Activities in Na₂O-CO₂-Sb₂O₅ Melts

Abstract

Activities of NaO_0.5 and Na(CO₃)_0.5 in Na₂O-CO₂-Sb₂O₅ melts were determined at 1423-1523 K by the EMF method, using beta″-alumina as a solid electrolyte, over the composition range N≥0.7{=n_Na2O⁄(n_Na2O+n_Sb2O5), n: the number of moles} under various partial pressures of CO₂. The activity of SbO_2.5 was calculated from the activity of NaO_0.5 by integrating the Gibbs-Duhem relation. The partial pressure of CO₂ has great influence on the activities of the components in the system. The existence of a liquid state miscibility gap was suggested in the Na₂CO₃-rich composition range. The solubility of CO₂ in the melts was also measured at 1523 K. The results of the solubility measurements of CO₂ imply that Na₂CO₃ is decomposed according to the stoichiometric reaction corresponding to the formation of Na₃SbO₄ species in the melts, and, therefore, the activity of Na₃SbO₄ was also discussed.