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| verifiedrevid = 440399955 |
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| verifiedrevid = 452010868 |
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| Name = Uranium trioxide |
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| Name = Uranium trioxide |
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| ImageFile = UO3 gamma lattice.jpg |
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| ImageFile = UO3 gamma lattice.png |
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| IUPACName = Uranium trioxide<br/>Uranium(VI) oxide |
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| IUPACName = Uranium trioxide<br />Uranium(VI) oxide |
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| OtherNames = Uranyl oxide<br/>Uranic oxide |
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| OtherNames = Uranyl oxide<br />Uranic oxide |
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| Section1 = {{Chembox Identifiers |
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|Section1={{Chembox Identifiers |
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| CASNo_Ref = {{cascite|correct|CAS}} |
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| CASNo = 1344-58-7 |
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| CASNo = 1344-58-7 |
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| ChemSpiderID = 66635 |
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| CASNo_Ref = {{cascite}} |
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| EINECS = 215-701-9 |
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| PubChem = 74013 |
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| UNII_Ref = {{fdacite|correct|FDA}} |
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| UNII = Q47SFG7DIQ |
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| StdInChI=1S/3O.U |
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| StdInChIKey = JCMLRUNDSXARRW-UHFFFAOYSA-N |
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| SMILES = O=(=O)=O |
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}} |
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}} |
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| Section2 = {{Chembox Properties |
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|Section2={{Chembox Properties |
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| Formula = UO<sub>3</sub> |
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| Formula = UO<sub>3</sub> |
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| MolarMass = 286.29 g/mol |
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| MolarMass = 286.29 g/mol |
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| Density = 5.5–8.7 g/cm<sup>3</sup> |
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| Density = 5.5–8.7 g/cm<sup>3</sup> |
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| Appearance = yellow-orange powder |
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| Appearance = yellow-orange powder |
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| Solubility = Partially soluble |
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| Solubility = insoluble |
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| MeltingPt = ~200–650 °C (decomposes) |
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| MeltingPt = ~200–650 °C (decomposes) |
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}} |
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}} |
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| Section3 = {{Chembox Structure |
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|Section3={{Chembox Structure |
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| CrystalStruct = ''see text'' |
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| CrystalStruct = ''see text'' |
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| SpaceGroup = ''I''4<sub>1</sub>/amd (''γ''-UO<sub>3) |
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| SpaceGroup = ''I''4<sub>1</sub>/amd (''γ''-UO<sub>3</sub>) |
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| Coordination = |
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| Coordination = |
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| Section7 = {{Chembox Hazards |
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|Section4={{Chembox Thermochemistry |
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| DeltaHf = −1230 kJ·mol<sup>−1</sup><ref name=b1>{{cite book| vauthors = Zumdahl SS |title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7|page=A23}}</ref> |
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| ExternalMSDS = |
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| Entropy = 99 J·mol<sup>−1</sup>·K<sup>−1</sup><ref name="b1" /> |
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| EUIndex = 092-002-00-3 |
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}} |
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| EUClass = Very toxic ('''T+''')<br/>Dangerous for the environment ('''N''') |
