A Study of Oxide Cathodes by X-Ray Diffraction Methods: Part I. Methods, Conversion Studies, and Thermal Expansion Coefficients

Two methods are described for obtaining x-ray diffraction patterns of oxide-coated cathodes. One method is used in the study of the conversion process in forming the oxide cathode while the other method is utilized in measuring the thermal expansion coefficients of barium, strontium, and thorium oxides. The conversion of an equal molar barium-strontium carbonate solid solution, (BaSr)CO3, involves (1) crystal growth in the carbonate, (2) decomposition to the mixed oxides, BaO and SrO, (3) formation of the oxide solid solution, (BaSr)O, and (4) crystal growth in the oxide. A similar sequence of events is observed in the conversion of a mixed carbonate, BaCO3+SrCO3. Crystal and particle size growth of carbonates and crystal growth of oxides are investigated and possible relationships are discussed.