View in EDS

A new approach for coupled modelling of the structural and thermo-physical properties of molten salts. Case of a polymeric liquid LiF-BeF2.

Saved in:
Bibliographic Details
Title: A new approach for coupled modelling of the structural and thermo-physical properties of molten salts. Case of a polymeric liquid LiF-BeF2.
Authors: Smith, A.L.1 (AUTHOR) a.l.smith@tudelft.nl, Capelli, E.1 (AUTHOR), Konings, R.J.M.2 (AUTHOR), Gheribi, A.E.3 (AUTHOR)
Source: Journal of Molecular Liquids. Feb2020, Vol. 299, pN.PAG-N.PAG. 1p.
Subjects: Polymer solutions, Molecular volume, Molecular dynamics, Chemical speciation, Fused salts, Polymeric nanocomposites
Abstract: The (Li,Be)F x fluoride salt is an ionic liquid with complex non-ideal thermodynamic behaviour due to the formation of short-range order. In this work, we explore the relationship between local structure, thermo-physical and thermodynamic properties in this system using a multidisciplinary approach that couples molecular dynamics simulations using the Polarizable Ion Model (PIM) and thermodynamic modelling assessment using the CALPHAD method. The density, thermal expansion, viscosity, thermal conductivity, molar and mixing enthalpies and heat capacity of the (Li,Be)F x melt are extracted from the polarizable ionic interaction potentials and investigated across a wide range of compositions and temperatures. The agreement with the available experimental data is generally very good. The local structure is also examined in detail, in particular the transition between a molecular liquid with Li+, BeF 4 2 − and F− predominant species at low BeF 2 content, and a polymeric liquid at high BeF 2 content, with the formation of polymers (Be 2 F 7 3 − , Be 3 F 10 4 − , Be 4 F 13 5 − , etc.), and finally of a three-dimensional network of corner-sharing tetrahedrally coordinated Be2+ cations for pure BeF 2. Based on the available experimental information and the output of the MD simulations, we moreover develop for the first time a coupled structural-thermodynamic model for the LiF-BeF 2 system based on the quasi-chemical formalism in the quadruplet approximation, that provides a physical description of the melt and reproduces (in addition to the thermodynamic data) the chemical speciation of beryllium polymeric species predicted from the simulations. • Thermo-physical and thermodynamic properties of the (Li,Be)Fx melt are calculated from Polarizable Ion Model (PIM) potentials. • A structural-thermodynamic model is reported coupling the output of molecular dynamics simulations and experimental data. • The chemical speciation of the melt, which includes Li+, F−, BeF 4 2 − , Be 2 F 7 3 − , and Be 3 F 10 4 − species, is reproduced in the model. • The non-ideal behaviour of the melt is illustrated by the excess molar volume, enthalpy of mixing, and activity data. • The non-ideal behaviour is discussed in relation with the local structure of the melt. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Molecular Liquids is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
Description
Abstract:The (Li,Be)F x fluoride salt is an ionic liquid with complex non-ideal thermodynamic behaviour due to the formation of short-range order. In this work, we explore the relationship between local structure, thermo-physical and thermodynamic properties in this system using a multidisciplinary approach that couples molecular dynamics simulations using the Polarizable Ion Model (PIM) and thermodynamic modelling assessment using the CALPHAD method. The density, thermal expansion, viscosity, thermal conductivity, molar and mixing enthalpies and heat capacity of the (Li,Be)F x melt are extracted from the polarizable ionic interaction potentials and investigated across a wide range of compositions and temperatures. The agreement with the available experimental data is generally very good. The local structure is also examined in detail, in particular the transition between a molecular liquid with Li+, BeF 4 2 − and F− predominant species at low BeF 2 content, and a polymeric liquid at high BeF 2 content, with the formation of polymers (Be 2 F 7 3 − , Be 3 F 10 4 − , Be 4 F 13 5 − , etc.), and finally of a three-dimensional network of corner-sharing tetrahedrally coordinated Be2+ cations for pure BeF 2. Based on the available experimental information and the output of the MD simulations, we moreover develop for the first time a coupled structural-thermodynamic model for the LiF-BeF 2 system based on the quasi-chemical formalism in the quadruplet approximation, that provides a physical description of the melt and reproduces (in addition to the thermodynamic data) the chemical speciation of beryllium polymeric species predicted from the simulations. • Thermo-physical and thermodynamic properties of the (Li,Be)Fx melt are calculated from Polarizable Ion Model (PIM) potentials. • A structural-thermodynamic model is reported coupling the output of molecular dynamics simulations and experimental data. • The chemical speciation of the melt, which includes Li+, F−, BeF 4 2 − , Be 2 F 7 3 − , and Be 3 F 10 4 − species, is reproduced in the model. • The non-ideal behaviour of the melt is illustrated by the excess molar volume, enthalpy of mixing, and activity data. • The non-ideal behaviour is discussed in relation with the local structure of the melt. [ABSTRACT FROM AUTHOR]
ISSN:01677322
DOI:10.1016/j.molliq.2019.112165