Experimental study of phase equilibria in the Al₂O₃–MgO–TiO₂ system and thermodynamic assessment of the binary MgO–TiO₂ system

Abstract

Phase relations in the MgO–TiO2 and Al2O3–MgO–TiO2 systems have been studied experimentally using X‐ray diffraction, scanning electron microscopy combined with dispersive X‐ray spectrometry, and differential thermal analysis. The heat capacity measurements of the Mg2TiO4, MgTiO3, and MgTi2O5 compounds have been carried out in the temperature range of 473‐1373 K using DSC. A new thermodynamic description of the MgO–TiO2 system has been derived based on obtained experimental results, data from literature, and taking into account the cation disordering of the intermediate compounds Mg2TiO4 and MgTi2O5. The liquid phase was described by the two‐sublattice partially ionic model (Mg+2,Ti+2,Ti+3)(O−2,Va,O,TiO2). For the Al2O3–MgO–TiO2 system: the solid‐state invariant reaction involving the intermediate phase of pseudobrookite solid solution have been found at the temperature of 1433 K. On the liquidus surface, the eutectic invariant reaction has been established at 1843 K and the transitional one—at 2006 K. Based on the obtained experimental results isothermal sections within the range 1269‐1697 K of the ternary system have been predicted. The MgTi2O5–Al2TiO5 section has been constructed.

Phase equilibria of MgO–Al2O3–TiO2 system at 1600°C in air: Emphasis on pseudobrookite and spinel solid solution phases

“…However, the three‐phase regions associated with MgO·TiO 2 phase and Al 2 O 3 phase was not found at 1600°C in present work, which may cause by the decomposition of MgO·TiO 2 into MgO and TiO 2 , which were further combined with Al 2 O 3 forming different solid solution phases, respectively. Similarly, the isothermal phase diagram of 1424°C experimentally determined by Ilatovskaia et al 65 . showed the similar trend with the results in the present work as well, as shown in Figure 9C.…”

“…(A) Results from FactSage 8.1 at 1600°C 50 ; (B) comparison of the 1550°C isothermal phase diagram by Boden et al 51 . with the results from present work at 1600°C; (C) comparison of the 1424°C isothermal phase diagram by Ilatovskaia et al 65 . with the results from present work at 1600°C.…”

“…Therefore, in order to enrich more TiO 2 in the pseudobrookite phase and to ensure a low TiO 2 concentration in the spinel phase, the MgO concentration in the pseudobrookite phase should be controlled below 16 wt.%. 65 with the results from present work at 1600 • C. Psb., pseudobrookite; Rt., rutile; Spl., spinel; Crn., corundum; Gk., MgO⋅TiO 2 ; Per., Periclase In Figure 9, the isothermal phase diagrams from calculation and literatures were compared with the present experimental results.…”

“…Comparison of the present experimental results at 1600°C with calculation 50 and literatures 51,65 . (A) Results from FactSage 8.1 at 1600°C 50 ; (B) comparison of the 1550°C isothermal phase diagram by Boden et al 51 .…”

“…However, the three-phase regions associated with MgO⋅TiO 2 phase and Al 2 O 3 phase was not found at 1600 • C in present work, which may cause by the decomposition of MgO⋅TiO 2 into MgO and TiO 2 , which were further combined with Al 2 O 3 forming different solid solution phases, respectively. Similarly, the isothermal phase diagram of 1424 • C experimentally determined by Ilatovskaia et al 65 showed the similar trend with the results in the present work as well, as shown in Figure 9C. The three-phase coexistence zones of pseudobrookite-spinel-MgO⋅TiO 2 and pseudobrookite-spinel-Al 2 O 3 were found at a lower temperature of 1424 • C. As the temperature increases, the two three-phase coexistence zones gradually decrease, showing a good regularity with the present experimental results.…”