Effect of alkali and alkaline-earth fluorides on surface tension of molten calcium silicates

The surface tension of molten CaO + SiO2 systems containing 0∼20 mol % LiF, NaF, KF, MgF2, CaF2 and BaF2 respectively, was measured as a function of composition and temperature. With increasing fluoride concentration, the surface tensions of these systems decrease, the trend of which depends on the basicity (or acidity) of silicates and the cation species of fluorides. The temperature coefficients are very small and slightly negative. The results are discussed in terms of the theory of the rigid sphere fluid. The surface tension as well as viscosity in these systems may be determined by non-coulombic short-range forces as for simple fused salts.