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I.

INTRODUCTION

CAF2-CONTAINING oxide systems have been widely used in many industrial processes including steelmaking. Although the CaO-CaF2 system is one of the most fundamental systems, there are still several inconsistencies among the available experimental data. In order to resolve these inconsistencies, the authors[1] performed new phase diagram experiments using equilibration/quenching technique using sealed Pt capsules and thermal analysis by DSC. The purpose of the current study is to achieve the thermodynamic optimization of the CaO-CaF2 system based on the new experimental data obtained in our study and carry out the critical evaluation of all the available experimental data in the literature. In the thermodynamic ‘‘optimization’’ of a system, all the available thermodynamic and phase-equilibrium data were evaluated simultaneously to obtain one set of model equations for the Gibbs energies of all phases as functions of temperature and composition. From these equations, all thermodynamic properties and phase diagrams can be back-calculated. In this way, all the data are rendered self-consistent and consistent with thermodynamic principles. Thermodynamic property data, such as activity data, can aid in the evaluation of DONG-GEUN KIM, Graduate Student, MARIE-ALINE VAN ENDE, Postdoctoral Fellow, and IN-HO JUNG, Professor, are with the Department of Mining and Materials Engineering, McGill University, 3610 University St., Montreal, QC, H3A 0C5, Canada. Contact e-mail: [email protected] CORRIE VAN HOEK and SIEGER VAN DER LAAN, Researchers, are with the Tata Steel Europe, Research Development and Technology, Ceramic Research Center, PO Box 10000, 1970 CA, IJmuiden, The Netherlands. CHRISTIAN LIEBSKE, Senior Scientist, is with the ETH Zu¨rich Institute for Geochemistry and Petrology, Sonneggstrasse 5, NO E 53.2, 8092, Zu¨rich, Switzerland. Manuscript submitted March 26, 2012. Article published online October 2, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B

the phase diagram, and phase diagram measurements can be used to deduce thermodynamic properties. Discrepancies in the available data can often be resolved, and interpolations and extrapolations can be made in a thermodynamically correct manner. The thermodynamic properties of liquid CaO-CaF2 solution were previously accessed by Zaitsev et al.[2] and Seo et al.[3,4] Zaitsev et al. tried to fit their experimental activity data of CaF2 and CaO in molten CaO-CaF2 solution using the subregular solution model, but no other experimental data were used in the evaluation of the model parameters. Seo et al. used the molecular dynamics approach to understand the thermodynamic interaction of CaO and CaF2 in liquid state. Based on the Gibbs energy of CaO-CaF2 solution derived from the mixing enthalpy calculated from the molecular dynamics simulation and the entropy from the assumption of an ideal ionic solution, they calculated the phase diagram of the CaO-CaF2 system. However, no critical reviews of all experimental data in the literature were performed in these s