Study of NaF–AlF 3 melts by coupling molecular dynamics, density functional theory, and NMR measurements

Kelly Machado (1) , Didier Zanghi (1) , Vincent Sarou-Kanian (2) , Sylvian Cadars (3) , Mario Burbano (4) , Mathieu Salanne (5) , Catherine Bessada (2)

1 CEMHTI - Conditions Extrêmes et Matériaux : Haute Température et Irradiation
2 RS2E - Réseau sur le stockage électrochimique de l'énergie
3 IMN - Institut des Matériaux de Nantes Jean Rouxel
4 MDLS - Maison de la Simulation
5 PHENIX - PHysicochimie des Electrolytes et Nanosystèmes InterfaciauX

Improvement of the industrial electrolytic process for aluminum production necessitates a thorough understanding of the underlying ionic structure of the electrolyte, which mainly comprises NaF and AlF3 at around 965 °C. The chemical and physical properties of this melt strongly depend on the aluminum speciation, which requires a multipronged approach in order to clarify its properties. Here we parametrize a new polarizable ion model (PIM) interatomic potential for the molten NaF−AlF3 system, which is used to study the liquid properties up to 50 mol % of AlF$_3$ at high temperatures. The potential parameters are obtained by force fitting to density functional theory (DFT) reference data. Molecular dynamics (MD) simulations are combined with further DFT calculations to determine NMR chemical shifts for $^{27}$Al, $^{23}$Na, and $^{19}$F. An excellent agreement is obtained with experimental values. This enables the study of the dynamic properties of the melts such as viscosity, electrical conductivity, and self-diffusion coefficient.

Domaines: Science des matériaux [cond-mat.mtrl-sci]

Kelly Machado, Didier Zanghi, Vincent Sarou-Kanian, Sylvian Cadars, Mario Burbano, et al.. Study of NaF–AlF 3 melts by coupling molecular dynamics, density functional theory, and NMR measurements. Journal of Physical Chemistry C, 2017, 121 (19), pp.10289 - 10297. ⟨10.1021/acs.jpcc.7b01530⟩. ⟨hal-01721020⟩