A thermodynamic study of liquid Cu-Cr alloys and metastable liquid immiscibility

Abstract

The thermodynamic acitivity of chromium in liquid Cu-Cr alloys is measured in the temperature range from 1473 to 1873 K using the solid state cell: Pt, W, Cr + Cr₂O₃ |(Y₂O₃) ThO₂|Cu - Cr + Cr₂O₃, Pt The activity of copper and the Gibbs energy of mixing of the liquid alloy are derived. Activities exhibit large positive deviations from Raoult's law. The mixing properties can be represented by a pseudo-subregular solution model in which the excess entropy has the same type of functional dependence on composition as the enthalpy of mixing: ΔG^E = X_Cr(1 - X_Cr)[60880 - 18750 X_Cr)-- T(16.25 - 7.55 XCr)]J mol^-1 Pure liquid Cu and Cr are taken as the reference states. The results predict a liquid-liquid metastable miscibility gap, with T_C = 1787 (±3) K and X_Cr = 0.436 (±0.02), lying below the liquidus. The results obtained in this study are in general agreement with experimental information reported in the literature, but provide further refinement of the thermodynamic parameters.