Showing papers on "Lanthanum published in 1981"

Preparation, structure, optical, and magnetic properties of lanthanide aluminate single crystals (LnMAl11O19)

Abstract: Rare‐earth aluminates having the general formula LnMAl11O19 with Ln3+ = La, Pr, Nd, Sm, Eu, Gd, and M2+ = Mg, Ni, Co, Mn, Fe have been synthetized. This paper is devoted to mixed compounds of the series La1−xNdx Mg Al11O19 of which large single crystals have been obtained by the flame fusion method. A full refinement of the pure lanthanum compound (x = 0) having a quasimagnetoplumbite structure has been performed (final R = 0.039). Spectroscopic investigations of the (La, Nd) aluminate have allowed the measurement of fluorescence yield and lifetime of Nd3+ in the host lattice as a function of the neodymium content. Additional results have been obtained on the magnetic anisotropy, from susceptibility measurements performed on the Nd3+ aluminate in the temperature range 4–300 K.

Clustering in rare-earth-doped alkaline earth fluorides (dielectric relaxation)

Abstract: Audio-frequency capacitance and conductance measurements have been carried out for calcium fluoride doped with 1.0 mol.% of thirteen rare earths, and 10 and 20 mol.% of erbium and lanthanum; strontium fluoride doped with 0.1 and 1.0 mol.% of twelve rare earths, yttrium and lanthanum; and barium fluoride doped with 0.1 mol.% of twelve rare earths, yttrium and lanthanum. For the moderately doped calcium fluoride samples, it is found that the low-temperature (RIII) relaxation dominates the spectrum for small rare earths. For large rare earths, the dimer-associated RIV ('gettered' 2:2:2) relaxation dominates the spectrum. The primary result for strontium fluoride is the observation of a new relaxation in the heavily doped samples with an activation energy which depends strongly upon the size of the rare earth and thus is attributed to RIV dimers. Other results may be summarised as follows. The RIV dimer becomes less stable as the host size increases but also as the rare earth size decreases. For smaller rare earth dopants, RIII is more stable in the smaller hosts and appears at lower concentrations in smaller hosts. Correspondingly, the complexity of the dielectric spectrum increases for smaller hosts and smaller rare earth dopants.

Hard magnetic alloys of a transition metal and lanthanide

Abstract: A hard magnetic alloy comprises iron, boron, lanthanum, and a lanthanide is prepared by heating the corresponding amorphous alloy to a temperature from about 850 to 1200 K. in an inert atmosphere until a polycrystalline multiphase alloy with an average grain size not exceeding 400 A is formed.

Superalloy coating composition with high temperature oxidation resistance

Abstract: Coatings for iron-, nickel- and cobalt-base superalloys and the resulting coated components having good high temperature oxidation resistance. The coatings consist essentially of, by weight, 5% to 50% chromium, 3% to 30% aluminum, 0.01% to 15% tantalum, up to 10% manganese, up to 5% tungsten, up to 12% silicon, up to 10% hafnium, up to 5% reactive metal from the group consisting of lanthanum, yttrium, and other rare earth elements, up to 5% of rare earth and/or refractory metal oxide particles, and the balance selected from the group consisting of nickel, cobalt and iron, and combinations thereof. Additions of titanium up to 5% and noble metals up to 15% are also contemplated.

Determination of rare earths in monazite sand and rare-earth impurities in high-purity rare-earth oxides by high-performance liquid chromatography

Abstract: Using high-performance liquid chromatography it has been possible to separate 14 lanthanide elements in less than 40 min by elution with an α-hydroxyisobutyric acid concentration gradient LiChrosorb KAT cation exchanger (10 µm) is used as the packing material and the eluted lanthanides are detected with an ultraviolet detector after complexation with Arsenazo III The detection limit is about 01 µgDeterminations of the rare-earth composition in monazite sand and rare-earth impurities in high-purity lanthanum(III), cerium(IV), samarium(III) and yttrium(III) oxides were carried out The proposed method is more convenient than others, and the separation of major components is not necessary in analyses of high-purity rare earths; the elution time is only about 1 h

Trivalent chromium passivate composition and process

Abstract: An aqueous acidic solution and process for treating metal surfaces, particularly zinc and zinc alloy surfaces, for depositing a passivate film of improved clarity and hardness and to impart improved corrosion resistance thereto. The solution contains effective amounts of chromium ions substantially all of which are in the trivalent state, hydrogen ions to provide a pH of about 1.2 to about 2.5, an oxidizing agent, a bath soluble and compatible silicate compound present in an amount to provide improved corrosion protection to the substrate and increased hardness to the passivate film and at least one additional metal ion selected from the group consisting of iron, cobalt, nickel, molybdenum, manganese, aluminum, lanthanum, cerium, lanthanide mixtures as well as mixtures thereof. The treating solution may optionally further contain halide ions, a carboxylic acid or salt and a wetting agent.

