Thermodynamic Optimization of the Ca-Fe-O System
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THE CaO-FeO-Fe2O3 portion of the Ca-Fe-O system is one of the essential subsystems for many metallurgical processes, including iron ore sintering, copper-making industry, and iron- and steel-making processes. The thermodynamic description of the solubility of oxygen in the Fe-Ca alloys is important for the deoxidation of steel. Comprehensive assessments of the Ca-Fe-O system are available in the literature.[1,2] Very good results were obtained; however, some previously existing[3,4] and new experimental data[4–6] were not taken into account in these studies. As a result, there is a discrepancy between model predictions and these experimental data. Furthermore, the oxygen content in the Fe-Ca liquid metal was not assessed. The purpose of the present study is to obtain a thermodynamic database capable of describing all experimental data available up-to-date. In order to achieve that, a thermodynamic optimization of the system is performed. The first step is selecting the appropriate thermodynamic models for all phases in the system. Then, a critical and simultaneous evaluation/ assessment of all available thermodynamic and phase diagram data is performed. Finally, the thermodynamic model parameters are optimized in order to obtain one self-consistent set of model equations for the Gibbs TAUFIQ HIDAYAT, Research Fellow, DENIS SHISHIN, Postdoctoral Research Fellow, and EVGUENI JAK, Professor, are with the Pyrometallurgical Research Laboratory, PYROSEARCH, School of Chemical Engineering, The University of Queensland, Brisbane, Australia. Contact e-mail: [email protected] SERGEI A. DECTEROV, Research Professor, is with the Center for Research in Computational Thermochemistry (CRCT), De´p. de Ge´nie Chimique, E´cole Polytechnique, Montre´al, Canada and Honorary Professor, School of Chemical Engineering, The University of Queensland, Brisbane, QLD, Australia. Manuscript submitted May 14, 2013. Article published online November 16, 2015. 256—VOLUME 47B, FEBRUARY 2016
energies of all phases, best reproducing the experimental data as functions of temperature and composition. The list of the stable phases, models, and notations used in the present study is given in Table I. Thermodynamic properties and phase diagrams can be back-calculated from the model equations. Thermodynamic property data, such as enthalpies and activities, can aid in assessing phase diagrams, and phase diagram measurements can be used to derive the thermodynamic properties. The described procedure is sometimes referred to as Calphad technique. The present thermodynamic optimization has been performed using the FactSage thermodynamic software package[7] as a part of the development of a self-consistent thermodynamic database for the Al-Ca-CuFe-Mg-Si-O-S multi-components system.
II.
BINARY SUBSYSTEMS
A. Fe-O The assessment of the Fe-O system was reported earlier.[8,9] In the present study, the properties of solid phases were adopted from Hidayat et al.[8] and the properties of slag and liquid metal are from Shishin et al.[9] The assessed phase dia
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