Showing papers on "Lanthanum published in 1984"

Chemistry of the elements

Abstract: Origin of the elements, isotopes and atomic weights Chemical periodicity and the periodic table Hydrogen Lithium, sodium, potassium, rubidium, caesium and francium Beryllium, magnesium, calcium, strontium, barium and radium Boron Aluminium, gallium, indium and thallium Carbon Silicon Germanium, tin and lead Nitrogen Phosphorus Arsenic, antimony and bismuth Oxygen Sulfur Selenium, tellurium and polonium The halogens: fluorine, chlorine, bromine, iodine and astatine The noble gases: helium, neon, argon, krypton, xenon, and radon Coordination and organometallic compounds Scandium, yttrium, lanthanum and actinium Titanium, zirconium and hafnium Vanadium, niobium and tantalum Chromium, molybdenum and tungsten Manganese, technetium and rhenium Iron, ruthenium and osmium Cobalt, rhodium and iridium Nickel, palladium, and platinum Copper, silver and gold Zinc, cadmium and mercury The lanthanide elements The actinideand transactinide elements (Z=90-112).

Thermochemistry of alloys of transition metals: Part IV. Alloys of copper with scandium, yttrium, lanthanum, and lutetium

Abstract: The enthalpies of mixing of liquid copper with liquid lanthanum, and with solid scandium, yttrium, and lutetium have been measured by high temperature reaction calorimetry at 1373 K. After correction for the enthalpies of fusion the limiting enthalpies of solution of the liquid metals in copper are-102 kJ mol-1 (Sc), —105 kJ mol-1 (Y), —103 kJ mol-1 (La), and —120 kJ mol-1 (Lu). We also report approximate enthalpies of solution of chromium and vanadium in copper; all values are compared with predictions published by Miedema and co-workers. The enthalpies of formation of eight congruent melting intermetallic compounds in the system Cu-Sc, Cu-Y, and Cu-La have been determined. The values are compared with corresponding data for the liquid alloys; this comparison provides approximate enthalpies and entropies of fusion for the intermetallic compounds. It is found that these entropies of fusion average 1. 1R to 1.2R,i.e., the values are comparable to those found for close-packed cubic metals. This indicates that the disordering of the two atoms probably contributes little to the entropies of fusion of the compounds.

Properties and Structure of Lanthanum Borate Glasses

Abstract: Glass formation limits were determined for the lanthanum borate glasses. Stable immiscibility prevents the formation of clear glasses over the range 0 to 20 mol% La2O3, but excellent quality glasses could be formed between 20 and 28 mol% La2O3. Data are reported for the density, refractive index, thermal expansion coefficient, glass transformation and dilatometric softening temperatures, transformation range viscosity, helium permeability, and chemical durability of these glasses. A limited Raman and infrared spectroscopy study suggests that lanthanum plays a similar structural role in these glasses and in the related crystals.

The direct observation of cation hydrolysis in lanthanum zeolite-Y by neutron diffraction

Abstract: Neutron diffraction studies on a partially dehydrated sample of lanthanum zeolite-Y (Si/Al = 2.61) reveal the locations of the hydrogen atoms, thus providing direct evidence for the cation hydrolysis and Bronsted acidity that account, tn part, for the catalytic activity of this faujasite zeolite.

Experimental and calculated enthalpies of formation of rare earth-tin alloys

Abstract: The partial enthalpies of some rare earth elements (lanthanum, cerium, thulium, lutetium and yttrium) at infinite dilution in liquid tin were determined by means of a calorimetric method. The change in this thermodynamic property with atomic number is discussed in terms of the contribution of the 4f electrons to the bonding. This assumption is used to calculate the hybridization term involved in Miedema's relation. Experimental results therefore allow an accurate determination of the parameters of Miedema's relation. These are used to calculate the enthalpies of formation of rare earth-tin compounds. The predicted values are compared with available experimental data.

Oxidation-reduction behaviour of La-doped SrTiO3

Abstract: Thermogravimetric measurements as a function of oxygen activity were performed in the temperature range of 1200 to 1400° C on a series of lanthanum SrTiO3 compounds. A model which assumes the absorption of excess oxygen in the structure which compensates the donors by formation of cationic defects is postulated. Comparison of this model with the experimental results show reasonable agreement.

