The binary system UF4?UCl4

Mass Spectrometric Identification of Gaseous Uranium(IV) Fluoride Chlorides: UF3Cl(g) and UF2Cl2(g)

“…Accordingly, the formation of fluoride chloride vapors can be considered as occurring via gas-phase halogen exchange processes involving the gaseous tetrafluoride, such as that indicated by equation (3). Such halogen exchange processes contrast with the low-temperature oxidative halogen addition reactions carried out in cold matrices (Ar); e. g., [ Although the solid uranium(IV) fluoride chlorides thermally decompose at temperatures as low as 444° C, miscible liquid UF 4 -UCI4 mixtures have been reported to form above a 426°C eutectic point [11]. It may thus be assumed that the molecular fluoride chloride vapors observed here were in equilibrium with a molten uranium fluoride chloride solution of indeterminate composition.…”

“…Early investigations of uranium halides [7][8][9] included the preparation of several U(III) and U(IV) mixed halide phases, including some fluoride chlorides. The three possible stoichiometric uranium(IV) fluoride chloride solid compounds, UF"Cl4_" with η = 1-3, have been prepared [10] ; each has been found to be thermally unstable and undergoes a peritectic decomposition so that only the binary tetrahalides, UF 4 and UC1 4 , are stable as solid phases above ~530°CC [11]. In accord with the expected increase in stability with higher fluorine content, the following order of fluoride chloride thermal stabilities has been established [11]: UF 3 Cl(s)/most stable > UF 2 C1 2 (S) > UFCl 3 (s).…”

“…The three possible stoichiometric uranium(IV) fluoride chloride solid compounds, UF"Cl4_" with η = 1-3, have been prepared [10] ; each has been found to be thermally unstable and undergoes a peritectic decomposition so that only the binary tetrahalides, UF 4 and UC1 4 , are stable as solid phases above ~530°CC [11]. In accord with the expected increase in stability with higher fluorine content, the following order of fluoride chloride thermal stabilities has been established [11]: UF 3 Cl(s)/most stable > UF 2 C1 2 (S) > UFCl 3 (s). Although the solid uranium(IV) mixed halide phases are often represented as discrete stoichiometric compounds, they are more generally and accurately described as solid solutions of the respective binary halides.…”