Solid state amperometric sensor for the in-situ monitoring of slag composition and transport properties

Abstract

Conventional oxygen sensors have been used for several decades for better process control in metals industries. Such devices can accurately determine the oxidation state of the molten metal phase. Investigators understand the importance of the slag phase on the quality of the final product and therefore similar devices have been implemented recently for analysis of molten oxides. While open circuit potential measurements yield important thermodynamic information, this thesis will show that additional information can be gained by using amperometric techniques. Three different amperometric techniques were examined for use in an in-situ, zirconia-based sensor to monitor the easily dissociable oxide composition of high temperature metallurgical slags. Applied DC potential steps and impedance frequency sweeps at applied DC potentials were shown to clearly distinguish between slags containing different quantities of FeOx while demonstrating similar oxygen activities - an improvement over conventional oxygen sensor technology. The techniques were also shown to reveal information on transport properties, dissociable oxide type, and buffering capacity of the slag to a given oxidation state. In a separate set of experiments, coulometric titration was shown to easily differentiate between slags containing different quantities of FeOx in large concentrations. The ion-selective membrane properties of the zirconia allowed the coulometric titration to proceed at current efficiencies near 100% and may be useful for the recovery of commercial metals from oxide waste streams.