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 a t 1600, 1400, and 1300 degrees C were experimentally determined using x-ray diffraction (XRD), scanning electron microscope with attached energy-dispe rsive detector system (SEM-EDX), and electron probe microanalyzer (EPMA). S ix quasibinary phases were observed: Y4Al2O9 (YAM), YAlO3 (YAP), Y3Al5O12 ( YAG), Y2SiO5, Y2Si2O7 (C and D modifications), and similar to 3Al(2)O(3) 2S iO(2) (mullite). Y4Al2O9 forms an extended ternary solid solution with the formula Y4Al2(1-x)Si2xO9+x (X = 0 - similar to 0.31). The lowest ternary eu tectic temperature was determined at 1371 +/- 5 degrees C by high-temperatu re 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.