(Invited) Physical Properties of High Temperature Molten Salts

Abstract

High temperature molten salts are very important in the industrial field such as active metal production. In any cases including the use as the electrolyte, the physical properties, for example, density, electrical conductivity, viscosity are essentially important. On the other hand, molten salts consist of ions and are agglutinated by the coulombic interaction. The ionicity of the molten salts is affected by the strength of coulombic force of the constituent ionic species. Too strong coulombic force makes the salts non ionic, for example, SiCl4, and prevents the formation of stable ionic molten salts. Therefore, the phenomena of complex formation are important to consider the properties of molten salts. The author studied various physical properties of many molten salts. In this paper, the physical properties are described related to the ionic constitution including complex formation in the molten salts.

On the Use of the Angell–Walden Equation To Determine the “Ionicity” of Molten Salts and Ionic Liquids

“…The primary method for determining ionicity − is to apply the Nernst–Einstein (NE) equation, which relies on measurements of ion self-diffusion coefficients as well as the conductivity. As self-diffusion coefficients are not always available and accurate determinations are not necessarily straightforward, − a secondary method based on the more readily measurable conductivity and viscosity employing the Walden plot is attractive, particularly in screening large numbers of compounds for potential electrochemical applications of ionic liquids.…”

Can the Transport Properties of Molten Salts and Ionic Liquids Be Used To Determine Ion Association?

“…The transport properties of ionic liquids are of prime importance in determining how such materials might be applied and much effort has been expended on computer simulation in attempts to understand these experimental properties in the absence of successful theoretical approaches. A simple empirical approach to their interpretation has been to postulate the formation of ion-pairs, a concept first employed by Walden for molten salts − and reintroduced many times since for both molten salts and ionic liquids. − This concept is commonly used to rationalize the differences observed between the experimentally measurable electrical conductivity (Λ) and that calculated from ion self-diffusion coefficients ( D Si ) for a salt formally dissociating as using the Nernst–Einstein (NE) relation, and expressed through the deviation parameter, Δ. F and R are the Faraday and gas constants in this equation, T is the absolute temperature, ν i are the stoichiometric numbers for the dissociated salt and z i are the ion charges, including the signs. Alternative forms employ the ionicity, , Y = Λ/Λ NE < 1, or its inverse, the Haven ratio, H R = Λ NE /Λ > 1: thus, …”

Nucleation-Controlled Production of Sub-50 nm Carbon Nanotubes through Electrochemical Conversion of Carbon Dioxide in Carbonate Molten Salt

“…Among the technologies, molten saltbased CO 2 conversion technology is particularly promising [1,2]. In molten salt electrolyte system, the molten salt exhibits significantly high electrical conductivity [3,4]. Furthermore, molten salt electrolytes have high ability to absorb CO 2 molecules in the form of carbonate salts, which renders them well suited for handling CO 2 and facilitating its reaction.…”