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

Abstract

Phase relations in the REM2O3-SiO2 (REM=Y/Yb/La) system have been studied with the equilibration/quenching/SEM-EPMA technique. The solvus and liquidus between 1400°C and 1650°C have been determined. Results obtained in this study show that Yb2O3 can dissolve maximumly 0.57 wt.% in SiO2 phases, and the maximum solubility of La2O3 and Y2O3 in SiO2 phase were 0.22 wt.% and 0.07 wt.% respectively. Correspondingly, SiO2 has a low solubility in La2Si2O7, and nearly doesn't dissolve in Y2Si2O7 or Yb2Si2O7. No liquid phase was detected in the Y2O3-SiO2 system or the Yb2O3-SiO2 system in the temperature range of interest. One oxide liquid phase composing of 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 locates between 1600 °C and 1653 °C. Results from this study were compared with previous observations, and differences were significant.