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|Section7={{Chembox Hazards |
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| RPhrases = {{R26/28}}, {{R33}}, {{R51/53}} |
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| ExternalSDS = |
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| SPhrases = {{S1/2}}, {{S20/21}}, {{S45}}, {{S61}} |
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| GHSPictograms = {{GHS06}}{{GHS08}}{{GHS09}} |
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| NFPA-H = |
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| GHSSignalWord = Danger |
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| HPhrases = {{H-phrases|300|330|373|411}} |
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| PPhrases = {{P-phrases}} |
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| NFPA-H = 4 |
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| NFPA-F = 0 |
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| NFPA-R = 1 |
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| NFPA-S =OX |
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| FlashPt = Non-flammable |
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| FlashPt = Non-flammable |
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| LD50 = |
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| LD50 = |
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| PEL = |
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| PEL = |
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| Section8 = {{Chembox Related |
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|Section8={{Chembox Related |
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| OtherAnions = |
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| OtherAnions = |
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| OtherFunctn = ]<br/>] |
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| OtherFunction = ]<br />] |
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| Function = ] ]s |
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| OtherFunction_label = ] ]s |
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'''Uranium trioxide (UO<sub>3</sub>)''', also called '''] oxide''', '''uranium(VI) oxide''', and '''uranic oxide''', is the hexavalent ] of ]. The solid may be obtained by heating ] to 400 °C. Its most commonly encountered ], γ-UO<sub>3</sub>, is a yellow-orange powder. |
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'''Uranium trioxide (UO<sub>3</sub>)''', also called '''] oxide''', '''uranium(VI) oxide''', and '''uranic oxide''', is the hexavalent ] of ]. The solid may be obtained by heating ] to 400 °C. Its most commonly encountered ] is amorphous UO<sub>3</sub>. |
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==Production and use== |
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== Production and use == |
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There are three methods to generate uranium trioxide. As noted below, two are used industrially in the reprocessing of nuclear fuel and uranium enrichment. |
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There are three methods to generate uranium trioxide. As noted below, two are used industrially in the reprocessing of nuclear fuel and uranium enrichment. |
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# U<sub>3</sub>O<sub>8</sub> can be oxidized at 500°C with oxygen.<ref>{{cite journal|author= Sheft I, Fried S, Davidson N|title= Preparation of Uranium Trioxide|journal=Journal of the American Chemical Society|year= 1950|volume= 72|issue= 5|pages= 2172–2173|doi= 10.1021/ja01161a082}}</ref> Note that above 750 °C even in 5 atm O<sub>2</sub> UO<sub>3</sub> decomposes into U<sub>3</sub>O<sub>8</sub>.<ref name="wheeler">{{cite journal|author= Wheeler VJ, Dell RM, Wait E| title= Uranium trioxide and the UO<sub>3</sub> hydrates|journal= J. Inorganic Nuclear Chemistry| year= 1964|volume= 26|issue= 11|pages= 1829–1845|doi= 10.1016/0022-1902(64)80007-5}}</ref> |
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# U<sub>3</sub>O<sub>8</sub> can be oxidized at 500 °C with oxygen.<ref>{{cite journal|vauthors=Sheft I, Fried S, Davidson N|title=Preparation of Uranium Trioxide|journal=Journal of the American Chemical Society|year= 1950|volume= 72|issue=5|pages=2172–2173|doi=10.1021/ja01161a082|bibcode=1950JAChS..72.2172S }}</ref> Note that above 750 °C even in 5 atm O<sub>2</sub> UO<sub>3</sub> decomposes into ].<ref name="wheeler">{{cite journal|vauthors=Wheeler VJ, Dell RM, Wait E|title= Uranium trioxide and the UO<sub>3</sub> hydrates|journal=Journal of Inorganic and Nuclear Chemistry|year=1964|volume=26|issue=11|pages= 1829–1845|doi=10.1016/0022-1902(64)80007-5}}</ref> |
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# ], UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>·6H<sub>2</sub>O can be heated to yield UO<sub>3</sub>. This occurs during the ]. Fuel rods are dissolved in ] to separate ] from ] and the fission products (the ] method). The pure uranyl nitrate is converted to solid UO<sub>3</sub> by heating at 400 °C. After reduction with hydrogen (with other inert gas present) to ], the uranium can be used in new ] rods. |
