Electrical Conductivity of Molten Cryolite and Potassium, Sodium, and Lithium Chlorides

Abstract

An improved technique has been developed for the determination of the electrical conductivity of reactive molten salts and has been applied to cryolite. The method employs a platinum cell with two concentric hemispherical electrodes. This cell is maintained a fixed distance below the surface of the molten salt which is held in a larger platinum container. Errors from lead resistance have been eliminated by measuring with a Kelvin double bridge (Thomson bridge) and polarization difficulties have been minimized by extrapolation of the nearly linear plot of resistance vs. frequency−1/2 to infinite frequency. Conductivities of molten potassium chloride, sodium chloride, and lithium cloride were determined with a quartz dip‐cell. Best values for the conductivities (ohm−1cm−1) at 1000°C were: cryolite 2.80; potassium chloride 2.65; sodium chloride 4.17; and lithium chloride at 700°C, 6.14. Densities (g/ml), measured by a platinum sinker, were found to follow these equations from the melting points to 1080°C : potassium chloride 1.964–0.574ċ10−3t; sodium chloride 1.969–0.524ċ10−3t; cryolite 3.032–0.937ċ10−3t. The logarithm of equivalent conductance (A) changed linearly with reciprocal absolute temperature (T). Best values for the activation energy for conductance (kcal/mole) (calculated as 2.303 times 1.986 cal/mole deg times slope of log A vs. 1/T) were: cryolite 4.48; potassium chloride 3.32; sodium chloride 3.04; lithium chloride 1.70. Maintaining the fused cryolite in contact with an atmosphere of argon as compared with room air had a negligible effect upon the measured conductivity values for cryolite.