Thermodynamics of phase formation in the V–Ge system

• Published in: Journal of alloys and compounds 2000-03, Vol.299 (1-2), p.126-136
• Main Authors: Zarembo, Sergei, Kematick, Robert J., Myers, Clifford E.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Enthalpy of phase formation; Exact sciences and technology; Heat capacities of solids; Knudsen cell; Mass spectrometry; Physics; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic properties; Thermodynamics; Vanadium germanides
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/S0925-8388(99)00801-4

Vaporization thermodynamics in the vanadium-rich portion of the vanadium–germanium system has been studied by high temperature Knudsen effusion mass spectrometry. Thermodynamic activities of V and Ge have been measured over the two-phase mixtures of V+V3Ge and V3Ge+V5Ge3 in a temperature range of ca. 1750–1980 K, and Ge activity was measured over the V5Ge3+V11Ge8 mixture. The activities were measured by direct comparison with solid V and liquid Ge metals. The standard free energies of formation of V3Ge and V5Ge3 at high temperature were determined from the activity data. The standard free energies of formation were then combined with published heat capacity and standard molar entropy data, and used in a third-law evaluation of the standard enthalpies of formation at 298 K of all the four intermediate compounds in this system. The results obtained are: 14V3Ge, −36.2±2.5 kJ; 18V5Ge3, −45.9±2.5 kJ; 119V11Ge8, −45.5±3.0 kJ; 148V17Ge31, −35.0±3.0 kJ. The results obtained in this work are compared with previous estimates and measurements.