An Oxygen Negative Ion Source of a New Concept Using Solid Oxide Electrolytes

A novel oxygen negative ion source named solid oxide ion source (SOIS) is proposed. To demonstrate its concept, thermionic emission of oxygen negative ions, O - , from a bare surface of yttria-stabilized zirconia (YSZ) was studied with a mass spectrometer capable of detecting negative ions. The emission current was investigated at the temperature range 750 to 950°C under pressures of about 2 x 10 3 to 4 x 10 4 Pa. O ions proved to he emitted into a vacuum from the hare YSZ surface at elevated temperatures. The emission current increased with temperature and applied voltage. From Richardson-Dushman plots, activation energy of the thermionic emission was estimated to be about 2 eV. In continuous operation, the emission current decreased with time, finally approaching zero; however, after intervals, the current recovered. On the basis of the results, a model for explaining the emission mechanism of O ions is proposed. The model is based on three key processes occurring on the surface of electrolytes: (1) formation of O ions on the surface by electron capture of oxygen atoms provided by the migration of oxide ions across electrolytes, (2) accumulation of O ions on the surface, and (3) emission of O ions from the surface.

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