Showing papers on "Lanthanum published in 2004"

Photocatalytic degradation of 2-mercaptobenzothiazole in aqueous La3+–TiO2 suspension for odor control

Abstract: The La3+–TiO2 photocatalysts were prepared by doping lanthanum ion into TiO2 structure in a sol–gel process. The catalyst samples were then characterized by XRD and XPS analyses. The analytical results demonstrated that the lanthanum doping could inhibit the phase transformation of TiO2 and enhance the thermal stability of TiO2 structure. In addition, it was found that the lanthanum doping could reduce the crystallite size and increase the Ti3+ content on the surface of the catalysts with the increase of lanthanum doping. With a purpose of odor control, 2-mercaptobenzothiazole (MBT) was used in this study as a model chemical and both the adsorption isotherm and photocatalytic activity of the La3+–TiO2 catalysts were evaluated based on the MBT photodegradation in aqueous solution. The experimental results showed that both the adsorption capacity and adsorption equilibrium constants of the La3+–TiO2 catalysts increased with an increase of lanthanum doping. The kinetics of the MBT photodegradation using different La3+–TiO2 catalysts was also studied. The experiments demonstrated that an optimum doping of lanthanum ion at 1.2% achieved the highest MBT photodegradation rate. It was concluded that the enhancement of MBT photodegradation using the La3+–TiO2 catalysts mainly involved in both the improvement of the organic substrate adsorption in catalysts suspension and the enhancement of the separation of electron-hole pairs owing to the presence of Ti3+.

Atomic layer deposited lanthanum hafnium oxide dielectrics

Abstract: Atomic layer deposited dielectric layers containing a lanthanum hafnium oxide layer and methods of fabricating such dielectric layers provide an insulating layer in a variety of structures for use in a wide range of electronic devices. In an embodiment, a lanthanum hafnium oxide layer is formed by depositing hafnium and lanthanum by atomic layer deposition onto a substrate surface. Embodiments include methods and apparatus in which precursors to deposit the lanthanum include a trisethylcyclopentadionatolanthanum precursor, a tris (2,2,6,6-tetramethl-3,5-heptanediaonato)lanthanum (III)precursor, a trisdipyvaloylmethanatolanthanum precursor, or a tris (2,2,6,6-tetramethyl-3,5-heptanedionato)lanthanum (III) tetraglyme adduct precursor.

Phase Transformations of Elements Under High Pressure

Abstract: Elements Under High Pressure: Hydrogen Deuterium Tritium Lithium Sodium Potassium Rubidium Cesium Beryllium Magnesium Calcium Strontium Barium Boron Aluminium Gallium Indium Thallium Carbon Fullerene C60 Fullerene C70 Silicon Germanium Tin Lead Nitrogen Phosphorus Arsenic Antimony Bismuth Oxygen Sulfur Selenium Tellurium Fluorine Chlorine Bromine Iodine Helium - 4 Helium - 3 Neon Argon Krypton Xenon Scandium Yttrium Titanium Zirconium Hafnium Vanadium Niobium Tantalum Chromium Molybdenium Tungsten Manganese Technecium Rhenium Iron Ruthenium Osmium Cobalt Rhodium Iridium Nickel Palladium Platinum Copper Silver Gold Zinc Cadmium Mercury Lanthanum Cerium Praseodymium Neodymium Prometium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thullium Ytterbium Lutecium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Crystallographic Data for the High-Pressure Phases of the Elements

CO2 reforming of methane over coprecipitated Ni–Al catalysts modified with lanthanum

Abstract: The influence of lanthanum oxide added to a Ni/Al2O3 catalyst has been studied in the carbon dioxide reforming of methane. The samples were prepared by variable pH coprecipitation, with different La2O3 contents: 0, 4, 8, and 12 wt.%. Although the NiO reducibility was not altered, the presence of La increased the metallic dispersion (XPS, XRD, TEM), slightly increased conversion levels, and also enhanced the catalyst stability due to a substantial decrease in coke formation during reaction. An increase in Ni dispersion in samples containing La leads to more metallic particles with diameters less than 10 nm that contribute to the catalytic conversion without producing large amounts of coke in filaments. However, there is a limit to the amount of lanthanum oxide (between 8 and 12 wt.%) above which metallic dispersion is not favored, and therefore coke filament formation and quick catalyst deactivation cannot be controlled. This is probably due to the poor La2O3 dispersion in these materials (XPS), leading to a loss in the improvement of Ni–Al–La catalyst properties. La atoms are included in the metallic nickel lattice after 4 h of reaction. After a long reaction time La is segregated and the Ni particle size increases, leading to greater coke production (in filaments).

