The Al-rich part of the system CaO-Al2O3-MgO .1. Phase relationships

In the Al-rich part of the ternary system CaO-Al2O3-MgO two new ternary phases Ca2Mg2Al28O46 (CAM-I) and CaMg2Al16O27 (CAM-II) with limited solid solution ranges were found. Due to the fact that the compositions of the Mg-rich end members of these solid solutions lie on the join between hibonite (CaAl12O19) and spinel (MgAl2O4), the model of the crystal structures of these phases can be constructed by a suitable combination of hibonite and spinel units. Both phases, CAM-I and CAM-II, exhibit solid solution ranges described by a substitution mechanism also found in the binary spinel phase, MgAl2O4: 3 Mg2+ = 2 Al3+ + square. Thus the ternary phases can be expressed by the chemical formulas. Ca(2)Mg(2-3x)A1(28+2x)square(x)O(46) for CAM-I with 0 less than or equal to x less than or equal to 0.30 and CaMg(2-3y)Al(16+2y)square(y)O(27) for CAM-II with 0 less than or equal to y less than or equal to 0.2. (C) 1995 Academic Press, Inc.