Saturated Vapor Composition and Volatility of Uranium and Some Other Metal Tetrachlorides (ThCl4, HfCl4, ZrCl4, TiCl4) from Their Molten Mixtures with Alkali Metal Chlorides

The changes in the saturated vapor composition and the volatility of the components of molten mixtures of uranium and some other metal tetrachlorides (ThCl4, HfCl4, ZrCl4, TiCl4) with alkali metal chlorides as functions of the temperature, concentration and cationic composition of the melts are discussed using our experimental data and those obtained by other researchers, mainly employees of the Institute of High-Temperature Electrochemistry (Ural Branch, Russian Academy of Sciences). The dissolution of UCl4 and other tetrachlorides in molten alkali metal chlorides is accompanied by complex formation, which manifests itself as a sharp decrease in the volatility of the corresponding tetravalent metal chloride and its content in saturated vapors. The strength of complex chloride anions of polyvalent metals formed in the melts increases significantly with a decrease in their concentration, replacement of the solvent salt in the series from LiCl to CsCl, and decreasing temperature. As a result, the volatilities of UCl4, ThCl4, HfCl4, ZrCl4, and TiCl4 and the composition of vapors above the solutions in the ionic melts vary over broad ranges. According to the experimental data, hafnium, zirconium, and titanium tetrachlorides (especially TiCl4), which are much more volatile in the individual state, have higher volatilities and contents in the saturated vapors over solutions in molten alkali metal chlorides.