Thermodynamics of Alon III : stabilization of Alon with MgO

The ceramic material g-aluminum oxynitride (Alon) has been shown earlier to be thermodynamically unstable at temps. below 1640 DegC. In this paper it is shown that it is possible to stabilize Alon below this temp. by addn. of MgO. For this purpose, the phase diagram Al2O3-AlN-MgO was investigated at 1750 and 1400 DegC. At 1750 DegC the homogeneity region of the spinel-type phase (MgAlon) extends from the Al2O3-MgO system to the Al2O3-AlN system. The lattice parameter of MgAlon can be represented by a = 0.7900 + 0.0160x + 0.0206y, in which a is the lattice parameter in nanometers and x and y are the mol fractions of AlN and MgO, resp. At 1400 DegC the homogeneity region of MgAlon extends from the Al2O3-MgO system towards Alon and AlN; however, it does not reach the Al2O2-AlN system. About 25 mol% of MgO (or .apprx. 50 mol% MgAl2O4) has to be added to Alon to stabilize it at 1400 DegC. For that reason, the properties of MgAlon which is stable at 1400 DegC will probably be more akin to those of MgAl2O4 than to those of Alon. [on SciFinder (R)]