a lanthanum compound, manganese or a manganese compound, a metal A or a compound of the metal A wherein A is at least one kind of metals selected from the group of strontium, calcium, manganese, barium, yttrium, cerium and ytterbium; calcining the resulting mixture at a temperature from 1,300°C to 1600°C to synthesize (La1-xAx)1-yMnO₃; grinding the synthesized material to a powder having the average particle diameter of 3 to 15 µm; adding at least an organic binder, water and 2 to 12 parts by weight of a pore-forming agent to 100 parts by weight of the resulting powder and kneading the resulting mixture; molding the kneaded material; and drying the molding and then firing the molding at a temperature not higher than the calcining temperature. A process for producing a solid oxide fuel with the above air electrode body is also disclosed.

Use of GEOCHEM-PC to predict rare earth element (REE) species in nutrient solutions

Abstract: The interpretation of results of some experiments examining effects of rare earth elements (REE) on plant growth may have been complicated by rare earth phosphate precipitation. Simulations were undertaken using the computer model GEOCHEM-PC to define REE solubility limits and predict REE species in low and high ionic strength nutrient solutions. In low ionic strength solutions containing 5 μM P, lanthanum phosphate (LaPO4) precipitation is predicted to occur at solution pH>4.0, reaching a maximum (>95% of total) at pH 5.5. In high ionic strength solutions (1000 μM P) over 95% of the La is predicted to precipitate as phosphate at pH>4.0. The predicted behaviour of cerium (Ce) was closely similar to that for La.

XPS investigations of lanthanum in faujasite-type zeolites

Abstract: Faujasite-type zeolites containing lanthanum introduced by various techniques and in different amounts were studied by X-ray photoelectron spectroscopy to elucidate the influence of the zeolite matrix on the binding energy and the shape of the La(3d) line. The results were discussed with regard to the spectral properties of the La(3d) line in La 2 O 3 . Significant differences in the La(3d) line shapes and binding energies between La 2 O 3 and La zeolites were ascribed to final-state effects arising from the hybridization of La final states with valence bands of different extension

Effect of Quaternary Ammonium Salts on Carrier-Mediated Transport of Lanthanide Ions through Cellulose Triacetate Membranes

Abstract: Fluxes of all lanthanides, except promethium, across cellulose triacetate membranes were determined by using mixtures of o-nitrophenyl n-octyl ether and quaternary ammonium salts as plasticizers, and 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone (BMPP) and 4-trifluoroacetyl-3-methyl-1-phenyl-5-pyrazolone (TMPP) as carriers. The quaternary ammonium salts used were didodecyldimethyl-, distearyldimethyl-, tetrahexyl-, tetraoctyl-, and tetradecylammonium bromides [referred to as (C12)2NBr, (C18)2NBr, (C6)4NBr, (C8)4NBr, and (C10)4NBr, respectively]. The effect of these ammonium bromides on the flux was demonstrated. For membranes containing 0.1 M (C12)2NBr and (C18)2NBr, BMPP exhibited considerably high fluxes. The fluxes of lanthanum and cerium using BMPP for (C12)2NBr were higher than those of the other lanthanides. For the membranes containing 0.5 M (C12)2NBr and 0.1 M (C18)2NBr, however, no difference in flux among the lanthanides was observed. The fluxes using TMPP for (C12)2NBr and (C18)2NBr were ve...

Structure and catalytic activity of perovskites La-Ni-O supported on alumina and zirconia

Abstract: Lanthanum nickelate binary oxidic species supported on alumina and zirconia were tested for their catalytic activity for the NO + CO reaction. The support took place by impregnation of Al2O3 or ZrO2 without any pretreatment or after addition of lanthana on the support surface. The zirconia based solids show a surface area (BET) of 5–7 m2 g−1, one order of magnitude smaller than those based on alumina (40–60 m2 g−1). The crystal phase developed on ZrO2 was only La2NiO4 while on Al2O3 the phases found by X-rays were LaNiO3 and LaAlO3. The solids La2NiO4/ZrO2 containing nickel in 2 + state, were more active than LaNiO3/Al2O3 containing Ni3+. The smaller activity of the La-Ni-O solids supported on Al2O3 is attributed to the stronger adsorption of oxygen, or oxygenated species, on Ni3+ as compared to the weaker adsorption on Ni2+ existed in the La-Ni-O solids supported on ZrO2. Especially the stronger adsorption of nitric oxide in the first case results in a reaction route where an excess of nitric oxide as large as 25–30% is eliminated as compared to the reacting carbon monoxide. The excess of eliminated nitric oxide undergoes disproportionation towards nitrous oxide and nitrogen, the former undergoing further decomposition towards nitrogen and oxygen. In the second case of ZrO2/La-Ni-O the weaker adsorption of nitric oxide results in a nearly equimolecular elimination of the two reactants and the excess of nitric oxide reacting does not exceed a 12–14% of carbon monoxide. The Arrhenius plots for the nitric oxide reduction on the alumina-based solids show a unique behaviour for the whole temperature range examined while similar plots for the zirconia-based solids show a two stage behaviour corresponding to different surface mechanism. The activation energies of nitric oxide elimination with carbon monoxide on the above solids are appreciably smaller than activation energies of nitrous oxide decomposition on the same materials, in accordance with previous observations. Finally the activity of La2NiO4/ZrO2 solids calculated per mass of perovskite is nearly five times that of La2NiO4 pure perovskites prepared through the nitrate or citrate routes although their surface areas are equal for the citrate and only double for the nitrate solids.

