CS-O SYSTEM - PHASE-DIAGRAM AND OXYGEN POTENTIALS

The determination of phase transition temperatures for Cs-O mixtures containing up to 32 at% oxygen has established that the hitherto accepted phase diagram in the literature must be modified in the composition interval Cs7O-Cs7O2. Oxygen potentials in Cs-O liquids with 3.3 to 17 at% oxygen at 500-700°C have been determined by EMF measurements using ThO2-10 mol% Y2O3 electrolyte. The results were accurately described by the expression Δ G ̄O (J/mol O2) = -583800+ 156T+ 2RT (2140/T- 1 3) In x0 where R is the gas constant, T in K and 0 is the atomic fraction of oxygen. Caesium potentials at 500°C, derived from the above equation for x0 = 0-0.17 using the Duhem-Margules equation, were in excellent agreement with an extrapolation of caesium vapour pressure measurements by Arnol'dov et al. (x0 = 0.05-0.18, 280-360°C). Extrapolation of the oxygen potentials and derivation of the caesium potentials in the range 17-33.3 at% oxygen, combined with the results of Berardinelli and Kraus for higher oxygen concentrations provides an almost complete potential description of the Cs-O system up to 66 at% oxygen. © 1979.