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Activated transport in AMTEC electrodesTransport 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.
Document ID
19930042007
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Williams, R. M.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Jeffries-Nakamura, B.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Ryan, M. A.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Underwood, M. L.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
O'Connor, D.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Kikkert, S.
(JPL Pasadena, CA, United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1992
Publication Information
Publication: 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)
Publisher: Society of Automotive Engineers, Inc.
Subject Category
Inorganic And Physical Chemistry
Accession Number
93A26004
Distribution Limits
Public
Copyright
Other

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