Showing papers on "Lanthanum published in 1988"
TL;DR: In this article, aldol addition of acetone was studied over alkaline earth oxides, La 2 O 3, ZrO 2, SiO 2 Al 2 O3 and Nb 2 O 5 at 0°C to elucidate the nature of active sites.
288 citations
TL;DR: In this paper, aluminum-based amorphous alloys were found to be formed in AlY-M and Al-La-M (M=Fe, Co, Ni or Cu) ternary systems by melt spinning, and compositional ranges were 3 to 33 at%M and 3 to 22 at%Y or 2 to 18 at%La.
Abstract: New aluminum-based amorphous alloys were found to be formed in Al-Y-M and Al-La-M (M=Fe, Co, Ni or Cu) ternary systems by melt spinning. Their compositional ranges are 3 to 33 at%M and 3 to 22 at%Y or 2 to 18 at%La. The alloys containing more than about 80 at%Al have good bend ductility. The crystallization temperature Tx increases from 414 to 831 K with an increase of M and yttrium or lanthanum contents. The effect of the solute elements on Tx is interpreted to be dominated by the attractive interaction between aluminum and M, yttrium or lanthanum atoms.
263 citations
TL;DR: The effects of this element and its compounds on cellular systems are of considerable interest because of their increasing use in industry and as a substitute or antagonist for calcium in a variety of cellular reactions.
Abstract: Lanthanum belongs to the group of elements known as "lanthanons," which also includes cerium, europium, promethium, and thulium. It is the most electropositive element of the rare earth group, is uniformly trivalent, and is similar in its chemical properties to the alkaline earth elements. The effects of this element and its compounds on cellular systems are of considerable interest because of their increasing use in industry and as a substitute or antagonist for calcium in a variety of cellular reactions. Lanthanum is also being employed extensively in studying anatomical barriers, membrane structure, and subcellular transport systems, particularly the calcium pathway.
127 citations
76 citations
TL;DR: In this paper, the Seebeck coefficient in the temperature interval 300 to 1250 K has been reported for Lanthanum and transition metal mixed oxides and it has been concluded that native defects are mainly responsible for electrical conduction in these solids.
Abstract: Lanthanum and transition metal mixed oxides form an interesting series of compounds with a general formula LaMO3 (with M = Ti, V, Mn, Cr, Co, Ni and Fe). These compounds have been investigated by many workers as regards to their various physical parameters including the electrical conductivity. The new data reported in this paper refer to the Seebeck coefficient (S) in the temperature interval 300 to 1250 K. Electrical conductivity as a function of temperature has also been reported in the same temperature range and this is quite consistent with the values reported in the literature. Using these and other relevant data reported in the literature it has been concluded that native defects are mainly responsible for the electrical conduction in these solids. The nature of defect centres, charge carrier and their electrical transport mechanism is briefly discussed.
56 citations
TL;DR: La substitution de Zn ou Cu a Cr dans LaCrO 3 permet l'obtention de ceramiques denses sans controle de la pression d'oxygene lors du frittage as mentioned in this paper.
Abstract: La substitution de Zn ou Cu a Cr dans LaCrO 3 permet l'obtention de ceramiques denses sans controle de la pression d'oxygene lors du frittage
55 citations
Patent•
18 Mar 1988TL;DR: A high temperature combustion catalyst for use in a catalytic combustion type gas turbine combustor and the like, having a superior low temperature ignitionability and a superior thermal durability at a high temperature, which comprises a porous carrier layer, a catalyst component such as palladium and platinum, and first, second and third promoter components, were presented in this paper.
