Heat contents of the intermetallics V3Ge and V5Ge3 and thermodynamic modeling of the Ge-V system

Fourteen alloys were prepared by arc-melting the pure elements and annealing the alloys at 850 oC for 30 days. The annealed alloys were examined by X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray analysis (SEM/EDX), differential scanning calorimetry (DSC) and drop calorimeter. The major experimental results are as follows. (I) The heat contents of V3Ge and V5Ge3 were measured by drop calorimeter from 400 to 900 oC. (II) The microstructure analysis of as-cast alloy V87.1Ge12.9 indicates that the eutectic composition of liquid ↔ (V) + V3Ge is above 12.9 at.% Ge, and that of V2.9Ge97.1 shows that the eutectic composition of liquid ↔ V17Ge31 + Ge is close to 97.1 at.% Ge. (III) The invariant reaction temperatures of liquid + V11Ge8 ↔ V17Ge31 and liquid ↔ V17Ge31 + Ge are at 960.0 ± 2 oC and 930.7 ± 2 oC, respectively. Based on the experimental results in this study and in the literature, the Ge-V system was modeled by CALPHAD approach.