Uranium oxide is an oxide of the element uranium. There are many of them.

The metal uranium forms half a dozen known oxides:

• Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende)

• Diuranium pentoxide or uranium(V) oxide (U2O5)

• Uranium trioxide or uranium(VI) oxide (UO3)

• Triuranium octoxide (U3O8, the most stable uranium oxide; yellowcake typically contains 70 to 90 percent triuranium octoxide)

• Uranyl peroxide (UO2O2 or UO4)

• Amorphous uranium(VI) oxide (Am-U2O7)

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

1. 3 UO2 + O2 → U3O8 at 250 °C (523 K)

Preparation 38

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

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