Neptunium(IV) oxide

Names
IUPAC name

Neptunium(IV) oxide

Other names

Neptunium oxide, neptunium dioxide

Identifiers

CAS Number

* 12035-79-9 Y

3D model (JSmol)

* Interactive image

ChemSpider |

* 34997056

EC Number |

* 234-830-1

PubChem CID

* 44148103

InChI

* InChI=1S/Np.2O/q+4;2*-2

Key: QKUTVYUEUPNRBO-UHFFFAOYSA-N

SMILES

* [O-2].[O-2].[Np+4]

Properties

Chemical formula

| NpO2
Molar mass | 269 g/mol
Appearance  | Green cubic crystals
Density | 11.1 g/cm3
Melting point |  2,800 °C; 5,070 °F; 3,070 K[1]
Structure[2]

Crystal structure

| Flourite (cubic), cF12

Space group

| Fm3m, #225

Lattice constant

a = 543.4 pm

Formula units (Z)

| 4
Thermochemistry

Std molar
entropy (S ~~o~~ 298)

| 19.19 ± 0.1 cal·mol−1·K−1
(80.3 ± 0.4 J·mol−1·K−1)[3]

Std enthalpy of
formation (ΔfH⦵298)

| −256.7 ± 0.6 kcal·mol−1
(−1074 ± 3 kJ·mol−1)[4]
Related compounds

Other anions

| Neptunium(III) chloride
Neptunium(IV) chloride

Other cations

| Protactinium(IV) oxide
Uranium(IV) oxide
Plutonium(IV) oxide
Americium(IV) oxide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

N verify (what is YN ?)
Infobox references

Tracking categories (test):

* SizeSet

Neptunium(IV) oxide, or neptunium dioxide, is a radioactive, olive green[5] cubic[6] crystalline solid with the formula NpO2. It emits both α- and γ-particles.[4]

## Contents

* 1 Production
* 2 Purification
* 3 Other properties
* 4 Uses
* 5 References

## Production

Industrially, neptunium dioxide is formed by precipitation of neptunium(IV) oxalate, followed by calcination to neptunium dioxide.[7]

Production starts with a nitric acid feed solution containing neptunium ions in various oxidation states. First, a hydrazine inhibitor is added to slow any oxidation from standing in air. Then ascorbic acid reduces the feed solution to predominantly neptunium(IV):

2Np5+ \+ C6H8O6 → 2Np4+ \+ C6H6O6 \+ 2H+
Np6+ \+ C6H8O6 → Np4+ \+ C6H6O6 \+ 2H+

Addition of oxalic acid precipitates hydrated neptunium oxalate...

Np4+ \+ 2H2C2O4 \+ 6H2O → Np(C2O4)2.6H2O(v) + 4H+

...which pyrolyzes when heated:[7]

Np(C2O4)2.6H2O Δ→ Np(C2O4)2 Δ→ NpO2 \+ 2CO(g)

Neptunium dioxide can also be formed from precipitation of neptunium(IV) peroxide, but the process is much more sensitive.[7]

## Purification

As a byproduct of nuclear waste, neptunium dioxide can be purified by fluorination, followed by reduction with excess calcium in the presence of iodine.[4] However, the aforementioned synthesis yields a quite pure solid, with less than 0.3% mass fraction of impurities. Generally, further purification is unnecessary.[7]

## Other properties

Neptunium dioxide contributes to the α-decay of 241Am, reducing its usual half-life an untested but appreciable amount.[8] The compound has a low specific heat capacity (900 K, compared with uranium dioxide's specific heat capacity of 1400 K), an abnormality theorized to stem from its 5f electron count.[9] Another unique trait of neptunium dioxide is its "mysterious low-temperature ordered phase". Mentioned above, it references an abnormal level of order for an actinitde dioxide complex at low temperature.[10] Further discussion of such topics could indicate useful physical trends in the actinoides.

