Experimental study of phase equilibria and thermodynamic optimization of the Fe-Zn-O system

Abstract

The Fe-Zn-O phase diagram in air was studied over the temperature range from 900 ЊC to 1500 ЊC. The compositions of the phases in quenched samples were obtained by electron probe X-ray microanalysis (EPMA). This experimental technique is not affected by zinc losses resulting from vaporization of zinc at high temperatures. The model for the spinel solid solution was developed within the framework of the compound-energy formalism (CEF). The choice of parameters of the CEF and the sequence of their optimization can have a major influence on the predictions in multicomponent phases. These choices can only be made rationally by reference to the specific model being represented in the CEF. This is discussed for the case of the two-sublattice spinel model. In the limiting case, the proposed model reduces to the model by O'Neill and Navrotsky for spinels. When the CEF is used in combination with the equation of Hillert and Jarl to describe the magnetic contribution to thermodynamic functions of a solution, it is necessary to assign certain values of magnetic properties to all pseudocomponents and to magnetic interaction parameters to obtain the most reasonable approximation of the magnetic properties of a solution. It was shown how this can be done based on very limited experimental data. The same equations can be used when the Murnaghan or the Birch-Murnaghan equation is combined with the CEF to describe the pressure dependence of thermodynamic functions. The polynomial model was used to describe the properties of wustite and zincite, and the modified quasichemical model was used for the liquid slag. All thermodynamic and phase-equilibria data on the Fe-O and Fe-Zn-O systems were critically evaluated, and parameters of the models were optimized to give a selfconsistent set of thermodynamic functions of the phases in these systems. All experimental data are reproduced within experimental error limits. These include the thermodynamic properties of phases (such as specific heat, heat content, entropy, enthalpy, and Gibbs energy); the cation distribution between octahedral and tetrahedral sites in spinel; the oxygen partial pressure over single-phase, twophase, and three-phase regions; the phase boundaries (liquidus, solidus, and subsolidus); and the tie-lines.

Experimental Study and Thermodynamic Re-optimization of the FeO-Fe2O3-SiO2 System

“…The model parameters for spinel solution from Decterov et al [55] were used in the present study. The spinel model was developed within the framework of the compound energy formalism (CEF).…”

Phase equilibria studies of zinc-containing copper smelting slags

“…Degterov et al [45] assessed the available phase equilibria data in the Fe-Zn-O system and performed a thermodynamic optimization of the system by combining different solution models. It can be seen from Figure 2.6 that the model fits well the experimental data between 800…”

“…at 827 °C [38] ; (b) at 927 °C [37] Figure 2.6 Phase diagram of the system "FeO"-ZnO under metallic iron saturation [45] It should be noticed that ZnO will be reduced by metallic iron under iron saturation according the following reaction: [44] to investigate ZnO-containing systems under metallic iron saturation. As shown in Method comment E. Jak [44] Iron saturation Pie-type sample applied with ZnO in the centre Po2 close to 10 -12 atm J.M.…”

“…The phase relations at sub-solidus temperatures were experimentally determined and the spinel solution present was further characterized by X-ray diffraction and Mössbauer Spectrum to understand the structural details. Degterov et al [45] performed the experiments in the Fe-Zn-O system under air condition with temperature ranging from 900 °C to 1500 °C. The quenched samples were further analysed by EPMA.…”

“…Good consistency can be seen between the model predictions and reported results [22,39,52] at sub-solidus temperatures. Another investigation on the same system was conducted by Hansson et al [49,53] in air at temperatures up to 1580 °C using similar methodologies as those adopted by Degterov [45] . The wet chemical analysis was performed to determine the amount of ferrous iron in the quenched samples.…”