Electrical Conductivity Measurements of Molten Alkaline-Earth Fluorides

The electrical conductivities of molten BeF₂, MgF₂, CaF₂, SrF₂, and BaF₂ were measured by electrochemical impedance spectroscopy. A new conductance cell was designed and constructed for the purpose of determining the electrical properties of highly conductive and very corrosive melts at temperatures as high as 1600°C. The cell is comprised of twin capillaries of pyrolytic boron nitride, 5 mm id x 10 cm long, two movable tungsten electrodes, and a molybdenum crucible. The ranking by specific electrical conductivity, k, was BeF₂ < MgF₂ < SrF₂ < BaF₂ < CaF₂ and by molar electrical conductivity, ⧍_m, was BeF₂ < MgF₂ < CaF₂ < SrF₂ < BaF₂. A_m was found to vary with the logarithm of the charge density of the metal cation over the entire series of alkaline–earth fluorides. With the exception of BeF₂, In ⧍_m was found to vary with In {V2/3M exp (Ec/RT)}, where V_m is the molar volume and E_c is the coulombic energy between nearest neighbor ions in the melt.