In this paper, we derive a new regularity for dense fluids, both compressed liquids and dense supercritical fluids based on the Lennard-Jones (12-6) potential function and using speed of sound results. By considering the internal pressure by modeling the average configurational potential energy, and then taking its derivative with respect to volume, we predict that isotherm [(partial differential E/partial differential V)(T)/rhoRT]V(2) is a linear function of rho(2), where E is the internal energy, (partial differential E/partial differential V)(T)) is the internal pressure, and rho = 1/V is the molar density. The regularity is tested with experimental data for ten fluids including Ar, N(2), CO, CO(2), CH(4,) C(2)H(6), C(3)H(8), C(4)H(10), C(6)H(6), and C(6)H(5)CH(3). These problems have led us to try to establish a function for the accurate calculation of the internal pressure based on speed of sound theory for different fluids. The results of the fitting show limited success of the pure substances. The linear relationship appears to hold from the lower density limit at the Boyle density and from the triple temperature up to about double the Boyle temperature. The upper density limit appears to be reached at 1.4 times the Boyle density. The results are likely to be useful, although they are limited.
In this paper, we use internal pressure to predict metal-nonmetal transitions in alkali metals. Isotherms of the internal pressure of cesium fluid versus molar volume show a maximum point around 1.3 g • cm -3 in agreement with X-ray diffraction and small-angle X-ray scattering. It is shown that at molar volumes higher than the maximum point the attractive force has a strong influence on the determination of internal pressure that similar studies have been made for negative compressibility. An accurate empirical potential was found for dense alkali fluids and used to test the applicability of the theory. These theoretical predictions are in good agreement with experimental results. Problems have led us to try to establish a function for the accurate calculation of the internal pressure and the prediction of metal-nonmetal transition alkali metals based on the internal pressure.
New parameters of the linear isotherm regularity, the so-called LIR equation of state, are
used to calculate the thermal pressure coefficient of dense fluids. The extent of the
deviation between real thermal pressure coefficients and thermal pressure coefficients by
applying LIR are best expressed through the use of new parameters in LIR. In this paper,
the temperature dependence of LIR parameters in the form of a first order have been
developed to second order and third order, and the temperature derivatives of new
parameters are used to calculate thermal pressure coefficients. The resulting model
accurately predicts thermal pressure coefficients from the lower density limit at the
Boyle density and from the triple temperature up to about double the Boyle
temperature. The upper density limit appears to be reached at 1.4 times the Boyle
density. These problems have led us to try to establish a function for accurate
calculation of the thermal pressure coefficients, based on LIR theory for different
fluids.
In this paper, we calculate internal pressure of sodium, potassium, and rubidium and then use the internal pressure to predict X-ray diffraction and small-angle X-ray scattering to the range where the compressibility of the interacting electron gas has been theoretically predicted to become negative. Isotherms of internal pressure of rubidium fluid versus molar volume show a maximum around 1.152 g • cm -3 in agreement with X-ray diffraction and small-angle X-ray scattering. An attempt is made to establish a function for the accurate calculation of the internal pressure and the prediction of metal-nonmetal transition alkali metals based on the internal pressure.
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