Heat capacity measurements of the Fe2Nb and Fe7Nb6 intermetallic compounds

• Published in: Journal of alloys and compounds Vol. 878; p. 160411
• Main Authors: Silva, Antonio A.A.P., Lamoglia, Marcela S., Silva, Gilbert, Fiorani, Jean-Marc, David, Nicolas, Vilasi, Michel, Coelho, Gilberto C., Nunes, Carlos A., Eleno, Luiz T.F.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.10.2021; Elsevier BV
• Subjects: Approximation; Arc heating; Argon; Assessments; Differential scanning calorimetry; Electric arc melting; Experimental calorimetry; Heat; Heat capacity; Heat treatment; Intermetallic compounds; Intermetallics; Mathematical analysis; Niobium; Phase equilibria; Specific heat; Ternary systems; Thermodynamic equilibrium; Thermodynamic properties; Tubes; Heat capacity; Intermetallics; Differential scanning calorimetry; Experimental calorimetry
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.160411

•Fe-Nb is of great interest for microstructure and manufacturing alloys.•Accurate heat capacity and other thermodynamic properties are key information.•For the first time, the molar heat capacities of Fe2Nb and Fe7Nb6 were measured.•Quasi-Harmonic Approximation (QHA) calculations were also performed.•Results show that Kopp-Neumann is insufficient for CALPHAD databases. [Display omitted] The molar heat capacities of the Fe2Nb and Fe7Nb6 intermetallic compounds are reported here for the first time. The results were obtained via Differential Scanning Calorimetry (DSC) measurements, performed in a temperature range between 348 and 1038 K. The alloys were prepared by arc-melting high purity metals under argon flux and later heat-treated at 1200 ∘C for 336 h encapsulated in quartz tubes under argon to ensure thermodynamic equilibrium. The resulting samples were then characterized using X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM). The heat-capacity DSC measurements were carried out using an alternating step method with 20 and 50 K steps, with the resulting Cp associated with the midpoint of each temperature interval. A fit to a simplified Cp(T) curve was employed, due to the scatter in the data. Quasi-Harmonic Approximation (QHA) calculations were also performed, showing a good agreement with the measured values. Experimental results of heat capacity, along with other thermodynamic properties and phase equilibria, are key information for binary and ternary systems, specially for CALPHAD-type assessments. The results were therefore compared with the Kopp-Neumann approximation, used in recent assessments, showing that the parameters of both compounds can be improved in current CALPHAD databases, which motivates future work on the Fe-Nb system.