Phase Equilibria in Ferrous Calcium Silicate Slags: Part II. Evaluation of Experimental Data and Computer Thermodynamic
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TRODUCTION
THIS article is the second of a series of articles investigating phase equilibria in ferrous calcium silicate slags described by the FeO-Fe2O3-CaO-SiO2 system, at intermediate oxygen partial pressures. In the first article,[1] the results of experiments equilibrated at 1200 C to 1350 C at 50 C intervals were presented at the oxygen partial pressures of 10-5 and 10-6 atm. Experimental work has been conducted on this slag system at similar oxygen partial pressures and temperatures by Henao et al.[2] and Kimura et al.[3] The experimental work of Henao et al. at 1300 C, 1350 C, and 1400 C investigated the slag system in the oxygen partial pressure range of 10-3.4 to 10-9 atm, with detailed results for the spinel isotherm at 10-6 atm. The experimental work of Kimura et al.,[3] which encompasses the previous work published by Tsukihashi,[4] investigated the slag system at a temperature of 1300 C and an oxygen partial pressure of 10-7.75, 10-5.75, and 10-2.7 atm. The work of Kimura et al.[3] and other authors[5] on the ferrous calcium silicate system at intermediate oxygen partial pressures did not investigate the slag at the specific oxygen partial pressure of 10-6 atm; therefore, direct experimental comparison can only be undertaken with the results of this work[1] and that of Henao et al.[2] STANKO NIKOLIC, Postdoctoral Student, HECTOR HENAO, Research Fellow, PETER C. HAYES, Centre Director, and EVGUENI JAK, Research Director, are with PYROSEARCH, Pyrometallurgical Research Centre, School of Engineering, The University of Queensland, Brisbane, 4072, Australia. Contact e-mail: [email protected] Manuscript submitted July 25, 2007. Article published online March 12, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
Comparison of the experimental results is coupled with an evaluation of existing thermodynamic models. A number of thermodynamic computer packages are available for the modeling of slag system phase equilibria. These models are based on thermodynamic principles and established experimental data. These packages are powerful and useful for predicting phase equilibria in complex systems that have not been fully experimentally investigated at specific conditions. Therefore, it is necessary to validate these models with all new experimental data[1] to allow for further development of these computer packages and their databases. II.
RESULTS AND DISCUSSION
A. Comparison of Experimental Results[1–4] at 1300 C For a true comparison of the work of the present series of studies[1] with that of Henao et al.[2] and Kimura et al.,[3] which encompasses the previous work of Tsukihashi,[4] all of the experimental results must be treated on the same compositional basis; the basis selected in this study is the FeO-CaO-SiO2 plane. Figure 1 illustrates the three possible projections, and hence the three possible selections for the basis, of the system considering iron oxide as FeO, Fe3O4, and Fe2O3. The selected basis and projection from the oxygen apex of the actual FeO-Fe2O3-CaO-SiO2 slag composition in gray, o
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