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

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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.