Combustion synthesis of lanthanum chromite starting from water solutions: Investigation of process mechanism by DTA–TGA–MS

Abstract: The mechanism of combustion synthesis of lanthanum chromite was investigated by carrying out simultaneous differential thermal analysis (DTA), thermal-gravimetric analysis (TGA) and quadrupole mass spectrometry measurements (MS). The whole process was found to involve several phenomena: urea and nitrates thermal decomposition, exothermal reactions occurring directly between nitrates and urea as well as between their decomposition products, final reaction between solid oxides. In order to better understand the complex calorimetric, thermal-gravimetric and mass spectrometric curves, the behaviour on heating of each single reagent as well as that of binary mixtures, made by combining urea with each single nitrate, were also studied. Combustion synthesis was performed either under an oxidizing atmosphere or under an inert one. Chemical reactions possibly occurring during this combustion synthesis have been proposed on the basis of MS analysis of gaseous reaction products. The effect of using an excess of sacrificial fuel jointly with the addition of ammonium nitrate was also investigated.

Preparation and photocatalysis of TiO2 nanoparticles co-doped with nitrogen and lanthanum

Abstract: Nanoparticles of TiO2 powder co-doped with La and N were prepared using a coprecipitation method followed by being two hours calcinated at a temperature ranging from 500 to 600°C in NH3/Ar atmosphere. Uniformly co-doped TiO2 nanocrystalline was 5–15 nm with surface area 65–125 m2/g. Optical absorption along with the microstructural investigation for monodoped and co-doped catalyst provided that a part of O vacancy of Ti5O9 was occupied by N, which is responsible for the band-gap narrowing of TiO2, while La3+ doping prevents the aggregation of powder in process of nitrification. Superior catalytic activity was observed in the co-doped TiO2 under visible light (350 < λ < 450 nm). 20 mg/l methyl orange solution could be docomposed completely within 1 h using the 0.5 at.% La3+ doped TiO2 calcinated in NH3 for 2 h.

Atomic layer deposited lanthanum aluminum oxide dielectric layer

Abstract: Atomic layer deposited lanthanum-metal oxide dielectric layers and methods of fabricating such dielectric layers provide an insulating layer in a variety of structures for use in a wide range of electronic devices. In an embodiment, a lanthanum aluminum oxide dielectric layer is formed by depositing aluminum and lanthanum by atomic layer deposition onto a substrate surface in which precursors to deposit the lanthanum include a trisethylcyclopentadionatolanthanum precursor and/or a trisdipyvaloylmethanatolanthanum precursor.

Sonochemical synthesis of nanocrystalline LaFeO3

Abstract: Nanocrystalline perovskite-type LaFeO3 with particle size of about 30 nm was prepared by a sonochemical method using iron pentacarbonyl and lanthanum carbonate as starting materials. The overall process involves three steps: formation of lanthanum carbonate using lanthanum nitrate and urea; reaction of the so-formed lanthanum carbonate with iron pentacarbonyl resulting in the formation of a precursor; calcination of the precursor to obtain nanocrystalline particles of LaFeO3. Transmission electron microscopy revealed the particles to have a mean size of about 30 nm. Study of the magnetic properties of nanocrystalline LaFeO3 particles shows a coercivity of ∼250 Oe, while the saturation magnetization is ∼40 memu g−1.

Rare-earths as catalytic centres in organo-inorganic polymeric frameworks

Abstract: New 3D polymeric succinates of rare-earths have been synthesised: [Sc2(C4H4O4)2.5(OH)], [Y2(C4H4O4)3(H2O)2]·H2O, [La2(C4H4O4)3(H2O)2]·H2O, and their structures solved by single crystal XRD. They were obtained as single phases, characterised and tested as heterogeneous catalysts as Lewis acids in the acetalization of aldehydes and as redox agents in the oxidation of sulfides showing them to be effective and selective catalysts, easy to recover and reusable. The scandium, yttrium and lanthanum oxides were also tested in the same catalytic reactions to prove the effect of the porous organo-inorganic framework.

