Showing papers on "Lanthanum published in 1987"

Surface characterization and catalytic properties of La1−x -Sr x CoO3

Abstract: The surface chemical states of the perovskite-type compounds, strontium doped lanthanum cobalt oxides (La1−xSrxCoO3), have been investigated using X-ray photoelectron spectroscopy (XPS). Catalytic oxidations of both methane and CO have also been investigated using flow methods. The chemical composition of the surface of La1−xSrxCoO3 was very different from that in the bulk, which was measured by X-ray fluorescence spectroscopy (XRFS). The catalytic activity of La1−xSrxCoO3 increased with an increase in the quantity of cobalt atoms on the surface.

Catalyst for the purification of exhaust gas

Abstract: A catalyst for the purification of exhaust gases capable of maintaining excellent durability at elevated temperatures and preventing the formation of LaAlO 3 , comprises a support substrate, a catalyst carrier layer formed on the support substrate and catalyst ingredients carried on the catalyst carrier layer. The catalyst carrier layer comprises oxides of lanthanum and cerium in which the molar fraction of lanthanum atoms to the total rare earth atoms is 0.05 to 0.20, and the ratio of the member of the total rare earth atoms to the number of aluminum atoms is 0.05 to 0.25.

Preparation of yttrium, lanthanum, cerium, and neodymium basic carbonate particles by homogeneous precipitation

Abstract: Uniform yttrium, lanthanum, cerium, and neodymium basic carbonate particles were prepared by homogeneous precipitation. Powders were characterized with respect to size, shape, crystal structure, and thermal decomposition behavior. Yttria precursor particles were spherical, monosized (0.4 {mu}m), and amorphous; whereas lanthana, neodymia, and ceria precursors were prismatic (ranging from 1 to 6 {mu}m in size) and crystalline. Crystal structure was found to be ancylite-type orthorhombic symmetry in all three cases. Upon heating in air, yttrium, lanthanum, and neodymium precursors underwent two-step decomposition to first form oxycarbonate and then oxide. Cerium hydroxycarbonate decomposed in a single step to form the oxide.

Catalyst for treatment of exhaust gases from internal combustion engines and method of manufacturing the catalyst

Abstract: This invention relates to a catalytic composite for treating an exhaust gas comprising a support which is a refractory inorganic oxide having dispersed thereon lanthanum, at least one other rare earth component and at least one noble metal component selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium. An essential feature of said catalytic composite is that the lanthanum be present as crystalline particles of lanthanum oxide which have an average crystallite size of less than about 25 Angstroms. The support may be selected from the group consisting of alumina, silica, titania, zirconia, aluminosilicates and mixtures thereof with alumina being preferred. This invention also relates to a method of manufacturing said catalytic composite. In particular, an important feature of said method of manufacturing is the dispersion of lanthanum oxide onto said refractory inorganic oxide support.

The ammonium-bromide route to anhydrous rare earth bromides MBr3

Abstract: The use of NH 4 Br in the conversion of rare earth oxides (M 2 O 3 ), hydrated bromides (MBr 3 · x H 2 O) or the metals scandium, yttrium and lanthanum to lutetium, to anhydrous tribromides (MBr 3 ) provides a plethora of chemistry. In general, the two-step procedures start with the synthesis of a ternary bromide: (NH 4 ) 2 MBr 5 for M ≡ La to Nd and (NH 4 ) 3 MBr 6 for M ≡ Sm to Lu, Y, Sc. This is achieved at 200–250 °C from hydrated ternary bromides in an HBr gas stream, at 280 °C from NH 4 Br and M 2 O 3 (a 10:1 molar ratio for M ≡ La to Nd and a 12:1 molar ratio for M ≡ Sm to Lu, Y, Sc) or at 300 °C from NH 4 Br and M mixtures. The subsequent step is the decomposition of the ternary bromide to the binary tribromide MBr 3 in a vacuum at 350–400 °C. The actual decomposition pathways are dependent upon the size of the trivalent cation and may pass through the intermediate NH 4 M 2 Br 7 (M ≡ Nd to Dy).

