STUDY ON THE Al_2O_3-SiO_2-La_2O_3 TERNARY SYSTEM AT l300deg.C

摘要

The ternary phase diagram Al_2O_3-SiO_2-La_2O_3 was investigated at l300deg.C. The samples were prepared by wet chemical route (sol-gel synthesis) and characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), and EDX microprobe analysis. The XRD powder pattern data of La_l4Si_9O39 compound, as obtained by us, reconfirm the structure proposed in the literature, though with significantly different lattice parameters. No truly ternary compound was found to form at l300degC. The La_14Si_9O_39 compound extends its stability range in the interior of the phase diagram, forming a solid solution of the type La_14 +x./3Si_9-x AlxO_39, which is stable from x = 0 to x = l.5. This substitutional stoichiometry can be described as a tetrahedral Al for Si substitution on the 6h position and contemporary occupation of vacant La sltes.