Heat capacity and enthalpy of palladium: A critical analysis of experimental information

Abstract

A description of the thermodynamic properties of FCC Pd above room temperature was developed by Dinsdale (1991) by relying on the heat capacity ($C_P$) measurements by Vollmer and Kohlhaas (1969). A subsequent assessment by Arblaster (1995) relied upon a combination of the enthalpy measurements by Cordfunke and Konings (1989) with the $C_P$ data reported by Miiller and Cezairliyan (1980). For temperatures in the range 400 K < T < 1200 K the $C_P$ values recommended by Dinsdale are smaller than those by Arblaster, with a maximum discrepancy of about 1.5 J/K.mol at 800 K. Later on, Milošević and Babić (2013) reported new $C_P$ data, which suggest that the discrepancy in the mentioned temperature range might be diminished. However, in the re-assessment reported by Arblaster (2018), the results by Milošević and Babić were not relied upon. Motivated by these various problems, exploratory Molecular Dynamics (MD) simulations of the thermal properties of FCC Pd were performed using the LAMMPS code and the Embedded Atom Model (EAM) interatomic potential developed by Sheng et al. (2011). The MD work predicted enthalpy values that are in reasonable agreement with the data of Milošević and Babić (2013). In view of this result, the full experimental database of $C_P$ and enthalpy measurements has been reanalyzed using a Maier-Kelley type thermodynamic model which accounts phenomenologically for the vibrational and electronic contributions to $C_P$. Systematic discrepancies between the enthalpy measurements and the direct determinations of $C_P$ are reported. An expression representing what is considered as the best possible account of the reliable experimental information available is presented.