Electro-mechanical degradation of polycrystalline beta-alumina

Deposition of metallic sodium under conditions of current flow of sodium ions through beta-alumina ceramics is an important cause of their breakdown when the solid electrolyte is used as a separator in various electrochemical devices. Cells of different combinations: Na/Beta-Alumina/Na amalgam, Na/Beta-Alumina/Cu(probe), and Na/Beta-Alumina/Na, etc have been investigated for sodium deposition at room temperature and at 350°C. A method is presented by which the progress of sodium deposition may be followed. A mechanism of formation of sodium deposition centers at impurity rich spots and other defect sites has been proposed.     

High-temperature electrical properties of lanthanum beta-alumina solid electrolytes

Impedance spectroscopy measurements were carried out in the 10 Hz to 10 MHz frequency range from 500 to 1200 °C in LaAl₁₁O₁₈ pellets sintered at 1600 °C. The powders were obtained by the polymeric precursor technique. The sintered pellets were nearly single phase LaAl₁₁O₁₈. The bulk electrical resistivity was evaluated from the [−Z″(ω) × Z′(ω)] impedance diagrams. The value of the activation energy for the ionic conduction, 0.89 eV, was determined from the Arrhenius plot of the bulk conductivity. An yttria-stabilized zirconia (YSZ) oxygen pump and an YSZ oxygen sensor were used for providing 10–1500 ppm of partial pressure of oxygen (pO₂) at 1000 °C for determining the electromotive force (emf) in a Pt/LaAl₁₁O₁₈/Cr₂O₃ + Cr electrochemical cell. The results follow the Nernst law. The high signal-to-noise ratio of the emf at low pO₂ values shows that the LaAl₁₁O₁₈ specimens may be used in sensors for detection of oxygen at high temperatures.     

Solid oxide galvanic cells involving exchanged beta-alumina electrolyte

Fe(II), Cu(I), Cu(II), and Zn(II)-exchanged beta-aluminas have been prepared and tested as solid electrolytes in oxide galvanic cells. The values of free enthalpies of Fe₃O₄, CuCrO₂, CuCr₂O₄, and Zn₂SiO₄ of formation at 1070 K have been calculated from the emf results. The reasonable agreement with literature data has been found for all compounds under study.     

Spin lattice relaxation and lithium motion in lithium-sodium beta-alumina

Pulsed nmr techniques were used to determine Li⁺ activation energies, spin lattice relaxation (T₁) times, observed linewidth (T*₂) and motional narrowing behavior in polycrystalline Li-Na beta-alumina having a nominal 1:1 Li⁺/Na⁺ ratio. Specimen heat treatment induced significant changes in all of the measured quantities.     

Synthesis of potassium beta-alumina by thermal decomposition of a complex

Potassium beta-alumina was synthesised from potassiumm-alumina by a new technique. Thermal decomposition of a complex, trioxalatoaluminate K _x (NH₄)_3–x [Al(C₂O₄)₃] ·3H₂O (0.091x 0.333), resulted in the formation of a fine powder of Km-alumina with mullite-like structure. The decomposition process was studied by thermal analysis and X-ray diffraction, and the phase relation of the K₂O-Al₂O₃ system is discussed in the mid-temperature region of 600–1200°C. The a.c. conductivity, the apparent density and the lattice parameters were measured. The complex decomposition was shown to be a suitable method for K-alumina synthesis.     

The failure of beta-alumina electrolyte by a dendritic penetration mechanism

A modified theory of beta-alumina breakdown is presented which takes into account factors not previously considered. Calculations show that whereas the population of critical surface flaws in a beta-alumina tube is likely to be initially zero, very small increases in the charge-transfer resistance at the sodium-electrolyte interface will result in previously sub-critical cracks attaining criticality. It is also shown that the time required for full penetration of the electrolyte tube is measured in minutes from the instant a crack achieves criticality. Thus electrolyte life is seen not as a continual process of degradation, but rather as an induction period, during which time changes are occurring at the sodium-electrolyte interface which ultimately lead to criticality and rapid electrolyte failure.     

Synthesis of lanthanum beta-alumina powders by the polymeric precursor technique

La-β-Al₂O₃ (LaAl₁₁O₁₈) powders were synthesized by the polymeric precursor technique using lanthanum nitrate and aluminum nitrate. The transformations during thermal treatment of the precursor solution with ethylene glycol and citric acid were evaluated by thermal analysis. Fourier transform infrared spectroscopy analysis was performed after calcinations of the polymeric resin for determination of residual carbon. The specific surface area was evaluated by the BET method. Fine powders with ∼121 m²/g specific surface area and 20 nm average particle size were obtained and observed by scanning and transmission electron microscopy. Nearly single phase LaAl₁₁O₁₈ was obtained after pressing and sintering these powders at 1600 °C with small additions of MgO. The sintered pellets were characterized by X-ray diffraction and scanning electron microscopy. Impedance spectroscopy measurements carried out in the 1000–1200 °C range show the electrolytic behavior of the La-β-Al₂O₃ pellets, suggesting their application as solid electrolytes in high temperature potentiometric oxygen sensors.     