Does the Phosphate Binder Lanthanum Carbonate Affect Bone in Rats with Chronic Renal Failure

Abstract: . Adequate control of phosphate levels remains an important issue in patients with chronic renal failure (CRF). Lanthanum carbonate has been proposed as a new phosphate binder. Previous studies have shown a high phosphate binding capacity (>97%) and low gastrointestinal absorption of lanthanum, without serious toxic side effects in the presence of a normal renal function (NRF). Because of lanthanum’s physicochemical resemblance to calcium, the possible effects of it on bone have to be considered. The aim of this study was to investigate the effects of lanthanum carbonate on bone histology in NRF and CRF rats after oral administration of the compound with doses of 100, 500, or 1000 mg/kg per d for 12 wk. Bone histomorphometry showed that CRF animals that received vehicle developed secondary hyperparathyroidism. Urinalysis of lanthanum-loaded CRF animals showed a dose-dependent decrease in urinary phosphorus excretion, which was clearly more pronounced in the CRF groups compared with NRF animals. Phosphatemia, however, remained normal. Lanthanum carbonate administration induced a dose-dependent decrease in bone formation rate and increase in osteoid area in CRF animals. Three of seven animals in the CRF-1000 group and one of eight animals in the NRF-100 group were classified as having a mineralization defect. The number of cuboidal osteoblasts, however, was not affected, indicating that bone changes were not due to a toxic effect of lanthanum on the osteoblast. Furthermore, lanthanum concentrations in the femur remained low and did not correlate with histomorphometric parameters. These findings suggest that the administration of high doses of phosphate binder (1000 mg/kg per d lanthanum carbonate), in combination with decreased 25-(OH) vitamin D 3 in the uremic state, resulted in phosphate depletion and followed by an increased mobilization of phosphorus out of bone and/or reduced incorporation into bone. There was no evidence that lanthanum had a direct toxic effect on osteoblasts.

The Removal of Fluoride Ion by Using Metal(III)‐Loaded Amberlite Resins

Abstract: Fluoride, although beneficial to humans in small quantities, causes dental fluorosis when consumed in larger quantities over a period of time. In the present study, a novel adsorbent was used to remove fluoride from hot spring water in Japan. The adsorbents, an amberlite‐type cation exchange resin, as Amb200CT resin, which is chemically modified by trivalent metal ions such as lanthanum(III), cerium(III), yttrium(III), iron(III) and aluminum(III), were used to remove fluoride ion from hot spring water and experimental results showed that La(III)‐loaded and Ce(III)‐loaded Amb200 resins were found to adsorb fluoride rapidly and effectively. The adsorption capacity of fluoride ion for different metal(III)‐loaded Amb200 resin was in the order La(III) ≥ Ce(III) > Y(III) > Fe(III) ≈ Al(III). The optimum conditions for loading metal ions on resin and the effect of pH and initial concentration of fluoride solution and shaking time and adsorbent doses on the removal of fluoride were investigated in this s...

Efficacy and safety of lanthanum carbonate for reduction of serum phosphorus in patients with chronic renal failure receiving hemodialysis.

Abstract: BACKGROUND Lanthanum carbonate is a highly effective phosphate binder with significant potential as a treatment for hyperphosphatemia in patients with end-stage renal disease (ESRD). Here, the results of a placebo-controlled, dose-ranging study are presented. METHODS 196 patients (> or = 18 years) receiving hemodialysis for at least 6 months entered a 1- to 3-week, single-blind, placebo run-in phase. Of these, 145 patients were randomized to a double-blind phase in which they received placebo or lanthanum carbonate in daily lanthanum doses of 225, 675, 1,350 or 2,250 mg for 6 weeks. Serum levels of phosphorus, calcium and parathyroid hormone, and adverse events were monitored throughout the study. RESULTS The intent-to-treat analysis (n = 144) showed significant dose-related reductions in serum phosphorus at lanthanum doses of 675, 1,350 and 2,250 mg. After 6 weeks of treatment, phosphorus levels were significantly lower in the lanthanum groups receiving 1,350 mg/day and 2,250 mg/day, compared with the placebo group (respective changes from randomization: -0.95 +/- 1.39 mg/dl (-0.31 +/- 0.45 mmol/l), -1.13 +/- 2.01 mg/dl (-0.36 +/- 0.65 mmol/l), 0.75 +/- 1.47 mg/dl (0.24 +/- 0.47 mmol/l), p < 0.001). Significant reductions in serum phosphorus, compared with placebo, occurred in the lanthanum 1,350 mg/day group from the second week of treatment and in the 2,250 mg/day group from the first week of treatment. Adverse events were mainly gastrointestinal (e.g. nausea and vomiting). Treatment-related adverse events occurred in 39% of patients treated with lanthanum carbonate and 44% of the placebo group. CONCLUSION Lanthanum carbonate is an effective and well-tolerated agent for the short-term treatment of hyperphosphatemia in patients with ESRD.

