THERMODYNAMIC PROPERTIES OF METASTABLE PHASES OF MAGNESIUM-GALLIUM SYSTEM

In order to obtain the thermodynamic properties of a glass-like phase occurring in the Mg-Ga system and of a metastable intermetallic compound obtained therefrom by heating, their decomposition enthalpies have been determined calorimetrically. The formation enthalpy ΔHSA of the glassy phase at 18.73 at.%Ga is -1076 J (g-atom)-1 and that of the metastable compound ΔHSM at the same concentration is 4.6 kJ (g-atom)-1; both values are related to the state of the pure solid components as initial phases of the formation reaction. Furthermore, the enthalpy ΔHSMg and the entropy ΔSSMg of formation of the stable phase Mg5Ga2 have been determined as - 9080 J (g-atom)-1 and 1.44 J (g-atom)-1 K-1, respectively. The strong interatomic interactions in the metastable phases, as well as in the stable compounds of this system, are attributed to a considerable charge transfer between the component atoms. © 1979.