## Uses

The neptunium dioxide complex is used as a means of stabilizing, and decreasing the "long term environmental burden"[11] of neptunium as a nuclear fission byproduct. Actinoide-containing nuclear waste will commonly be treated so that various AnO2 (where An = U, Np, Pu, Am, etc.) complexes form. In neptunium dioxide, neptunium is of reduced radio toxicity compared with elemental neptunium and is thus more desirable for storage and disposal. Neptunium dioxide has also been shown to contribute to increased decay rates of radioactive elements, an application which is currently being explored.[11]

Neptunium dioxide is also used experimentally for research into nuclear chemistry and physics, and it is speculated that it could be used to make efficient nuclear weapons. In nuclear reactors, neptunium dioxide can also be used as the target for plutonium bombardment.[11]

Furthermore, a patent for a rocket powered by neptunium dioxide is held by Shirakawa Toshihisa,[12] but there is little information available into research and production associated with such a product.

## References

1. ↑ Böhler, R.; M. J. Welland; F. De Bruycker; K. Boboridis; A. Janssen; R. Eloirdi; R. J. M. Konings; D. Manara (2012). "Revisiting the melting temperature of NpO2 and the challenges associated with high temperature actinide compound measurements". Journal of Applied Physics (American Institute of Physics) 111 (11): 113501–113501–8. doi:10.1063/1.4721655. Bibcode: 2012JAP...111k3501B. http://repository.tudelft.nl/islandora/object/uuid:0d8eb6d1-9919-448b-b222-d8dec5528ff1/datastream/OBJ/view.
2. ↑ Christine Guéneau; Alain Chartier; Paul Fossati; Laurent Van Brutzel; Philippe Martin (2020). "Thermodynamic and Thermophysical Properties of the Actinide Oxides" (in en). Comprehensive Nuclear Materials 2nd Ed. 7: 111–154. doi:10.1016/B978-0-12-803581-8.11786-2. ISBN 9780081028667.
3. ↑ Westrum, Jr., Edgar F.; J. B. Hatcher; Darrell W. Osborne (March 1953). "The Entropy and Low Temperature Heat Capacity of Neptunium Dioxide". Journal of Chemical Physics 21 (3): 419. doi:10.1063/1.1698923. Bibcode: 1953JChPh..21..419W. https://digital.library.unt.edu/ark:/67531/metadc172565/.
4. ↑ 4.0 4.1 4.2 Huber Jr, Elmer J.; Charles E. Holley Jr (October 1968). "Enthalpy of formation of neptunium dioxide". Journal of Chemical & Engineering Data 13 (4): 545–546. doi:10.1021/je60039a029.
5. ↑ Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill Professional. p. 271. ISBN 0-07-049439-8.
6. ↑ Lide, D. R. (1998). Handbook of Chemistry and Physics 87 ed.. CRC Press. p. 471. ISBN 0-8493-0594-2.
7. ↑ 7.0 7.1 7.2 7.3 Porter, J. A. (1964). "Production of Neptunium Dioxide". Industrial & Engineering Chemistry Process Design and Development 4 (3): 289–292. doi:10.1021/i260012a001. Equations extrapolated from verbal description.
8. ↑ Colle, J.-Y. (2011). "(Solid + gas) equilibrium studies for neptunium dioxide". Journal of Chemical Thermodynamics 43 (3): 492–498. doi:10.1016/j.jct.2010.10.027.
9. ↑ Serizawa, H.; Arai, Y.; Nakajima, K. (2001). "The estimation of the heat capacity of NpO2". The Journal of Chemical Thermodynamics 33 (6): 615–628. doi:10.1006/jcht.2000.0775.
10. ↑ Hotta, T. (2009). "Microscopic analysis of multipole susceptibility of actinide dioxides: A scenario of multipole ordering in AmO2". Physical Review B 80 (2): 024408–1–024408–7. doi:10.1103/PhysRevB.80.024408. Bibcode: 2009PhRvB..80b4408H.
11. ↑ 11.0 11.1 11.2 Colle, J.-Y. (2011). "(Solid + gas) equilibrium studies for neptunium dioxide". Journal of Chemical Thermodynamics 43 (3): 492–498. doi:10.1016/j.jct.2012.10.027.
12. ↑ Toshihisa, Shirakawa. "Bibliographic data: JP2007040768 (A) - 2007-02-15". Espacenet, patent search. http://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&II=0&ND=3&adjacent=true&locale=en_EP&FT=D&date=20070215&CC=JP&NR=2007040768A&KC=A.

