Thermodynamics of Na2O in the molten CaO-CaF2-SiO2 system

The activity of a few percent of Na₂O in the CaO-CaF₂-SiO₂ system doubly saturated with CaO and 3CaO·SiO₂ has been determined between 1423 and 1623 K by a chemical equilibration technique. The temperature dependence of the activity coefficient of Na₂O may be expressed as follows. {fx553-01} It was found that Henry’s law holds up to 5 mass pct of Na₂O in the flux at 1473 K. The activity of a small amount of Na₂O in the CaO-CaF₂-SiO₂ flux is discussed in comparison with that for the Na₂O-SiO₂ system in terms of their refining characteristics.