Neptunium trioxide

Neptunium trioxide

Names
Other names Neptunium(VI) oxide
Identifiers
CAS Number	65597-34-4  N
Properties
Chemical formula	NpO3
Molar mass	285 g·mol−1
Appearance	dark brown crystals (hydrate)
Solubility in water	insoluble
Related compounds
Other cations	Plutonium trioxide Uranium trioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Neptunium trioxide is an inorganic compound of neptunium and oxygen with the chemical formula NpO₃. ^[1]

Synthesis

Neptunium trioxide can be obtained by oxidating neptunium(V) nitrate solution in a molten eutectic mixture of potassium and lithium nitrates with ozone at 150 °C. The reaction by-products are washed out with water. ^[2] Other methods are also known. ^{[3] [4]}

Physical properties

The compound is highly volatile and exists only in the hydrated form.

Neptunium trioxide forms dark brown hydrate crystals of variable composition NpO₃•xH₂O, where x = 1–2. ^[5]

The NpO₃•H₂O hydrate crystals are of orthorhombic system.

It is insoluble in water.

References

1. Domanov, V. P. (1 August 2009). "Formation of volatile neptunium trioxide NpO3 and two other products of neptunium oxidation" . Radiochemistry. 51 (4): 350–353. doi:10.1134/S1066362209040031. ISSN   1608-3288 . Retrieved 17 October 2025.
2. Morss, L. R.; Edelstein, Norman M.; Fuger, Jean (31 December 2007). The Chemistry of the Actinide and Transactinide Elements (3rd ed., Volumes 1-5). Springer Science & Business Media. p. 770. ISBN   978-1-4020-3598-2 . Retrieved 17 October 2025.
3. Lemire, Robert J. (26 August 2001). Chemical Thermodynamics of Neptunium and Plutonium. Elsevier. p. 118. ISBN   978-0-444-50379-4 . Retrieved 17 October 2025.
4. Plutonium Abstracts. Hanford Laboratories. 1964. p. 8. Retrieved 17 October 2025.
5. Bagnall, K. W.; Laidler, J. B. (1 January 1964). "516. Neptunium and plutonium trioxide hydrates" . Journal of the Chemical Society (Resumed) (0): 2693–2696. doi:10.1039/JR9640002693. ISSN   0368-1769 . Retrieved 17 October 2025.