Experimental Determination of Phase Equilibria in the REM₂O₃-SiO₂ (REM = Y/Yb/La) Systems at Elevated Temperature

Phase relations in the REM₂O₃-SiO₂ (REM = Y/Yb/La) systems have been studied using the equilibration/quenching/scanning electron microscopy (SEM)-electron probe microanalysis (EPMA) technique. The solvus and liquidus between 1400°C and 1650°C have been determined. The results obtained in this study show that a maximum of 0.57 wt.% Yb₂O₃ can dissolve in SiO₂ phase, while the maximum solubility of La₂O₃ and Y₂O₃ in SiO₂ phase was 0.22 wt.% and 0.07 wt.%, respectively. Correspondingly, SiO₂ shows low solubility in La₂Si₂O₇, and nearly does not dissolve in Y₂Si₂O₇ or Yb₂Si₂O₇. No liquid phase was detected in the Y₂O₃-SiO₂ or Yb₂O₃-SiO₂ system in the temperature range of interest. One oxide liquid phase comprising 39.27 wt.% SiO₂ and 59.07 wt.% La₂O₃ was found in the La₂O₃-SiO₂ system sample equilibrated at 1653°C, revealing that the eutectic point temperature between La₂Si₂O₇ and SiO₂ is located between 1600°C and 1653°C. Results of this study were compared with previous observations, revealing significant differences.