High temperature calorimetric study of liquid (gallium-gadolinium-germanium) alloys

(Gallium-gadolinium-germanium) liquid alloys have been studied by a high-temperature isoperibolic calorimetry at (T = 1760 ± 5) K. The measurements have been performed along five sections with xGe:xGa = 0.15:0.85, 0.3:0.7, 0.5:0.5, 0.7:0.3 and 0.85:0.15 for 0.0 ⩽ xGd ⩽ 0.55. It has been determined that Gd mixes with the ternary alloys with significant heat evolution. The partial enthalpy of mixing of gadolinium (ΔmixH¯Gd) reaches negative extreme at xGd = 0.1 for each studied section. The ΔmixH¯Gd values for the xGe:xGa = 0.7:0.3 and 0.85:0.15 sections at xGd = 0.45 sharply tends to zero that can be evidence of transition to heterogeneous area. The integral enthalpy of mixing (ΔmixH) was calculated from the experimental ΔmixH¯Gd by the Darken's equation and independently from literature data on the boundaries using five geometric models. The Bonnier model shows the best agreement with the experimental data. The difference (ΔΔmixH) between experimental and calculated by the model ΔmixH values was fitted through a polynomial dependence on xGa and xGd. The integral enthalpy of mixing in the ternary system was represented by sum of the ΔmixH calculated by the Bonnier model and the polynomial dependence of ΔΔmixH. The extreme of the ΔΔmixH term is −5.9 kJ · mol−1 at xGd = 0.52 and xGa = 0.24, which is about 7% of the experimental ΔmixH. It has been stated that the thermodynamics of the liquid (Ga-Gd-Ge) alloys is predominately determined by component interaction in the boundary (Ge-Gd) and (Ga-Gd) systems.