Abstract: A high temperature combustion catalyst for use in a catalytic combustion type gas turbine combustor and the like, having a superior low temperature ignitionability and a superior thermal durability at a high temperature, which comprises a porous carrier layer, a catalyst component such as palladium and platinum, and first, second and third promoter components, the latter four components being carried on the porous carrier layer, in which the first promoter component includes one of rare earth elements such as lanthanum, cerium, praseodymium and neodymium, alkaline earth metals such as barium, strontium and calcium, and oxides thereof, in which the second promoter component includes magnesium, silicon and oxides thereof, and in which the third promotor component includes one of heavy metals such as nickel, zirconium, cobalt, iron and manganese, and oxides thereof. A method for producing this high temperature combustion catalyst is also disclosed.
54 citations
TL;DR: In this article, the acidity and catalytic properties of LaHY zeolites, La3+ or by Ce3+ improved thermal stability, probably owing to the formation of stable oxygen complexes between rare earth cations and lattice oxygen atoms.
50 citations
TL;DR: Modified lead titanate (PT) oxalates were prepared by mixing an ethanol solution with (calcium, lanthanum, neodymium, samarium or gadolinium) and titanium with an ethanol mixture of oxalic acid containing lead, and (cobalt and tungsten) or manganese by blending.
Abstract: Modified lead titanate (PT) oxalates were prepared by mixing an ethanol solution with (calcium, lanthanum, neodymium, samarium or gadolinium) and titanium with an ethanol solution of oxalic acid containing lead, and (cobalt and tungsten) or manganese by blending. The resulting complex oxalate, after washing with ethanol for several times, was an amorphous powder with a very fine particle size. The amorphous coprecipitate gave, on calcining, a high sinterable modified lead titanate powder of compositions (Pb0.76Ca0.24) ((Co0.5W0.5)004Ti0.96)O3 or (Pb0.88La0.08) (Ti0.98Mn0.02)O3 which, on sintering, produced highly densified bodies (⩾98% theoretical density) at relatively low temperatures (1100 and 1150°C for Ca-PT and Ln-PT, respectively). Linear thermal expansion measurements, microstructural development of the modified lead titanates, and the influence of grain size onc/a ratio have also been studied.
47 citations
Patent•
23 May 1988TL;DR: In this article, a honeycomb carrier has been used for treating automotive exhaust, consisting of a layer of alumina which has dispersed of lanthanum oxide, cerium oxide, palladium oxide and rhodium metal.
Abstract: This application relates to a catalyst for treating automotive exhaust. The catalyst comprises a honeycomb carrier having deposited thereon a layer of alumina which has dispersed thereof lanthanum oxide, cerium oxide, palladium oxide and rhodium metal. The lanthanum oxide is present as crystallites that are less than about 25 Angstroms in size. The cerium oxide contains 3% lanthanum in the cerium oxide crystal lattice and the palladium oxide is present as crystallites which are less than about 25 Angstroms in size. A method of manufacturing the catalyst and process for using the catalyst are also disclosed and claimed.
45 citations
TL;DR: In this paper, it was shown that the true composition of this tetragonal phase (a = 7.355 A and c = 14.51 A ) is LaNi2.
Abstract: Seven alloys near the LaNi2 composition were studied by metallographie and X-ray techniques. Alloys that were cooled slowly were found to consist of two phases: from x = 1.75 to 2.25 and from x = 2.40 to 2.50, where x is the Ni:La ratio. A single-phase alloy was found near x = 2.30. A complete single-crystal structure analysis showed that the true composition of this tetragonal phase ( a = 7.355 A and c = 14.51 A ) is LaNi2.286. The space group is I42m and the unit cell contains 32 nickel atoms and 14 lanthanum atoms. This tetragonal structure is related to the cubic C15 Laves phase such that at ≈ ac and ct ≈ 2ac and two lanthanum atoms are removed from the tetragonal structure. The formation of this phase is thought to result from the large disparity between the lanthanum and nickel radii ( r La r Ni = 1.506 ) relative to that expected for the ideal constituent atoms of the AB2 cubic Laves phase ( r A r B = 1.225 ), which prevents the formation of the ideal C15 Laves phase.
