17 Matching Results

Search Results

Advanced search parameters have been applied.

Enhanced ionic conduction at the film/substrate interface in LiI thin films grown on sapphire(0001)

Description: The ionic conductivity of LiI thin films grown on sapphire(0001) substrates has been studied in-situ during deposition as a function of film thickness and deposition conditions. LiI films were produced at room temperature by sublimation in an ultra-high-vacuum system. The conductivity of the LiI parallel to the film/substrate interface was determined from frequency-dependent impedance measurements as a function of film thickness using Au interdigital electrodes deposited on the sapphire surface. The measurements show a conduction of {approximately}5 times the bulk value at the interface which gradually decreases as the film thickness is increased beyond 100 nm. This interfacial enhancement is not stable but anneals out with a characteristic log of time dependence. Fully annealed films have an activation energy for conduction ({sigma}T) of {approximately}0.47{plus_minus}.03 eV, consistent with bulk measurements. The observed annealing behavior can be fit with a model based on dislocation motion which implies that the increase in conduction near the interface is not due to the formation of a space-charge layer as previously reported but to defects generated during the growth process. This explanation is consistent with the behavior exhibited by CaF{sub 2} films grown under similar conditions.
Date: December 1, 1993
Creator: Lubben, D. & Modine, F. A.
Partner: UNT Libraries Government Documents Department

Mechanisms of enhanced ionic conduction at interfaces in ceramics

Description: A large enhancement in the ionic conductivity of certain compounds occurs when the compound is produced as a composite material containing a finely-dispersed non-conductor such as SiO{sub 2} or Al{sub 2}O{sub 3}. This paper describes recent experiments which proposes that extended defects such as dislocations and grain boundaries, either resulting from or stabilized by the interface, are responsible for the enhancement. The ionic conductivities of LiI and CaF{sub 2} thin films grown on sapphire(0001) substrates were monitored in-situ during deposition as a function of film thickness and deposition conditions. LiI films grown at 27{degrees}C exhibited a region of enhanced conduction within 100 nm of the substrate and a lesser enhancement as the film thickness was increased further. This conduction enhancement was not stable but annealed out with a characteristic log(time) dependence. The observed annealing behavior was fit with a model based on dislocation motion which implies that the increase in conduction near the interface is due to extended defects generated during the growth process. CaF{sub 2} films grown at 200{degrees}C showed a behavior similar to the 27{degrees}C LiI films, with a region of thermally unstable enhanced conduction that occurs within 10 nm of the substrate. Amorphous Al{sub 2}O{sub 3} films deposited over the CaF{sub 2} layers created no additional enhancement but did increase the stability of the conduction, consistent with an extended defect model. Simultaneous deposition of CaF{sub 2} and Al{sub 2}O{sub 3} produced films consisting of very-fine-grained CaF{sub 2} and particles of amorphous Al{sub 2}O{sub 3} (5-10 nm grain and particle size) and a high defect density which was stable even well above the growth temperature. Measured conduction in the composite at 200{degrees}C was approximately 360 times that of bulk CaF{sub 2}.
Date: November 1, 1994
Creator: Lubben, D. & Modine, F.A.
Partner: UNT Libraries Government Documents Department

Development of a bipolar cell for lithium production

Description: The authors report development and bench-scale testing of an electrolytic process for reduction of LiOH to lithium metal through an amalgam intermediate. The amalgam is formed in an aqueous-electrolyte cell and stripped in a molten salt cell using a LiI-CsI eutectic at 225 C. Total energy efficiency is >70%. The process obviates high temperature materials problems, chlorine evolution and anhydrous feedstocks. While the principle is proven, sustained operation of the cell is now needed to obtain statistical data on reliability and maintainability.
Date: July 1, 1995
Creator: Cooper, J.F.; Ebbinghaus, B.B.; Peterman, K.; Weinland, S. & McKenzie, P.
Partner: UNT Libraries Government Documents Department

Development of a bipolar cell for electrochemical production of lithium

Description: Lithium metal can be electrolytically refined from aqueous solutions of its compounds by partial reduction to form a lithium amalgam, followed by reduction of the amalgam to liquid lithium in a molten salt cell at 225 C. A bipolar cell (with a continuous, amalgam electrode circulating between the aqueous and salt cells) was designed, constructed and successfully tested on the bench scale, as a proof of principle of an efficient, safe and low-temperature alternative to existing processes.
Date: February 22, 1995
Creator: Cooper, J.F.; Mack, G.; Peterman, K.; Weinland, S. & McKenzie, P.
Partner: UNT Libraries Government Documents Department

Excess Thermodynamic Properties of Concentrated Aqueous Solutions at High Temperatures

