Viscosity of Molten Alkaline-Earth Fluorides

The viscosities of molten alkaline-earth fluorides MgF₂, CaF₂, SrF₂ BaF₂ were measured using the oscillating crucible method, which is especially suitable for measuring molten salts with low viscosity. The results showed a good Arrhenius linearity over a wide temperature range. The measured viscosities and activation energies increased in the following order: MgF₂ < CaF₂ < BaF₂ < SrF₂. Judging by the charge density, the viscosity of alkaline-earth fluorides should increase from molten BaF₂ to MgF₂. However, the results indicate a different tendency, which may be explained by a Coulomb force that is very strong. The low viscosity of MgF₂ can be attributed to a decreased cohesive force, due to a partial loss of the Coulomb force caused by a higher charge density of the material. The viscosities were also compared to those of molten alkali fluorides and alkaline-earth chlorides. The viscosities of molten alkaline-earth fluorides were higher than those of molten alkali fluorides and alkaline-earth chlorides. The CaF₂ viscosity determined in this study was compared to literature values and showed a reasonable value in the relatively low-viscosity region.