Lewis Acidity and Basicity Diagnostics of Molten Salt for its Properties and Structure Online Monitoring

TL;DR

This study develops UV-Vis spectroscopy-based ion probes to quantify and monitor the acidity-basicity of molten NaCl-AlCl3 salts, linking their composition, structure, and properties for improved online diagnostics.

Contribution

It introduces a novel method for in-situ acidity-basicity measurement of molten salts, correlating structural features with thermophysical properties.

Findings

Established a quantitative acidity-basicity scale for NaCl-AlCl3 salts.

Linked acidity-basicity to salt composition and structure.

Enabled real-time online monitoring of molten salt properties.

Abstract

Analogous to the aqueous solution where the pH of the solvent affects its multiple behaviors, the Lewis acidity-basicity of molten salts also greatly influences their thermophysical and thermochemical properties. In the study, we develop ion probes to quantitatively determine the acidity-basicity scale of molten NaCl-xAlCl3 (x = 1.5-2.1) salt using in-situ ultra-violet visible (UV-Vis) spectroscopy. With the accumulation of acidity-basicity data of NaCl-AlCl3 molten salt for a variety of compositions, the correlation between the acidity-basicity of salt and its measured fundamental properties are derived. To understand the physical and chemical features controlling the acidity-basicity variations, the structures of NaCl-xAlCl3 molten salts with different chemical compositions are investigated in terms of bonded complexes and coordination numbers. The comprehensive understanding of the correlation between composition, acidity-basicity, properties, and structures of molten salt can serve for the full screening and online monitoring of salt melt in extreme environments by simply measuring the salt acidity-basicity as developed in this study.