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# ], UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>·6H<sub>2</sub>O can be heated to yield UO<sub>3</sub>. This occurs during the ]. Fuel rods are dissolved in ] to separate ] from ] and the fission products (the ] method). The pure uranyl nitrate is converted to solid UO<sub>3</sub> by heating at 400 °C. After reduction with hydrogen (with other inert gas present) to ], the uranium can be used in new ] rods. |
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# ] or ] (Na<sub>2</sub>U<sub>2</sub>O<sub>7</sub>·6H<sub>2</sub>O) may be decomposed. ], also known as ], is converted to uranium trioxide in the ]. ] and ] are intermediates in the process which ends in ].<ref>{{cite journal|author= Dell RM, Wheeler VJ|title= Chemical Reactivity of Uranium Trioxide Part 1. — Conversion to U<sub>3</sub>O<sub>8</sub>, UO<sub>2</sub> and UF<sub>4</sub>| journal= Transactions of the Faraday Society|year= 1962|volume= 58|pages= 1590–1607|doi= 10.1039/TF9625801590}}</ref> |
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# ] or ] (Na<sub>2</sub>U<sub>2</sub>O<sub>7</sub>·6H<sub>2</sub>O) may be decomposed. ], also known as ], is converted to uranium trioxide in the ]. ] and ] are intermediates in the process which ends in ].<ref>{{cite journal|vauthors=Dell RM, Wheeler VJ |title= Chemical Reactivity of Uranium Trioxide Part 1. — Conversion to U<sub>3</sub>O<sub>8</sub>, UO<sub>2</sub> and UF<sub>4</sub>|journal=Transactions of the Faraday Society|year=1962|volume= 58|pages= 1590–1607|doi=10.1039/TF9625801590}}</ref> |
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Uranium trioxide is shipped between processing facilities in the form of a gel. |
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Uranium trioxide is shipped between processing facilities in the form of a gel, most often from ] to conversion plants. |
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], which operates at the world's largest uranium refinery at ], produces high-purity uranium trioxide. |
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], which operates at the world's largest uranium refinery at ], produces high-purity uranium trioxide. |
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It has been reported that the corrosion of uranium in a silica rich aqueous solution forms both ] and uranium trioxide.<ref>Trueman ER, Black S, Read D, Hodson ME (2003) "Alteration of Depleted Uranium Metal" ''Goldschmidt Conference Abstracts,'' p. A493 </ref> In pure water, ] (UO<sub>2</sub>)<sub>8</sub>O<sub>2</sub>(OH)<sub>12</sub>·12(H<sub>2</sub>O) is formed<ref>. Webmineral.com. Retrieved on 2011-07-19.</ref> in the first week and then after four months ] (UO<sub>2</sub>)O<sub>2</sub>·4(H<sub>2</sub>O) was produced. Reports on the corrosion of uranium metal have been published by the ].<ref>Ander L, Smith B (2002) "" ''The health hazards of depleted uranium munitions, part II'' (London: The Royal Society)</ref><ref>Smith B (2002) "" ''The health hazards of depleted uranium munitions, part II'' (London: The Royal Society)</ref> |
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It has been reported that the corrosion of uranium in a silica rich aqueous solution forms ], uranium trioxide,<ref>Trueman ER, Black S, Read D, Hodson ME (2003) "Alteration of Depleted Uranium Metal" ''Goldschmidt Conference Abstracts,'' p. A493 </ref> and ].<ref>{{cite journal|vauthors= Guo X, Szenknect S, Mesbah A, Labs S, Clavier N, Poinssot C, Ushakov SV, Curtius H, Bosbach D, Rodney RC, Burns P, Navrotsky A|title=Thermodynamics of Formation of Coffinite, USiO4|journal=Proc. Natl. Acad. Sci. USA|year=2015|volume=112|issue= 21|pages= 6551–6555|doi=10.1073/pnas.1507441112|pmid=25964321|pmc=4450415|bibcode=2015PNAS..112.6551G|doi-access=free}}</ref> In pure water, ] (UO<sub>2</sub>)<sub>8</sub>O<sub>2</sub>(OH)<sub>12</sub>·12(H<sub>2</sub>O) is formed<ref>. Webmineral.com. Retrieved on 2011-07-19.</ref> in the first week and then after four months ] (UO<sub>2</sub>)O<sub>2</sub>·4(H<sub>2</sub>O) was produced. This alteration of uranium oxide also leads to the formation of ],<ref>{{cite journal|author1=Weck P. F.|author2=Kim E. |author3=Jove-Colon C. F. |author4=Sassani D. C |title=Structures of uranyl peroxide hydrates: a first-principles study of studtite and metastudtite|journal=Dalton Trans|year= 2012|volume= 111|issue= 41|pages= 9748–52| doi= 10.1039/C2DT31242E|pmid=22763414|url=https://zenodo.org/record/1230018 }}</ref><ref>{{cite journal|vauthors= Guo X, Ushakov SV, Labs S, Curtius H, Bosbach D, Navrotsky A |title= Energetics of Metastudtite and Implications for Nuclear Waste Alteration|journal=Proc. Natl. Acad. Sci. USA|year=2015|volume=111|issue=20|pages=17737–17742|doi=10.1073/pnas.1421144111|pmid=25422465|pmc=4273415|doi-access= free}}</ref> a more stable uranyl peroxide, often found in the surface of spent nuclear fuel exposed to water. Reports on the corrosion of uranium metal have been published by the ].<ref>Ander L, Smith B (2002) "" ''The health hazards of depleted uranium munitions, part II'' (London: The Royal Society)</ref><ref>Smith B (2002) "" ''The health hazards of depleted uranium munitions, part II'' (London: The Royal Society)</ref> |
