THERMODYNAMICS OF THE LIQUID (XCU-X-Y)GE), 5-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1, SS-THAN-OR-EQUAL-TO-Y-LESS-THAN-OR-EQUAL-TO-0.125) ALLOYS AT 1550-K BY KNUDSEN EFFUSION MASS-SPECTROMETRY(YAU+(1)

Partial pressures and thermodynamic activities in four liquid Cu-Au-Ge alloys from the compositional section x(Au) = x(Ge) and x(Cu) greater -than-or-equal-to 0.75 have been determined by Knudsen effusion mass s pectrometry (KEMS) at 1550 K. The experimental data were also used for the thermodynamical description of the terminal compositional region of these alloys with x(Cu) greater-than-or-equal-to 0.75 using Darken' s ternary quadratic formalism. The binary interaction parameters for C u-Au and Cu-Ge as well as the limiting activity coefficients of Au and Ge in their solute alloys with Cu have been evaluated from literature data. The ternary interaction parameter in the alloys investigated wa s determined experimentally as -3.15 +/- 0.36. These parameters enable d the determination of equations describing the activity coefficients and the excess Gibbs free energies for the limited ternary region with x(Cu) greater-than-or-equal-to 0.75 as a function of the alloy compos ition: ln f(Cu) = -2.10 x(Au)2 - 5.73 x(Ge)2 - 3.15 x(Au)x(Ge) In f(Au ) = -2.07 + ln f(Cu) + 4.20 x(Au) + 3.15 x(Ge) ln f(Ge) = -3.62 + lnf( Cu) + 3.15 x(Au) + 11.46 x(Ge) G(m)E = RT(-ln f(Cu) - 2.07 x(Au) - 3.6 2 x(Ge)) The activities obtained from Darken's model agree very well w ith those calculated from the partial pressures for the four alloys st udied. All the alloy components show negative deviations from ideality .