TL;DR: Two series of lanthanum promoted nickel-alumina catalysts have been prepared by coprecipitation of the metal nitrates, using potassium carbonate, and their methanation activities of the final catalysts were determined by differential scanning calorimetry as discussed by the authors.
Patent•
26 Sep 1988
TL;DR: In this paper, a novel dehydrogenation process is described which utilizes a catalyst comprising a platinum group component, a component selected from the group comprising scandium, yttrium, lanthanum, and actinium, less than 0.3 wt. % of a halogen component, and an optional Group IA or IIA component.
Abstract: A novel dehydrogenation process is disclosed which utilizes a catalyst comprising a platinum group component, a component selected from the group comprising scandium, yttrium, lanthanum, and actinium, a component selected from the group comprising tin, lead, and germanium, less than 0.3 wt. % of a halogen component, and an optional Group IA or IIA component, all on a refractory inorganic oxide support.
Patent•
28 Sep 1988TL;DR: In this paper, 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 another noble metal component is selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium.
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. Illustrative of the other rare earth components are cerium, neodymium, praeseodymium, dysprosium, europium, holmium and ytterbium. An important feature in manufacturing the catalytic composite is the dispersion of lanthanum oxide onto said refractory inorganic oxide support. In a specific example, lanthanum may be dispersed on alumina as follows. A solution of a lanthanum salt is mixed with a hydrosol of aluminum, particles are formed from said lanthanum containing hydrosol, calcined to form an inorganic oxide particle containing lanthanum oxide, ground to give a powder of alumina containing finely dispersed lanthanum oxide. This powder in turn can be mixed with another rare earth oxide such as cerium oxide to a slurry which in turn is used to coat a solid monolithic carrier. Finally, at least one noble metal component is dispersed on said coated solid monolithic carrier.
TL;DR: La 2 Pd 2 O 5 cristallise dans P4 2 /m. as mentioned in this paper La 4 PdO 7 cristalle dans C2/m avec affinement.
Abstract: La 2 Pd 2 O 5 cristallise dans P4 2 /m. La 4 PdO 7 cristallise dans C2/m avec affinement jusqu'a 0,126
Patent•
13 Dec 1988TL;DR: Alkylene oxide adducts of organic compounds having active hydrogen atoms are prepared by a process which comprises contacting and reacting an alkyene oxide reactant comprising one or more C 2 to C 4 vicinal alkylene oxides as mentioned in this paper.
Abstract: Alkylene oxide adducts of organic compounds having active hydrogen atoms are prepared by a process which comprises contacting and reacting an alkylene oxide reactant comprising one or more C 2 to C 4 vicinal alkylene oxides with an active hydrogen containing reactant comprising one or more compounds having active hydrogen atoms in the presence of a catalytically effective amount of one or more soluble basic compounds of one or more elements of the lanthanum series (atomic numbers 57-71, inclusive) The product alkoxylates are known to be useful, for instance, as nonionic surfactants, wetting and emulsifying agents, solvents, and chemical intermediates When the process is applied to the preparation of alkylene oxide, particularly ethylene oxide, adducts of alkanols, particularly primary alkanols in the C 6 to C 24 range, the product is a valuable narrow range nonionic surfactant, characterized by relatively narrow distribution of alkylene oxide adducts
TL;DR: In this paper, the cubic phase becomes stabilized with the incorporation of either La(III or Rh(III) into the ZrO2 structure, and the properties of these compounds were studied by x-ray analysis and temperature programmed reduction.
TL;DR: In this paper, superconducting materials made of aligned eutectic-type structures were grown from the melt by a floating zone technique in the La 2− x Sr x CuO 4 -copper oxide system.
TL;DR: Two series of lanthanum promoted nickel-alumina catalysts have been prepared by coprecipitation of the metal nitrates, using potassium carbonate, and their methanation activities of the final catalysts were determined by differential scanning calorimetry as mentioned in this paper.