Solubility of Lanthanum in Strontium Titanate

Abstract: The compound LaxSr,1-xTiO3 with x up to 40 at. % is observed to be homogeneous by microscopic examination. The observed X-ray powder pattern corresponds to the cubic perovskite structure. The plot of lattice constant a0 vs x indicates a Vegard's law dependence within the experimental error. There were no extraneous lines in the X-ray powder pattern.

Effect of lanthanide ions on histamine secretion from rat peritoneal mast cells.

Abstract: 1 Ions of the lanthanide series (lanthanum-lutetium) inhibit histamine release induced by allergen and anti-IgE in the presence of extracellular calcium. The inhibition is dose-dependent in the range 10(-6) to 10(-9) M and there is no marked difference in potency between the lanthanides. 2 The response to lanthanum is biphasic and higher concentrations (10(-4) M) potentiate the release. Maximal concentrations (10(-3) M) again abolish secretion. 3 The effect of concanavalin A is weakly antagonized by lanthanum but strongly inhibited by higher lanthanides. 4 Inhibition of histamine release evoked by basic agents is markedly dependent on the ionic radius of the lanthanide. In the presence of extracellular calcium, dysprosium is the most effective inhibitor. Similar results are observed with dextran. In the absence of calcium, there is a regular increase in inhibition with decreasing ionic radius. 5 Inhibition of release in the presence of calcium is immediate and does not require preincubation with the lanthanide. The antagonism due to lanthanum is competitive and the pA2 values vary with the secretagogue. In contrast, the inhibitory effect in the absence of extracellular calcium increase progressively with time. 6 These results are discussed in terms of the calcium-pools important in histamine release and the mode of action of different secretagogues.

Catalysts and process for unsaturated aldehydes

Abstract: A catalyst composition useful for the oxidation of olefins, particularly the vapor phase oxidation of isobutylene and/or tertiary butyl alcohol to produce methacrolein, consists essentially of the combination of oxides of molybdenum, cobalt, iron, bismuth, thallium, antimony, silicon, and nickel, along with one or more members of the groups consisting of the alkali metals, the alkaline earth metals, the rare earth metals including lanthanum, tungsten, and mixtures thereof. The catalyst has a BET surface area within the range of about 0.5-10 m 2 /gm and preferably within the range of about 2-6 m 2 /gm. Preferably, the catalyst has no more than about 3% of the surface area associated with pores smaller than about 100 A°. The catalyst is heated during its preparation to a temperature above 525° C., preferably above 550° C., most preferably to about 600° C., for a time sufficient to achieve the desired surface area and pore size distribution and thereby to improve selectivity to methacrolein.

Amorphous transition metal-lanthanide alloys

Abstract: An amorphous alloy of iron, boron, lanthanum, and a lanthanide wherein lanthanum and the lanthanide comprise up to 15 atomic percent of the alloy is obtained by rapidly quenching the molten alloy. The amorphous alloy is useful as a soft magnetic alloy.

Crystal fields and intensities of triply ionized rare-earth ions in cubic lanthanum oxyfluoride: an efficient 4 F 3/2 → 4 I 9/2 LaOF:Nd laser

Abstract: We report the first known completely a priori attempt to predict crystal-field splittings and luminescence properties of rare-earth impurity ions in a host crystal. Starting with the reported crystal structure, we calculate crystal-field parameters Bkm (from the three-parameter theory) and intensity parameters Ωλ (from the Judd–Ofelt theory) for the 4fn configurations of the thirteen rare-earth ions Ce3+ through Yb3+ in cubic lanthanum oxyfluoride. The Stark-splitting schemes of the 4F3/2, 4I9/2, and 4L11/2 levels of Nd3+ in LaOF are presented, and possible laser emissions originating from the 4F3/2 level are examined. Multiplet-to-multiplet and line-to-line fluorescence branching ratios are given and compared with those calculated for existing Nd3+ lasers. It is predicted that cubic LaOF that is doped with Nd3+ may be a promising tunable, efficient laser material in the wavelength region from 850 to 950 nm, corresponding to optical transitions from 4F3/2 to 4I9/2.

