Thermodynamic Properties of Solid Neon from a Helmholtz Energy Equation of State up to 328 K and 5800 MPa

Abstract

Thermodynamic property data for solid neon have been analyzed to construct a new fundamental equation of state (EOS) expressed in terms of the Helmholtz energy. The formulation follows the quasi-harmonic Debye–Grüneisen framework and adopts the same Helmholtz energy structure as that used for solid argon, consistent with the general strategy previously developed for solid CO₂, benzene, and argon. The solid EOS is thermodynamically coupled to a reference fluid EOS along the sublimation and melting curves, enabling consistent calculations of solid–fluid phase equilibrium as well as single-phase solid properties up to 328 K and 5800 MPa. Model parameters were obtained by regression to a comprehensive literature dataset including cell volume, isobaric heat capacity, thermal expansivity, isothermal and isentropic bulk modulus, phase-equilibrium pressure, and phase-transition enthalpy. Within its intended range of application, the EOS reproduces fitted molar volumes typically within about 0.1 % along the sublimation curve and 0.5 % along both the melting curve and in the compressed solid. Heat capacity and thermal expansivity are represented with uncertainties of approximately 3 % to 10 % depending on temperature. Isothermal and isentropic bulk modulus are described to within about 3 % and 4 %, respectively, while sublimation and melting pressures are represented within approximately 2 % and 5 %. Overall, the new Helmholtz energy EOS provides a compact and internally consistent representation of solid neon thermodynamic properties suitable for cryogenic and high-pressure applications.