La Powders Research Articles

Effect of water addition into the precursor powders on microstructure and tensile mechanical properties of a Mo-0.5La alloy

The effect of water addition into the precursor powders consisting of ultrafine La(OH)3 particles and MoO2 powders on the microstructure and tensile mechanical properties of a Mo-0.5La (wt%) alloy has been studied. The results showed that the water addition improved the homogeneity of the La(OH)3 particles in the precursor powders after mechanical blending. The average powder size of the hydrogen-reduced Mo–La powders was nearly unchanged regardless of the water addition, while the apparent density was remarkably increased with the increase in the amount of water addition. A polycrystalline phase that has a chemical formula of La5Mo4O16 and a subgrain size of 0.2∼1 μm was discovered in the hydrogen-reduced powders. This means that a small portion of the powders were transformed into composite powders during the hydrogen reduction process. Particularly, this La-containing polycrystalline phase can decompose during sintering, and the decomposition may activate and promote the grain growth kinetics. A similar effect also occurred due to the doping form of La(OH)3 which underwent decomposition during sintering as well. After sintering, the grain size of the alloy was found to depend on the quantity of the water addition. As the water addition was increased from 0 to 0.15 L/Kg, the grain size was increased from a typical size of 60–80 μm up to an extraordinarily large size of 1000–3000 μm. Interestingly, this drastic grain coarsening did not deteriorate the mechanical properties of the alloy, but improved the ultimate tensile strength from 367 to 457 MPa which is a value comparable to that of the Mo-0.5La alloy fabricated with the more conventional solid-liquid doping route, on condition that the relative sintering density can reach above 98%. The improved ultimate tensile strength can be attributed to the change in the fracture mechanism from a nearly fully intergranular mode to a mixed transgranular and intergranular mode.

Viability of Lactobacillus acidophilus NRRL B-4495 encapsulated with high maize starch, maltodextrin, and gum arabic

The effects of different protective agents, high maize starch (HM), maltodextrin (MD), and gum arabic (GA) on the viability of Lactobacillus acidophilus after spray drying and during storage at different conditions were investigated. Also, the physicochemical properties of the spray dried powders were evaluated. Lactobacillus acidophilus NRRL B-4495 (LA) was suspended in a 20% w/v solution of HM, MD, or GA. The solutions were separately spray dried at 140 °C to obtain LA powders: LAHM, LAMD, and LAGA. The powders were separately placed in aluminum bags and packed under 97 and 10% vacuum. The powders were stored at refrigerated (4 °C) and at room (23 °C) temperatures for 60 days. The moisture content of LA powders ranged from 5.63 to 8.98% with the LAMD powders showing lower moisture content than LAGA and LAHM powders. More than 6 log CFU/g of LA/g powder survived at 4 °C at 60 days of storage. LAGA and LAMD powders packed under 97% vacuum and stored at 4 °C had significantly higher cell viability than other powders. The study demonstrated that viability of LA powders packed under 97% vacuum and stored at refrigerated temperature meets the recommended levels to have therapeutic effects.

Sn4+ and La3+ co doped TiO2 nanoparticles and their optical, photocatalytic and antibacterial properties under visible light

Sn4+ and La3+ co-doped TiO2 photocatalytic material with nanoparticle structure have been successfully prepared using SnCl2·2H2O and La(NO3)3·6H2O as precursors. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy and UV–visible spectroscopy have been used to for the characterization of the morphology, crystal structure, particle size and optical properties of the samples. The photocatalytic properties of sample with various amount of La doped TiO2 have been studied by photo degradation of methyl orange (MO) in water under visible light. XRD patterns showed both rutile and anatase phases for 5 mol% of Sn and 5–10 mol% of La. But anatase phase with a little rutile phase was formed for 5 mol%Sn and 10 mol%La. The prepared Sn and La co doped TiO2 photo-catalyst showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of MO solution under visible irradiation. Antibacterial behavior towards E. coli was then studied under visible irradiation. The synthesized T-5%Sn-10%La powder exhibited superior antibacterial activity under visible irradiation compared to the pure TiO2.