Atomic layer deposition of lanthanum aluminum oxide nano-laminates for electrical applications

Abstract: Lanthanum aluminum oxide thin films were grown by atomic layer deposition from a lanthanum precursor, tris(N,N′-diisopropylacetamidinato)lanthanum (La(iPrAMD)3), trimethylaluminum and water. Smooth, amorphous films having compositions La0.5Al1.5O3 and La0.9Al1.1O3 were deposited on HF-last silicon and characterized without postdeposition annealing. The films contained less than 1 at. % of carbon according to Rutherford backstattering spectrometry and secondary ion mass spectrometry. A thin (9.8 nm) film showed low leakage current (<5*10−8 A/cm2 at 1 V for an equivalent oxide thickness of 2.9 nm), flatband voltage of −0.1 V and low hysteresis (20 mV). Thicker films had even lower leakage currents (<10−8 A/cm2 at 2 MV/cm) but larger flatband shifts and more hysteresis. The permittivity of the films was 13 and the dielectric strength 4 MV/cm. Cross sectional high-resolution transmission electron microscopy showed a sharp interface between the film and the silicon substrate.

Effect of substituting cerium-rich mischmetal with lanthanum on high temperature properties of die-cast Mg-Zn-Al-Ca-RE alloys

Abstract: Mg–Zn–Al–Ca–RE alloys have been found to be promising materials for substituting aluminum alloys used for automatic transmission case applications in the automobile industry. Particularly, Mg–0.5%Zn–6%Al–1%Ca–3%RE (ZAXE05613) alloy exhibits comparable creep resistance as ADC12 die-casting aluminum alloy that is currently used for automatic transmission case applications. Changing the rare earth (RE) content of the alloy from mischmetal to lanthanum gives a further improvement in the creep properties of the alloy. Lanthanum addition results in the crystallization of a large amount of acicular Al11RE3 (Al11La3) compound along the grain boundaries as well as across the grain boundaries and this effectively controls grain boundary sliding and dislocation motion in the vicinity of the grain boundaries. As a result, die-cast ZAXLa05613 alloy exhibits a higher creep resistance than that of ZAXE05613 alloy.

Raman studies of Rh and Pt on La2O3 catalysts used in a membrane reactor for hydrogen production

Abstract: Rh and Pt catalysts supported on lanthanum oxide were prepared by wet impregnation. The solids were used in a Pd–Ag membrane reactor to produce hydrogen through the carbon dioxide reforming of methane. The effect of the sweep gas flow rate and W/F upon the conversions of CO 2 and CH 4 , as well as on the production of H 2 was studied. The best performing catalyst was Rh (0.6%). It yielded a methane conversion 38% higher than the thermodynamic value and the highest H 2 permeate flux across the membrane. Lanthanum phases on the support and the catalysts were characterized by Laser Raman spectroscopy, FTIR, and XRD. The support and the calcined fresh catalysts exhibited a mixture of phases which were influenced by the metal type. Furthermore, platinum seemed to favor the formation of Ia-La 2 O 2 CO 3 after a short treatment in flowing CO 2 . However, the only remaining crystalline phase after 100 h on stream was II-La 2 O 2 CO 3 . A small amount of graphitic carbon was detected using Laser Raman spectroscopy, despite the fact that no carbon deposition was observed through TGA measurements. The graphite crystallization order seemed to be dependent upon the contact time of the reactants.

Reducing high phosphate levels in patients with chronic renal failure undergoing dialysis: a 4-week, dose-finding, open-label study with lanthanum carbonate

Abstract: Background. The majority of patients with end-stage renal disease on dialysis are hyperphosphataemic. Lanthanum carbonate has been shown to be a highly effective phosphate binder in pre-clinical studies. A 4week, open-label, dose-titration trial was conducted to assess the ability of lanthanum carbonate to control phosphate levels in patients with chronic renal failure. Methods. This preliminary study was of 6 weeks duration: 2 weeks of washout followed by 4 weeks of dose titration. Patients (n ¼ 59) were titrated on the basis of weekly serum phosphate levels from a daily dose of 375 mg lanthanum carbonate to a maximum dose of 2250 mg. Patients were maintained on the dose that controlled serum phosphate to between 1.30 and 1.80 mmol/l (4.03–5.58 mg/dl). Serum phosphate levels represented the main efficacy assessment. Safety was also evaluated. Results. Most patients were successfully titrated to 1500 and 2250 mg lanthanum/day (mean dose at end of titration: 1278 mg). At completion of the study 70% of patients achieved a serum phosphate of � 1.80 mmol/l. The use of lanthanum carbonate in patients undergoing continuous ambulatory peritoneal dialysis or haemodialysis was generally well tolerated. Conclusions. Lanthanum carbonate, a new nonaluminium, non-calcium phosphate binder, effectively reduces serum phosphate levels. Results of longer-term efficacy and safety studies are awaited with interest.