Description: Measurements of the vapor pressure of the solvent in wide ranges of concentration and temperature provide information on solute solvation and ion pairing--the two phenomena most often invoked for description of dilute solutions. Even in moderately concentrated solutions, as interionic distances become comparable to ionic diameters, these simple concepts gradually lose their meaning and solutions behave like molten salts. The usefulness of experimental vapor pressure results increases rapidly with their accuracy, since derived properties, such as solution enthalpies and heat capacities, can be calculated. Very accurate results can be obtained by the isopiestic method, but primary vapor pressure data for standard solutions are needed. In order to obtain vapor pressures at conditions where accurate isopiestic standards are not available and to establish more accurate standards, the ORNL isopiestic apparatus was modified for simultaneous direct vapor pressure measurements and isopiestic comparisons. There are no comprehensive solution theories derived from molecular level models and able to predict thermodynamic properties of various electrolytes as the composition changes from dilute solutions to molten salts in a wide range of temperatures. Empirical and semi-empirical models are useful for representation of experimental results, interpretation of measurements of other properties such as conductance., solubility or liquid-vapor partitioning of solutes, and for verification of theoretical predictions. Vapor pressures for aqueous CaCl{sub 2}, CaBr{sub 2}, LiCl, LiBr, LiI, NaI were measured at temperatures between 380 and 523 K in the concentration range extended to water activities below 0.2 (over 30 mol/kg for LiCl). General equations based on the modified Pitzer ion-interaction model were used to obtain enthalpy and heat capacity surfaces, which are compared with direct calorimetric measurements.
Date: June 7, 2001
Creator: Guszkiewicz, M.S.
Partner: UNT Libraries Government Documents Department

Modification of LiCl-LiBr-KBr electrolyte for LiAl/FeS{sub 2} batteries

Description: The bipolar LiAl/FeS{sub 2} battery is being developed to achieve the high performance and long cycle life needed for electric vehicle application. The molten-salt (400 to 440 C operation) electrolyte composition for this battery has evolved to support these objectives. An earlier change to LiCl-LiBr-KBr electrolyte is responsible for significantly increased cycle life (up to 1,000 cycles). Recent electrolyte modification has significantly improved cell performance; approximately 50% increased power, with increased high rate capacity utilization. Results are based on power-demanding EV driving profile test at 600 W/kg. The effects of adding small amounts (1--5 mol%) of LiF and LiI to LiCl-LiBr-KBr electrolyte are discussed. By cyclic voltammetry, the modified electrolytes exhibit improved FeS{sub 2} electrochemistry. Electrolyte conductivity is little changed, but high current density (200 mA/cm{sup 2}) performance improved by approximately 50%. A specific feature of the LiI addition is an enhanced cell overcharge tolerance rate from 2.5 to 5 mA/cm{sup 2}. The rate of overcharge tolerance is related to electrolyte properties and negative electrode lithium activity. As a result, the charge balancing of a bipolar battery configuration with molten-salt electrolyte is improved to accept greater cell-to-cell deviations.
Date: June 1, 1996
Creator: Kaun, T.D.; Jansen, A.N.; Henriksen, G.L. & Vissers, D.R.
Partner: UNT Libraries Government Documents Department

Simultaneous transport of synthetic colloids and a nonsorbing solute through single saturated natural fractures

Description: Tracer transport experiments involving colloids that showed little tendency to attach to rock surfaces and a nonsorbing solute (iodide) -were conducted in three different well-characterized natural fractures in tuff. The colloids always arrived earlier in the effluent than the iodide, which we believe is evidence of (1) hydrodynamic chromatography and/or (2) the fact that the colloids experience a smaller effective volume in the fracture because they diffuse too slowly to enter low-velocity regions (dead zones) along the rough fracture walls. The iodide also approached the inlet concentration in the effluent more slowly than the colloids, with the concentration at a given elution volume being greater at higher flow rates. By contrast, the rate of approach of the colloid concentration to the inlet concentration did not vary with flow rate. We attribute this behavior to matrix diffusion of the iodide, with the colloids being too large/nondiffusive to experience this phenomenon. Dispersion of all tracers was greatest in the fracture of widest average aperture and least in the fracture of narrowest aperture, which is consistent with Taylor dispersion theory. The tracer experiments were modeled/interpreted using a three-step approach that involved (1) estimating the aperture distribution in each fracture using surface profiling techniques, (2) predicting the flow field in the fractures using a localized parallel-plate approximation, and (3) predicting tracer transport in the fractures using particle-tracking techniques. Although considered preliminary at this time, the model results were in qualitative agreement with the experiments.
Date: September 1, 1994
Creator: Reimus, P.W.; Robinson, B.A.; Nuttall, H.E. & Kale, R.
Partner: UNT Libraries Government Documents Department