Hydrogen storage properties of a Mg-La-Fe-H nano-composite prepared through reactive ball milling

In the present work, a Mg-La-Fe-H nano-composite was prepared through reactive ball milling of the mixture of MgH2, Fe and La powders. The phase components, microstructure and hydrogen sorption properties of the composite powders were carefully investigated. After milling, an unsaturated hydride LaH2.3 formed in the Mg-La-Fe-H composite. It is observed that since Mg(102) and α-Fe(110) planes have the similar interplanar spacing, Mg grains preferentially nucleate at the interface of MgH2/α-Fe when MgH2 transforms to Mg. Based on the Pressure-Composition-Temperature measurements, the hydrogenation enthalpy of the Mg-La-Fe-H composite is determined to be −72.0 kJ/mol H2. Meantime, the hydrogen absorption kinetics can be significantly improved and the hydrogen desorption temperature can be reduced in the Mg-La-Fe-H composite when compared to those in the Mg-La-H or Mg-Fe-H composites. This is especially promising for the Mg-La-Fe-H composite, which can absorb 5.0 wt% of hydrogen within 8 h at room temperature and desorb hydrogen at 463 K. Such rapid absorption kinetics at low temperatures can be attributed to the synergetic catalytic effects from both LaH2.3 and α-Fe. The above results indicated that simultaneous addition of La and Fe to MgH2 through the reactive ball milling can effectively improve the hydrogen sorption kinetic properties of MgH2.

Proton Conducting Ceramic Powder Synthesis by a Low Temperature Method.

Molten salt synthesis (MSS) is a simple method for the preparation of ceramic powders with specific morphology. The main role of the molten salts is to increase the reaction rate and lower the reaction temperature. It occurs because of much higher mobility of reactants in the liquid medium than in the solid state. In this work the molten salt synthesis was applied to produce ceramic powders of La0.995Ca0.005NbO4 and BaCe(0.9-x)Zr(x)Y0.1O3. Single-phase lanthanum niobate formed in all studied conditions of the synthesis, whereas in the case of barium cerate-zirconate MSS led to forming two crystalline phases: barium cerate and barium zirconate. The heating temperature and time as well as the salt content most strongly influenced the shape and size of particles. The influence of other parameters on the powder morphology was weaker. Despite differences in size and morphology, all groups of the La0.995Ca0.005NbO4 powder obtained with the MSS method pressed into pellets and sintered gave a dense ceramic material. On the other hand in the case of barium cerate-zirconate regardless of synthesis and sintering conditions the ceramics were porous.

(La, Pr)0.8Sr0.2FeO3−δ–Sm0.2Ce0.8O2−δ composite cathode for proton-conducting solid oxide fuel cells

Mixed rare-earth (La, Pr)0.8Sr0.2FeO3−δ–Sm0.2Ce0.8O2−δ (LPSF–SDC) composite cathode was investigated for proton-conducting solid oxide fuel cells based on protonic BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte. The powders of La0.8−xPrxSr0.2FeO3−δ (x = 0, 0.2, 0.4, 0.6), Sm0.2Ce0.8O2−δ (SDC) and BaZr0.1Ce0.7Y0.2O3−δ (BZCY) were synthesized by a citric acid-nitrates self-propagating combustion method. The XRD results indicate that La0.8−xPrxSr0.2FeO3−δ samples calcined at 950 °C exhibit perovskite structure and there are no interactions between LPSF0.2 and SDC at 1100 °C. The average thermal expansion coefficient (TEC) of LPSF0.2–SDC, BZCY and NiO-BZCY is 12.50 × 10−6 K−1, 13.51 × 10−6 K−1 and 13.47 × 10−6 K−1, respectively, which can provide good thermal compatibility between electrodes and electrolyte. An anode-supported single cell of NiO-BZCY|BZCY|LPSF0.2–SDC was successfully fabricated and operated from 700 °C to 550 °C with humidified hydrogen (∼3% H2O) as fuel and the static air as oxidant. A high maximum power density of 488 mW cm−2, an open-circuit potential of 0.95 V, and a low electrode polarization resistance of 0.071 Ω cm2 were achieved at 700 °C. Preliminary results demonstrate that LPSF0.2–SDC composite is a promising cathode material for proton-conducting solid oxide fuel cells.

Preparation of La-Mg-Ni Hydrogen Storage Composite Alloys by Mechanical Alloying

LaNi5-xwt%Mg hydrogen storage alloys with different Mg content were made from pure La, Mg and Ni metal powder by mechanical alloying, selecting appropriate ball-milling parameters in 0.4MPa hydrogen atmosphere. The characterizations for hydrogen storage alloy show that a multi-phase alloy composed of MgH2, LaH3, Mg2NiH4 and Ni was obtained, the alloy have two hydrogen desorption temperature range, and the alloy with 25wt% Mg content can desorb hydrogen up to 4.02wt%.