Recent progress in the development of beta-alumina for the sodium-sulphur battery

The development of beta-alumina as the electrolyte and separator for the sodium-sulphur battery is described. The requirements of cell performance and durability determine the mechanical and electrical properties of the electrolyte. Changes in the cell configuration also have an effect in so far as extending the area of the electrodes and electrolyte and reducing their thickness will reduce the overall impedance of a cell. The manner in which this interacts with the manufacturing route is outlined. The methods by which high ionic conductivity are achieved whilst maintaining adequate mechanical strength are described and the extent to which these are mutually exclusive is discussed. Some of the factors responsible for the failure of beta-alumina in sodium-sulphur cells are considered in relation to recent experimental studies.     

Self-stabilizing mount for impedance measurements of solid electrolytes-with special applications to beta-alumina ceramics

Because of deficiencies in the common methods, a new self-stabilizing mount has been developed for the impedance measurement of solid electrolytes. The prominant feature of the new mount is that clamping of the electrodes to the sample faces is not executed by springs or spring shackle screws or by other elastic forces, but instead just by weight. Its design allows quick sample change even at elevated temperatures, and it is, at the same time, suited for accurate laboratory investigations of samples of varying configurations and for routine quality control work. The versatility of the new self-stabilizing mount is demonstrated by the application of beta-alumina ceramic tubes. The temperature dependence of the axial and radial resistivities of different tubes of a special sintering lot is investigated and compared to a Na/Na-cell test result.     

粗钯的精炼提纯

论述了粗钯精炼提纯的方法 ,利用本方法可获得品位为 99.99%的海绵钯     

Solvothermal oxidation of gallium metal

Solvothermal oxidation of gallium metal in various organic solvents at 300 °C under the autogenous vapor pressure of the solvents was examined. The reaction of gallium metal in 1-butanol or 2-methoxy-ethanol at 300 °C did not proceed and unreacted gallium metal was recovered even with prolonged reaction time. On the other hand, gallium metal reacted in aminoalcohols such as 2-aminoethanol, 2-methylaminoethanol, 2,2′-iminodiethanol and 2,2′,2″-nitrilotriethanol yielding γ-Ga₂O₃. The product obtained by this reaction has a relatively large crystallite size as compared with γ-Ga₂O₃ prepared by the conventional method.     

更改澄清剂

介绍了生产荧光灯玻管的玻璃厂由原来的锑粉与硝酸钠澄清改为芒硝与煤粉澄清的过程。     

聚氨酯泡沫塑料法从粉煤灰中回收镓研究

基于在酸性溶液中镓可形成酸根阴离子并可和复杂阳离子形成离子缔合物的性质,研究了以聚氨酯泡沫塑料(PU)为吸附材料,在盐酸介质中吸附富集镓的性能和条件。结果表明,在6 mol/L的HCl溶液中,PU对镓有良好的吸附性能,在含镓10 mg/L,液固比50 mL/g下,吸附率可达98%以上,静态饱和吸附容量为46.7 mg/g-PU。实验证实,除Fe3+外,溶液常见共存离子对吸附无影响;获得了一种新的有应用价值的从粉煤灰中吸附回收镓的工艺方法。     

Diffusion of gallium in sapphire

In this paper, the characteristics of the diffusion of gallium into sapphire are investigated by SIMS analysis, as a step towards the fabrication of optimized Ga:sapphire optical waveguides. The diffusion coefficient was obtained for temperatures between 1400 °C and 1600 °C, and the results confirm that sapphire substrates can be readily doped with gallium, to depths in the order of microns, at a temperature of 1600 °C. The procedure yields samples with low surface roughness and no apparent unwanted surface features, and the dopant concentration can be selected over a wide range, as gallium has a high solid solubility in sapphire.     