Solid compositions for fuel cells, sensors and catalysts

Abstract: Solid materials for use as electrolyte (62) for a fuel cell, or for a sensor, or as a catalyst. Representative structures include lanthanum fluoride, lead potassium fluoride, lead bismuth fluoride, lanthanum strontium fluoride, lanthan strontium lithium fluoride, calcium uranium cesium fluoride, PbSnF4, KSn2F5, SrCl2.KCl, La1-pOF1+2p 0.1 < p < 0.3, PbSnFq.PbSnOr 0.0001 < q, r < 1, lanthanumoxyfluoride, SmaNdbFcOd 2.18 < a, b < 9.82, 12 < c < 29.45, 3.25 < d < 12, a+b ~ 12, c+2d ~ 36 and the like. In another aspect, the present invention relates to a composite and a process to obtain it of the formula: A1-yByQO3 having a perovskite or a perovskite-type structure as an electrode catalyst in combination with: AyB1-yF2+y as a discontinuous surface coating solid electrolyte, wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, and scandium, B is independently selected from strontium, calcium, barium or magnesium, Q is independently selected from nickel, cobalt, iron or manganese, and y is between about 0.0001 and 1, which process comprises: (a) obtaining a particulate of: A1-yByQO3, wherein A, B and y are defined hereinabove having an average size distribution of between about 50 and 200 Angstroms in diameter; (b) reacting the particle of step (a) with a vapor comprising: AyB1-yF2+y, wherein A, B and y are defined hereinabove, at about ambient pressure at between about 0 and 1000°C; for between about 10 and 30 hr. obtain a composite of between about 25 to 1000 microns in thickness; (c) recovering the composite of step (b) having multiple interfaces between the electrode and electrolyte. In another aspect the invention relates to the heating of these solid materials with oxygen and water to obtain higher ionic conductivity. In another aspect the invention relates to the electrochemical doping of oxide ions present by treatment of the electrode-lanthanum fluoride interface at between about 0 and 400°C in an oxygen environment at between about 10-3 and 10-6 amperes per square centimeter for between about 1 and 60 minutes. The invention also includes the use of the fuel cells disclosed to generate electricity.

Sintering aid for lanthanum chromite refractories

Abstract: An electronically conductive interconnect layer for use in a fuel cell or other electrolytic device is formed with sintering additives to permit densification in a monolithic structure with the electrode materials. Additions including an oxide of boron and a eutectic forming composition of Group 2A metal fluorides with Group 3B metal fluorides and Group 2A metal oxides with Group 6B metal oxides lower the required firing temperature of lanthanum chromite to permit densification to in excess of 94% of theoretical density without degradation of electrode material lamina. The monolithic structure is formed by tape casting thin layers of electrode, interconnect and electrolyte materials and sintering the green lamina together under common densification conditions.

Synthesis, structure, and superconductivity of single crystals of high-Tc La1.85Sr0.15CuO4, a lanthanum strontium copper oxide

Abstract: Le compose du titre cristallise dans le systeme quadratique, groupe d'espace I4/mm et sa structure est affinee jusqu'a R=0,016. Coordination octaedrique quadratique allongee autour de Cu

Luminescent mixed borates based on rare earths.

Abstract: Monophase crystalline mixed borates having the formula: M(II)1-xEu(II)xM(III)pEu(III)qTb(III)rB9O16 wherein M(II) is at least one bivalent metal selected amongst barium, strontium, lead and calcium, it being understood that, in a given mixed borate, the lead and the calcium, together represent not more than 20% by moles based on the total number of moles of metals M(II); M(III) is a metal selected amongst lanthanum, gadolinium, yttrium, serium, lutetium and bismuth; x is a number higher or equal to zero and smaller than or equal to 0.2; p, q and r represent each a number which may vary from 0 to 1, it being understood that, for a given borate: one of the numbers x, q and r is different from zero; and the sum p + q + r equals 1; preparation method and luminescent composition containing them.

