Development of a Calibration-Free High Temperature Electrical Conductivity Measurement for CaF2 Melts and Slag Systems

The specific electrical conductivity of slags is a thermo-physical property that strongly influences the power consumption of metallurgical smelting processes that are based on the principle of resistance heating. Currently, worldwide no measurement technology is available to precisely measure the electrical conductivity of molten CaF2 and its slag systems. Therefore, the aim of this thesis is to develop a measurement technology that is calibration-free, achieves highest accuracy and stable measurement results over a broad conductivity spectrum up to high temperatures of ~1,750°C. The herein developed technology combines best practices indentified in literature for cell design, measurement technique and measurement method (electrochemical impedance spectroscopy) with an innovative data evaluation process based on simulation of the measurement and fitting of equivalent circuit diagrams to create a new measurement technology. The developed technology is evaluated in several aqueous solutions, molten KCl and NaCl as well as in molten CaF2. The technology is tested on its robustness and calibration-freeness, accuracy and overall measuring error over a wide temperature range from 16 °C up to 1,720 °C and over an electrical conductivity range starting from 1.356 mS/cm up to ~7 S/cm. Finally, the technology limitations are determined and an outlook to further optimization options is given.