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.