thumb|230px|[[Yellowcake, a mixture of uranium oxides.]]

Uranium oxide is an oxide of the element uranium.

The metal uranium forms half a dozen known oxides:

  • Uranium dioxide or uranium(IV) oxide (UO<sub>2</sub>, the mineral uraninite or pitchblende)
  • Diuranium pentoxide or uranium(V) oxide (U<sub>2</sub>O<sub>5</sub>)
  • Uranium trioxide or uranium(VI) oxide (UO<sub>3</sub>)
  • Triuranium octoxide (U<sub>3</sub>O<sub>8</sub>, the most stable uranium oxide; yellowcake typically contains 70 to 90 percent triuranium octoxide)
  • Uranyl peroxide (UO<sub>2</sub>O<sub>2</sub> or UO<sub>4</sub>)
  • Amorphous uranium(VI) oxide (Am-U<sub>2</sub>O<sub>7</sub>)

Uranium dioxide is oxidized in contact with oxygen to form triuranium octoxide.

:3 UO<sub>2</sub> + O<sub>2</sub> → U<sub>3</sub>O<sub>8</sub> at 250 °C (523 K)

Preparation 38

During World War II, "Preparation 38" was the codename for uranium oxide used by German scientists.

References