Internal Pressures of Lithium and Cesium Fluids at Different Temperatures

Abstract

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.

Calculation of Thermal Pressure Coefficient of Lithium Fluid by pVT Data

“…An accurate empirical potential was found for dense cesium fluid and used to test the applicability of the theory. These theoretical predictions are in good agreement with experimental results [17][18][19][20].…”

“…In fact, the repulsive forces have an important role in the determination of the fluid structure, and the cohesive or attractive interactions in a fluid only define the fluid volume. The precise meaning of the metalnonmetal transition is contained in a generalized manner shows well depth in agreement with X-ray diffraction and small-angle X-ray scattering that the position of well depth maximum is a temperature-dependent quantity, and it also shows the metal-nonmetal transition residential [17][18][19][20][21].…”

“…Based on (17), to obtain thermal pressure coefficient, it is necessary to determine values Figures 7 and 8 show the experimental values of thermal pressure coefficient versus density for liquid lithium that are compared with thermal pressure coefficient using the TPC (1) , TPC (2) , and TPC (3) at 600 and 1600 K, respectively. Figure 5: The experimental values of thermal pressure coefficient versus density for Li fluid are compared with thermal pressure coefficient using the LIR (1) and LIR (2) at 600 K.…”

“…These measurements involve its magnetic, electrical, structural, optical, and thermophysical properties with optimal control of temperature in the critical region. The fundamental difficulty in dealing with fluid metals is that the electronic structures of liquid and gas phases are completely different [17][18][19][20][21]. The electronic structure of lithium (and other molten metals) at low temperatures can be well approximated by the structure of the free electron gas, and thus the thermodynamic properties of metals can be obtained by the same cohesion mechanism of the free electron gas.…”

“…In Section 2.4, temperature dependency of parameters has been developed to third order, and then thermal pressure coefficient is calculated by pVT data in each state for lithium fluid [16]. In Section 3, it has been shown that a gradual transition from metallic lithium to non-metallic lithium occurs when density decreases [17][18][19][20][21]. While the transition is occurring, a number of changes in the liquid structure happen, since the repulsion term of lithium potential energy versus temperature contains anomalous behavior, and it shows a well depth that the position of well depth maximum is the metal-nonmetal transition region of lithium.…”