A chemical theory for the thermodynamics of highly‐solvated liquid metal mixtures

Abstract

SCOPEThe proper use of liquid metals as solvents makes possible a wide range of new and advantageous chemical processes. For example the carbothermic reduction of reactive metal oxide ores in appropriate solvents could represent very substantial savings over the conventional, highly energy-intensive electrochemical production of aluminum, magnesium, and titantium. Traditionally the refining of pure reactor grade zirconium from ziconia by chemical separation of the hafnium impurities has been most difficult, but the Zn-Hf reduction and separation may be. accomplished directly and virtually quantitatively in a proper metal solvent. Solvent metal processes have even been shown to be successful in the separation of uranium from fission byproducts, thus leading to an environmentally acceptable and secure method for the reprocessing of spent nuclear fuel elements. All of these processes are currently at bench scale, and for implementation a mathematical model is required for scale-up. All depend on the unique thermodynamic properties of liquid metal solutions, and in this work a chemical theory of solutions is used to characterize the strong interactions of solutions forming intermetallic compounds, when activity coefficients may deviate from Raoult's law by many orders of magnitude. Such models should be instrumental in the investigation, development, and rational design of liquid metal solvent processes. CONCLUSION AND SIGNIFICANCEStrongly solvating (compound-forming) liquid metal mixtures can be well characterized thermodynamically by a chemical model of solution behavior. Using such a model, the liquid activities are well represented for mixtures forming either a single or multiple compounds. In addition the method is successfully extended to multicomponent systems and to the representation of the solid-liquid phase boundary. Since such systems always exhibit strong negative derivations from Raoult's Law, liquidliquid equilibria never occurs. The model presented is capable of accounting for both "physical" and "chemical" forces, and the general equations are developed. For the systems studied the compound formation is generally quite strong and the physical forces may be considered negligible by comparison. This assumption permits a direct linear least-squares solution of the equations to find the equilibrium constants for compound formation, which are the only parameters in the excess Gibbs energy equation. The chemical model is shown to be far superior for these systems to the traditional solutions to the Gibbs-Duham Equation; the Redlich-Kister, Van Laar, and Wilson equations are mathematically incapable of representing such systems.

Essential Magnesium Alloys Binary Phase Diagrams and Their Thermochemical Data

“…Higher negative heat of formation values of Mg 2 Sn were reported by Sharma [127], Eldridge et al [245] and Biltz and Holverscheit [250] than those by Nayeb-Hashemi and Clark [239]. NayebHashemi and Clark [239] along with others like Egan [254], Eckert et al [255], Pavlova and Poyarkov [256] optimized the phase diagram using measured thermodynamic data. Very recently, Jung and Kim [257], Meng et al [258] and Kang and Pelton [259] optimized the same system and modeled the liquid phase by the MQM.…”

Nonideal behavior in liquid metal solutions. 1. Physical theory model

“…The utility of different expressions based on semiempirical interpretations such as the Wohl expansion, the Scatchard formula, the van Laar equation, the Wilson equation, and the NRTL equation are discussed by Tomiska (1980) and Eckert et al (1982) and were shown to be generally not applicable for regression of experimental data. Despite the higher temperatures, the interatomic forces are a great deal stronger for metals, and few mixtures exhibit anything like ideality.…”

“…The calculational method is straightforward and has been described recently byEckert et al (1982), as the Liquid-liquid coexistence curve for the aluminum-indium system calculated with the physical theory model.1 o Predel m i Sandip' Equilibrium phase d i a g r d of the aluminum-tin system.…”

Analytical model for excess Gibbs energy of nonspecific liquid metal interactions

“…More recently it has become apparent that many high-temperature processes can be run in liquid metal solutions quite successfully, if the thermodynamic behavior of the mixture can be modeled. Intermolecular forces in metals are a great deal stronger than those in hydrocarbons; so, in spite of the very high temperatures, solution nonidealitics in liquid metal solutions are significantly greater than those observed in organic solutions, and the common methods for representing solution behavior simply do not work for metals (Eckert et al, 1982a).…”

“…This paper describes a method for the representation of physical interactions in metal solutions, excluding mixtures which are strongly solvated by the formation of intermetallic compounds. Methods for describing liquid metal thermodynamics strictly in terms of intermetallic compound formation are described by Eckert et al (1982a) and by Alger and Eckert (1983). Recently, Stoicos and Eckert (1983) have demonstrated that these two types of representations can be profitably combined to characterize certain classes of metal mixtures.…”