The Solubilities of NiO , Co3 O 4, and Ternary Oxides in Fused Na2 SO 4 at 1200°K

The solubilities of the oxides and in molten have been established as a function of activity at 1200°K. A reference electrode of in a mullite tube was used as a sodium activity probe for the melt. A second reference electrode of Pt, (air)/zirconia served as an oxygen activity probe for . The combination of measurements of the sodium probe and oxygen probe in the melt provided the activity in directly, and eliminated the necessity for any bare metal electrode. Saturated melts were analyzed by atomic absorption spectroscopy for the dissolved metal contents. The observed dependences of the solubilities of and in on the activities of sodium oxide are in agreement with those predicted from the Na‐Ni‐S‐O and N‐Co‐S‐O phase stability diagrams, respectively. Activity coefficients were calculated for the solute species. Preliminary measurements were made of the aluminum contents in melts saturated with and in an alumina crucible. The unusual dependences of aluminum content on salt basicity suggested the existence of the ternary oxides and . While the preliminary aluminum measurements were not considered reliable, a theoretical model was developed to predict the expected solubility behavior for a ternary oxide in .