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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of applied electrochemistry 19 (1989), S. 813-818 
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Niobium triselenide is one of the cathode materials being evaluated at JPL for ambient temperature secondary lithium batteries for space applications. The mechanism of reduction of NbSe3 involves two steps, 1 mole of Li intercalating in the first step and 2 moles of Li intercalating at lower potentials in the second step. The a.c. impedance behaviour of the NbSe3 cathode under various conditions, i.e. at different reduction potentials, after discharges at various d.c. potentials and after charge/discharge cycling is discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of applied electrochemistry 20 (1990), S. 357-364 
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In order to circumvent the corrosion problems prevalent in many existing electrochemical couples using the Na/β″-alumina half cell, a new class of high energy density organic materials was studied as cathode materials. In particular, one material tetracyanoethylene (TCNE), has favourable electrochemical characteristics with a potential 〉3.0 V against Na+/Na and energy density ∼620 Wh kg−1. Adopting a cell designed to permit sealing the anode half cell, the performance of TCNE was evaluated under various experimental conditions, that is, at different concentrations of TCNE in the catholyte and with different current collectors. The electrochemical behaviour of the TCNE cathode and the kinetics of TCNE reduction were examined. The kinetic parameters, exchange current density and diffusion coefficient, were determined from different a.c. and d.c. electrochemical techniques and evaluated with respect to the changes in TCNE concentrations in the catholyte. A chemical transformation occurring in the cell operating conditions which does not reduce the electrochemical activity of TCNE was identified from FTIR spectra. Finally, possible approaches to the use of TCNE or other organic materials in sodium or lithium rechargeable batteries are outlined.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Columnar, porous, magnetron-sputtered molybdenum and tungsten films show optinum performance as AMTEC electrodes at thicknesses less than 1.0 μm when used with molybdenum or nickel current collector grids. Power densities of 0.40 W cm−2 for 0.5 μm molybdenum films at 1200 K and 0.35 W cm−2 for 0.5 μm tungsten films at 1180 K were obtained at electrode maturity after 40–90 h. Sheet resistances of magnetron sputter deposited films on sodium beta″-alumina solid electrolyte (BASE) substrates were found to increase very steeply as thickness is decreased below about 0.3–0.4 μm. The a.c. impedance data for these electrodes have been interpreted in terms of contributions from the bulk BASE and the porous electrode/BASE interface. Voltage profiles of operating electrodes show that the total electrode area, of electrodes with thickness 〈2.0 μm, is not utilized efficiently unless a fairly fine (∼1×1mm) current collector grid is employed.
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  • 4
    ISSN: 0308-0501
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Data are presented which show the effect of elevated environmental temperature upon smoke particle characteristics of wood (Douglas fir) and a rigid PVC, under both flaming and nonflaming combustion in air. The physical data obtainbed include the smoke particle average diameter, the smoke optical densities in red and blue light, and the weight loss of the sample. The average particle dimeter, the smoke optical densities in red and blue light, and the weight loss of the sample. The average particle diameter and optical densities in red and blue light, and the weight loss of the sample. The average particle dimater and optical densities were obtained uwing in in situ optical system which measures forward scattered light at two angles and transmitte light at two wavelengths. Data were taken for vertically mounted samples exposed to a radiant flux of 5 W cm-2 in environments at a room temperatures, 100°C, 200°C and 300°C. The result indicate that in flaming test higher environmental temperatures general result in greater smoke optical densities and larger smoke particles, while in nonflaming tests higherl temperatures in lower smoke densities and smaller smoke particles, for wood. These results may explain why small-scale test data (room temperature environment) do not often correlate well with full-scale data (often at elevated environmental temperatures).
