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{{Unreferenced|date =September 2007}}
{{chembox
{{chembox
| Verifiedfields = changed
| verifiedrevid = 406132615
| Watchedfields = changed the wa
⚫
| Name = Triuranium octoxide

⚫
| ImageFile = U3O8lattice.jpg
| verifiedrevid =and 9l9 987ood79769
<!-- | ImageSize = 250px -->
⚫
| Name = Triuranium octoxide
| OtherNames = pitchblende
⚫
| ImageFile = U3O8lattice.jpg
⚫
| Section1 = {{Chembox Identifiers
| ImageFile2 = Triuranium octoxide.JPG
⚫
| CASNo = 1317-99-3
| OtherNames = Uranium(V,VI) oxide<br>Pitchblende<br>C.I. 77919
⚫
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
⚫
| CASNo = 1344-59-8
| ChemSpiderID = 10142128
| EINECS = 215-702-4
| PubChem = 11968241
| SMILES = [O].[O].[O].[O].[O].[O].[O].[O].[U].[U].[U]
| StdInChI=1S/8O.3U
| StdInChIKey=IQWPWKFTJFECBS-UHFFFAOYSA-N
}}
}}
| Section2 = {{Chembox Properties
|Section2={{Chembox Properties
| Formula = U<sub>3</sub>O<sub>8</sub>
| Formula = U<sub>3</sub>O<sub>8</sub>
| MolarMass = 842.1 g/mol
| MolarMass = 842.08 g/mol
| Solvent = other solvents
| Solvent = other solvents
| SolubleOther = Insoluble in water;
| SolubleOther = Insoluble in water;
Soluble in nitric and sulfuric acids.
Soluble in nitric and sulfuric acids.
| MeltingPt = 1150°C
| MeltingPtC = 1150
| BoilingPt = decomposes to UO<sub>2</sub> at 1300 °C}}
| BoilingPt= decomposes to UO<sub>2</sub> at
| BoilingPtC = 1300
}}
|Section4={{Chembox Thermochemistry
| DeltaHf = −3575&nbsp;kJ·mol<sup>−1</sup><ref name=b1>{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7|page=A23}}</ref>
| Entropy = 282&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup><ref name=b1/>
}}
|Section7={{Chembox Hazards
| GHSPictograms = {{GHS06}}{{GHS08}}{{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|300|330|373|411}}
| PPhrases = {{P-phrases|}}
}}
}}
}}
'''Triuranium octoxide''' (U<sub>3</sub>O<sub>8</sub>) is a compound of [[uranium]]. It is present as an olive green to black, odorless solid. In spite of its color, it is one of the more popular forms of [[yellowcake]] and is shipped between mills and refineries in this form.
'''Triuranium octoxide''' (U<sub>3</sub>O<sub>8</sub>)<ref>{{Cite web |title=triuranium octaoxide |url=https://webbook.nist.gov/cgi/cbook.cgi?Formula=u3o8&NoIon=on&Units=SI |access-date=2022-12-20 |website=webbook.nist.gov |language=en}}</ref> is a compound of [[uranium]]. It is present as an olive green to black, odorless solid. It is one of the more popular forms of [[yellowcake]] and is shipped between mills and refineries in this form.


