Equation of state and thermodynamic parameters of NaCl to 300 kbar in the high‐temperature domain

Data of several kinds (ultrasonic, volumetric, shock compression) are combined to produce a set of isotherms for NaCl in the temperature-pressure region between 25° and 500°C and 0–300 kbar. A preliminary examination of the Boehler-Kennedy measurements of linear compression to 30 kbar and 500°C supports the provisional assumption that (∂P/∂T)v is independent of P and possibly also of T in the “high-temperature” domain. The equation of state may consequently take the form P(V, t) = P25(V) + (t - 25)(∂P/∂T)v, where t is Celsius temperature. P25(V) is the 25°C isotherm of an earlier paper, with small adjustments; this equation was controlled at 300 kbar by the shock measurements and at zero pressure by ultrasonic measurements. Isotherms of the BE2 form are constructed for the five additional temperatures of the Boehler-Kennedy data with (∂P/∂T)v = 0.0286 kbar/deg. These are in nearly as good agreement with the volumetric data as were the curves fitted to these measurements alone. At the same time, the parameters of these isotherms show a regular dependence upon temperature. Various thermo dynamic parameters are tabulated, with the aid of handbook values of CP and zero-pressure thermal expansion coefficients. In particular, Gruneisen's ratio γ is found to be nearly independent of temperature, while γ/V is nearly independent of pressure.

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