Thermodynamic study of liquid manganese-copper alloys

Abstract

Using a high-temperature torsion-effusion technique, vapour pressures of manganese have been measured over liquid manganese-copper alloys containing 5–100 atom % Mn and at temperatures between 1280 and 1600°K. These have been used to calculate the partial and integral thermodynamic properties of the liquid alloys. Activities and free energies show strong positive deviations from ideality in Mn-rich regions, but negative in Cu-rich alloys; a rapid variation of Mn activities being observed at approximately 18 atom % Mn. Integral heats and excess entropies of formation are also asymmetric in form, changing from positive to negative with increasing Mn content. Factors influencing the thermodynamic properties are discussed; it is suggested that the liquid properties reveal the persistence of factors operative in the solid state and are particularly influenced by the variation of the magnetic interaction between manganese atoms.