On Transformations of Cerium Dioxide under Hydrothermal Conditions in the Presence of Fluoride and Citrate Ions

It is shown that the interaction of nanocrystalline cerium dioxide and ammonium fluoride (CeO2 : NH4F = 1 : 5) in the presence of ammonium citrate (pH 5) under hydrothermal conditions (molar ratio of citrate : CeO2 = 1 : 1, 120°C, 24 h) leads to the formation of single-phase cerium(III) fluoride (yield of ~40%). This interaction also occurs at lower temperatures (at 50°C), but at a significantly lower rate (yield of ~7% in 14 days). The precipitate formed under similar conditions in an alkaline medium (pH 9) is a mixture of nanocrystalline CeO2 and CeF3; in a more alkaline environment (pH 11), the formation of solid-phase CeF3 is not observed. The data obtained expand the existing information on the transformations of poorly soluble substances in the nanodisperse state.