Electrical Conductivity Measurements of Binary Solutions of Molten Alkaline-Earth Fluorides

The electrical conductivities of binary solutions of molten MgF₂-CaF₂, MgF₂-SrF₂, MgF₂-BaF₂, CaF₂-SrF₂, CaF₂-BaF₂, and SrF₂-BaF₂ were measured by electrochemical impedance spectroscopy in a conductance cell comprising twin capillaries of pyrolytic boron nitride, movable tungsten electrodes, and a molybdenum crucible. In three of the systems, MgF₂-CaF₂, CaF₂-SrF₂, and SrF2-BaF2, the specific electrical conductivity was found to vary linearly with composition at constant temperature, while in the other three systems, MgF₂-SrF₂, MgF₂-BaF₂, and CaF₂-BaF₂, there were pronounced negative deviations from additivity. In a given binary system, the relative excess specific conductivity was found to vary parabolically with composition at constant temperature. In a homologous sequence the parabolic constant was proportional to the relative polarizability of the cations comprising the binary system.