Physical properties of some rare earth tellurite glasses

Abstract: Mossbauer and IR spectra as well as the electrical conductivity have been measured to give an idea about the structure and the electrical properties of some rare earth tellurite glasses containing Fe2O3. The glasses denoted [1 − (2x + 0.05)] TeO2 ·xFe2O3 · (x + 0.05) Ln2O3, wherex = 0.0 and 0.05 and Ln = lanthanum, neodymium, samarium, europium or gadolinium, were prepared by fusing a mixture of their respective reagent grade oxides in a platinum crucible at 800° C for one hour. The Mossbauer parameters such as isomer shift, quadruple splitting and line width were found to be a function of the polarizing power (charge/radius) of the rare earth cations. The Mossbauer parameters were not affected by the heat treatment of the glass samples. Both of the Te-O-Ln and Te-O-Fe stretching vibrations were obtained from the IR results which indicate that the rare earth oxides and iron oxide are partially covalent. The electrical resistivity was measured as a function of temperature from 293 to 520 K. Both the electrical resistivity and the activation energy were found to be a function of the atomic number (Z) of the rare earth cations. The results were interpreted on the basis of the electronic structure of the glass.

Precise measurement of cerium and lanthanum isotope ratios.

Abstract: The isotope ratios of cerium and lanthanum are determined precisely by a surface ionization mass spectrometer. 138Ce/142Ce and 140Ce/142Ce ratios for Ce standard solution are 0.0225762± 0.0000014 (2σ) and 7.9471±0.0003 (2σ), normalized to 136Ce/142Ce=0.01688, respectively. 138La/139La ratio is 0.0009025±0.0000005 (2σ). The oxygen isotope ratios in measurements of REE as oxide ions are 0.0003916±0.0000014 (2σ) and 0.002129±0.000010 (2σ) for 17O/16O and 18O/16O. The isotopic abundances (%) of 136Ce, 138Ce, 140Ce and 142Ce are calculated to be 0.1878, 0.2512, 88.433 and 11.128, respectively. The isotopic abundances (%) of 138La and 139La are calculated to be 0.09016 and 99.9098. These isotopic abundances obtained here give the following relation:(138La/142Ce)ATOMIC=0.008173×(La/Ce)WEIGHT.These precise isotopic abundances on Ce and La are fundamental values in a La-Ce geochronometer.

Even Lanthanum Copper Oxide is Superconducting

Abstract: The current excitement in superconductivity started with the discovery last year that lanthanum copper oxide when suitably doped with barium or strontium is a superconductor at temperatures up to 40 K. Now, researchers from France, IBM San Jose and Yorktown Heights and Bell Communications Research report that even the undoped lanthanum copper oxide is a superconductor with critical temperature up to 40 K. On the other hand, researchers at Exxon Research and Engineering Company have obtained definitive evidence for a transition to an antiferromagnetic phase in this compound (see figure, this page). Whether the low‐temperature phase of lanthanum copper oxide is antiferromagnetic or superconducting, researchers believe, depends very sensitively on lanthanum and oxygen concentrations.

Superconductivity in square-planar compound systems

Abstract: A superconducting composition comprising an oxide complex of the formula [L1-xMx]aAbOy wherein L is lanthanum, lutetium, yttrium or scandium; A is copper, bismuth, titanium, tungsten, zirconium, tantalum, niobium, or vanadium; M is baryum, strontium, calcium, magnesium or mercury; and ''a'' is 1 to 2; ''b'' is 1; ''x'' is a number in the range of 0.01 to 1.0; and ''y'' is about 2 to about 4. The oxide complexes of the invention are prepared by a solid-state reaction procedure which produce oxide complexes having enhanced superconducting transition temperatures compared to an oxide complex of like empirical composition prepared by a coprecipitation - high temperature decomposition procedure. With a solid-state reaction prepared oxide complex of the invention a transition temperature as high as 100° K has been observed even under atmospheric pressure.

