The ZrO2-rich region of the ZrO2-MgO system

The solubility limits of MgO in tetragonal zirconia were studied by combining the differential thermal analysis data and X-ray disappearing phase method. From these experiments a eutectoid reaction, tetragonal ZrO₂ solid solution monoclinic ZrO₂ solid solution + MgO, at 1120±10 °C and 1.6±0.2 mol% MgO was established. The solubility of MgO in tetragonal ZrO₂ diminished as the temperature increased, and at 1700 °C the solubility was less than 0.5 mol% MgO. The extent of the cubic zirconia solid solution single field was determined by using precise lattice parameter measurements and SEM observations. In this way an invariant eutectoid point, cubic ZrO₂ solid solution tetragonal ZrO₂ solid solution + MgO, was located at 1420±10 °C and 14.8±0.5 mol% MgO.