Expanded Fluid Alkali Metals in the Partially Ionized Plasma Model

Abstract

The model of a partially ionized gas is utilized to calculate the equation of state, electrical conductivity, and electronic magnetic susceptibility of expanded metal fluids along the coexistence curve. The effects of screening, self-energy and cluster formation are found to be essential. The implications on the mechanism of the metal-nonmetal transition are discussed.Fluid metals undergo a transition to a nonmetallic state when they are thermally expanded from the melting point up to supercritical conditions. The coincidence of two instability mechanisms, the ordinary liquid-gas phase instability and the metalnonmetal transition, leads to some peculiarities in the behavior of expanded fluid metals compared with that of nonconducting fluids (for a review, see [l]). The electrical conductivity shows a sharp decrease near the critical point from values characteristic of the degenerate electron gas in metals to values typical for nonmetallic vapors. The coexistence curve of the alkali-atom metals shows a strong asymmetry relative to that of nonconducting fluids such as the inert gases. There is clearly no common law of corresponding states for both the liquid metals and the inert gases, and even not for the liquid metals as one group. The magnetic properties such as the susceptibility [2] or the Knight shift [3] as function of density and temperature are especially sensitive with respect to the interactions in these systems.Various aspects of metal-nonmetal transitions have been studied on the basis of existing theories (for a review, see [4]. Utilizing concepts of solid state physics, the Hubbard model, one-electron (band) theory, and Anderson localization have been applied to study the influence of correlation, the variation of the liquid structure, and of disorder during the expansion. Another approach to the properties of expanded fluids starts with the plasma state at supercritical temperatures. Consistent quantum statistical methods have been developed (for a review, see [5]) to treat many-particle effects such as dynamic screening and self-energy, arbitrary degeneracy, the Pauli exclusion principle, and the structure factor for the thermodynamic, transport, and optical properties. A special effect in low-temperature plasmas is the formation of neutral and charged clusters such as atoms A , disiiers Az, and molecular ions A; or A-out of the elementary particles electrons e and ions At so that the vapor becomes partially ionized. Taking into account the chemical equilibria between various polyatomic species, thermodynamic and transport properties of weakly ionized alkali vapors and fluids were calculated within simple