Improvements in apparatus and procedures for using an organic liquid scintillator as a fast-neutron spectrometer for radiation protection applications

Description: For use in radiation protection measurements, a neutron spectrometer must have a wide energy range, good sensitivity, medium resolution, and ease of taking and reducing data. No single spectrometer meets all of these requirements. Several experiments aimed at improving and characterizing the detector response to gamma rays and neutrons were conducted. A light pipe (25 mm) was needed between the scintillator cell and the photomultiplier tube to achieve the best resolution. The light output of the scintillator as a function of gamma-ray energy was measured. Three experiments were conducted to determine the light output as a function of neutron energy. Monte Carlo calculations were made to evaluate the effects of multiple neutron scattering and edge effects in the detector. The electronic systems associated with the detector were improved with a transistorized circuit providing the bias voltage for the photomultiplier tube dynodes. This circuit was needed to obtain pulse-height linearity over the wide range of signal sizes. A special live-time clock was built to compensate for the large amount of dead time generated by the pulse-shape discrimination circuit we chose to use. 64 refs., 58 figs., 9 tabs.
Date: May 15, 1987
Creator: Thorngate, J.H.
Partner: UNT Libraries Government Documents Department

Basic research on ceramic materials for energy storage and conversion systems. Progress report, December 1, 1979-November 30, 1980

Description: The present research program involves utilizing appropriate experimental probes for measuring the movement of ionic and electronic charge carriers in ceramic materials suitable for solid electrolyte and electrode applications in high-performance, secondary battery and fuel cell systems. Special emphasis is placed on developing: (1) a better understanding of the effects of structure, impurities and composition on charge carrier transport mechanisms in such materials; and (2) detailed knowledge of the kinetics and mechanism of reactions occurring (on a microscopic scale) at the electrode-electrolyte interfaces of energy storage and conversion systems.
Date: December 1, 1980
Creator: Whitmore, D.H.
Partner: UNT Libraries Government Documents Department

Lithium--water--air battery project: progress during the month of March 1977. [LLL]

Description: The electrode behavior of the system, Ca/aq.-NaOH, NaCl, was investigated at ambient temperatures. Limiting currents were noted for intermediate concentrations of NaOH and NaCl, while rapid passivation at high ratios of NaOH to NaCl occurred. Low ratios of NaOH/NaCl yielded uncontrollable hydrogen evolution and rapid calcium dissolution. A model of the aqueous cell of the proposed system for the production of lithium was completed. The apparatus allows simultaneous determination of current efficiency and electrode polarization for the Li(Hg)/aq.-LiOH electrode upon cathodic polarization. Cooling curves indicate the existence of a LiI--KI--LiCl eutectic with a melting point of approximately 230/sup 0/C; possible errors are being considered arising from artifacts of the system and possible impurities in the salts. 2 figures.
Date: April 11, 1977
Creator: Cooper, J. F.; Hosmer, P. K.; Kelly, B. E.; Krikorian, O. H. & Parrish, W. H.
Partner: UNT Libraries Government Documents Department

Reactions of the toluene-insoluble, pyridine-soluble fraction of Illinois No. 6 coal

Description: Illinois No. 6 coal was extracted with pyridine at 100/sup 0/ and the toluene-insoluble, pyridine-soluble (TIPS) fraction of the extract was used as a model for the 84% of insoluble coal. Various TIPS fractions had number-average molecular weights (anti M/sub n/) in pyridine of 980 to 1380 but were insoluble or only partly soluble in most other solvents. Elemental and /sup 1/H and /sup 13/C NMR analyses indicate an H/C ratio of only 1.3 in the aliphatic portions of the TIPS molecules. The TIPS fraction was treated with a variety of reagents and their abilities to cleave ether and ester bonds were measured by decreases in anti M/sub n/: ZnCl/sub 2/ > LiI.H/sub 2/O > ZnBr/sub 2/ > pyridine.HI > methyl iodide > benzylamine > alcoholic KOH > toluene sulfonic acid. Evidence for ester groups comes from saponification equivalents and the effects of alcoholic KOH and amines on anti M/sub n/. HI appears to cleave all the bonds that Na cleaves and more, suggesting that there are few diaryl ether bonds and more phenyl alkyl and benzyl ether than dialkyl ether bonds.
Date: January 1, 1979
Creator: Mayo, F.R.; Buchanan, D.H. & Pavelka, L.A.
Partner: UNT Libraries Government Documents Department