EQUATION OF STATE FOR PURE SODIUM-CHLORIDE

An equation of state for pure sodium chloride has been developed on the basis of experimental data and results of Monte Carlo simulations for the restricted primitive model (RPM). The experimental data base included limited vapor pressure and saturated liquid density data as well as dimerization equilibrium constants. The liquid densities have been extrapolated to the supercooled region using liquid-phase Monte Carlo data. For this purpose, the parameters of the primitive model have been calculated by assuming that sodium chloride and RPM obey the corresponding states principle over a limited range of conditions. In the near-critical region Monte Carlo data as well as results of cluster calculations have been used with parameters scaled to reproduce the critical temperature obtained by extrapolating saturation data. The RPM parameters employed in the calculations are close to those for crystalline NaCl. The experimental and scaled Monte Carlo data have been reproduced within their accuracy using a van der Waals-type equation of state with two temperature-dependent parameters a and b. The functions representing the temperature dependence of the parameters have been designed to ensure reliable extrapolation to lower and higher temperatures. Formation of Na2Cl2 clusters has been allowed for by using a closed-form term representing the effect of association on the compressibility factor. The performance of the equation has been additionally verified by predicting compressibility factors at low reduced temperatures outside the saturation region and comparing them with scaled Monte Carlo data.