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Quantitative analysis on the microstructure of molten binary KF‐AlF 3 system by in situ Raman spectroscopy assisted with first principles method
Author(s) -
Ma Nan,
You Jinglin,
Lu Liming,
Xie Yingfang,
Wan Songming
Publication year - 2020
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.5751
Subject(s) - raman spectroscopy , chemistry , binary system , analytical chemistry (journal) , octahedron , microstructure , dimer , aluminium , crystallography , crystal structure , binary number , organic chemistry , physics , arithmetic , mathematics , optics
In order to help predict the properties of molten salts electrolytes and aluminium brazing flux used in the Hall–Héroult process and in aluminium brazing, the microstructure of binary KF‐AlF 3 system from 298 K to its molten states was explored by in situ high‐temperature Raman spectroscopy in argon atmosphere. Comparing with experimental Raman spectra in molten system, quantum chemistry ab initio simulations were used to calculate the symmetric stretching vibrational modes of probable clusters in the melts. The molten KF‐AlF 3 system was found to comprise monomer [AlF 6 ] 3− , [AlF 5 ] 2− , [AlF 4 ] − , and dimer [Al 2 F 7 ] − clusters. With the increase of KF content in the melts, the major species changes from [AlF 4 ] − tetrahedra to [AlF 6 ] 3− octahedra. From the deconvoluted measured Raman spectra, the mole fractions of varied clusters in the system were also calculated. As the KF:AlF 3 ratio was increased from 1 to 3, the content of [AlF 6 ] 3− in the melt increased from 22.30 to 98.83 mol%, whereas the [AlF 4 ] − content decreased from 68.92 to 0.33 mol%. [AlF 5 ] 2− and [Al 2 F 7 ] − clusters were also found in small amounts in the melts.