Phase equilibria and thermodynamics in the Y₂O₃-Al₂O₃-SiO₂ system

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.