Hydrogen storage properties of Mg–TM–La (TM = Ti, Fe, Ni) ternary composite powders prepared through arc plasma method

For the first time, Mg based Mg–Transition metal (TM) –La (TM = Ti, Fe, Ni) ternary composite powders were prepared directly through arc plasma evaporation of Mg–TM–La precursor mixtures followed by passivation in air. The composition, phase components, microstructure and hydrogen sorption properties of the composite powders were carefully investigated. Composition analyses revealed a reduction in TM and La contents for all powders when compared with the compositions of their precursors. It is observed that the composites are all mainly composed of ultrafine Mg covered by nano La2O3 introduced during passivation. Based on the Pressure–Composition–Temperature measurements, the hydrogenation enthalpies of Mg are determined to be −68.7 kJ/mol H2 for Mg–Ti–La powder, −72.9 kJ/mol H2 for Mg–Fe–La powder and −82.1 kJ/mol H2 for Mg–Ni–La powder. Meantime, the hydrogen absorption kinetics can be significantly improved and the hydrogen desorption temperature can be reduced in the hydrogenated ternary Mg–TM–La composites when compared to those in the binary Mg–TM or Mg–RE composites. This is especially true for the Mg–Ni–La composite powder, which can absorb 1.5 wt% of hydrogen at 303 K after 3.5 h. Such rapid absorption kinetics at low temperatures can be attributed to the catalytic effects from both Mg2Ni and La2O3. The results gathered in this study showed that simultaneous addition of 3d transition metals and 4f rare earth metals to Mg through the arc plasma method can effectively alter both the thermodynamic and kinetic properties of Mg ultrafine powders for hydrogen storage.

Characterization of La0.995Ca0.005NbO4/Ni anode functional layer by electrophoretic deposition in a La0.995Ca0.005NbO4 electrolyte based PCFC

The Electrophoretic Deposition (EPD) technique has been applied to the preparation of a porous La0.995Ca0.005NbO4/Ni composite anode layer, deposited on a porous pre-sintered La0.995Ca0.005NbO4/Ni support. Powders of La0.995Ca0.005NbO4 and NiO were suspended in a solution of acetylacetone, iodine and water. Selectivity in the composition of the deposited layer was analyzed as a function of the suspension compositions and deposition conditions. A quasi-symmetrical cell was produced by depositing La0.995Ca0.005NbO4 electrolyte layer on the anode layer by EPD, and by applying a porous La0.995Ca0.005NbO4/Ni counter electrode on the dense electrolyte layer by brushing. The performance of the electrodes was evaluated by electrochemical impedance spectroscopy in 3% wet H2.

Low‐Temperature Preparation of La0.6Sr0.4Fe0.8Co0.2O3–δ Sinterable Nanopowders by the Polymeric Organic Complex Solution Method

AbstractIn this work, powders of La0.6Sr0.4Fe0.8Co0.2O3–δ were prepared by the auto‐combustion of ethylene glycol–metal nitrate polymerised gel precursor. This method (polymeric organic complex solution) allows decreasing the processing temperature and simplifies the whole procedure. A single phase material is obtained at 300 °C lower than that needed by conventional solid state reaction (SSR). The reduced particle size and low agglomeration increases the reactivity of powders and therefore, the sintering temperature is also reduced in 200 °C with respect to the conventional SSR method. As a consequence of that, the microstructures are controlled maintaining the grain size in an almost nanometric range.

Preparation and characterization of La-doped Ba (1 − x) Sr xTiO 3 powders and thin films

Ba (1 − x) Sr x TiO 3 powders with different Ba/Sr ratios ( x = 0.10, 0.25, 0.40, 0.55, 0.70) and La-doped Ba 0.9Sr 0.1TiO 3·yLa powders ( y = 0.002, 0.004, 0.006, 0.008, 0.010) have been prepared by sol–gel technology using dehydrated barium-acetate, strontium-carbonate, lanthanum-nitrate, and titanium-isopropoxide as raw materials. The experimental results show that the dielectric properties of Ba (1 − x )Sr x TiO 3 powders depend on the Ba/Sr ratios. When the Sr fraction is 0.10, the dielectric constant is relatively higher and the dielectric loss is relatively lower, which are more than 2000 and less than 2.0 × 10 − 2 at 1000 Hz, respectively, the most important is that this kind of powder has better frequency stability. La-doping can increase the dielectric constant distinctly, but the dielectric loss can also be increased. Their dielectric properties at 1.0 × 10 3 Hz are better than those at 1.0 × 10 5 Hz. At 1.0 × 10 3 Hz the dielectric constant is much higher, while the dielectric loss is much lower. The dielectric constant of different La-doping contents is nearly 3.5 × 10 4 and the dielectric loss is less than 0.20 when La fraction is 0.008. The La-doped BST sample also has better frequency stability, especially at high frequency. La-doped BST thin films are successfully deposited on mild steel substrates by using plasma spray system with suspension precursors of Ba 0.90Sr 0.10TiO 3·0.8La powders. The XRD patterns of Ba 0.90Sr 0.10TiO 3 and Ba 0.90Sr 0.10TiO 3·0.8La powders are almost the same. No new peaks appear after La-doping, but the peaks move slightly to a larger degree, which indicates that the element La has entered the lattice of the Ba 0.90Sr 0.10TiO 3 and has made the constant of the crystal cell reduce. The XRD pattern of the thin films is just like that of the Ba 0.90Sr 0.10TiO 3·0.8La powders except a peak corresponding to Fe substrate. The SEM results show that the thin films have a uniform and smooth surface. The morphology of cross-section shows a columnar grain structure indicating smooth surface and uniform thickness of the film. The thickness of the film is about 15 um. The thin films obtained are expected to be prospective material for applications in tunable microwave devices.

