Phase Equilibria and Thermodynamics in the Y2O3-Al2O3-SiO2 System

Abstract

The enthalpy of formation of YAM (Y4Al2O9) and Y2Si2O7 (γ) has been derived using high-temperature drop solution calorimetry at 1073 K in molten alkali borate. The enthalpy of formation from oxides at 298 K is -6.24 6.21 and -67.08 5.98 kJ/mol for YAM and disilicate, respectively. The thermodynamic functions in the Y2O3-Al2O3 and Y2O3-SiO2 systems are assessed from phase equilibrium data and calorimetric measurements for YAG (Y3Al5O12), YAP (YAlO3), YAM (Y4Al2O9), Y2SiO5 and Y2Si2O7 phases. The calculated phase diagrams of the Al2O3-Y2O3 and Y2O3-SiO2 systems are in reasonable agreement with the experimental data. Suggestions for further experimental measurements on solid phases are given. Using limited phase equilibrium data for the ternary system Y2O3-Al2O3-SiO2, the thermodynamic functions are assessed. The liquidus surface, an isothermal section at 1673 K and isopleths in the systems Y3Al5O12-SiO2, YAlO3-SiO2, Y4Al2O9-SiO2, Y2SiO5-Al6Si2O13 and Y2Si2O7-Al6Si2 O13 are presented.

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