* v
* t
* e

Neptunium compounds

Np(III)|

* NpF3
* NpCl3
* NpBr3
* NpI3

Np(IV)|

* NpF4
* NpCl4
* NpBr4
* NpO2
* Np(C8H8)2

Np(V)|

* NpF5

Np(VI)|

* NpF6

* v
* t
* e

Oxides

Mixed oxidation states|

* Antimony tetroxide (Sb2O4)
* Cobalt(II,III) oxide (Co3O4)
* Europium(II,III) oxide (Eu3O4)
* Iron(II,III) oxide (Fe<sub>3O4)
* Lead(II,IV) oxide (Pb3O4)
* Manganese(II,III) oxide (Mn3O4)
* Silver(I,III) oxide (Ag2O2)
* Triuranium octoxide (U3O8)
* Carbon suboxide (C3O2)
* Mellitic anhydride (C12O9)
* [[Chemistry:Praseodymium(III,IV) Praseodymium(III,IV) oxide]] (Pr6O11)
* Terbium(III,IV) oxide (Tb4O7)

+1 oxidation state|

* Copper(I) oxide (Cu<sub>2O)
* Caesium oxide (Cs2O)
* Dicarbon monoxide (C2O)
* Dichlorine monoxide (Cl2O)
* Gallium(I) oxide (Ga2O)
* Lithium oxide (Li2O)
* Potassium oxide (K2O)
* Rubidium oxide (Rb2O)
* Silver oxide (Ag2O)
* Thallium(I) oxide (Tl2O)
* Sodium oxide (Na2O)
* Water (hydrogen oxide) (H2O)

+2 oxidation state|

* Aluminium(II) oxide (AlO)
* Barium oxide (BaO)
* Beryllium oxide (BeO)
* Cadmium oxide (CdO)
* Calcium oxide (CaO)
* Carbon monoxide (CO)
* Chromium(II) oxide (CrO)
* Cobalt(II) oxide (CoO)
* Copper(II) oxide (CuO)
* Europium(II) oxide (EuO)
* Germanium monoxide (GeO))
* Iron(II) oxide (FeO)
* Lead(II) oxide (PbO)
* Magnesium oxide (MgO)
* Manganese(II) oxide (MnO)
* Mercury(II) oxide (HgO)
* Nickel(II) oxide (NiO)
* Nitric oxide (NO)
* Palladium(II) oxide (PdO)
* Silicon monoxide (SiO)
* Strontium oxide (SrO)
* Sulfur monoxide (SO)
* Disulfur dioxide (S2O2)
* Thorium monoxide (ThO)
* Tin(II) oxide (SnO)
* Titanium(II) oxide (TiO)
* Vanadium(II) oxide (VO)
* Zinc oxide (ZnO)

