Condensed Phase Relations in the Systems ZrO2‐WO2‐WO3 and HfO2‐WO2‐WO3

Phase relations for the systems ZrO2–WO2–WO3 and HfO2–WO2–WO3 from 1000° to 1700° C were determined by the quenching technique using sealed sample containers. In the system ZrO2–WO3, 1:2 compound, ZrW2O8 forms, having a cubic structure with a= 9.159 A. The ZrW2O8 melts incongruently at 1257°± 3°C to ZrO2 and liquid and has a lower limit of stability at 1105°C, below which ZrO2 and WO3 coexist in equilibrium. One eutectic and one peritectic were established: at 1231°± 3°C and 74 mole % WO3, and at 1257°± 3°C and 71 mole % WO3, respectively. Along the join ZrO2–WO2, no compound formed. Two invariant points were determined: ZrO2, WO2, W, and liquid are in equilibrium at 1430°± 5°C and 76 mole % WO2, whereas WO2, W18O49, W, and liquid coexist at 1530°± 5°C and 89 mole % WO2- Equilibrium relations in the system ZrO2–WO2–WO3 were investigated at four temperatures. At 1200°C, a cubic phase with composition near W20O58 was found; it exists in equilibrium with ZrO2, W18O49, W20O58, and WO3. As the temperature increases, the liquid formed along the ZrO2–WO3 join extends into the ternary system, crosses the join ZrO2–W20O58 at 1300°C, and crosses the join ZrO2–W18O49 at 1400°C. The cubic phase can take more zirconium into its solid solution at 1300° than at 1200°C. At 1500°C, the system can no longer be treated as a simple ternary oxide system because of the presence of metallic tungsten, and equilibrium relations are presented on the basis of the system ZrO2–W–WO3. Phase equilibrium relations in the systems HfO2–WO3, HfO2–WO2, and HfO2–WO2–WO3 in the temperature ranges studied are much like those in the corresponding zirconium system.