Liquid Immiscibility and Thermodynamic Assessment of the Al2O3–TiO2–SiO2 System

Abstract

Phase equilibria in the TiO2–SiO2 system have been studied experimentally using DTA and SEM/EDX. The thermodynamic parameters for the TiO2–SiO2 system have been assessed considering new experimental data of the present work and from the literature. Moreover, the miscibility of the liquid in the Al2O3–TiO2–SiO2 system has been studied at 2013 K in air and shrinkage of the miscibility gap at 3.8 mol% Al2O3 has been demonstrated. The experimental data obtained in the present work and literature as well as the thermodynamic databases for the binary Al2O3–TiO2, TiO2–SiO2, and Al2O3–SiO2 systems have been used to derive the thermodynamic description of the Al2O3–TiO2–SiO2 system using the CALPHAD approach. Solid phases have been modeled using the compound energy formalism. The liquid phase has been described by the two-sublattice partially ionic liquid model. A set of self-consistent parameters have been proposed, which resulted in a reasonably good agreement between the calculated and experimental data on the phase equilibria, liquid immiscibility, and thermodynamic properties in the Al2O3–TiO2–SiO2 system.

High‐temperature mass spectrometric study of thermodynamic properties in the TiO2–Al2O3–SiO2 system and modeling

“…The quantitative diffraction analysis of samples NN 13 and 14 showed that the main phases in these samples were rutile (40 and 53 mol%, respectively), cristobalite (40 and 35 mol%, respectively), and quartz (20 and 12 mol%, respectively). These results agree with the available data on the phase equilibria in the TiO 2 –SiO 2 system 22 . The presence of quartz in the samples might be explained by the partial transformation of cristobalite during cooling of samples NN 13 and 14 at room temperature from the synthesis temperature 1573 K when the samples were extracted from the furnace after the synthesis.…”

“…From Table 2, the obtained values of the SiO 2 activities in the TiO 2 -SiO 2 system were characterized by positive deviations from Raoult's law at 1973 K. One of the possible reasons for this may be related to the fact that, according to the phase diagram of the TiO 2 -SiO 2 system, 21,22 above 2046 K there exists the miscibility gap in the melt of the system under study. 21 Existence of this miscibility gap in the melt might explain why the SiO 2 activity values were higher than the SiO 2 mole fractions.…”

“…These results agree with the available data on the phase equilibria in the TiO 2 -SiO 2 system. 22 The presence of quartz in the samples might be explained by the partial transformation of cristobalite during cooling of samples NN 13 and 14 at room temperature from the synthesis temperature 1573 K when the samples were extracted from the furnace after the synthesis.…”

“…Ilatovskaia and Fabrichnaya 22 optimized the phase equilibria in the TiO 2 –Al 2 O 3 –SiO 2 system using the CALculation of PHAse Diagrams (CALPHAD)) approach 23 obtaining a self‐consistent set of thermodynamic interaction parameters. However, the phase equilibria in the TiO 2 –Al 2 O 3 –SiO 2 system 22 were optimized using only the thermodynamic properties of the TiO 2 –SiO 2 system 24 without consideration of the thermodynamic values in the ternary system under study, which can lead to some uncertainties in the derived thermodynamic parameters. Therefore, examination of the thermodynamic properties in the TiO 2 –Al 2 O 3 –SiO 2 system is needed to check the correctness and to modify, if necessary, the thermodynamic description of this system derived earlier 22 based on only the phase equilibrium data.…”

“…It should be mentioned that phase equilibria in the TiO 2 -Al 2 O 3 -SiO 2 system have been examined earlier. [20][21][22] In the study, 20 the invariant points on the liquidus of the system under consideration were reviewed in an attempt to predict possible invariant reactions in the quaternary TiO 2 -Al 2 O 3 -SiO 2 -ZrO 2 system. Ilatovskaia and Fabrichnaya 22 optimized the phase equilibria in the TiO 2 -Al 2 O 3 -SiO 2 system using the CALculation of PHAse Diagrams (CALPHAD)) approach 23 obtaining a self-consistent set of thermodynamic interaction parameters.…”