Refining sub-solidus phase relations in the systems CaO–RuO2–SiO2 and CaO–RuO2–V2O5

Abstract

Sub-solidus phase relations in the ternary systems CaO–RuO2–SiO2 and CaO–RuO2–V2O5 have been refined using thermodynamic data on calcium ruthenates, silicates and vanadates. Tie lines are established by considering Gibbs energy change for exchange reactions. Quaternary oxides have not been detected in these systems. Because of the relatively large entropy associated with phase transition of Ca2SiO4 from olivine to α′ structure at 1120K, reversal of one tie line is seen in the system CaO–RuO2–SiO2 between 950 and 1230K. There is no change in sub-solidus phase relation as a function of temperature in the system CaO–RuO2–V2O5. Since vanadium can exist in several lower oxidation states, the computed sub-solidus phase relations are valid only at high oxygen partial pressures. There is fair agreement between the computed phase diagram and the limited experimental information available for CaO-deficient compositions in the literature.