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==Health and safety hazards== |
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== Health and safety hazards == |
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Like all hexavalent uranium compounds, UO<sub>3</sub> is hazardous by inhalation, ingestion, and through skin contact. It is a poisonous, slightly radioactive substance, which may cause shortness of breath, coughing, acute arterial lesions, and changes in the chromosomes of ]s and ] leading to ] if inhaled.<ref name="morrow">{{cite journal|author= Morrow, PE, Gibb FR, Beiter HD|title= Inhalation studies of uranium trioxide|journal= Health Physics|year= 1972|volume= 23|pages= 273–280|doi= 10.1097/00004032-197209000-00001|pmid= 4642950|issue= 3}} </ref><ref>{{cite journal|author= Sutton M, Burastero SR|title= Uranium(VI) solubility and speciation in simulated elemental human biological fluids|journal= Chemical Research in Toxicology|year= 2004| volume= 17| pages= 1468–1480| doi= 10.1021/tx049878k|pmid= 15540945|issue= 11}}</ref> However, once ingested, uranium is mainly toxic for the ]s and may severely affect their function. |
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Like all hexavalent uranium compounds, UO<sub>3</sub> is hazardous by inhalation, ingestion, and through skin contact. It is a poisonous, slightly radioactive substance, which may cause shortness of breath, coughing, acute arterial lesions, and changes in the chromosomes of ]s and ] leading to ] if inhaled.<ref name="morrow">{{cite journal|vauthors=Morrow PE, Gibb FR, Beiter HD|title= Inhalation studies of uranium trioxide|journal= Health Physics|year= 1972|volume= 23|pages= 273–280|doi= 10.1097/00004032-197209000-00001|pmid= 4642950|issue= 3|s2cid= 39514654}} </ref><ref>{{cite journal|vauthors=Sutton M, Burastero SR|title=Uranium(VI) solubility and speciation in simulated elemental human biological fluids|journal=]|year= 2004| volume= 17|pages=1468–1480| doi=10.1021/tx049878k|pmid=15540945|issue=11}}</ref> However, once ingested, uranium is mainly toxic for the ]s and may severely affect their function. |
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==Structure== |
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== Structure == |
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===Solid state structure=== |
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The only well characterized binary trioxide of any ] is UO<sub>3</sub>, of which several ] are known. Solid UO<sub>3</sub> loses O<sub>2</sub> on heating to give green-colored ]: reports of the decomposition temperature in air vary from 200–650 °C. Heating at 700 °C under H<sub>2</sub> gives dark brown ] (UO<sub>2</sub>), which is used in ] ] rods. |
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====Alpha==== |
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=== Solid state structure === |
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The only well characterized binary trioxide of any ] is UO<sub>3</sub>, of which several ] are known. Solid UO<sub>3</sub> loses O<sub>2</sub> on heating to give green-colored ]: reports of the decomposition temperature in air vary from 200 to 650 °C. Heating at 700 °C under H<sub>2</sub> gives dark brown ] (UO<sub>2</sub>), which is used in ] ] rods. |
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''The α (alpha) form: a layered solid where the 2D layers are linked by oxygen atoms (shown in red)'' |
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Hydrated uranyl peroxide formed by the addition of ] to an aqueous solution of ] when heated to 200–225 °C forms an amorphous uranium trioxide which on heating to 400–450 °C will form alpha-uranium trioxide.<ref name="wheeler" /> It has been stated that the presence of nitrate will lower the temperature at which the ] change from the ] form to the alpha form occurs.<ref>{{cite journal|doi= 10.1002/jctb.5010130807|author= Sato T|title=Preparation of uranium peroxide hydrates|journal= Journal of Applied Chemistry|year= 1963|volume= 13|issue= 8|page= 361}}</ref> |
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====Beta==== |
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==== Alpha ==== |
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| ''The α (alpha) form: a layered solid where the 2D layers are linked by oxygen atoms (shown in red)'' |