The action of lanthanum ions and formaldehyde on the proton-pumping function of bacteriorhodopsin.

Abstract: The photochemical cycle and the proton-pumping function of bacteriorhodopsin modified with lanthanum and formaldehyde has been studied. In both preparations, the M412 leads to BR570 transition time has been found to increase considerably. The deceleration of the photochemical cycle has been shown to be accompanied by inhibition of the millisecond phase of the photoelectrical response of bacteriorhodopsin membranes associated with phospholipid-impregnated collodion film. Photoelectrogenic activity measured with permeable ion probe in proteoliposomes was also inhibited. Effects of lanthanum were reversed by EDTA. Formation of M412 was slightly accelerated and the microsecond electrogenic phase was not affected by lanthanum and by formaldehyde. It is concluded that lanthanum, but not formaldehyde, can be used as a specific reversible inhibitor of the second half of the bacteriorhodopsin photocycle and of the associated H+ uptake on the cytoplasmic side of the halobacterial membrane. Possible mechanisms of these effects are discussed.

Electrical properties of La-doped SrTiO3 (La: 0.1 to 2.0 at %) single crystals grown by xenon-arc image floating zone method

Abstract: Lanthanum-doped semiconducting strontium titanate single crystals having various lanthanum contents were grown in an air atmosphere by the xenon-arc image floating zone method. The crystals were characterized by X-ray powder diffraction, EPMA analysis and chemical analysis. Each lanthanum was accompanied by a trivalent titanium ion in the grown crystal. The electrical conductivity of these crystals was measured at 20 to 1150° C, and it was found to increase linearly with increasing lanthanum content. The mobility of the charge carrier was estimated from the concentration of trivalent titanium and the conductivities of the crystals. The mobility in the low temperature region agreed with previous studies. However, a significant difference was found at high temperatures. An error in the temperature dependence in the previous study is responsible for this difference. It is stressed that care is necessary in applying the results of single crystalline studies when discussing high-temperature bulk defect chemistry.

Catalytic cracking catalysts

Abstract: Catalytic cracking catalysts and catalytic cracking process wherein the cracking catalysts are prepared by: (1) contacting a mixture of a large pore zeolite and an inorganic oxide matrix at effective conditions of temperature, pH and time with a fluoro salt; and (2) ammonium exchanging the product of step (1) to provide a catalyst having less than 03 percent by weight Na 2 O Optionally, the product is provided with an effective amount of at least one cation selected from the class consisting of cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, lutetium, gadolinium, terbium, dysprosium, holmium, erbium, thulium and ytterbium

Superconductive material of oxide and manufacture thereof

Abstract: PURPOSE:To obtain a high critical temperature by using a composite oxide composed of barium, bismuth, and oxygen and expressed by a specific chemical formula. CONSTITUTION:After uniform mixing of a Ba compound with a Bi compound or a Ba compound with an A compound [where, A is Sr, Pb, Sc, Y, or a lanthanum group element; the atomic ratio of Ba to A: A/(Ba+A) is 0.5 or less] and a Bi compound, the powder obtained by calcination at a temperature of 600 deg.C or more is molded by pressing in an oxidizing atmosphere, and next a large amount of oxygen defect produced at the step of calcination is repaired by firing at 700 deg.C or more under a pressure of 10kg/cm or more of oxygen or 10kg/cm or more of partial pressure of oxygen, thereby forming BaBiO3-delta (0<=delta<0.5) or a material with the Ba in this chemical formula replaced with Sr, Pb, Sc, Y, or a lanthanum group element within a range of 50atm% or less. This manner enables the production of the titled material having a superconductive transfer temperature TC of approx. 12K.

Analytical and structural analysis of the lanthanum-deficient lanthanum hexaboride

Abstract: The blue lanthanum boride LaB/sub 6+delta/ previously reported as LaB/sub 9/, was investigated in arc-melted samples of LaB/sub 9/ bulk stoichiometry. The samples were structurally analyzed by high-resolution transmission electron microscopy including comparative computer imaging and analytically studied by using backscattered electron imaging, quantitative characteristic x-ray analysis, nuclear magnetic resonance, and other techniques. The blue boride observed has a composition of LaB/sub 6.13 +- 0.03/ due to random La vacancies in the LaB/sub 6/ structure and is interpreted as belonging to the nonstoichiometric LaB/sub 6/ phase region. The color change from purple to blue occurs for decreasing lanthanum content roughly at a composition LaB/sub 6/ /sub 07/. A modification of the La-B phase diagram is proposed.

