Effect of fluoride ions on coordination structure of titanium inmolten NaCl–KCl

The effects of fluoride ions (F⁻) on the electrochemical behavior and coordination properties of titanium ions (Tiⁿ⁺) were studied in this work, by combining electrochemical and mathematical analysis as well as spectral techniques. The α was taken as a factor to indicate the molar concentration ratio of F⁻ and Tiⁿ⁺. Cyclic voltammetry (CV), square wave voltammetry (SWV), and open circuit potential method (OCP) were used to study the electrochemical behavior of titanium ions under conditions of various α, and in-situ sampler was used to prepare molten salt samples when α equal to 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, and 8.0. And then, samples were analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results showed that F⁻ in molten salt can reduce the reduction steps of titanium ions and greatly affects the proportion of valence titanium ions which making the high-valence titanium content increased and more stable. Ti²⁺ cannot be detected in the molten salt when α is higher than 3.0 and finally transferred to titanium ions with higher valence state. Investigation revealed that the mechanism behind those phenomenon is the coordination compounds (\textTiCl_j\textF_i^m-) forming.