Analysis of Cationic Structure in Some Room-Temperature Molten Fluorides and Dependence of Their Ionic Conductivity and Viscosity on Hydrofluoric Acid Concentration

Abstract

To understand the ionic and nonionic species in (CH(3))(4)NF·mHF, (CH(3))(3)N·mHF, (C(2)H(5))(4)NF·mHF, and (C(2)H(5))(3)N·mHF melts, the structures of these melts were investigated by infrared spectroscopy, NMR, and high-energy X-ray diffraction. Infrared spectra revealed that three kinds of fluorohydrogenate anions, (FH)(n)F(-) (n = 1, 2, and 3), and molecular hydrofluoric acid (HF) are present in every melt. Ionic conductivity and viscosity of these melts were measured and correlated with their cationic structure. The ionic conductivity of the R(4)N(+)-systems was higher than that of corresponding R(3)NH(+)-systems because a strong N-H···F(HF)(n) interaction prevents the motion of R(3)NH(+) cations in the R(3)N·mHF melts. (CH(3))(4)N(+) and (CH(3))(3)NH(+) cations gave higher ionic conductivity than (C(2)H(5))(4)N(+) and (C(2)H(5))(3)NH(+) cations, respectively, because the ionic radii of former cations were smaller than those of latter. It was concluded that these effects on ionic conductivity can be explained by the cationic structure and the concentration of molecular HF in the melts.

A Review of High-Energy X-Ray Diffraction from Glasses and Liquids

“…In the case of liquids, several metals and alloys [131][132][133][134] have been studied in the molten state, along with Ge [135], tellurites [136,137], aluminates [138,139], silicates [140], and aluminosilicates [141]. Molecular liquids have also been investigated extensively with high energy X-ray diffraction, including the electron density in water [142], the effect of strong hydrogen bonding in deeply supercooled water [143], flourides [144][145][146][147][148][149][150], the structure of molten salts [151,152], as well as temperature and compositiondependent intermediate range order in ionic liquids [153][154][155][156][157][158][159][160][161][162][163]. The structural chemistry of actinide solutions has also been explored [164][165][166][167][168].…”

Electrochemical Fluorination Using Halogen Mediators in Ionic Liquid Hydrogen Fluoride Salt

“…28 The differences of the diffusion coefficient between the media containing Et 3 N-4HF and Et 3 N-5HF were owing to the dif-ference of viscosity of those salts, namely, the viscosity of Et 3 N-5HF is smaller than that of Et 3 N-4HF. 29 From the CV analyzes, Et 4 NBr and Et 4 NI were found to show reversible redox response in both Et 3 N-nHF/MeCN and in Et 3 N-nHF, where they are expected to be mediator for electrochemical fluorination.…”

Influence of triethylamine on the anodic dissolution characteristics of Ni, Cu and their alloys in non-aqueous solvents containing fluoride media: voltammetric and surface morphologic study

“…Et 3 N addition in a small ratio, for example, leads to further dissociation of HF leading to enhanced fluoride ion concentration [31] …”