Solution to the bioheat equation for hyperthermia with La1−xAgyMnO3-δ nanoparticles: The effect of temperature autostabilization

This work aimed to analyze the possibility and performance of the temperature controlled hyperthermia based on AC heating of magnetic nanoparticles with low Curie temperature. Temperature dependence of dynamic magnetic susceptibility has been studied experimentally on fine powders of La0.8Ag0.15MnO2.95 in the frequency range of 0.5–2.0 MHz. Critical drop of the AC magnetic losses was found in the vicinity of the Curie point, TC = 42°C. The obtained data was used in the numerical analysis of the bioheat equations under typical conditions of the hyperthermia treatment. The mathematical model includes a spherical tumor containing magnetic particles and surrounded by concentric healthy tissue, with account made for the blood perfusion. The calculations performed for various AC power, tumor sizes and doping geometries predict effective autostabilization of the temperature at T ≅ TC inside the tumor and steep temperature profile at the interface with the healthy tissue.

Formation of La-modified L1 2–Al 3Ti by mechanical alloying and annealing

DO 22–Al 3Ti can be transformed into the related cubic L1 2 structure, with more slip systems, by the addition of ternary elements, such as the rare earth Lanthanum. It is believed that combined processing by mechanical alloying and annealing is conducive to the structural evolution and crystal growth. Appropriate and economical processing parameters were determined as: milling time of 40 h, annealing temperature of 750 °C and annealing time of 40–60 min. With increased milling time, fine and uniform particles, which originally possess a flake-like morphology, are produced. The Vickers hardness of the as-milled Al–Ti and Al–Ti–La powders increases rapidly at the initial milling stage, then increases slowly at final stage due to lattice distortion and solid solution strengthening. However, the Vickers hardness of the two materials decreases with increased of annealing time. The Vickers hardness of the Al–Ti powders is higher than that of the Al–Ti–La powders.

La-doping effects on pinning properties of MgB 2

The La-doped MgB 2 samples were sintered from the mixture of Mg, B and La powder with the mole ratio of Mg:B:La=1.2:2(1+3 x): x, where x was 0, 0.01 and 0.02. The solid reaction of the powder mixture was performed in the microreactor at 1023 K under Ar-atmosphere of 40 MPa. For the prepared samples, the X-ray diffraction results showed the production of impurity phase of LaB 6 nano-particles within the bulk MgB 2 except for small amount of MgO. The slight reduction of T c's and the decreasing of decay rates of J c against the magnetic field could be characterized for x=0.01 sample.

Processing and Conductivity of Lanthanum Gallate

The relationship between processing, structure and conductivity of lanthanum gallate was investigated. Powders of La0.8Sr0.2Ga1−yMgyO3-δ were synthesized by both solid oxide/carbonate reaction and citric acid/nitrate combustion processing. The latter method provided much finer and more homogeneous powders. The sintering of combustion synthesized powders, however, was more difficult. Accordingly, with the same sintering schedule the samples made from the combustion powder had lower density and lower conductivity than those made by routine ceramic processing. SEM micrographs showed that during sintering, the surfaces of LSGM samples sintered first, which left stranded porosity inside, particularly for samples made from the combustion powders. This difficulty could be overcome by two stage sintering and/or by isostatic pressing. By this technique, densities greater than 98% of theoretical were achieved. Conductivity was measured as a function of temperature and composition, and at 800°C, the maximum conductivity of 0.17 S cm−1 was obtained for the composition La0.8Sr0.2Ga0.875Mg0.125O1−δ.

