Showing papers on "Lanthanum published in 1982"

Production of strontium-substituted lanthanum manganite perovskite powder by the amorphous citrate process

Abstract: The amorphous citrate process has been used to produce Mn2O3, Mn3O4, LaMnO3, SrMnO3 and strontium-substituted LaMnO3. The citrate-nitrate gels were dehydrated at 70‡ C to yield solid precursor materials. The decomposition/oxidation of the precursors have been studied using thermogravimetry and evolved gas analysis. The products of decomposition have been characterized by X-ray diffraction analysis, scanning electron microscopy and, in the case of the strontium-substituted LaMnO3, by analytical electron microscopy. The surface area and residual carbon content of the strontium-substituted LaMnO3 have been determined as a function of the decomposition/oxidation temperature. Both the process yield and compositional homogeneity of the strontium-substituted LaMnO3 have been shown to increase as the decomposition temperature increases. The residual carbon content has been shown to decrease as decomposition temperature increases. However, the surface areas of the powders decrease significantly as decomposition temperature increases. Consequently, it is evident that there is a conflict in the experimental conditions required for optimum yield, homogeneity and residual carbon content compared to those required for maximum surface area.

Iron-chromium-aluminium alloy and article and method therefor

Abstract: A ferritic stainless steel alloy is provided which is hot workable and is resistant to thermal cyclic oxidation and scaling at elevated temperatures. The iron-chromium-aluminum alloy contains cerium, lanthanum and other rare earths and is suitable for forming thereon an adherent textured aluminum oxide surface. An oxidation resistant catalytic substrate made from the alloy and a method of making the alloy are also provided.

The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table

Abstract: The debate as to whether lanthanum and actinium or lutetium and lawrencium should be placed in group IIIB of the periodic table along with scandium and yttrium has along but poorly publicized history.

Process for producing conjugated diene polymer using a solubilized lanthanum carboxylate catalyst

Abstract: A process for producing a conjugated diene polymer, characterized by polymerizing at least one conjugated diene with a catalyst consisting of (A) a reaction product of a Lewis base and a carboxylate of a rare earth element of the lanthanum series represented by Ln(R1 CO2)3 wherein Ln is a rare earth element of the lanthanum series having an atomic number of 57 to 71 and R1 is a hydrocarbon substituent having 1 to 20 carbon atoms, (B) an organic aluminum compound represented by AlR2 R3 R4 wherein R2, R3 and R4, which may be identical or different, represent hydrogen atoms or hydrocarbon substituents having 1 to 8 carbon atoms, excluding the case where all of R2, R3 and R4 are hydrogen atoms at the same time, and (C) an (alkyl)aluminum halide represented by AlXn R5 3-n wherein X is Cl, Br, F or I; R5 is a hydrocarbon substituent having 1 to 8 carbon atoms; and n has a value of 1, 1.5, 2 or 3, or consisting of these (A), (B) and (C) components and (D) a conjugated diene. A polymer obtained by said process has a high cis-1,4-configuration content and is excellent in physical properties of vulcanizate.

Self-consistent electronic structure of lanthanum dihydride and lanthanum trihydride

Abstract: The electronic structures of lanthanum dihydride and trihydride have been evaluated self-consistently using a semirelativistic Korringa-Kohn-Rostoker method. The results indicate a charge transfer to the tetrahedral hydrogen for the dihydride, but no charge transfer to the additional octahedral hydrogen for the trihydride. The energy gap in the trihydride is found to be greatly reduced from the value obtained from non-self-consistent calculations, but otherwise the effects of self-consistency are minor. The results are discussed together with recent experimental and theoretical studies which have focused on the observed metal-semiconductor phase transition.

Heptamethylindenyl lanthanide(III) complexes of lanthanum, neodymium, and erbium

Abstract: Both the steric bulk and the electronic character of this ligand resulting from the seven methyl groups favor the stabilization of the lanthanide-carbon bonds. Alkali metal salts of heptamethylindenide(Hmi) were used as precursors of the lanthanide complexes. Lanthanum, erbium or neodymium chlorides were added to a stoichiometric amount of potassium Hmi, allowing the mixture to stand at 25/sup 0/C ca 2 days. The product was crystallized and purified by slowly evaporating the remaining THF solution. Solid impurities had already been removed by centrifugation. Complexes were all soluble in THF, benzene, cyclohexane, and unstable in carbon disulfide, alcohols, ketones, DMSO. Each complex was distinguished from the starting material by NMR, and was characterized by ir, uv and visible spectroscopy. 1 table.

Effect of rare-earth oxide on the properties of piezoelectric ceramics

Abstract: The influence of rare-earth oxide on the Sr0.02Pb0.98(Li0.008W0.012Ti0.46Zr0.52)O3 composition is studied. The ion size of rare-earth oxide are between those of Pb2+ and Zr4+, so both A-and B-sites are occupied for the same kind of doping. By the weight change method and lattice parameter variation method, the percent substitution of each kind doping can be calculated. For the lanthanum series, La3+, Nd3+ favor to the production of A-site vacancy, and Er3+ favor to the production of O-site vacancy. The piezoelectric properties of each kind of doping were measured too.