Preparation and crystal structure of lanthanum molybdenum silicon oxide (La3MO4SiO14), an unusual cluster compound of molybdenum

Abstract: Preparation du compose a haute temperature par reduction electrolytique d'une phase fondue contenant Na 2 MoO 4 , MoO 3 et La 2 O 3 . Cristallisation dans le reseau orthorhombique, groupe Pnma. Affinement jusqu'a R=0,042. La structure presente des motifs triangulaires Mo 3 O 13 et des chaines d'octaedres MoO 6 a aretes communes. Coordination tetraedrique autour de Si et prismatique rhomboedrique autour de La

Crystal and Molecular Structure of the 4:3 Complex between Lanthanum Nitrate and Pentaethyleneglycol Dimethyl Ether†

Abstract: The crystal and molecular structure of [La(NO3)3]4(C12H26O5)3 has been determined from low-temperature single-crystal X-ray diffraction data. The complex crystallizes in the monoclinic space group I2 with Z = 2. Lattice parameters at 150 K are a = 12.234 (6) A, b = 11.105 (5), c = 26.613 (9), β = 90.65 (4)°. The structure was solved by Patterson and Fourier techniques and refined to a conventional RF-value of 0.068. The compound contains three dinitrato complex cations [La(NO3)2C12H26O6]+ with 10-coordinate lanthanum ions and one hexanitrato anion, [La(NO3)6]3−, with a 12-coordinate La(III)-ion. One complex cation has a C2-symmetry while the two others, which are crystallographically equivalent, have no symmetry and contain a disordered ligand molecule. The polyther adopts a ring-like conformation in all the complex moietis. The LaO(nitrate) distances lie in the ranges 2.52–2.53 and 2.49–2.62 A, with average values of 2.53 (7) and 2.56 (6) A, respectively, fo the species with C2- and C1-symmetry; the LaO(ether) bond lengths lie int he range 2.54–2.79 A (average: 2.6 (1)) for the C2-moiety and their mean value amounts to 2.6 (2) for the disordered species. The hexanitrate has a C2-symmetry and the LaO distances range between 2.56 and 2.67 A with an average value fo 2.64 (4) A. The effective ionic radii of the 10- and 12-coordinate La(III) ions are estimated as 1.28 and 1.33 A, respectively.

The leaching behavior of a glass waste form -- Part I: The characteristics of surface layers

Abstract: The Soxhlet-type leaching test was carried out on borosilicate glass that contained 14 wt% simulated high-level waste. The morphology, texture, composition, and crystallography of the surface layers that formed were examined using optical microscopy, scanning electron microscopy, electron probe microanalysis, and analytical electron microscopy. Four surface layers, made up of 100- to 1000-A crystalline and noncrystalline particles, formed on the glass. The elements found were classified into three groups based on their behavior in the surface layers. Group I contained the alkali metals, such as sodium, potassium, and cesium, which were strongly depleted from the layers as a result of leaching. Group II contained elements such as manganese, iron, nickel, zirconium, lanthanum, cerium, and neodymium, which were more concentrated in the surface layers than in the unleached part of the specimen, probably because the layers had shrunk during the drying process. Group III contained the elements which behaved inconsistently as a group: Some, such as calcium, silicon, and aluminum, were poor in the layers; magnesium and barium were present, but had concentration profiles that differed from those of Group II. Only one crystalline phase, a sheet silicate, formed in the layers. It had the expected chemical form, (Ca, Ba, La,more » Ce, Nd) /sub x/ (Mn, Fe, Zr, Mg, Ni, Al) /sub y/ (Si, Al) /sub z/ (O, OH) /sub m/ ; its formation probably influenced the leaching mechanisms.« less

Enhancement Errors in the Determination of Platinum Group Metals in Alumina-Based Matrices by Direct-Current Plasma Emission Spectrometry

Abstract: Direct-current plasma emission spectrometric analysis of platinum group metals in solutions from automobile catalyst shows significant enhancement of analyte values. Addition of a lithium buffer does not remove the interference. The only matrix constituents in these solutions were aluminum and magnesium, both of which were found to cause enhancement in the determination of platinum, palladium, and rhodium. A buffer consisting of 3500 mg/L lithium and 2500 mg/L lanthanum removed the enhancement effect of both magnesium and aluminum on these metals. 8-hydroxyquinoline also reduced the degree of interference due to aluminum, although not as efficiently as lanthanum, indicating that formation of compounds in the dc plasma is a possible source for the observed interference.