Triuranium octoxide occurs naturally as the olive-green-colored mineral [[pitchblende]]. U<sub>3</sub>O<sub>8</sub> is readily produced from UF<sub>6</sub> and has potential long-term stability in a geologic environment. In the presence of [[oxygen]] (O<sub>2</sub>), [[uranium dioxide]] (UO<sub>2</sub>) is [[oxidized]] to U<sub>3</sub>O<sub>8</sub>, whereas [[uranium trioxide]] (UO<sub>3</sub>) loses oxygen at temperatures above 500°C and is [[Redox|reduced]] to U<sub>3</sub>O<sub>8</sub>. The compound can be produced by any one of three primary chemical conversion processes, involving either [[uranium tetrafluoride]] (UF<sub>4</sub>) or [[uranyl fluoride]] (UO<sub>2</sub>F<sub>2</sub>) as intermediates. It is generally considered to be the more attractive form for disposal purposes because, under normal environmental conditions, U<sub>3</sub>O<sub>8</sub> is one of the most kinetically and thermodynamically stable forms of uranium and also because it is the form of uranium found in nature. Its particle density is 8.3 g cm<sup>−3</sup>.
U<sub>3</sub>O<sub>8</sub> has potential long-term stability in a [[deep geological repository|geologic environment]]. In the presence of [[oxygen]] (O<sub>2</sub>), [[uranium dioxide]] (UO<sub>2</sub>) is [[oxidized]] to U<sub>3</sub>O<sub>8</sub>, whereas [[uranium trioxide]] (UO<sub>3</sub>) loses oxygen at temperatures above 500&nbsp;°C and is [[Redox|reduced]] to U<sub>3</sub>O<sub>8</sub>. The compound can be produced by any one of three primary chemical conversion processes, involving either [[uranium tetrafluoride]] (UF<sub>4</sub>) or [[uranyl fluoride]] (UO<sub>2</sub>F<sub>2</sub>) as intermediates. It is generally considered to be the more attractive form for disposal purposes because, under normal environmental conditions, U<sub>3</sub>O<sub>8</sub> is one of the most kinetically and thermodynamically stable forms of uranium. Its particle density is 8.3 g cm<sup>−3</sup>.{{fact|date=March 2024}}

Triuranium octoxide is converted to [[uranium hexafluoride]] for the purpose of [[uranium enrichment]].{{fact|date=March 2024}}


==Solid state structure==
==Solid state structure==
⚫
The solid is a layered structure where the layers are bridged by [[oxygen]] atoms, each layer contains uranium atoms which are in different coordination environments.{{fact|date=March 2024}}

⚫
The solid is a layered structure where the layers are bridged by [[oxygen]] atoms, each layer contains uranium atoms which are in different coordination environments in the above diagram these are shown in plum and green.


===Bond valence study===
===Bond valence study===
⚫
Using a {{nowrap|6Å × 6Å × 6Å}} box with the uranium atom in the centre, the bond valence calculation was performed for both U1 and U2 in solid. It was found, using the parameters for U(VI), that the calculated oxidation states for U1 and U2 are 5.11 and 5.10. Using the parameters for U(IV), the calculated oxidation states are 5.78 and 5.77 for U1 and U2, respectively. These studies suggests that all the uranium atoms have the same oxidation state, so that the oxidation states are disordered through the lattice.{{fact|date=March 2024}}


Other studies have shown evidence that a two U<sup>5+</sup> and a single U<sup>6+</sup>, or other similar combinations, may be a more correct representation.<ref>{{cite journal |last1=Huang |first1=Zhiyuan |last2=Ma |first2=Lidong |last3=Zhang |first3=Jianbao |last4=Zhou |first4=Qing |last5=Yang |first5=Lei |last6=Wang |first6=Haifeng |title=First-principles study of elastic and thermodynamic properties of UO2, γ-UO3 and α-U3O8 |journal=Journal of Nuclear Materials |date=December 2022 |volume=572 |pages=154084 |doi=10.1016/j.jnucmat.2022.154084 }}</ref>
⚫
Using a 6Å x 6Å x 6Å box with the uranium atom in the centre the bond valence calculation was performed for both U1 and U2 in solid. It was found using the parameters for U(VI) that the calculated oxidation states for U1 and U2 are 5.11 and 5.10. Using the parameters for U(IV) the calculated oxidation states are 5.78 and 5.77 respectively for U1 and U2. These study suggests that all the uranium atoms have the same oxidation state, so that the oxidation states are disordered through the lattice.