Journal Article•
TL;DR: The incorporation of lanthanum in the form of 140-lanthanum onto the surface of teeth, bone and synthetic hydroxyapatite was investigated and may be responsible for increased resistance of the hard tissues to acid dissolution.
TL;DR: In this article, the thermal decomposition kinetics of anhydrous lanthanide nitrates were investigated and compared with those of neodymium nitrate, and the enthalpy of decomposition was estimated as 119.6 kJ mol −1.
TL;DR: In this paper, the structure of triscyclopentadienyl-potassium with lanthanum trichloride in tetralaydrofuran was characterized by X-ray diffraction.
Abstract: [La(CsHs)a], Mr= 334.20, monoclinic, P21/c, a = 15.237 (2), b = 9.790 (2), c = 16.721 (4) A, t = 93.93 (3) °, V= 2489 (2)/~3, Z = 8, D x = 1.784 Mg m -a, 2(Mo Ka---) = 0.71073 A, g = 3.4171 mm -1, F(000) = 1296, T = 295 (1) K, R = 0.028 for 2129 observed reflections. Each La atom is r/5 bonded to three cyclopentadienide rings and r/~ bonded to a ring of an adjacent (CsHs)aLa molecule. This sharing of one C atom between the molecular units produces zigzag polymeric chains along the b axis of the unit cell. 1986) in contrast shows molecules containing just three CsH 5 ligands bonded to the metal ion. On the other hand, (CsHs)aLu , which is isotypic with (CsHs)aSc (Eggers, Schultze, Kopf & Fischer, 1986), shows an infinite chain arrangement in which each Lu atom is bounded in a pentahapto fashion to two rings and in a monohapto fashion to two other bridging rings. A novel experimental technique of preparation allowed us to obtain single crystals of a polymorphic variety of (CsHs)aLa. Its characterization by X-ray diffraction is reported here: Introduction. Molecular and crystal structures of a number of tris(cyclopentadienyl) complexes of the lanthanoids, (CsHs)3Ln, have been reported in the literature. They show various polymeric arrangements of (CsHs)aLn units. The first (rather inaccurate) structure of (CsHs)aSm (Wong, Lee & Lee, 1969) revealed a complex polymeric chain structure in which each metal ion forms contacts with four disordered tings. (CsHs)3Pr (Hinrichs, Melzer, Rehwoldt, Jahn & Fischer, 1983) also exhibits an infinite chain arrangement but each Pr ion is ~ coordinated to three close-lying CsH 5 ligands and r/z coordinated to a fourth bridging CsH 5 ligand. The La derivative (Eggers, Kopf & Fischer, 1986) was found to be isotypic with (CsHs)3Pr. The structures of (CsHs)aEr and its isotype (CsHs)aTm (Eggers, Hinrichs, Kopf, Jahn & Fischer, 0108-2701/88/040614-03503.00 Experimental. Tris(cyclopentadienyl)lanthanum was prepared under argon atmosphere, b y reaction of (cyclopentadienyl)potassium with lanthanum trichloride in tetralaydrofuran. The THF adduct was removed under controlled conditions [10 -4 tOll\" (,~ 10 -2 Pa), 363K]. Colourless prismatic single crystals obtained by extraction with n-pentane followed by recrystallization. Crystals sealed in thin-walled glass capillaries under argon. The specimen selected for X-ray analysis was 0.25 x 0.25 x 0.30 mm. Intensity data recorded on an Enraf-Nonius CAD-4 X-ray diffractometer, graphite-monochromated Mo K~ radiation. Cell parameters refined by least squares from angle data of 25 reflections. Space group unambiguously determined from systematic absences. 