Coupled Experimental and Thermodynamic Modeling of A12O3-CaO-FeO-Fe2O3-MgO-MnO-Mn2O3-SiO2- TiO3-TiO2 System

Book excerpt: "The phase diagram and thermodynamic properties of the Al2O3-CaO-FeO-Fe2O3-MgO-MnO-Mn2O3-SiO2-Ti2O3-TiO2 system are important in various applications such as steelmaking, refractories, advanced ceramics, petrology and geochemistry. In the present work, the available thermodynamic database for the Al2O3-CaO-FeO-Fe2O3-MgO-SiO2 system was expanded toward the Mn and Ti oxide systems to develop an accurate thermodynamic database for the ten-component system. For this purpose, a complete literature review, critical evaluation and thermodynamic optimization of the phase diagrams and thermodynamic properties of related systems at 1 atm was performed. As part of the thermodynamic study, key phase diagram experiments were performed in the Fe-Ti-O, Mn-Ti-O, Al-Ti-O, Fe-Mn-Ti-O, Mg-Mn-Ti-O, Mn-Si-Ti-O, and Mn-Al-Ti-O systems in air to obtain unknown phase equilibria between the liquid phase and complex solid solutions and resolve any inconsistencies among existing experimental data in the literature.Phase diagram experiments were performed using the classical equilibration and quenching technique. Phase analysis was performed using Electron Probe Microanalysis (EPMA) and X-ray Diffraction (XRD) on all the quenched samples. In the Al-Ti-O system, the solubility of Al2O3 in the rutile (TiO2) solid solution was measured at high temperature. In the Fe-Ti-O system, the liquidus, solubility of Fe2O3 in the rutile (TiO2) solution, and the homogeneity ranges of Fe2O3-FeTiO3 ilmenite and Fe2TiO5-Ti3O5 pseudobrookite solutions were determined at high temperature. In the Mn-Ti-O system, the liquidus, MnO solubility in rutile and the homogeneity range of Mn3O4-Mn2TiO4 spinel were measured. In the Mg-Mn-Ti-O, Fe-Mn-Ti-O and Mn-Si-Ti-O systems, the complex phase equilibria between liquid and solid solutions were experimentally elucidated for the first time in air atmosphere. For the thermodynamic optimization, the liquid phase was described using the Modified Quasichemical Model considering short-range ordering in the molten oxide and the Gibbs energies of the complex solid solutions pseudobrookite, ilmenite and spinel were described using the Compound Energy Formalism considering the crystal structure of each solid solution. Using the thermodynamic models with optimized model parameters in binary and ternary systems, the phase diagrams and thermodynamic properties of higher order systems in the Al2O3-CaO-FeO-Fe2O3-MgO-MnO-Mn2O3-SiO2-Ti2O3-TiO2 system were well calculated. The database containing the optimized model parameters in this study is compatible with the other FactSage thermodynamic databases and can be used to calculate any unexplored phase diagram and thermodynamic properties within the ten-component system. The database can be used for the complex thermodynamic calculations applicable to pyrometallurgy and advanced ceramics and used for the optimization of industrial processes and the development of new materials. " --