Mass‐Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO‐Al ₂ O ₃

Abstract

The activities of CaO and Al 2 O 3 in lime‐alumina melts were studied by Knudsen cell‐mass spectrometry at 2060 K. Emf of solid state cells, with CaF 2 as the electrolyte, was measured from 923 to 1223 K to obtain the free energies of formation of the interoxide compounds. The results are critically evaluated in the light of data reported in the literature on phase equilibria, activities in melts, and stabilities of compounds. A coherent set of data is presented, including the previously unknown free energy of formation of CaO.6Al 2 O 3 and the temperature dependence of activities in the liquid phase.