3632 unique reflections measured (0-20 scan mode) in range © 1988 International Union of Crystallography J. REBIZANT, C. APOSTOLIDIS, M. R. SPIRLET AND B. KANELLAKOPULOS 615 Table 1. Atomic positional and isotropic thermal parameters (A 2) with e.s.d.'s in parentheses Table 2. Selected distances (A) and angles (o) in (C5Hs)3La with e.s.d. 's in parentheses Beq=~[a2B(1 ,1 ) + b2B(2,2) + c2B(3,3) + a b c o s y B ( l , 2 ) + La(I)-C(I) 2.872(7) La(2)-C(16) 2.927(8) accosflB(1,3) + bccoso.B(2,3)]. c ( 2 ) 2.829 (7) c ( 1 7 ) 2.887 (8) c ( 3 ) 2.865 (8) -C(18) 2.874 (8) c ( 4 ) 2.892 (7) c (19 ) 2.878 (7) x y z Beq -C(5) 2.905 (8) -C(20) 2.899 (7) La(I) 0.33659 (2) 0.23895 (4) 0.81940 (3) 1.904 (9) -C(6) 2.839 (8) -C(21) 2.767 (9) La(2) 0.16422 (3) 0.74114 (4) 0.91531 (2) 1.825 (9) -C(7) 2.825 (8) -C(22) 2.81 (I) -C(8) 2.792 (9) -C(23) 2.844 (8) Ring A -C(9) 2.830 (8) -C(24) 2.827 (7) C(I) 0.2404 (5) -0-0082 (8) 0.8436 (5) 3.7 (2) -C(10) 2.842 (9) -C(25) 2.826 (8) C(2) 0.2973 (6) 0-0107 (8) 0.9143 (6) 5.1 (2) C ( I I) 2.823 (9) -C(26) 2.840 (7) C(3) 0.2647 (6) 0.1220 (8) 0.9577 (5) 5.2 (2) --C(12) 2.851 (8) -C(27) 2.819 (8) C(4) 0.1882 (5) 0.1708 (9) 0.9108 (5) 4.5 (2) -C(13) 2.869 (8) -C(28) 2.819 (8) C(5) 0.1738 (5) 0.0948 (9) 0.8434 (6) 4.7 (2) -C(14) 2.826 (8) -C(29) 2.831 (8) -C(15) 2.812 (8) -C(30) 2.840 (8) Ring B C(6) 0.5202 (5) 0.187 (1) 0.8254 (6) 5.7 (3) -C(16) 3.640 (9) C ( I ) 2.999 (8) C(7) 0.5132 (5) 0.327 (1) 0.8199 (6) 5.3 (2) -C(19) 3.404 (8) -C(2) 3.329 (9) C(8) 0.4841 (5) 0.3716 (9) 0.8906 (6) 5.6 (2) -C(20) 2.972 (7) -C(5) 3.671 (9) C(9) 0.4712 (5) 0.257 (1) 0.9442 (5) 8.0 (4) C(10) 0.4957 (5) 0.1420 (9) 0.8983 (6) 5.2 (2) -RcA* 2.609 (8) -RcD 2.630 (8) -RoB 2.563 (9) -RcD 2.554 (9) Ring C -RcC 2.575 (9) -RcF 2.561 (8) C(I I) 0.3878 (6) 0.243 (I) 0.6603 (5) 5.3 (3) RcA-La(I)-RcB 117.3 (2) ReD-La(2)-RcE 116.5 (2) C(12) 0.3322 (6) 0.1272 (9) 0.6617 (5) 5.0 (2) RcA-La(I)-RcC 115.7 (2) ReD-La(2)-RcF 114.5 (3) C(13) 0.2462 (5) 0-1774 (9) 0.6675 (5) 4.2 (2) ReA-La(I)-C(20) 95.6 (2) RcD-La(2)-C(I) 96.0 (2) C(14) 0.2494 (5) 0.3175 (9) 0.6719 (5) 3.9 (2) RcB-La(I)-RcC 116.4 (2) RcE-La(2)-RcF 117.5 (3) C(15) 0.3360 (6) 0.3609 (9) 0.6671 (1) 4.5 (2) RcB-La(I)-C(20) 109.5 (2) RcE-La(2)-C(I) 110.5 (2) RcC-La(I).-C(20) 97.6 (2) RcF-La(2)-C(1) 97.5 (3) Ring D La(2)--La(1)--La(2) 114.149 (9) La ( l ) -La (2 ) -La ( l ) 114.149 (9) C(16) 0.2834 (5) 0.6014 (9) 0.8123 (5) 4.8 (2) C(I 7) 0.3377 (6) 0.6707 (9) 0.8691 (6) 5.0 (2) C(18) 0.3335 (5) 0.6144 (9) 0-9448 (6) 4.7 (2) C(19) 0.2715 (5) 0.5001 (8) 0.9359 (5) 4.0 (2) C(20) 0.2419 (5) 0.4952 (8) 0.8543 (5) 3.5 (2)
TL;DR: The first example that demonstrates the distinct shift in selectivity towards methanol formation on the addition of Fe or La to Pd zeolite catalysts, together with enhanced activity, is reported in this article.
