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Published on: May 2, 2016
Experimental study and thermodynamic modelling of the Nb-Sb system
Pavel Brož1, Jan Vřešťál1, Vitaliy Romaka2
1Masaryk University, Faculty of Science, Department of Chemistry Kotlářská 2 611 37 Brno Czech Republic broz@chemi.muni.cz.
Abstract:
Thermodynamic modelling of the Nb-Sb system was performed by the CALPHAD method, based on SGTE data of the Gibbs energy for pure elements, as well as on data from experimental studies in the literature combined with our new information, obtained via DTA, EDX-EPMA, XPD and ab initio calculations. Our re-investigation confirms the three intermetallic compounds reported earlier: Nb3Sb, Ni5Sb4 and NbSb2. Particularly, our detailed study of the Nb-rich part of the system revealed an intermediate phase with a narrow composition range for Nb3Sb, extending at 950 °C from 74.0 at% Nb to 75.3 at% Nb (EMPA-WDX data). Battling a high Sb evaporation above about 1300 °C (monitored by thermogravimetry) high-temperature DTA data (Y2O3 crucibles) unambiguously defined the peritectic decomposition of Nb3Sb at 1840 ± 25 °C. In contrast to earlier information in the literature, Nb5Sb4 was found to form peritectically at 1550 ± 10 °C, whereas the temperature of the peritectic reaction of NbSb2 appeared at 1320 ± 10 °C. The eutectic temperature of 624 ± 8 °C was confirmed by low-temperature DTA measurement (sealed quartz ampoules). Furthermore, data on heat of formation for all the compounds were provided by ab initio calculations, which served to optimize model parameters for the calculation of the Nb-Sb phase diagram. The calculated binary phase diagram obtained agrees well with the experimentally determined one. The thermodynamic database is attached.
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