The aluminum-rich part of the system BaO-Al2O3-MgO - I: Phase relationships

摘要

The subsolidus phase relations in the Al-rich part of the system BaO-Al2O3-MgO at 1800 degrees C in air have been determined. The hexaaluminate phases in this part of the system all exhibit beta-alumina structure types. In the binary system BaO-Al2O3, the phases Ba1.21Al11O17.71 and Ba0.75Al11O17.25 were confirmed. In the ternary system, two solid solution series, BAM-I and BAM-II, exist, The solid solution range of BAM-I between the defect-free beta-alumina end member BaMgAl10O17 and the Mg-free end member Ba0.75Al11O17.25 can be described by the formula Ba1-x/4Mg1-xAl10+xO17+x/4 (0 less than or equal to x less than or equal to 1). The solid solution series BAM-II contains higher Mg concentrations. It can be expressed by the formula Ba(2)Mg(6-3y)Al(28+2y)square(y)O(50) (O less than or equal to y less than or equal to 0.3). The Mg-rich end member of BAM-II is plotted exactly at the join between the defect-free end member of BAM-I and the stoichiometric Mg-Al-spinel. Thus it is concluded that the structure of BAM-II is a mixed-layer model containing both structure units. (C) 1998 Academic Press. [References: 23]