==References==
==References==
{{reflist}}
{{reflist}}


[[Category:Uranium compounds]]
{{Uranium compounds}}
{{Oxides}}

{{DEFAULTSORT:Uranium oxide}}
⚫
[[Category:Uranium(IV,VI) compounds]]
[[Category:Oxides]]
[[Category:Oxides]]
[[Category:Mixed valence compounds]]
[[Category:Nuclear materials]]
[[Category:Nuclear materials]]

⚫
{{Uranium compounds}}

{{Inorganic-compound-stub}}

[[ca:Octaòxid de triurani]]
[[de:Uran(IV,VI)-oxid]]
[[fr:Octaoxyde de triuranium]]
[[it:Octaossido di triuranio]]
[[ru:Оксид урана(VI)-диурана(V)]]
[[zh:八氧化三鈾]]

Latest revision as of 13:04, 20 March 2024

Triuranium octoxide
Names
Other names
Uranium(V,VI) oxide
Pitchblende
C.I. 77919
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.014.275 Edit this at Wikidata
EC Number
  • 215-702-4
  • InChI=1S/8O.3U
    Key: IQWPWKFTJFECBS-UHFFFAOYSA-N
  • [O].[O].[O].[O].[O].[O].[O].[O].[U].[U].[U]
Properties
U3O8
Molar mass 842.08 g/mol
Melting point 1,150 °C (2,100 °F; 1,420 K)
Boiling point decomposes to UO2 at 1,300 °C (2,370 °F; 1,570 K)
Solubility in other solvents Insoluble in water;

Soluble in nitric and sulfuric acids.

Thermochemistry
282 J·mol−1·K−1[1]
−3575 kJ·mol−1[1]
Hazards
GHS labelling:
GHS06: ToxicGHS08: Health hazardGHS09: Environmental hazard
Danger
H300, H330, H373, H411
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Triuranium octoxide (U3O8)[2] is a compound of uranium. It is present as an olive green to black, odorless solid. It is one of the more popular forms of yellowcake and is shipped between mills and refineries in this form.

U3O8 has potential long-term stability in a geologic environment. In the presence of oxygen (O2), uranium dioxide (UO2) is oxidized to U3O8, whereas uranium trioxide (UO3) loses oxygen at temperatures above 500 °C and is reduced to U3O8. The compound can be produced by any one of three primary chemical conversion processes, involving either uranium tetrafluoride (UF4) or uranyl fluoride (UO2F2) as intermediates. It is generally considered to be the more attractive form for disposal purposes because, under normal environmental conditions, U3O8 is one of the most kinetically and thermodynamically stable forms of uranium. Its particle density is 8.3 g cm−3.[citation needed]

Triuranium octoxide is converted to uranium hexafluoride for the purpose of uranium enrichment.[citation needed]

Solid state structure

[edit]

The solid is a layered structure where the layers are bridged by oxygen atoms, each layer contains uranium atoms which are in different coordination environments.[citation needed]

Bond valence study

[edit]

Using a 6Å × 6Å × 6Å box with the uranium atom in the centre, the bond valence calculation was performed for both U1 and U2 in solid. It was found, using the parameters for U(VI), that the calculated oxidation states for U1 and U2 are 5.11 and 5.10. Using the parameters for U(IV), the calculated oxidation states are 5.78 and 5.77 for U1 and U2, respectively. These studies suggests that all the uranium atoms have the same oxidation state, so that the oxidation states are disordered through the lattice.[citation needed]

Other studies have shown evidence that a two U5+ and a single U6+, or other similar combinations, may be a more correct representation.[3]

References

[edit]
  1. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 978-0-618-94690-7.
  2. ^ "triuranium octaoxide". webbook.nist.gov. Retrieved 2022-12-20.
  3. ^ Huang, Zhiyuan; Ma, Lidong; Zhang, Jianbao; Zhou, Qing; Yang, Lei; Wang, Haifeng (December 2022). "First-principles study of elastic and thermodynamic properties of UO2, γ-UO3 and α-U3O8". Journal of Nuclear Materials. 572: 154084. doi:10.1016/j.jnucmat.2022.154084.
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