Method for Measuring the Electrical Conductivity of Oxide–Fluoride Systems in a Coaxial Cell
Tóm tắt
The corrosion of structural materials in fluoride media is a key problem on organizing many technological processes and scientific research. In this connection, when the physicochemical properties of fluoride melts are studied, specific requirements are imposed on the structural materials of electrochemical devices. In this work, a method is developed to measure the electrical conductivity of liquid fluoride systems in a conductometric cell with coaxially arranged electrodes. The electrodes are made of glassy carbon, which is resistant to fluoride melts under the action of rf alternating current. The inner electrode is a rod disposed coaxially inside the outer electrode (tube). The electrode system can be dipped to any depth; in this case, the melt volume is constant over wide temperature range. Electrochemical impedance spectroscopy is used to measure the electrical resistance of the melt in the ac frequency range from 1 Hz to 105 kHz at a voltage amplitude of 5 mV. The coaxial cell was calibrated against molten CsCl salt in the temperature range 660–880°C on heating and cooling. The temperature dependence of the cell constant is used to calculate the electrical conductivity of oxide–fluoride systems 0.565KF–AlF3 with a molar fraction ratio xKF/
$${{x}_{{{\text{Al}}{{{\text{F}}}_{3}}}}}$$
= 1.3 and (KF–AlF3)–Sc2O3 with Sc2O3 contents of 1, 2, and 3 wt %. The electrical conductivities of the 0.565KF–AlF3 melt measured in cells of various designs (coaxial, with parallel molybdenum electrodes, and with a BN capillary) coincide within 1%. In the range 590–720°C, the temperature dependences of the electrical conductivity of the (KF–AlF3)–Sc2O3 systems have inflection points corresponding to their liquidus temperatures. The coaxial cell can be used to measure the electrical conductivity of aggressive fluoride and oxide–fluoride systems over a wide temperature range, including a heterogeneous region.
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