Site-selective excitation of europium-doped lanthanum oxycarbonates

Abstract: The excitation at 77 K of the fluorescence of europium in two europiumdoped polymorphs of lanthanum oxycarbonate (LaO)2CO3, type Ia and type II, by UV light yielded several5D0 →7F0 transitions around 5800 A for both compounds. Selective excitation at 77 K of these5D0 levels with a Rhodamine 6G dye laser permitted the identification of La2O3 as a trace impurity in both compounds, and demonstrated the existence in both of two nearly axial sites for the europium atoms. Second-rank crystal field parameters are large (1000 cm−1) for one of the two sites. In the case of type Ia the spectrum is very close to that found for other oxysalts with the quadratic (LnO)nn+ layer such as the oxyhalides.

Lanthanum-139 nuclear magnetic resonance spectra of lanthanum complexes

Abstract: Lanthanum-139 n.m.r. spectra are reported for a variety of lanthanum complexes and systems. The 139La linewidths vary greatly and, as expected, an important factor appears to be the symmetry of the environment around the lanthanum. Information concerning complex formation by the La3+ ion is obtained from the variations in both the 139La chemical shifts and the linewidths when a ligand is progressively added to anhydrous La[ClO4]3 in MeCN. Slow ligand exchange is found with the [La{P(NMe2)3O}6]3+ ion, and with the ethylenediamine and diethylenetriamine complexes.

Reduction of matrix interferences in the determination of lead in aqueous samples by atomic-absorption spectrophotometry with electrothermal atomisation with lanthanum pre-treatment

Abstract: A previous paper described a lanthanum pre-treatment procedure for overcoming matrix interferences in the determination of lead in drinking water. In this paper, the amounts of lanthanum and nitric acid employed have been optimised such that the technique is now applicable to a wide range of aqueous samples, for example river waters, borehole waters, sewage effluents and trade effluents. The technique has been tested and found to be satisfactory for samples containing up to 1150 mg l–1 of chloride, 1420 mg l–1 of sulphate, 760 mg l–1 of sodium and 1530 mg l–1 total hardness (as calcium carbonate). The optimum pre-treatment conditions for samples was 1%V/V nitric acid and 0.05%m/V of lanthanum (as lanthanum chloride), which completely overcame suppressive interferences in the determination of lead, and gave a furnace tube lifetime of approximately 600 firings. This investigation enabled a close study to be made of the processes by which interferences are overcome by nitric acid-lanthanum matrix modification, and some possible mechanisms are presented and discussed.

Catalytic system for producing mixtures of methanol and higher alcohols

Abstract: A catalytic system and process for producing mixtures of methanol and higher alcohols from synthesis gas, the catalytic system comprising zinc, chromium, copper, one or more alkaline metals, and possibly one or more metals chosen from molybdenum, manganese, lanthanum, cerium, aluminum, titanium and vanadium, either all or only part of said elements being chemically bonded to oxygen and/or together.

Self-compensation in lanthanumdoped calcium titanate

Abstract: The reversible change of oxygen content observed by gravimetric measurements on lanthanum (donor)-doped calcium titanate between specified states of reduction and oxidation is proportional to the lanthanum concentration. These measurements indicate that the lanthanum addition is compensated by additional oxygen up-take in the oxidized state. The range of this reversible change in oxygen stoichiometry is up to more than an order of magnitude larger than the oxygen non-stoichiometry of the undoped CatiO3. There is excellent agreement between the calculated amounts of oxygen necessary to compensate the donor-dopant and the measured reversible oxygen weight-change between the oxidized and reduced state of equilibration. A single-phase region from La0.06Ca0.94Ti 0.06 3+ Ti 0.06 4+ O3 to La0.94Ca0.94TiO3.03 has been confirmed. The gravimetric measurements can be explained by a model involving a shear structure.

Computer Modeling of Simple Point Defects in Rare Earth Doped Alkaline Earth Fluorides.

Abstract: The results of a package of FORTRAN computer programs for modelling defects in ionic crystals and for fitting experimental data are described. The fundamental concept of the defect simulation is similar to HADES except that the minimisation procedure is different since the package is designed to run on small computers. As an example of the use of this package, the relative stabilities of NN and NNN complexes for various rare earths, Ianthanum and yttrium are considered. First, the data-fitting routine was used to analyse relaxation data for NN and NNN complexes in rare-earth-doped strontium fluoride. The experimental results for strontium fluoride were then used in conjunction with the defect-simulation program to determine potentials for all of the rare earths, yttrium and lanthanum. Those rare-earth potentials were then used in the simulation of calcium fluoride and show that the NNN complex should not be observable except for possibly the smallest rare earths. This implies that the B site of Wright and co-workers or the RII relaxation requires another explanation. Also, the potentials were used in the simulation of barium fluoride, showing that the NN complex should be observable only for the largest rare earths or lanthanum. Next, the enthalpy for NN to NN reorientation via the interstitialcy mechanism was calculated for rare earths in calcium and strontium fluoride. In general, the calculated reorientation enthalpies are larger than the experimental values. However, the variation of the enthalpy with the size of the rare earth is in reasonable agreement with experiment. Finally, the variation of the calculated enthalpy with pressure is found to be in excellent agreement with experiment.