Process for the production of methanol from synthesis gas

Abstract: Lanthanum rhodate, or metal substituted lanthanum rhodate, having a perovskite structure is a highly active catalyst for the production of methanol from hydrogen and carbon monoxide. The lanthanum rhodate displays excellent stability and excellent selectivity to methanol.

Zone refining of rare earth metals: Lanthanum, cerium and gadolinium

Abstract: Three rare earth metals were zone refined under low contamination conditions. Where possible, effective distribution coefficients for the major impurities were determined, and these were used to estimate the ultimate potential for zone refining as a purification technique for the rare earth metals. It is concluded that zone refining will be of most value for refining with respect to certain common metallic impurities. The metallic impurity levels at one end of a zone-refined gadolinium rod are believed to be the lowest ever recorded for a rare earth metal.

Unit-cell dimensions of phases that are formed by calcium, strontium and barium or scandium, yttrium and lanthanum with other elements

Abstract: The lattice parameters of triads of intermetallic phases MxNy where M ≡ Ca, SrorBa or M ≡ Sc, YorLa with the same crystal structure and N component are found to be much more closely a linear function of the atomic numbers of the M components (atomic number rule) than they are of the diameters of the components for coordination number 12 (Dm rule). Observation of the empirical atomic number rule has previously been reported without explanation and it is confirmed by 47 sets of cell dimensions taken from triads of phases in 14 different crystal structure types. It is now shown to be a triviality resulting from, and not causing, the fact that the atomic arrays that control the cell dimensions of phases of barium or the rare earths are different from those that control the cell dimensions of phases of calcium and strontium, or scandium and yttrium and of other M components.

Gold free alloys for firing on ceramic compositions

Abstract: There is provided a gold free alloy for firing on ceramic compositions, especially for dental purposes consisting essentially of 1-70 weight % palladium, 01-35 weight % chromium, and the balance consisting essentially of cobalt There can also be present up to 1 weight % boron, up to 20 weight % molybdenum and/or tungsten, up to 8 weight % scandium, yttrium, lanthanum and/or the rare earths and up to 5 weight % aluminum, silicon, tin, indium and/or gallium

Synthetic willemite phosphors and fluorescent lamp containing the same

Abstract: Synthetic willemite phosphor for use in fluorescent lamps in the form of particles coated with from 0.001% to 0.5% of an oxide of scandium, yttrium, lanthanum or a rare earth element. Fluorescent lamps comprising the phosphor which have improved aging qualities are also provided.

Process for the o-substitution of phenols

Abstract: This invention relates to a process for reacting phenol, mono- and di-alkyl phenols having at least one free o-position with methanol and/or dimethyl ether in the gas phase to form o-substituted phenols in the presence of a catalyst of oxides of iron, chromium, silicon and at least one oxide of an alkaline-earth metal, lanthanum and manganese or in the presence of a catalyst of oxides of iron, chromium, a metal from the group comprising germanium, titanium, zirconium, tin, lead, and at least one oxide of an alkali metal, alkaline-earth metal, lanthanum and manganese.

Lanthanoid nickel arsenides with the Zr2Fe12P7 structure

Abstract: The compounds Y2Ni12As7 and Ln2Ni12As7 (Ln, all the lanthanoids except lanthanum, promethium and europium) were prepared by the reaction of stoichiometric mixtures of the elemental components in evacuated silica tubes. Their X-ray powder patterns show that they crystallize with the Zr2Fe12P7 structure. Their lattice constants are reported. The chemical bonding, the cell volumes and the valencies of the lanthanoid components in these compounds are briefly discussed.

Determination of lead in drinking water by atomic-absorption spectrophotometry with electrothermal atomisation

Abstract: The use of electrothermal atomisation to determine concentrations of lead in water, although sensitive, generally suffers from suppressive interference effects that can produce large and variable negative bias. This paper describes a procedure that employs a lanthanum pre-treatment technique, which when tested with a range of 14 drinking water samples is shown to overcome such interference. The pre-treatment technique can be either impregnation of the furnace tube with lanthanum or the addition of lanthanum (as lanthanum chloride) to each sample. The procedure has a limit of detection of less than 1.0 µg l–1, a total standard deviation of less than 1.5 µg l–1, or 5% of the concentration, and a bias of less than 5 µg l–1, or 10% of the concentration over a working range of 0–100 µg l–1, for both manual and automated injection of samples.

Synthetic Inorganic Ion-exchange Materials. XXXI. Ion-exchange Behavior of Tervalent Metals and Rare Earth Elements on Crystalline Antimonic(V) Acid Cation Exchanger

Abstract: The increasing order of ion-exchange selectivity for tervalent metal ions: Al3+<