The Molar Volumes and the Surface Tensions of Melts in the Systems CaF₂-MF (M:Li, Na) and CaF₂-MF₂ (M: Mg, Sr, Ba)

Abstract

Surface tension and density of molten CaF₂-based binary system were measured. From the measurement, the following results were obtained.
(1) Molar volumes of the melts in the systems CaF₂-NaF, and CaF₂-BaF₂ are deviated positively from the additive rule, while for CaF₂-LiF and CaF₂-MgF₂ melts negative deviation from the additive rule on volume is found, but CaF₂-SrF₂ melt behaves ideally on volume.
(2) Surface tensions of the melts in the binary systems can be expressed by Guggenheim's equation for regular solution, if a suitable interaction energy ω of each binary system is selected.
(3) The interaction energy ω, estimated from surface tension of binary fluoride systems, is related to the excess volume on mixing for CaF₂-M_xF₂ equi-molar composition (x=1 for divalent and x=2 for monovalent fluoride).
(4) Liquidus lines for the systems, calculated from the interaction energy ω in combination with the thermochemical data are fairly in good agreement with those reported, but that for CaF₂-NaF system is exceptional.
(5) Surface tensions of binary fluoride melts are strongly depended on packing density of fluorine ions on the surface.