Porous lanthanum manganite sintered bodies and solid oxide fuel cells

Abstract: A porous sintered body composed mainly of lanthanum manganite in which a part of lanthanum atoms at A-sites of the lanthanum manganite are substituted by atoms of a metal selected from the group consisting of alkaline earth metals and rare earth metals. The dimensional shrinkage amount of the porous sintered body in heat cycling between room temperature and 1,000° C. is not more than 0.01% per one heat cycle.

Acid extractable rare earth elements in Florida citrus soils and trees

Abstract: To determine the levels of elements not usually included in soil analyses, aqua regia extracts from 10 soils in eight locations throughout the Florida citrus belt were analyzed for 14 rare earth elements (lanthanides), scandium, and yttrium with an IGP spectrophotometer. Leaves, bark, wood, and roots of citrus trees growing at two of the sampling locations, a fertilizer (14% N‐l.7% P‐11.6% K), and a dolomite sample were also analyzed. Scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), and holmium (Ho) were found in the soil samples in amounts above detection limits varying from 0.002 to 0.017 mg/L. Cerium, La, and Nd were the elements present in the largest amounts. The levels showed no particular regional pattern and a great amount of variability, even between adjacent sites at the same location. A soil with a relatively high organic matter content and cation exchange capacity (...

Thin film oxygen sensor

Abstract: An oxygen sensor is based on a thin film of a compound oxide supported on a substrate such as quartz. The compound oxide has a general formula ABO 2 .5+x, where A is an element of the lanthanum family, alkaline earth metal or their mixture, and B is a transition metal or a mixture of transition metals. X is a variable number, changing from about 0 to about 0.5 between the reversible oxygen-deplete and oxygen-rich forms of the oxide. In an elevated temperature and oxygen-containing atmosphere, the thin film can undergo reversible bulk oxidation resulting in a detectable change of its physical properties such as mass, optical transmissivity and electrical resistance.

Fluxed lanthanum chromite for low temperature air firing

Abstract: A lanthanum chromite ceramic powder consisting essentially of 1 mol of LaCr1-xMxO3, where M is a divalent metal selected from the group of zinc, copper and mixtures thereof and x ranges from about 0.02 to 0.2, y mols of B2O3, where y ranges from 0.0005 to 0.04, and z mols of La2O3, where the ratio z/y ranges from 1 to 3, the powder is sintered to high density by firing a compact thereof at a temperature of about 1400 °C in air or other atmosphere, and is particularly suited for use as interconnect material for solid oxide fuel cells.

Studies of the hydrogen evolution reaction on lanthanum phosphate-bonded composite nickel- ruthenium electrodes in 1 M alkaline solutions

Abstract: The electrocatalytic properties of lanthanum phosphate-bonded composite nickel-ruthenium electrodes for the hydrogen and oxygen evolution reactions were studied in 1 M KOH at 25°C. Ruthenium was chemically deposited on nickel powder particles,prior to polymerization of Ni/Ru powder with lanthanum phosphate. X-ray diffraction (XRD), X-ray fluorescence (XRF), BET, differential thermal analysis (DTA), scanning electron microscopy (SEM), EDX and u.v./vis. spectrophotometry were used to investigate the composition, morphology and characteristics of the electrodes. The influence of the ruthenium content and polymerization temperature on the electrocatalytic activity for hydrogen and oxygen evolution were studied. The mechanism and kinetics of the hydrogen evolution reaction (HER) were investigated using both steady-state polarization and a.c. impedance techniques.