+3 oxidation state|

* Aluminium oxide (Al<sub>2O3)
* Antimony trioxide (Sb2O3)
* Arsenic trioxide (As2O3)
* Bismuth(III) oxide (Bi2O3)
* Boron trioxide (B2O3)
* Cerium(III) oxide (Ce2O3)
* Dibromine trioxide (Br2O3)
* Chromium(III) oxide (Cr2O3)
* Dinitrogen trioxide (N2O3)
* Dysprosium(III) oxide (Dy2O3)
* Erbium(III) oxide (Er2O3)
* Europium(III) oxide (Eu2O3)
* Gadolinium(III) oxide (Gd2O3)
* Gallium(III) oxide (Ga2O3)
* Holmium(III) oxide (Ho2O3)
* Indium(III) oxide (In<sub>2O3)
* Iron(III) oxide (Fe2O3)
* Lanthanum oxide (La2O3)
* Lutetium(III) oxide (Lu2O3)
* Manganese(III) oxide (Mn2O3)
* Neodymium(III) oxide (Nd2O3)
* Nickel(III) oxide (Ni2O3)
* Phosphorus trioxide (P4O6)
* Praseodymium(III) oxide (Pr2O3)
* Promethium(III) oxide (Pm2O3)
* Rhodium(III) oxide (Rh2O3)
* [[Chemistry:Samarium(III) Samarium(III) oxide]] (Sm2O3)
* Scandium oxide (Sc2O3)
* Terbium(III) oxide (Tb2O3)
* Thallium(III) oxide (Tl2O3)
* Thulium(III) oxide (Tm2O3)
* Titanium(III) oxide (Ti2O3)
* Tungsten(III) oxide (W2O3)
* Vanadium(III) oxide (V2O3)
* Ytterbium(III) oxide (Yb2O3)
* Yttrium(III) oxide (Y2O3)

+4 oxidation state|

* Americium dioxide (AmO2)
* Carbon dioxide (CO2)
* Carbon trioxide (CO3)
* Cerium(IV) oxide (CeO2)
* Chlorine dioxide (ClO2)
* Chromium(IV) oxide (CrO<sub>2)
* Dinitrogen tetroxide (N2O4)
* Germanium dioxide (GeO<sub>2)
* [[Chemistry:Hafnium(IV) Hafnium(IV) oxide]] (HfO2)
* Lead dioxide (PbO2)
* Manganese dioxide (MnO2)
* Neptunium(IV) oxide (NpO2)
* Nitrogen dioxide (NO2)
* Osmium dioxide (OsO2)
* Plutonium(IV) oxide (PuO2)
* Praseodymium(IV) oxide (PrO2)
* Protactinium(IV) oxide (PaO2)
* Rhodium(IV) oxide (RhO2)
* Ruthenium(IV) oxide (RuO<sub>2)
* Selenium dioxide (SeO2)
* Silicon dioxide (SiO2)
* Sulfur dioxide (SO2)
* Tellurium dioxide (TeO<sub>2)
* [[Chemistry:Terbium(IV) Terbium(IV) oxide]] (TbO2)
* Thorium dioxide (ThO2)
* Tin dioxide (SnO2)
* Titanium dioxide (TiO<sub>2)
* Tungsten(IV) oxide (WO2)
* Uranium dioxide (UO2)
* Vanadium(IV) oxide (VO2)
* Zirconium dioxide (ZrO2)

+5 oxidation state|

* Antimony pentoxide (Sb2O5)
* Arsenic pentoxide (As2O5)
* Dinitrogen pentoxide (N2O5)
* Niobium pentoxide (Nb2O5)
* Phosphorus pentoxide (P2O5)
* Protactinium(V) oxide (Pa2O5)
* Tantalum pentoxide (Ta2O5)
* Vanadium(V) oxide (V2O5)

+6 oxidation state|

* Chromium trioxide (CrO3)
* Molybdenum trioxide (MoO3)
* Rhenium trioxide (ReO3)
* Selenium trioxide (SeO3)
* Sulfur trioxide (SO3)
* Tellurium trioxide (TeO3)
* Tungsten trioxide (WO3)
* Uranium trioxide (UO3)
* Xenon trioxide (XeO3)
* Iridium trioxide (IrO3)

+7 oxidation state|

* Dichlorine heptoxide (Cl2O7)
* Manganese heptoxide (Mn2O7)
* [[Chemistry:Rhenium(VII) Rhenium(VII) oxide]] (Re2O7)
* Technetium(VII) oxide (Tc2O7)

+8 oxidation state|

* Osmium tetroxide (OsO4)
* Ruthenium tetroxide (RuO4)
* Xenon tetroxide (XeO4)
* Iridium tetroxide (IrO4)
* Hassium tetroxide (HsO4)

Related|

* Oxocarbon
* Suboxide
* Oxyanion
* Ozonide
* Peroxide
* Superoxide

Oxides are sorted by oxidation state. Category:Oxides

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