Effect of lanthanide ion substitutions for lanthanum sites on superconductivity of (La1−xSrx)2CuO4−δ

Abstract: By substituting various lanthanide ions for La sites up to 90% level, the effect of foreign magnetic ions on the superconductivity of (La1-xSrx)2CuO4-δ was examined. None of the 4f transition metal ions at 5% substitution level substantially destroyed the superconductivity, while a strong correlation was observed between the total spin of the 4f magnetic ions and the superconducting critical temperature, suggesting the exchange interaction between the conduction electrons and the 4f shell spins.

Determination of phosphorus by graphite furnace atomic absorption spectrometry. Part 2. Comparison of different modifiers

Abstract: Various modifiers were investigated with respect to the highest applicable pyrolysis temperature and best characteristic mass for phosphorus and also their influence on the tube lifetime and the reproducibility of integrated absorbance values. Palladium alone or with the addition of calcium was found to be the best modifier for the determination of phosphorus by graphite furnace atomic absorption spectrometry. The maximum applicable pyrolysis temperature is 1400 °C. The best sensitivity is obtained for atomisation from a pyrolytic graphite platform in a pyrolytic graphite-coated tube. The characteristic mass is around 5.5 ng (0.0044 A s)–1 with Zeeman-effect background correction. Lanthanum, yttrium and nickel modifiers permit essentially the same pyrolysis temperature and give comparable sensitivity but not short- and long-term stability of integrated absorbance signals. Lanthanum exhibits in addition a pronounced memory effect and attacks graphite when used at high concentration. Mechanisms involved in the various reactions are discussed and experiments with a dual-cavity platform were carried out to distinguish between possible mechanisms.

Catalyst and method of making a precursor for the catalyst

Abstract: A CO shift catalyst comprises the calcined form of a precursor of the approximate formula, the precursor having a layer structure (Cu+Zn).sub.6 Al.sub.x R.sub.y (CO.sub.3).sub.(x+y/2 OH.sub.12+2(x+Y) nH 2 O where R is lanthanum, cerium or zirconium x is not less than 1 and not greater than 4; y is not less than 0.01 and not greater than 1.5 n is approximately 4.

Luminescent alumino-silicate and/or alumino-borate glass comprising lanthanum and/or gadolinium and luminescent screen provided with such a glass

Abstract: Luminescent alumino-silicate and/or alumino-borate glass comprising lanthanum and/or gadolinium and activated by Tb 3+ and/or Ce 3+ and have a composition comprising 35-85 mol % of SiO 2 and/or B 2 O 3 , 1-35 mol % of La 2 O 3 and/or Gd 2 O 3 , 5-45 mol % of Al 2 O 3 and 0.5-30 mol % of Tb 2 O 3 and/or Ce 2 O 3 . The La 2 O 3 and/or Gd 2 O 3 may be replaced up to not more than 50 mol % by Y 2 O 3 , Sc 2 O 3 , Lu 2 O 3 , ZrO 2 , P 2 O 5 and/or alkaline earth metal oxides. The glass can be used in a luminescent screen, for example, of a low-pressure mercury vapour discharge lamp.

Process for removing nitrogen oxides from exhaust gases

Abstract: A process for removing nitrogen oxides from an exhaust gas containing the nitrogen oxides and an arsenic compound, which comprises bringing said exhaust gas into contact with a reducing gas in the presence of a catalyst to reduce the nitrogen oxides in the exhaust gas and render them nontoxic. There are disclosed two types of catalysts: (1) a catalyst comprising (A) an oxide of titanium, (B) an oxide of at least one metal selected from tungsten and molybdenum, (C) an oxide of vanadium, and (D) an oxide and/or a sulfate of at least one metal selected from the group consisting of yttrium, lanthanum, cerium and neodymium, and (2) the above (A), (B), (C) components and (D)' at least one metal selected from the group consisting of yttrium, lanthanum, cerium, neodymium, copper, cobalt, manganese and iron, the component (D)' being deposited on zeolite.