3rd-INCC

Synthesis and study of uranyl orthovanadate (UO2)3(VO4)2*4H2O

19 Sept 2011, 17:30

1h 30m

Paladini (Città del Mare, Terrasini - Palermo - Sicily - Italy)

poster Nuclear Chemistry and Radiochemistry Poster Section 1

Speaker

Ms Anna Eremina (Nizhni Novgorod state University)

Description

Uranyl orthovanadate (UO2)3(VO4)2•4H2O was synthesized by heating of uranyl divanadate, (UO2)2V2O7. Structure of this compound was studied with X-ray fluorescence analysis, high temperature X-ray diffraction, scanning calorimetry, IR-spectroscopy. X-ray and IR characteristics of products of its dehydration were determined. Synthesis has consisted of uranyl divanadate (UO2)2V2O7 heating in aqueous solution at pH 7 for 48 hours in hydrothermal conditions at 200oC. 200oC 3(UO2)2V2O7+8H2O→2(UO2)3(VO4)2•4H2O+V2O5 Admixture of free V2O5 has been deleted by washing of precipitate with ammonium aqueous solution at 50oC. The results of chemical analysis showed that obtained compound is tetrahydrate 3UO3•V2O5•4H2O. X-ray data for the compound indicates that it is crystallographic analogue of the known uranyl orthovanadate (UO2)3(VO4)2•5H2O. Part of molecular H2O is weakly associated and water molecules do not fill crystallographic positions by themselves and conversion (UO2)3(VO4)25H2O → (UO2)3(VO4)24H2O does not lead to any significant changes of crystal lattice. Dehydration of tetrahydrate in wide temperature range (70-325oC) includes some stages. The crystal lattice of anhydrous composition (UO2)3(VO4)2 holds its layered structure with special set of crystallographic characteristics. However, dehydration is reversible. Compound is hydroscopic and its cooling leads to absorbing of three molecules H2O from air with subsequent returning into the original crystalline state. Addition of the fourth water molecule takes place after direct contact with aqueous phase at temperature that is not more than 20oC. IR-spectrum of (UO2)3(VO4)24H2O is very characteristic and informative. There are well expressed three groups of vibrations. We have found vibrations of water molecules, uranyl group UO22+ and vanadate tetrahedra. Form of water vibrations one could conclude that all water molecules hold their vibration individuality. From the results obtained it was concluded that compound (UO2)3(VO4)2*4H2O belongs to the family of uranium derivatives with the layered type of crystal lattice.