Some crystallochemical peculiarities of the cubic form of hydrated uranium tetrafluoride

Characterizing the solid hydrolysis product, UF4(H2O)2.5, generated from neat water reactions with UF4 at room temperature

“…Water can also occupy vacancy sites of the U 4+ ion to form two hydrate phases: the pseudo-cubic UF4(H2O)n where 0.5 ≤ n ≤ 2 and UF4(H2O)2.5. 13,14 The 2.5 hydrate, which has been minimally characterized to-date, has been shown to form when anhydrous UF4 is placed in dilute aqueous HF solutions. 15,16 The pseudo-cubic phase, which is a derivative of the CaF2-type phase, can form from a number of reactions, including electrolytic reduction of uranyl fluoride (UO2F2) in aqueous hydrofluoric acid, 17,18 addition of aqueous hydrofluoric acid to aqueous uranium tetrachloride (UCl4), 19 and hydration of UF4 formed from various dehydration reactions.…”

“…15,16 The pseudo-cubic phase, which is a derivative of the CaF2-type phase, can form from a number of reactions, including electrolytic reduction of uranyl fluoride (UO2F2) in aqueous hydrofluoric acid, 17,18 addition of aqueous hydrofluoric acid to aqueous uranium tetrachloride (UCl4), 19 and hydration of UF4 formed from various dehydration reactions. 13,14 One report has even shown that UF4(H2O)n might hydrate as low as n = 0.4. 20 Elevated-temperature interactions of UF4 and water produce a variety of compounds.…”

Structural Characterization of Uranium Tetrafluoride Hydrate (UF4·2.5H2O)

“…Uranium tetrafluoride (UF 4 ) is an important compound in the nuclear fuel cycle for the production of uranium hexafluoride (UF 6 ) and uranium metal and as a fuel for fluoride-based molten salt reactors . Though UF 4 is insoluble in water, there are several known crystalline UF 4 hydrates, including the pseudocubic hydrates UF 4 · x H 2 O where x = 0.7, 1.2, 1.5, or 2.0 and orthorhombic UF 4 ·2.5H 2 O. − The pseudocubic hydrates can be formed via electrolytic reduction of uranyl fluoride (UO 2 F 2 ) in hydrofluoric acid, reacting uranium tetrachloride (UCl 4 ) with HF, or rehydrating previously dehydrated UF 4 ; the 2.5 hydrate can be prepared from UF 4 and dilute HF. − The importance of the 2.5 hydrate has been elevated recently, however, because Christian et al reported preparing UF 4 ·2.5H 2 O by contacting anhydrous UF 4 with neat H 2 O for 24 h at room temperature . Additionally, UF 4 ·2.5H 2 O has also been formed via prolonged exposure of anhydrous UF 4 to high relative humidity conditions .…”