Thermochemical And Thermophysical Properties Of Molten Salts/slags: From Experiment To Modelling

Abstract:

In high temperature processes are molten salts/slag often used as solvent or reaction medium due to their specific properties or simply as reaction product. Both exhibit partial ionic character which enhances the dissociation of foreign species. This specificity is widely employed when used as solvent for purification. Molten salts/slags are encountered is a wide range of domains such aluminium, sodium electrolysis, metallurgy, thermal batteries, glass industry, gasification, earth science (magma) …The modelling of such industrial or natural processes requires the knowledge of a number of thermochemical and thermophysical properties of these media. Their properties are closely related to their local microstructure and environmental conditions. The latter can be determined by Ab-Initio calculations combined with Molecular Dynamics simulation whereas experimental data can be gained from X-ray or neutrons scattering using containerless techniques or by high temperature spectroscopy (Raman, NMR..). This provides valuable information on the solvatation of cations which depends on the environmental conditions, e.g. oxygen partial pressure for slags. This data can be further used as input for phase diagram modelling using the Calphad approach. In addition number of experimental information may be required for the optimisation of complex multicomponent systems: chemical activity (emf…), vapour pressure (KEMS), Cp(T), ΔHf° (calorimetry), phase composition (XRD). Finally, the challenging step for this research field is the modelling of thermophysical properties such as viscosity, surface tension, thermal and electrical conductivity as a function of the Gibbs’ energy. This approach combining experimental and theoretical considerations from the atomistic to the macroscopic scale will be illustrated through examples for different applications. Finally, the discussion will be extended to the case of Room-Temperature-ionic-Liquids: can we use this approach and the experience gained with molten salts/slags to this new class of materials and where the key factor of success are.

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