THE SYSTEM HFO2-Y2O3-ER2O3

A mathematical model of the liquidus surface based on a reduced polyno mial method was proposed for the system HfO2-Y2O3-Er2O3, The results o f calculations according to this model agree fairly well with the expe rimental data. Phase equilibria in the system HfO2-Y2O3-Er2O3 were stu died on melted (as-cast) and annealed samples using X-ray diffraction (at room and high temperatures) and micro-structural and petrographic analyses. The crystallization paths in the system HfO2-Y2O3-Er2O3 were established. The system HfO2-Y2O3-Er2O3 is characterized by the forma tion of extended solid solutions based on the fluorite-type (F) form o f HfO2 and cubic (C) and hexagonal (H) forms of Y2O3 and Er2O3. The bo undary curves of these solid solutions have the minima at 2370 degrees C (15.5 mol% HfO2, 49.5 mol% Y2O3) and 2360 degrees C (10.5 mol% HfO2 , 45.5 mol% Y2O3). No compounds were found to exist in the system inve stigated.