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| Hydrated uranyl peroxide formed by the addition of ] to an aqueous solution of ] when heated to 200–225 °C forms an amorphous uranium trioxide which on heating to 400–450 °C will form alpha-uranium trioxide.<ref name="wheeler" /> It has been stated that the presence of nitrate will lower the temperature at which the ] change from the ] form to the alpha form occurs.<ref>{{cite journal|doi= 10.1002/jctb.5010130807|author=Sato T|title=Preparation of uranium peroxide hydrates|journal=Journal of Applied Chemistry|year=1963|volume=13|issue=8|pages=361–365}}</ref> |
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''β (beta) UO<sub>3</sub>. This solid has a structure which defeats most attempts to describe it.'' |
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This form can be formed by heating ammonium diuranate, while P.C. Debets and B.O. Loopstra, found four solid phases in the UO<sub>3</sub>-H<sub>2</sub>O-NH<sub>3</sub> system that they could all be considered as being UO<sub>2</sub>(OH)<sub>2</sub>.H<sub>2</sub>O where some of the water has been replaced with ammonia.<ref>{{cite journal|author=Debets PC, Loopstra BO|title=On the Uranates of Ammonium II: X-Ray Investigation of the Compounds in the system NH<sub>3</sub>-UO<sub>3</sub>-H2O|journal= Journal of Inorganic Nuclear Chemistry|year= 1963|volume= 25|issue=8|page= 945|doi=10.1016/0022-1902(63)80027-5}}</ref><ref>{{cite journal|author=Debets PC|title=The Structure of β-UO3|journal= Acta Crystallographica|year= 1966|volume= 21|issue=4|page= 589 |doi =10.1107/S0365110X66003505}}</ref> No matter what the exact stoichiometry or structure, it was found that ] at 500°C in air forms the beta form of uranium trioxide.<ref name="wheeler" /> |
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====Gamma==== |
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==== Beta ==== |
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| ''The β (beta) UO<sub>3</sub> form: This solid contains multiple unique uranium sites and distorted polyhedra.'' |
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| This form can be formed by heating ammonium diuranate, while P.C. Debets and B.O. Loopstra, found four solid phases in the UO<sub>3</sub>-H<sub>2</sub>O-NH<sub>3</sub> system that they could all be considered as being UO<sub>2</sub>(OH)<sub>2</sub>·H<sub>2</sub>O where some of the water has been replaced with ammonia.<ref>{{cite journal|vauthors=Debets PC, Loopstra BO |title=On the Uranates of Ammonium II: X-Ray Investigation of the Compounds in the system NH<sub>3</sub>-UO<sub>3</sub>-H<sub>2</sub>O|journal=Journal of Inorganic and Nuclear Chemistry|year=1963|volume=25|issue=8|pages=945–953|doi=10.1016/0022-1902(63)80027-5}}</ref><ref>{{cite journal|author=Debets PC|title=The Structure of β-UO3|journal=Acta Crystallographica|year=1966|volume=21|issue=4|pages=589–593 |doi =10.1107/S0365110X66003505|bibcode=1966AcCry..21..589D }}</ref> It was found that ] at 500 °C in air forms the beta form of uranium trioxide.<ref name="wheeler" /> Later experiments found the most reliable method for synthesizing pure β-UO<sub>3</sub> was to calcinate uranyl nitrate hexahydrate at 450 °C for 6 days and cool slowly over 24 hours.<ref>{{cite journal |last1=Spano |first1=Tyler |last2=Shields |first2=Ashley |last3=Barth |first3=Brodie |last4=Gruidl |first4=Jeremiah |last5=Niedziela |first5=Jennifer |last6=Kapsimalis |first6=Roger |last7=Miskowiec |first7=Andrew |title=Computationally Guided Investigation of the Optical Spectra of Pure β-UO3 |journal=Inorganic Chemistry |date=2020 |volume=59 |issue=16 |pages=11481–11492 |doi=10.1021/acs.inorgchem.0c01279 |pmid=32706579 |osti=1649257 |s2cid=220746556 |url=https://www.osti.gov/biblio/1649257}}</ref> |
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''The γ (gamma) form, with the different uranium environments in green and yellow'' |
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The most frequently encountered polymorph is γ-UO<sub>3</sub>, whose ] has been solved from powder diffraction data. The compound crystallizes in the space group ''I4<sub>1</sub>/amd'' with two uranium atoms in the asymmetric unit. Both are surrounded by somewhat distorted octahedra of oxygen atoms. One uranium atom has two closer and four more distant oxygen atoms whereas the other has four close and two more distant oxygen atoms as neighbors. Thus it is not incorrect to describe the structure as <sup>2+</sup><sup>2- </sup>, that is uranyl uranate.<ref>{{cite journal|author= Engmann R, de Wolff PM| title= The Crystal Structure of γ-UO<sub>3</sub>|journal=Acta Crystallographica|year= 1963|volume=16|issue= 10|page=993| doi= 10.1107/S0365110X63002656}}</ref> |
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==== Gamma ==== |
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| ''The γ (gamma) form: with the different uranium environments in green and yellow'' |