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2011-08-24
    Description: Titanium disulfide and niobium triselenide are two well-studied candidate materials for positive electrodes in rechargeable lithium cells. A comparative study of the kinetics of intercalation of lithium in both the cathodes is made here based on various electrochemical techniques, i.e., linear polarization, potentiodynamic polarization, and ac impedance under different experimental conditions such as prismatic or disk configuration of fresh, partially discharged, or cycled electrode. Further, the diffusion coefficients of lithium ions in these cathodes are estimated under these conditions using conventional techniques, i.e., ac impedance, chronocoulometry, chronoamperometry, and current pulse relaxation. Based on the values of the diffusion coefficients, the applicability of these methods for the determination of diffusion coefficients is discussed.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Electrochemical Society, Journal (ISSN 0013-4651); 139; 6, Ju
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  • 6
    Publication Date: 2011-08-19
    Description: The exchange current, transfer coefficient, mass-transport parameters, and electrode capacitance at the Na(g)/porous Mo/Na-Beta-double prime alumina solid electrolyte (BASE) phase boundary have been evaluated from 740 to 1220 K. The transfer coefficient exhibits a value close to 0.5 and the exchange current is dominated by collision frequency, with no significant activation energy. Since the porous Mp-electrode adopts a fairly regular microstructure on the BASE surface, the magnitude of the exchange current of mature electrodes directly depends on the actual contact zone of the porous metal film with the BASE ceramic, and decreases slightly as grain growth occurs. The exchange currents and the mass-transport parameters derived for very porous, thin Mo electrodes indicate that the charge-transfer reaction occurs at a small fraction of the interface. High-frequency limiting capacitance and resistance values due to the interface show potential dependence and a value on the order of 1 F/sq m and 0.1-1.0 Ohm-sq cm.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Electrochemical Society, Journal (ISSN 0013-4651); 137; 1716-172
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  • 7
    Publication Date: 2011-08-19
    Description: Mixed mass-transport and kinetic control of sodium ion reduction at porous inert electrodes on sodium beta-double-prime alumina solid electrolyte (BASE) ceramic in a high-temperature electrochemical cell has been observed and modeled. The high ionic conductivity of BASE and the reversibility of the liquid sodium/BASE anodic half-cell led to assignment of potential-dependent (nonohmic) resistances to kinetic and mass-transport processes associated with the porous electrode. The morphology of these electrodes and typical sodium gas pressures are consistent with Knudsen, or free-molecular, flow through the electrode.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Electrochemical Society, Journal (ISSN 0013-4651); 137; 1709-171
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  • 8
    Publication Date: 2011-08-19
    Description: The overcharge condition in secondary lithium batteries employing redox additives for overcharge protection, has been theoretically analyzed in terms of a finite linear diffusion model. The analysis leads to expressions relating the steady-state overcharge current density and cell voltage to the concentration, diffusion coefficient, standard reduction potential of the redox couple, and interelectrode distance. The model permits the estimation of the maximum permissible overcharge rate for any chosen set of system conditions. Digital simulation of the overcharge experiment leads to numerical representation of the potential transients, and estimate of the influence of diffusion coefficient and interelectrode distance on the transient attainment of the steady state during overcharge. The model has been experimentally verified using 1,1-prime-dimethyl ferrocene as a redox additive. The analysis of the experimental results in terms of the theory allows the calculation of the diffusion coefficient and the formal potential of the redox couple. The model and the theoretical results may be exploited in the design and optimization of overcharge protection by the redox additive approach.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Electrochemical Society, Journal (ISSN 0013-4651); 138; 2224-222
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  • 9
    Publication Date: 2011-08-19
    Description: The behavior of the reverse flow ceiling jet against the ventilation flow from 0.58 to 0.87 m/s was investigated in a 1/3 scale model of a wide body aircraft interior. For all tests, strong reverse-flow ceiling jets of hot gases were detected well upstream of the fire. Both thicknesses of the reverse-flow ceiling jet and the smoke layer increased with the fire-crossflow parameter. The thickness of the smoke layer where the smoke flows along the main flow below the reverse-flow ceiling jet was almost twice that of the reverse-flow ceiling jet. Detailed spatial and time-varying temperatures of the gas in the test section were measured, and velocity profiles were also measured using a temperature compensated hot film.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 10
    Publication Date: 2011-08-19
    Description: Voltammetry of partially oxidized porous molybdenum alkali metal thermoelectric converter (AMTEC) electrodes from about 600 to 1000 K revealed a series of redox processes within the AMTEC operational voltage range which can be used to establish the electronic and ionic conductivities of these electrodes. Improved estimates of the free energies of formation of Na2Mo3O6, NaMoO2, and Na3MoO4 are obtained. Evidence is provided for the slow corrosive attack by Na2MoO4 on molybdenum. The ionic conductivity of Na2MoO4 is found to be sufficiently large at temperatures of greater than 700 K to explain the observed electrochemical phenomena in addition to the enhanced sodium transport in AMTEC electrodes below the freezing point of Na2MoO4.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Electrochemical Society, Journal (ISSN 0013-4651); 133; 2253-225
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