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

Abstract

(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 x Ge: x Ga = 0.15:0.85, 0.3:0.7, 0.5:0.5, 0.7:0.3 and 0.85:0.15 for 0.0 ⩽ x Gd ⩽ 0.55. It has been determined that Gd mixes with the ternary alloys with significant heat evolution. The partial enthalpy of mixing of gadolinium ( Δ mix H ¯ Gd ) reaches negative extreme at x Gd = 0.1 for each studied section. The Δ mix H ¯ Gd values for the x Ge: x Ga = 0.7:0.3 and 0.85:0.15 sections at x Gd = 0.45 sharply tends to zero that can be evidence of transition to heterogeneous area. The integral enthalpy of mixing (Δ mix H) was calculated from the experimental Δ mix H ¯ 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 (ΔΔ mix H) between experimental and calculated by the model Δ mix H values was fitted through a polynomial dependence on x Ga and x Gd. The integral enthalpy of mixing in the ternary system was represented by sum of the Δ mix H calculated by the Bonnier model and the polynomial dependence of ΔΔ mix H. The extreme of the ΔΔ mix H term is −5.9 kJ · mol −1 at x Gd = 0.52 and x Ga = 0.24, which is about 7% of the experimental Δ mix H. 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.