Stabilization of Zirconia with Calcia and Magnesia

The minimum amount of calcia or magnesia required to stabilize zirconia into the cubic form is about 16 mole %. X‐ray diffraction studies show that both calcia and magnesia are in solid solution in cubic zirconia. This solid‐solution phase extends from 16 to 30 mole % in the case of calcia and from 16 to 25 mole % in the case of magnesia. These results are for specimens cooled from 2000°C. After heating at various temperatures between 815° and 1375°C., the calcia‐stabilized zirconia remains cubic, whereas the magnesia‐stabilized zirconia reverts to the monoclinic form. On the basis of the results obtained from X‐ray diffraction and dilatometric measurements, information was obtained on the phase relationships in the systems zirconia‐calcia and zirconia‐magnesia, and some modifications to the previously published phase diagrams of these systems are proposed.