Thermodynamic optimization of the systems PbO-SiO 2 , PbO-ZnO, ZnO-SiO 2 and PbO-ZnO-SiO 2
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INTRODUCTION
THE present study of the PbO-ZnO-SiO2 system is part of a wider research program aimed at characterization of phase equilibria and thermodynamic properties of the sixcomponent PbO-ZnO-FeO-Fe2O3-CaO-SiO2 system for zinc/lead smelting slags and sinters, through an interactive combination of experimental investigations and thermodynamic modeling. This overall research program has already been described in previous publications by the present authors.[1–8] In the thermodynamic ‘‘optimization’’ of a chemical system, all available thermodynamic and phase equilibrium data are evaluated simultaneously in order to obtain one set of model equations for the Gibbs energies of all phases as functions of temperature and composition. From these equations, all of the thermodynamic properties and the 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 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. For the molten slag phase, a modified quasichemical model has been used.[9–12] The model has been described in several publications.[3,7,9–12] Parameters for the computer model of the slag system are obtained from thermodynamic and phase equilibrium information on binary and ternary systems. The optimizations for the binary and ternary systems are performed using least-squares optimization programs which are part of the F*A*C*T computer database system.[13] Binary- and ternary-phase diagrams are calcuEVGUENI JAK, Research Fellow, and PETER C. HAYES, Associate Professor, are with the Department of Mining, Minerals and Materials Engineering, The University of Queensland, St. Lucia, Queensland, 4072, Australia. SERGEI DEGTEROV, Senior Research Scientist, and ARTHUR D. PELTON, Professor, are with the Centre for Research in Computation Thermochemistry, Ecole Polytechnique de Montreal, Montreal, PQ, Canada H3C 3A7. PING WU, Senior Research Scientist, formerly with the Centre for Research in Computation Thermochemistry, Ecole Polytechnique de Montreal, is with the National Supercomputing Research Centre, National University of Singapore, Singapore, 118261. Manuscript submitted November 22, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
lated from the optimized parameters using the software of the F*A*C*T system. In the present study, preliminary critical evaluations of all available, reliable phase diagrams and thermodynamic data for the PbO-SiO2, ZnO-SiO2, and PbO-ZnO binary systems have been conducted.[7] With these binary parameters, the quasichemical model was used to predict the thermodynamic properties of the slag phase in the PbO-ZnO-SiO2 ternary system. The computer modeling of the PbO-ZnO-SiO2 ternary system indicated significant discrepancies between th
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