A STUDY OF THE INTERFACIAL REACTION KINETICS IN THE IRON - CALCIUM-FLUORIDE SYSTEM AT 1450 DEGREES C

Abstract

<p>An understanding of the chemical reaction kinetics at a slag/metal interface requires knowledge of both transport and interfacial properties. However, fundamental interfacial reaction rate data are largely unavailable. Consequently, the ion exchange current density and interfacial capacitance have been measured with the double pulse galvanostatic method for the anodic dissolution of an iron electrode in liquid CaF(,2) and CaF(,2)-CaO slags. Both the exchange current and capacitance are strongly increasing functions of concentration. The measured exchange current densities are large (ranging from 4.5 to 400 amperes/cm('2)), so that a non-linear extrapolation of the experimental data is necessary. The kinetics of oxygen transfer at the Fe/CaF(,2) interface was studied in independent experiments. The reaction was driven by an FeO activity gradient. The kinetic information obtained in this manner compares favourably with that derived from the electrochemical technique. With suitable information on the relative magnitudes of transport and reaction rates, it is possible to predict the kinetic regime for the entire system (i.e. transport, reaction, or mixed control). The experimental data indicate that mixed control of the reaction kinetics will prevail at the Fe/CaF(,2) interface in the absence of forced stirring. If the kinetic parameters in more complex metallurgical systems are similar to those measured at the Fe/CaF(,2) interface, the influence of interfacial charge transfer reactions may be greater than is normally supposed.</p>