Preparation, characterization and thermal stability of tellurites and tellurates of uranium

Uranium tellurates, UTeO5 and UTe3O9 were prepared by heating UO2 + TeO2 an d U3O8 + TeO2 in air/oxygen and the tellurite UTe3O8 by heating UO2 + TeO2 in vacuum sealed quartz ampoule. The compounds were characterized by X-ray diffraction (XRD) and thermogravimetry (TG). A new tellurite compound UTeO4 was synthesized. Their thermal stability was determined in oxygen, argon a nd argon-8%hydrogen in the temperature range of ambient temperature to 950 degrees C. UTeO5 and UTe3O9 are stable in flowing oxygen up to 925 and 750 degrees C, respectively under dynamic heating at 10 K/min. UTe3O9 decompose s in O-2/Ar/Ar-8%H-2 via formation of UTeO5, whereas UTe3O8 decomposes in A r-8%H-2 via formation of UTeO4. UTe3O9 decomposes at 560 degrees C but all the other compounds decompose at 460 degrees C in Ar-8%H-2. (C) 2000 Kluwer Academic Publishers.