Subsolidus equilibria and kinetics of decomposition of solid solutions in the HfO 2(ZrO 2MgO systems

Abstract

The subsolidus equilibrium diagram in the HfO 2MgO system has been constructed and contains a eutectoid point similar to the ZrO 2MgO system. A comparative study of the stabilities of solid solutions of MgO in HfO 2 and in ZrO 2 has been made. The difference in phase stability of the solid solutions in the temperature range 1300 to 1450°C is due to the difference of eutectoid temperatures in the two systems. The mechanism and kinetics of decomposition of the HfO 2MgO solid solutions have been studied. The decomposition process of solid solutions in this system and in the ZrO 2MgO system is a particular case of the wide-spread type of eutectoid decomposition which is governed by the laws of eutectoid equilibria. The decomposition of the cubic solid solutions in both systems proceeds in two steps.