Solubility limit of La in SrZrO3

Abstract: X-ray fluorescence, X-ray diffraction and scanning electron microscopy were used to determine the solubility limit of lanthanum in SrZrO3. The solubility limit was reached at approximately 6 at % La addition, with acicular La2Zr2O7 precipitates forming at higher amounts. The lattice parameter of SrZrO3 decreased linearly from 0.580 28 to 0.580 00 nm with increasing lanthanum content up to the solubility limit.

Scanning Auger microscopy study of lanthanum partitioning in sphene-based glass‐ceramics

Abstract: Glass-ceramics are being investigated as possible hosts for the radioactive wastes that would result from recycling irradiated nuclear fuels. For a glass‐ceramic to be a superior waste form to a single-phase glass, some of the long-lived actinides and fission products must be preferentially incorporated into the lattice of the crystalline phase. The partitioning of lanthanum in sphene-based glass‐ceramics has been studied by scanning Auger electron microscopy for lanthanum concentrations from 0.2 to 2.0 mol.%. Sphene crystals (CaTiSiOs) were located in the silica-rich glass matrix by recording digital Auger images of the calcium and titanium distributions. The sphene crystals .were typically 0.5 to 5 μn in size and occupied approximately 40% of the total specimen volume. Auger spot analyses revealed that lanthanum was strongly partitioned (by at least a factor of 10) into the sphene phase of phosphorus-free glass-ceramics; however, when a small amount of phosphorus (0.7 mol.%) was included in the...

Specific heat studies of lanthanum and yttrium sesquicarbides

Abstract: The specific heats of the sesquicarbides LaC1.35 and La0.9Th0.1C1.6 (prepared by arc melting) and YC1.35 (prepared by a high-pressure technique) have been measured for the first time. No bulk specific heat anomaly appears in either lanthanum compound, even though (1) inductively measured super-conducting transition temperatures are respectively high (11.0 K for LaC1.35 and 12.7 K for La0.9Th0.1C1.6) and (2) YC1.35 is a bulk superconductor with aT c =10.5 K and Y0.7Th0.3C1.58 (also prepared by high pressure) was previously reported to be a bulk superconductor with aT c =17.1 K. The apparent correlation with preparation technique is discussed.

Development Of Calcium Lanthanum Sulfide As An 8-12μm Transmitting Ceramic

Abstract: Calcium lanthanum sulfide (nominally CaLa 2 S 4 ) has been under development for almost 4 years as an 8-12 μm transmitting ceramic. During that time, by concentrating the effort on optimizing the optical properties of this material, the absorption coefficient at 10.6 um has been decreased from 40 cm -1 to 0.6 cm -1 . Most of the present absorption is thought to be extrinsic. Studies this year have dealt with a number of areas. One of these studies was an attempt to determine the cause of the remaining extrinsic absorption. During the course of this investigation, the presence of additional phases, including calcium sulfide (CaS), has been noted. The presence of CaS is somewhat surprising as all material investigated was 12-30 mole percent calcium deficient. Point defects and "trace" impurities have also been observed. These have been characterized using electron paramagnetic resonance and excitation/emission spectroscopies. Some of the defects and impurities have been identified and their location in either calcium lanthanum sulfide or second phase CaS determined. The possible effects of these defects and impurities on the observed infrared absorption of calcium lanthanum sulfide ceramics will be discussed.

Silicon nitride bodies

Abstract: Compositions consisting of silicon nitride, hard materials such as titanium carbide and titanium nitride, and densifying agents such as lanthanum oxide or lanthanum aluminum compounds are disclosed for silicon nitride bodies.