Phase equilibria and crystal chemistry in the Y₂O₃–Al₂O₃–SiO₂ system

In order to clarify inconsistencies in the literature and to verify assumed ternary solubilities, the phase equilibria in the Y₂O₃–Al₂O₃ –SiO₂ system at 1600, 1400, and 1300 °C were experimentally determined using x-ray diffraction (XRD), scanning electron microscope with attached energy-dispersive detector system (SEM-EDX), and electron probe microanalyzer (EPMA). Six quasibinary phases were observed: Y₄Al₂O₉ (YAM), YAlO₃ (YAP), Y₃Al₅O₁₂ (YAG), Y₂SiO₅, Y₂Si₂O₇ (C and D modifications), and ˜₃Al₂O₃· 2SiO₂ (mullite). Y₄Al₂O₉ forms an extended ternary solid solution with the formula Y₄Al_2(1-x)Si_2xO_9+x (x = 0 2 ˜0.31). The lowest ternary eutectic temperature was determined at 1371 ± 5 °C by high-temperature differential scanning calorimetry (DSC). The results were compared with previous data available for the Y₂O₃–Al₂O₃ –SiO₂ system and with data for other RE₂O₃–Al₂O₃ –SiO₂ (RE = rare earth element) systems.