Thermodynamic Properties of Hume-Rothery Type Ag-Mg Alloys. (II). Activity of Mg in α Phase, and Free Energy, Entropy, etc. of α and β Phases

Abstract

The thermodynamic activity of Mg in α Ag-Mg alloys has been determined by the electrochemical method at 350° to 550°. The activity exhibits large negative deviation from Raoult’s law, and the existence of Ag₃Mg supperlattice is expected from this tendency. By the integration of experimental data concerning α and β phases, the free energy, the entropy of this alloy system have been evaluated. The enthalpy has its marked maximum value of 4.7 kcal/atom at the composition of 1:1, and shows a high stability of the AgMg compound. The range of soild solution formation in α phase is diminished by the stable ordered β phase. This may be attributed to the marked electrochemical differences of these components. The enthalpy and the activity of α phase alloys can not be represented by ordinary statistical formulae.