Electronic and lattice excitations in BaTiO3:La

We report lattice and electronical properties of BaTiO3:La powders and ceramics with 0<xLa<20 at.%. Dielectric measurements and x-ray scattering evidence a continuous decrease of the ferroelectric transition temperature when the La content is increased. For xLa=20 at.%, no dielectric maximum is found for temperatures higher than 20 K. At the same time, an impurity mode at 840 cm-1 increases linearly with xLa. We have modelled these data using a linear chain model with one polarizable ion. The electric excitations were probed using DC conductivity, EPR spectroscopy and optical absorption. This last technique was applied to BaTiO3:La single crystals, which were grown for the first time in our laboratory. Our main result is that the conductivity maximum at xLa approximately=0.5 at.% is related to an impurity level lying 2.1 eV below the conduction band.

Synthesis and Characterization of La 3NbSe 2O 4F 2

Crystals of the unusual oxyfluoroselenide La 3NbSe 2O 4F 2 were obtained during the exploration of the quaternary La/Nb/Cu/Se system. Oxygen was extracted from the silica tube, while fluorine was present as a minor impurity in the La powder. The compound crystallizes in space group D 16 2 h - Pnma of the orthorhombic system with four formula units in a cell with dimensions: a = 11.290(4), b = 4.001(1), and c = 18.062(4) Å ( T = 113 K). The structure has been determined by single-crystal X-ray methods. The presence of F in the crystals was confirmed by windowless EDAX measurements. The two F sites were distinguished from the four O sites from a combination of the X-ray refinement and a bond-valence parameter calculation made with the program EUTAX. In the structure the Nb atom is octahedrally coordinated while each of the three independent La atoms is in a tricapped trigonal prism. The Nb atom is bound to one Se atom and five O atoms while the three La sites are coordinated by various combinations of Se, O, and F atoms. The NbO 5Se octahedra corner share and the LaSe x O y F z tricapped trigonal prisms face share in the b direction.

Synthesis and molecular structure of lanthanum tris[cyclopentadienylmolybdenotricarbonylate] tetrahydrofuranate, (THF)5La[CpMo(CO)3]3 · THF

Abstract The interaction of activated La powder with [CpMo(CO) 3 ] 2 or Hg[CpMo(CO) 3 ] 2 in THF resulted in the formation of crystalline (THF) 5 La[CpMo(CO) 3 ] 3 · THF (I), which oxidized readily on exposure to air with cleavage of [CpMo(CO) 3 ) 2 . Complex I was characterized by X-ray structural analysis. The La atom is bound to three equivalent CpMo(CO) 3 fragments via almost linear carbonyl bridges, MoCOLa (MoCO 177.9(7)°). The coordination of La with the terminal CO group (LaO av 2.444(5) A) leads to elongation of the CO bond from an average value of 1.16(1) to 1.21(1) A, and to shortening of the MoC bond from an average value of 1.943(9) to 1.874(9) A, compared with the unbridged CO. The coordination of La is complemented to CN = 8 at the expense of binding of five THF molecules (LaO(THF) av = 2.580(6) A; the sixth THF molecule is crystallizable).

Interactions in Various Magnetic Compounds

Susceptibility measurements on single crystals of KFe11O17 show an anomalous antiferromagnetic behavior, which we propose to call antiferrimagnetism. The behavior follows from Weiss field theory on a simplified (i.e., two-sublattice) model. The magnetic structure of K2NiF4 has been determined by neutron diffraction by Legrand and Plumier at C.E.N., Mol (Belgium). Measurements on their single crystal show that χ∥ and χ⊥ become nearly equal at ≈100°K, i.e., far below the temperature where χ is maximum. This is believed to be due to a gradual breaking up of the long-range order in the basal layers. Results obtained on powders of La0.5Sr1.5MnO4 and La1.5Sr0.5CoO4 are also given. Pure polycrystalline samples of EuS, EuSe, and EuTe with rocksalt structure show θ values of +16, +6, and −7°K; EuTe has a Néel temperature at +11°K. The ferromagnetism of EuO, EuS, and EuSe is due to a predominant direct positive exchange interaction Eu-Eu, the antiferromagnetism of EuTe to a predominant next-nearest neighbor superexchange interaction Eu-X-Eu. Neither interaction is believed to change sign in the series. Measurements of M vs T at various field strengths are in very good agreement with Weiss field theory. Oxidic spinels with diamagnetic ions in A sites have so far shown negative θ values. The substances Ge[Fe2]O4, Ge[Co2]O4, and Ge[Ni2]O4 have θ values of −15, +90, and 0°K, respectively. The materials Ge[Ni2−2δLiδFeδIII]O4 have positive θ values, increasing linearly with δ to 180°K for δ=0.5. Here the Ni2+–Fe3+ interaction must be positive and this interaction is thought to be a direct one, as is discussed.