Mechanochemical synthesis of lanthanum aluminate by grinding lanthanum oxide with transition alumina

Abstract: Grinding lanthanum oxide (La2O3) with Al2O3 was conducted to investigate their mechanochemical reactions to form lanthanum aluminate (LaAlO3) powder using a planetary ball mill. Grinding for 120 min allowed us to obtain single-phase LaAlO3 with a large surface area when transition alumina was used, whereas no formation of LaAlO3 was achieved when α-Al2O3 was used. The mechanochemical process can be applied to synthesize other rare-earth (RE) aluminates (REAlO3) from mixtures of a rare-earth oxide and transition alumina.

Novel lanthanum(III) membrane sensor based on a new N-S Schiff’s base

Abstract: A novel lanthanum(III) sensor based on bis(thiophenal)phenylen-1,3-diamine (TPD) is described. The sensor was prepared by incorporating the TPD into plasticized PVC membrane. The sensor displays high selectivity for lanthanum with respect to many common alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition and pH and influence of additive anionic on the response properties of were investigated. The sensor with 35% PVC, 54% solvent mediator, 8% ionophore and 3% anionic additive, shows the best potentiometric response characteristics. It displays a Nernstian behavior (19.6 mV per decade) over the concentration range 1.0×10 −7 to 1.0×10 −1 M. The detection limit of the electrode is 2.0×10 −8 M (∼3.0 ng/ml). The response time of the electrode is very fast (10 s) in whole concentration range. The sensor can be used in the pH range 3.5–9.5 for at least 2 months. The membrane sensor was used as an indicator electrode in potentiometric titration of lanthanum ions with EDTA. It was successfully applied in determination of fluoride ions in mouth wash preparations.

Dependence of the Microstructure and the Electrical Properties of Lanthanum‐Substituted (Na1/2Bi1/2)TiO3 on Cation Vacancies

Abstract: The sintering and electrical characteristics of La-modified Na1/2Bi1/2TiO3 (NBT) was investigated from a defect structure viewpoint. To reveal the role of cation vacancies, two series of ceramics, with different cation vacancies, were processed to compensate the excess positive charge of lanthanum ions. In a region of complete solid solution, the grain size of NBLT-B {[(Na0.5Bi0.5)1−xLax]Ti1−0.25xO3} was smaller than that of NBLT-A {[(Na0.5Bi0.5)1−1.5xLax]TiO3} and densification was enhanced more effectively in NBLT-B. With the aid of thermoelectric power, electric conductivity, and electrotransport measurements, it was found that different sintering behaviors between NBLT-A and NBLT-B specimens were related to the change in the type of cation vacancies present and that lanthanum ion–cation vacancy pairs played an important role in reducing the grain growth and enhancing the densification process.

Effects of lanthanum addition on Ni-B/γ-Al2O3 amorphous alloy catalysts used in anthraquinone hydrogenation

Abstract: A series of amorphous Ni-B/γ-Al 2 O 3 catalysts with different La loadings were prepared by KBH 4 reduction, characterized by inductively coupled plasma (ICP), DSC, H 2 -TPD, X-ray photoelectron spectroscopy (XPS) and H 2 -chemisorption, and studied in the hydrogenation of anthraquinone (AQ). In comparison with the catalyst without La loadings, the presence of proper amounts of lanthanum in the supported amorphous alloy catalyst leads to more active centers, higher extents of H 2 -chemisorption, the shift of H 2 desorption peaks to lower temperatures, the enhancement of thermal stability as well as higher reaction rates and higher TOF values. The effects of lanthanum were attributed to both its structure effect, dispersing Ni, leading to more active centers and enhancing the thermal stability, and its electronic effect, resulting in electron-rich Ni, weakening the adsorption of anthraquinone and the bond strength of NiH and therefore activating the adsorbed hydrogen. However, higher La loadings were harmful to the activity because too many surface Ni active centers might be covered by La 3+ species.