Via fill paste and method of using the same containing specific amounts of silver, gold and refractory oxides

Abstract: The present invention provides a new and useful via fill paste for use in the construction of electronic circuit devices. The unique via fill paste is capable of electrically connecting conductive layers made of dissimilar metals such as gold and silver. The via fill paste includes gold, silver, palladium and a refractory oxide. The refractory oxide comprises one or more metals selected from the group consisting of zirconium, yttrium, niobium, tantalum, lanthanum, thorium, hafnium, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

Low-temperature chemical routes to formation and IR properties of lanthanum sesquisulfide (La2S3) ceramics

Abstract: Lanthanum sulfide (La2S3) exists in three different allotropic forms in the crystalline state. The low-temperature orthorhombic phase (α) transforms to the intermediate tetragonal phase (β) which further undergoes transformation to the high-temperature cubic phase (γ). The intermediate tetragonal phase (β) is an oxysulfide with possible use as a phosphor, and the cubic phase (γ) of La2S3 shows potential for application as a far IR (8–14 µm) window material. We report metal-organic synthesis routes for the preparation of the β- and γ-phases of La2S3 by processing modifications and choice of precursor chemistry. The alkoxide-derived precursors and the transformed sulfide powders were characterized for morphology, microstructure, and thermal stability. Phase evolution studies were also conducted, and the results are discussed in the context of formation of the β- and γ-phases. Results of densification, microstructure, and infrared transmission characteristics are also presented.

Air-sinterable lanthanum chromite and process for its preparation.

Abstract: A sinter-reactive lanthanum chromite powder is prepared from the lanthanum chromite precursor LaCr1-xMxO3 (Adsorbate). The powder is crystalline, has the formula LaCr1-xMxO3, where M is selected from the group consisting of zinc, copper and mixtures thereof and x ranges from about 0.02 to 0.2, and sinters to densities higher than about 95 % of theoretical density at a temperature as low as 1400 °C in oxidizing atmospheres. Sintering to such high density at temperatures in the vicinity of 1400 °C makes the powder particularly suited for use as interconnect material for solid oxide fuel cells.

Catalysts for the removal of sulfur compounds from industrial gases, a process for their production and their use

Abstract: Catalysts useful for the removal of volatile sulfur compounds from industrial gases composed of an inorganic, abrasion-resistant, incombustible support which is uniformly impregnated with either (a) an oxide or hydroxide of niobium or tantalum or (b) an oxide or hydroxide of manganese and an oxide or hydroxide of hafnium, lanthanum or an element in the Lanthanide Series of Elements

Non-aqueous chemical synthesis of tetragonal (β-La2S3) lanthanum sulfide powders

Abstract: Lanthanum sulfide (La2S3) exhibits several different allotrophic forms, of which β-La2S3 is an intermediate polymorph that is stable at temperatures of 900 °C. It exhibits the tetragonal structure and could be a potential phosphor material. Traditionally, β-La2S3 has been synthesized using melt solidification and gas-solid reactions which require extended heat treatment cycles, invariably resulting in the formation of mixed phases. In this paper, low temperature non-aqueous chemical synthesis routes have been developed using inorganic and metallorganic starting materials to synthesize ultrafine ( ≈ 20 nm ) sulfide precursors. The precursors on sulfidization at 1000 °C for 8 result in the formation of fine ( ≈0.5–1.0 μ m ) β-La2S3 particles. The physical, thermal, and microstructural chemistry of these precursors have been assessed using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and electron microscopy (SEM/TEM) with a view to understand the synthesis mechanism and the tetragonal phase formation.

Multicomponent oxide catalyst

Abstract: The present invention relates to a novel multicomponent oxide catalyst, more specifically, a highly active and selective catalyst composition which plays a vital role to produce unsaturated nitrile compounds by reacting paraffinoid hydrocarbons with ammonia and oxygen. The formula of catalyst composition of the present invention is represented as A a B b C c D d In e Ga f Bi g Mo i O x . wherein: A is alkali metal, alkali earth metal, silver or copper; B is nickel, cobalt, iron, chromium, ruthenium, palladium or manganese; C is zinc, cadmium, cerium, tin, phosphorus, antimony, lead, tellurium, germanium or aluminum; D is titanium, zirconium, vanadium, niobium, tantalum, lanthanum, neodymium, gadolinium or tungsten; and, a, b, c, d, e, f, g and i is the mole of each component, wherein, a is 0 to 10; b is 0 to 5; c is 0 to 15; d is 0 to 14; e is 0 to 2; f is 0 to 7; g is 1 to 25; i is 12 to 40; and, 12≦a+b+c+d+e+f+g≦40.