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

Open-circuit potential (OCP) measurements with zirconia-based sensors have been used for several decades in the metals industries to determine the oxi dation state of high-temperature melts. Although amperometric techniques ar e known to provide additional kinetic and compositional analysis of the sys tem, they have not been utilized by the metals industries to the same exten t. In this work, three different amperometric techniques were examined to m onitor high-temperature slags by utilizing zirconia-based sensors. Applied direct current (DC) potential steps and impedance frequency sweeps at fixed applied DC potentials were shown to clearly distinguish between slags havi ng the same oxidation state but different quantities of FeOx in low concent rations. The techniques were also shown to reveal information on the transp ort properties, slag structures, dissociable oxide type, and buffering capa city of the slag to a given oxidation state. The third technique, coulometr ic titration, was shown to easily differentiate between slags containing di fferent quantities of FeOx in larger concentrations. The ion-selective memb rane properties of the zirconia allowed the coulometric titration to procee d at current efficiencies near 100 pet. This may be useful in developing te chnology for the recovery of metals from oxide waste streams.