Uranium trioxide

Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is an oxide of uranium. UO3 is a hexavalent oxide, which means that the uranium in the compound has an oxidation state of +6. It can be formed by heating uranyl nitrate to 400 °C.
UO3 is a poisonous and slightly radioactive substance. It can be harmful if it is breathed in, ingested, or makes contact with skin.