THERMODYNAMIC ACTIVITY MEASUREMENTS OF THE LIQUID CU-GD ALLOY BY HIGH-TEMPERATURE MASS-SPECTROMETRY

The thermodynamic activity of Cu in the Cu-Gd liquid ahoy has been mea sured by the multiple effusive cell-mass spectrometry method for x(Gd) = 0.276-0.844 (atomic composition) in the 1282 K-1644 K temperature r ange. The activity of Gd has been calculated from the integration of t he Gibbs-Duhem equation. From the expression of the molar excess Gibbs energy of the liquid system, vs. temperature and composition, we show that the liquid alloy presents a strong negative deviation from the i deal behaviour and specify some points of the phase diagram especially on the Cu-rich liquidus curve. Our values of the Gibbs energies of fo rmation of the intermetallic compounds CuGd and Cu2Gd, Delta G(f)(0)(C uGd) = 42.2 +/- 2 kJ mol(-1) at 1073 K and Delta G(f)(0)(Cu2Gd) = 68 /- 4 kJ mol(-1) at 1113 K, are in good agreement with the literature.