Chemistry and pharmacokinetics of gallium maltolate, a compound with high oral gallium bioavailability

Gallium maltolate, tris(3-hydroxy-2-methyl-4H-pyran-4-onato)gallium (GaM), is an orally active gallium compound for therapeutic use. It is moderately soluble in water (10.7 +/- 0.9 mg/mL at 25 composite functionC) with an octanol partition coefficient of 0.41+/-0.08. The molecule is electrically neutral in aqueous solution at neutral pH; a dilute aqueous solution (2.5 x10-(-5) M) showed little dissociation at pH 5.5-8.0. Single crystal X-ray diffraction analysis found the GaM molecule to consist of three maltolate ligands bidentately bound to a central gallium atom in a propeller-like arrangement, with one of the ligands disordered in two possible orientations. The compound is orthorhombic, space group Pbca, unit cell a = 16.675(3), b = 12.034(2), c = 18.435(2) A at 158K. GaM was administered to healthy human volunteers at single doses of 100, 200, 300, and 500 mg (three subjects per dose). GaM was very well tolerated. Oral absorption of Ga into plasma was fairly rapid (absorption half life = 0.8-2.0h), with a central compartment excretion half life of 17-21h. Absorption appeared dose proportional over the dosage range studied. Estimated oral gallium bioavailability was approximately 25-57%, based on comparison with published data on intravenous gallium nitrate. Urinary Ga excretion following oral GaM administration was approximately 2% of the administered dose over 72h, in contrast to 49-94% urinary Ga excretion over 24h following i.v. gallium nitrate administration. We suggest that oral administration of GaM results in nearly all plasma gallium being bound to transferrin, whereas i.v. administration of gallium nitrate results in formation of considerable plasma gallate [Ga(OH)(4) (-)], which is rapidly excreted in the urine. These data support the continued investigation of GaM as an orally active therapeutic gallium compound.     

Plasma Enhanced atomic layer deposited amorphous gallium oxide thin films using novel trimethyl[N-(2-methoxyethyl)-2-methylpropan-2-amine]gallium

We developed a novel liquid type Ga precursor, trimethyl [N-(2-methoxyethyl)-2-methylpropan-2-amine]gallium (TMGON, Ga(CH₃)-₃ [CH₃OCH₂CH₂NHtBu]) with a reasonable vapor pressure (0.5 Torr at 54 °C), to deposit GaO_x via plasma-enhanced atomic layer deposition (PEALD) using a mixture gas of Ar/O₂ as a reactant at low temperature. In this study, the growth per cycle (GPC) was 1.0 Å/cycle at deposition temperatures between 100 °C and 250 °C. As the deposition temperature increased, the amount of remaining carbon decreased. The ratio of Ga/O came close to the ideal ratio of 2:3, and the optical band gap increased, respectively. In addition, all films had amorphous phases and low surface roughness. The GaO_x films also exhibited acceptable insulator properties, with a leakage current of 3.2?10^?9 A/cm² at 0.5 MV/cm and breakdown fields of 1.52 MV/cm. These results demonstrate that TMGON is a promising ALD precursor for the deposition of GaO_x as well as a multi-component oxide layer including Ga, due to a high GPC and good film properties.     

Synthesis of gallium nitride nanostructures by nitridation of electrochemically deposited gallium oxide on silicon substrate

Gallium nitride (GaN) nanostructures were successfully synthesized by the nitridation of the electrochemically deposited gallium oxide (Ga₂O₃) through the utilization of a so-called ammoniating process. Ga₂O₃ nanostructures were firstly deposited on Si substrate by a simple two-terminal electrochemical technique at a constant current density of 0.15 A/cm² using a mixture of Ga₂O₃, HCl, NH₄OH and H₂O for 2 h. Then, the deposited Ga₂O₃ sample was ammoniated in a horizontal quartz tube single zone furnace at various ammoniating times and temperatures. The complete nitridation of Ga₂O₃ nanostructures at temperatures of 850°C and below was not observed even the ammoniating time was kept up to 45 min. After the ammoniating process at temperature of 900°C for 15 min, several prominent diffraction peaks correspond to hexagonal GaN (h-GaN) planes were detected, while no diffraction peak of Ga₂O₃ structure was detected, suggesting a complete transformation of Ga₂O₃ to GaN. Thus, temperature seems to be a key parameter in a nitridation process where the deoxidization rate of Ga₂O₃ to generate gaseous Ga₂O increase with temperature. The growth mechanism for the transformation of Ga₂O₃ to GaN was proposed and discussed. It was found that a complete transformation can not be realized without a complete deoxidization of Ga₂O₃. A significant change of morphological structures takes place after a complete transformation of Ga₂O₃ to GaN where the original nanorod structures of Ga₂O₃ diminish, and a new nanowire-like GaN structures appear. These results show that the presented method seems to be promising in producing high-quality h-GaN nanostructures on Si.     

Low temperature growth of gallium nitride

Radio frequency reactive sputtering was used to produce gallium nitride films on glass and silicon substrates at close to room temperature. The films were analysed by transmission electron microscopy and Rutherford backscattering spectroscopy. The films were found to consist of nanocrystalline wurtzite GaN with c-axis-oriented columnar grains growing perpendicular to the substrate. Varying the N₂:Ar sputtering gas ratio was found to have little effect on the grain size. Annealing the films at 400°C was found to increase the E₁(TO) signal observed by Fourier transform IR spectroscopy and to reduce the porosity of the columnar structure.