1700°C Isothermal Phase Diagram of the MgO-Al2O3-TiO2 System in Air Related to Pseudobrookite and Spinel Ceramics

The spinel and pseudobrookite type ceramic materials have been widely used in different industries including ceramics, refractory and metallurgy. Therefore, their physicochemical properties are important for the development of related processes. In this regard, it is important to understand the formation principles of the spinel and pseudobrookite solid solutions. In the present work, the equilibrium phase relations for the MgO-Al 2 O 3 -TiO 2 system at 1700°C in air were experimentally determined by high-temperature equilibration-quenching technique followed by XRD and SEM–EDS analyses. The pseudobrookite solid solution was found to be coexisting with spinel solid solution and rutile phase, respectively. The composition evolution and formation principles of the pseudobrookite and spinel solid solutions were further elucidated from the corresponding crystal structures and composition relations. Furthermore, great discrepancies were observed when the 1700°C isotherm from the present work was compared with the isotherm simulated by FactSage 8.1. The evolution of the solid solution existing area was intuitively presented with reference to the experimental data from the literature. The results from present work are important for the development of spinel and pseudobrookite solid solution ceramics as well as the optimization of the thermodynamic database for oxide systems.