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

Abstract

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 Y4Al2(1-x)Si2xO9+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.

Nucleation and Growth of Mullite Whiskers from Lanthanum‐Doped Aluminosilicate Melts

“…It is well known that a small fraction of liquid phase decreases the mullitization temperature. The volume of Al,0 3 and SiO, involved in mullitization is much higher than the glass volume at the eutectic temperature. Therefore, the mullite transformation temperature is highly sensitive to the appearance of the glass phase in the system and must be a good expression of the eutectic temperature.…”

“…The phase equilibria and crystal chemistry of this system were recently studied by Kolitsch et al , 3 who reported the ternary eutectic temperature to be 13710 ± 5°C. Six quasi-binary phases were found: three yttrium aluminates, two yttrium silicates, and mullite.…”

“…about which more details are available. 3 ' 0 the phase diagram becomes more complex as the temperature increases, even without considering the two mullite compositions. Moreover, the diphasic gel preparation route used in the present work does not promote the uniform dispersion of the components.…”

“…The last possibility was disregarded because no whisker-grain agglomerate was observed in our studies. The air/glass interface may be preferential, according to Schmelzer et al,' 3 if the interfacial energies involved in the nucleation process satisfy certain equations. The unknown values of these surface energies leave the definition of the nucleation site-the air/glass interface or the bulk of the glass layer-to experimental evidence.…”

Deformación plástica de compuestos mullita/óxido de itrio

“…En el caso de la mullita, a partir de una exhaustiva revisión bibliográfica [1][2][3][4][5][6][7] y algunas pruebas preliminares, el aditivo elegido en este estudio fue óxido de itrio (Y 2 O 3 ). Con este aditivo la mullita sinteriza por fase líquida, como cabe esperar a partir del diagrama de fases del sistema ternario SiO 2 -Al 2 O 3 -Y 2 O 3 , que ha sido publicado en un trabajo reciente 9 . En un sistema de micromorfología análoga a la mullita, como es el Si 3 N 4 , está bien documentado que la adición de Y 2 O 3 mejora la sinterización mediante la formación de líqui-dos [10][11][12] .…”