Free energy of mixing of divalent basic oxides with silica
An expression derived for the free energy of mixing of a divalent basic oxide (MO) with SiO2 based on a model of silicate structure, takes into account the distribution of O2–(from MO) into the silica network, the mixing of silicate ions with O2– and the enthalpy of mixing. The resulting expression is [graphic omitted].
For the proper choice of β, calculated values of the activity of MO for the system PbO—SiO2, MnO—SiO2, FeO—SiO2 and CaO—SiO2 are in good agreement with experiment. The model predicts that the activity of the basic oxide decreases with increase in temperature.