Researchers at Caltech investigated a pre-operational annealing process as a potential means of preventing a sudden reduction of ionic conductivity in a beta-alumina solid electrolyte (BASE) during use. On the basis of tests described below, the sudden reduction of ionic conductivity, followed by a slow recovery, has been found to occur during testing of the solid electrolyte and electrode components of an alkali metal thermal-to-electric converter (AMTEC) cell. This conductivity reduction may be observed quite infrequently; at lower operating temperatures, T < 1,073 Kelvin, it is not usually observed at all, while at T = 1,123 to 1,173 Kelvin, hundreds of hours may pass before conductivity reduction occurs. Only on tests running at higher operating temperatures for thousands of hours is this phenomenon regularly exhibited. The reduction of ionic conductivity would degrade the performance of an AMTEC cell. A pre-operational annealing process would help to sustain performance.
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