DOI: 10.57760/sciencedb.30635
title: Application of 19F NMR for the Structure Investigation of Fluoride Molten Salts
title: 核纯级氟盐离子络合结构的19F核磁共振研究

description: Molten fluorides (e.g., FLiBe) are widely employed in molten salt reactors as coolants and fuel solvents due to their excellent heat transfer properties and favorable neutronic characteristics. [Purpose]: This study aims to utilize the unique chemical characteristics of fluoride salts and apply high-resolution 19F nuclear magnetic resonance (NMR) techniques to investigate their microscopic structures and temperature-driven transformation mechanisms. [Methods]: High-resolution 19F NMR was combined with magic-angle spinning (MAS), high-temperature, and variable-temperature experiments to systematically characterize molten fluorides. Furthermore, the solid–liquid phase transition was investigated, and a quantitative 19F NMR method based on cooled solid samples was established to speculate the distribution and concentration of ionic structures in the molten state. [Results]: The results demonstrate that variations in chemical shifts observed in high-temperature 19F NMR spectra provide key structural information and reveal temperature-dependent transformation mechanisms. In addition, the proposed quantitative solid-state NMR approach successfully enabled the analysis of ionic structures of molten salt in high temperature, showing the promising applicability for evaluating the Lewis acidity and basicity of fluoride ions. [Conclusions]: By combining multiple 19F NMR analytical strategies, this study provides comprehensive insights into the composition, structural evolution mechanisms of molten fluorides, thereby offering a solid foundation for establishing component-structure–property relationships in molten salt systems.
description: Molten fluorides (e.g., FLiBe) are widely employed in molten salt reactors as coolants and fuel solvents due to their excellent heat transfer properties and favorable neutronic characteristics. [Purpose]: This study aims to utilize the unique chemical characteristics of fluoride salts and apply high-resolution 19F nuclear magnetic resonance (NMR) techniques to investigate their microscopic structures and temperature-driven transformation mechanisms. [Methods]: High-resolution 19F NMR was combined with magic-angle spinning (MAS), high-temperature, and variable-temperature experiments to systematically characterize molten fluorides. Furthermore, the solid–liquid phase transition was investigated, and a quantitative 19F NMR method based on cooled solid samples was established to speculate the distribution and concentration of ionic structures in the molten state. [Results]: The results demonstrate that variations in chemical shifts observed in high-temperature 19F NMR spectra provide key structural information and reveal temperature-dependent transformation mechanisms. In addition, the proposed quantitative solid-state NMR approach successfully enabled the analysis of ionic structures of molten salt in high temperature, showing the promising applicability for evaluating the Lewis acidity and basicity of fluoride ions. [Conclusions]: By combining multiple 19F NMR analytical strategies, this study provides comprehensive insights into the composition, structural evolution mechanisms of molten fluorides, thereby offering a solid foundation for establishing component-structure–property relationships in molten salt systems.