Abstract: The first example that demonstrates the distinct shift in selectivity towards methanol formation on the addition of Fe or La to Pd zeolite catalysts, together with enhanced activity, is reported.
TL;DR: In this article, structural studies in solution show that when lanthanum nitrate is used as a template in the reaction of 2,6-diacetylpyridine and 1,3-diamino-2-hydroxypropane a ‘3 + 3’ macrocycle containing three Lanthanum ions is the predominant species formed.
Abstract: Structural studies in solution show that when lanthanum nitrate is used as a template in the reaction of 2,6-diacetylpyridine and 1,3-diamino-2-hydroxypropane a ‘3 + 3’ macrocycle containing three lanthanum ions is the predominant species formed. Hydrogen-1 n.m.r. decoupling and n.O.e. difference spectroscopy confirms the presence of a two-fold axis of symmetry where two ‘sides’ of the macrocycle are identical and different from the third.
TL;DR: The influence of modifiers such as barium and lanthanum on the physical properties of γ-alumina has been studied in this paper, where it is assumed that the oxide layers over the surface of alumina prevent the interaction between nickel and γAl2O3, making more nickel available on the surface.
Abstract: The influence of modifiers such as barium and lanthanum on the physical properties of γ-alumina has been studied. Calcination of the modified alumina at 723 K for 5 h does not result in any compound formation as evidenced from X.r.d. Ca. 8–9 wt% nickel was prepared by impregnation method using this modified alumina. Ba and La modifiers improve the reducibility of nickel and the metal area measured by hydrogen adsorption. It is presumed that the oxide layers over the surface of alumina prevent the interaction between nickel and γ-Al2O3, making more nickel available on the surface. The activity and turnover number (TON) for benzene hydrogenation vary directly with the available metal area, irrespective of the modifier.
Patent•
15 Mar 1988
TL;DR: In this paper, the phase diagram of a single crystal of lanthanum cuprate was determined using differential thermal analysis and X-ray difractometry, and a large scale single crystal was prepared.
Abstract: Lanthanum cuprate, La₂CuO₄, is a superconductive oxide. In order to prepare a single crystal of lanthanum cuprate, the phase diagram of La₂O₃-CuO system is determined utilizing their differential thermal analysis and X-ray difractometry. Cu oxide and at least one of lanthanum oxide and lanthanum carbonate are mixed in the molar ratio of 71.1-92.9:28.9-7.1. The resulting mixture is heated to be molten. While slowly cooling the melt, nuclei of La₂CuO₄ precipitate from the melt, growing to single crystals in the melt. As a result, large scale single crystals are prepared.
TL;DR: In this paper, a method was proposed to produce films over the entire range of composition from La 2 S 3, which is an insulator, to La 3 S 4 which is a metal and a superconductor.
TL;DR: In this article, two crystalline samples of zeolite Y have been obtained in which all of the sodium ions in the original sample have been replaced by lanthanum, but which contain 26 and 19 Lanthanum ions per u.c., respectively.