Vinyl chloride resin composition

Abstract: PURPOSE:To prepare the titled resin composition having excellent thermal stability, colorability, transparency, processability, etc, by adding a specific organic rare earth metal compound to a vinyl chloride resin CONSTITUTION:100ptswt of a vinyl chloride resin is incorporated with 01- 100ptswt, pref 20-50ptswt of an organic rare earth metal compound of formula (R, R' and R'' are 1-18C saturated, unsaturated or aromatic hydrocarbon group or alkoxyalkyl; M is rare earth element composed mainly of cerium and lanthanum; Z is residue of saturated, unsaturated or aromatic dibasic acid) Said metal compound is pref an organic lanthanum compound, and the effect is kept at a high level even at a low lanthanum content Addition of a fatty acid zinc salt, esp an organic phosphite ester and an epoxidized oil in combination, exhibits a remarkable synergistic effect

Crystal data for lanthanum chromate(V)

Abstract: LaCrO4 crystallizes in the monoclinic monazite-type structure, space group P21/n; lattice parameters and powder diffraction data are reported.

Austenitic stainless steel

Abstract: An austenitic stainless steel having good corrosion resistance, particularly in chloride environments; this is achieved by the use of a rare earth element, preferably lanthanum, singly or in combination with nitrogen, along with nickel and molybdenum at relatively low levels for an austenitic stainless steel. The composition includes 15 to 25% chromium, greater than 16 to 25% nickel, 3 to 7% molybdenum, with a rare earth element consisting of lanthanum within the range of 0.005 to 0.05% in combination with 0.1 to 0.5% nitrogen.

Lanthanum as an intracellular stain for electron microscopy

Abstract: Results obtained after the normal aldehyde fixation of duodenal enterocytes for electron microscopy have been compared with results obtained when 0.1% Malachite Green or 10mm lanthanum chloride had been added during aldehyde fixation. Sections were examined without further staining, and after counterstaining with lead citrate and uranyl acetate. In unstained sections, lanthanum-treated material showed improved contrast when compared to results from the other two methods. Also, after counterstaining, areas showing excellent contrast were much more frequent and more readily detected in the lanthanum-treated material. In the microvilli of enterocytes fixed in the presence of lanthanum, the plasmalemma-glycocalyx was defined more clearly and the results were more pleasing subjectively. When Malachite Green was present in the fixative, good contrast was observed more frequently than in routinely fixed tissues, but less often than in those treated with lanthanum. It is suggested that the addition of lanthanum chloride or Malachite Green to the fixative may prove useful in many ultrastructural studies.

Ethylene oxide catalyst

Abstract: The performance of a silver on alumina catalyst for the oxidation of ethylene to ethylene oxide is improved by the inclusion, in the raw mix for the carrier of an oxide, or oxide precursor, of zinc, lanthanum, or magnesium in the amount of 7 to 40%, calculated as the oxide.

Effects of lanthanum on the electrical and mechanical activities of frog ventricular muscle.

Abstract: The effects of lanthanum on the resting membrane potential, action potential, membrane resistance, twitch tension, and potassium contracture were investigated and the localization of the drug was studied electron microscopically in isolated frog ventricular muscle. Lanthanum in concentrations of 0.2 to 5 mm decreased the resting potential by about 5-8 mV, which was accompanied by an increase in the membrane resistance of about 43% for the depolarizing and 40% for the hyperpolarizing direction. Lanthanum caused a decrease in height and a prominent shortening of the action potential, and also, a depression of the plateau level. In addition, it increased the threshold for action potential generation depending on its concentration. The slow response action potential was inhibited by lanthanum in parallel with twitch inhibition. This finding suggests that the twitch inhibition resulted from the suppression of the slow inward calcium current. In contrast, potassium contracture was not inhibited by lanthanum. When the muscle preparation was treated with neuraminidase, the twitch inhibition caused by lanthanum was strongly depressed.Electron microscopic observation revealed that the precipitates of lanthanum were localized on the external lamina of myocytes as well as in the extracellular spaces but could never be found within the cytoplasm. No such precipitates could be detected in the neuraminidase-treated muscle.From these results it is suggested that lanthanum takes the place of calcium at the membrane surface: it modifies permeabilities to sodium, potassium and calcium ions and the excitation-contraction coupling of the ventricular muscle by replacing calcium bound to the membrane surface.