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  • 1
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    Activated transport in AMTEC electrodes (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Transport of alkali, metal atoms through porous cathodes of alkali metal thermal-to-electric converter (AMTEC) cells is responsible for significant reducible losses in the electrical performance of these cells. Experimental evidence for activated transport of metal atoms at grain surfaces and boundaries within some AMTEC electrodes has been derived from temperature dependent studies as well as from analysis of the detailed frequency dependence of ac impedance results for other electrodes, including thin, mature molybdenum electrodes which exhibit transport dominated by free molecular flow of sodium gas at low frequencies or dc conditions. Activated surface transport will almost always exist in parallel with free molecular flow transport, and the process of alkali atom adsorption/desorption from the electrode surface will invariably be part of the transport process, and possibly a dominant part in some cases. The temperature dependence of the diffusion coefficient of the alkali metal through the electrode in several cases provides an activation energy and preexponential, but at least two activated processes may be operative, and the activation parameters should be expected to depend on the alkali metal activity gradient that the electrode experiences. In the case of Pt/W/Mn electrodes operated for 2500 hours, limiting currents varied with electrode thickness, and the activation parameters could be assigned primarily to the surface/grain boundary diffusion process.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: In: IECEC '92; Proceedings of the 27th Intersociety Energy Conversion Engineering Conference, San Diego, CA, Aug. 3-7, 1992. Vol. 3 (A93-25851 09-44); p. 3.19-3.24.
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  • 2
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    Kinetics and transport at AMTEC electrodes. II - Temperature dependence of the interfacial impedance of Na(g)/porous Mo/Na-Beta-double prime alumina (1990)
    In:  Other Sources
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    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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  • 3
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    Kinetics and transport at AMTEC electrodes. I - The interfacial impedance model (1990)
    In:  Other Sources
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    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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  • 4
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    Oxygen extraction from lunar materials - An experimental test of an ilmenite reduction process (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The reaction of ilmenite with hydrogen to produce water has been studied experimentally in order to evaluate the effectiveness of using a cold trap to improve yields in a continuous flow process. Yields were enhanced, but not to the degree observed in batch processing systems. The terrestrial simulant used in these studies contained traces of iron sulfide, which released H2S during processing with a deleterious effect on several components of the test system. More sophisticated testing should be undertaken to obtain kinetic data and attention given to the removal of sulfides in the pre-process beneficiation.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
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  • 5
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    Photoelectrochemical electrodes (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The surface of a moderate band gap semiconductor such as p-type molybdenum sulfide is modified to contain an adherent film of charge mediating ionene polymer containing an electroactive unit such as bipyridimium. Electron transport between the electrode and the mediator film is favorable and photocorrosion and recombination processes are suppressed. Incorporation of particles of catalyst such as platinum within the film provides a reduction in overvoltage. The polymer film is readily deposited on the electrode surface and can be rendered stable by ionic or addition crosslinking. Catalyst can be predispersed in the polymer film or a salt can be impregnated into the film and reduced therein.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
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  • 6
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    JSC systems using solid ceramic oxygen electrolyte cells to measure oxygen fugacites in gas-mixing systems (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Details are given for the construction and operation of a 101.3 KN/sq meter (1 atmosphere) redox control system. A solid ceramic oxygen electrolyte cell is used to monitor the oxygen fugacity in the furnace. The system consists of a vertical quench gas mixing furnace with heads designed for mounting the electrolyte cell and with facilities for inserting and removing the samples, a simplified version of a gas mixing apparatus, and devices for experiments under controlled rates of change of temperature. A thermogravimetric analysis system employing these techniques of redox control and measurement is also described. The calibration and maintenance of the system are discussed.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA-TM-58234 , JSC-17022
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  • 7
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    A system using solid ceramic oxygen electrolyte cells to measure oxygen fugacities in gas-mixing systems (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Details are given for the construction and operation of a 101.3 kN/sq m (1 atmosphere) redox control system. A solid ceramic oxygen electrolyte cell is used to monitor the oxygen fugacity in the furnace. The system consists of a vertical quench, gas mixing furnace with heads designed for mounting the electrolyte cell and with facilities for inserting and removing the samples. The system also contains the high input impedance electronics necessary for measurements, a simplified version of a gas mixing apparatus, and devices for experiments under controlled rates of change relative to temperature and redox state. The calibration and maintenance of the system are discussed.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA-TM-X-58167 , JSC-09909
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  • 8
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    Carbon dioxide electrolysis using a ceramic electrolyte (1979)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper discusses the results of an experimental study of the electrical aspects of carbon dioxide electrolysis using a ceramic electrolyte. The electrolyte compositions used in this study are 8% Y2O3 stabilized ZrO2, 7.5% CaO stabilized ZrO2, and 5% Y2O3 stabilized ThO2. Results indicate that the 8% Y2O3 stabilized ZrO2 is the best material to use for electrolysis, in terms of current as a function of voltage and temperature, and in terms of efficiency of oxide ion flow through it. The poorest results were obtained with the 5% Y2O3 stabilized ThO2 composition. An electrolysis system which might be employed to reclaim oxygen and carbon from effluents of space manufacturing, assuming that an industry would have to electrolyze 258,000 tonnes of CO2 per year, is predicted to require a total cell area of 110,000 sq m of 1 mm thickness and electrical capacity of 441 MW.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 79-1375 , Princeton University and American Institute of Aeronautics and Astronautics, Conference on Space Manufacturing Facilities, 4th, Princeton University; May 14, 1979 - May 17, 1979; Princeton, NJ
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  • 9
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    High temperature electrolytic recovery of oxygen from gaseous effluents from the carbo-chlorination of lunar anorthite and the hydrogenation of ilmenite: A theoretical study (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A thermodynamic analysis discusses the compositions of gaseous effluents from the reaction of carbon and chlorine and of hydrogen with lunar anorthite and ilmenite, respectively. The computations consider the effects of the indigenous volatiles on the solid/gas reactions and on the composition of the effluent gases. A theoretical parameterization of the high temperature electrolysis of such gases is given for several types of solid ceramic electrolytes, and the effect of oxygen removal on the effluents is computed. Potential chemical interactions between the gases and the ceramic electrolytes are analyzed and discussed.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA-TM-58214 , JSC-14649
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  • 10
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    Experimental observation of electrochemical rate limitations affecting sodium ion-electron recombination at electrodes of the alkali metal thermoelectric converter at T about 1200 K (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper considers a model of the internal impedances of thin porous Mo and W alkali metal thermoelectric converter (AMTEC), in which the kinetic parameters associated with the reaction of the beta-double-prime alumina solid electrolite (BASE)/porous metal/gas three-phase boundary can be evaluated. Impedance data in the frequency range 0.01-100,000 Hz were collected over a range of AMTEC cell operating voltages for small-area thin porous Mo and W electrodes, yielding apparent charge transfer resistances at a series of cell potentials/currents. The ohmic resistance in the AMTEC cell could be broken down and characterized with three parameters: the BASE ionic resistance, the electrode film sheet resistance, and the contact/lead resistance, all of which could be calculated or measured independently and used to calculate power curves in good agreement with observed power curves. It is shown that these calculations can be used to predict the properties of electrodes with optimized parameters or to detect enhanced transport modes.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Symposium on High Temperature Materials Chemistry - IV; Oct 19, 1987 - Oct 23, 1987; Honolulu, HI; United States
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