Experimental study and thermodynamic modelling of the Nb-Sb system

Area of Science:

• Materials Science
• Thermodynamics
• Computational Materials Science

Background:

• The Niobium-Antimony (Nb-Sb) system is crucial for various material applications.
• Accurate thermodynamic data and phase diagrams are essential for predicting material behavior and designing new alloys.
• Previous studies on the Nb-Sb system have presented varying data, necessitating re-investigation.

Purpose of the Study:

• To perform thermodynamic modeling of the Nb-Sb system using the CALPHAD method.
• To experimentally re-investigate and refine the phase boundaries and reaction temperatures of Nb-Sb intermetallic compounds.
• To develop an accurate thermodynamic database for the Nb-Sb system.

Main Methods:

• CALPHAD (Calculation of Phase Diagrams) method utilizing SGTE (Scientific Group Thermodata Europe) Gibbs energy data.
• Experimental techniques including Differential Thermal Analysis (DTA), Energy Dispersive X-ray Spectroscopy with Electron Probe Microanalysis (EDX-EPMA), X-ray Powder Diffraction (XPD), and Thermogravimetry.
• Ab initio calculations for heats of formation and optimization of thermodynamic model parameters.

Main Results:

• Confirmation of three intermetallic compounds: Nb₃Sb, Nb₅Sb₄, and NbSb₂.
• Refined composition range for Nb₃Sb on the Nb-rich side (74.0–75.3 at% Nb at 950 °C).
• Precise determination of peritectic decomposition/formation temperatures for Nb₃Sb (1840 ± 25 °C), Nb₅Sb₄ (1550 ± 10 °C), and NbSb₂ (1320 ± 10 °C).
• Confirmation of the eutectic temperature at 624 ± 8 °C.
• Ab initio calculations provided heats of formation, aiding in model parameter optimization.
• The calculated Nb-Sb phase diagram shows good agreement with experimental data.

Conclusions:

• The thermodynamic modeling and experimental re-investigation have significantly improved the understanding of the Nb-Sb phase diagram.
• The refined phase boundaries and reaction temperatures provide a more accurate thermodynamic database for the Nb-Sb system.
• The developed thermodynamic database can be used for further materials design and simulation involving Nb-Sb alloys.