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| The most frequently encountered polymorph is γ-UO<sub>3</sub>, whose ] has been solved from powder diffraction data. The compound crystallizes in the space group ''I4<sub>1</sub>/amd'' with two uranium atoms in the asymmetric unit. Both are surrounded by somewhat distorted octahedra of oxygen atoms. One uranium atom has two closer and four more distant oxygen atoms whereas the other has four close and two more distant oxygen atoms as neighbors. Thus it is not incorrect to describe the structure as <sup>2+</sup><sup>2− </sup>, that is uranyl uranate.<ref>{{cite journal|vauthors=Engmann R, de Wolff PM|title=The Crystal Structure of γ-UO<sub>3</sub>|journal=Acta Crystallographica|year= 1963|volume=16|issue=10|pages=993–996|doi=10.1107/S0365110X63002656|url=http://journals.iucr.org/q/issues/1963/10/00/a03972/a03972.pdf|doi-access=free}}</ref> |
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''The environment of the uranium atoms shown as yellow in the gamma form'' |
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| ] |
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<td> |
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| ''The environment of the uranium atoms shown as yellow in the gamma form'' |
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] |
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| ] |
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</td> |
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| ''The chains of U<sub>2</sub>O<sub>2</sub> rings in the gamma form in layers, alternate layers running at 90 degrees to each other. These chains are shown as containing the yellow uranium atoms, in an octahedral environment which are distorted towards square planar by an elongation of the ] ]-] bonds.'' |
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<td> |
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|} |
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''The chains of U<sub>2</sub>O<sub>2</sub> rings in the gamma form in layers, alternate layers running at 90 degrees to each other. These chains are shown as containing the yellow uranium atoms, in an octahedral environment which are distorted towards square planar by an elongation of the ] ]-] bonds.'' |
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</td> |
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</table> |
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====Delta==== |
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==== Delta ==== |
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<table border="1" cellpadding="3" cellspacing="0"> |
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{| border="1" cellpadding="3" cellspacing="0" |
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| ] |
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<td> |
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|
| ''The delta (δ) form is a ] solid where the oxygen atoms are arranged between the uranium atoms.''<ref>{{cite journal|author1=M. T. Weller|author2=P. G. Dickens|author3=D. J. Penny|year=1988|title=The structure of δ-UO<sub>3></sub> |journal=Polyhedron|volume=7|issue=3|pages=243–244|doi=10.1016/S0277-5387(00)80559-8}}</ref> |
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] |
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|} |
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</td> |
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<td> |
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==== Epsilon ==== |
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''The delta (δ) form is a ] solid where the oxygen atoms are arranged between the uranium atoms.''<ref>{{cite journal|author=M. T. Weller, P. G. Dickens, D. J. Penny |year=1988 |title=The structure of δ-UO<sub>3></sub> |journal=Polyhedron |volume=7|issue=3 |pages=243–244|doi=10.1016/S0277-5387(00)80559-8}}</ref> |
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{| border="1" cellpadding="3" cellspacing="0" |
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</td> |
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| |
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</tr> |
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] |
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</table> |
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| ''The proposed crystal structure of the epsilon (ε) form consists of sheets of uranium hexagonal bipyramids connected through edge-sharing polyhedra. These sheets are connected through the axial uranyl oxygen atoms. The proposed structure is in the ] ''P-1'' space group.''<ref>{{cite journal |last1=Spano |first1=Tyler |last2=Hunt |first2=Rodney |last3=Kapsimalis |first3=Roger |last4=Niedziela |first4=Jennifer |last5=Shields |first5=Ashley |last6=Miskowiec |first6=Andrew |title=Optical vibrational spectra and proposed crystal structure of ε-UO3 |journal=Journal of Nuclear Materials |date=2022 |volume=559 |page=153386 |doi=10.1016/j.jnucmat.2021.153386 |osti=1843704 |s2cid=244423124 |url=https://www.sciencedirect.com/science/article/pii/S0022311521006061#sec0011}}</ref> |
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====High pressure form==== |
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==== High pressure form ==== |
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There is a high-pressure solid form with U<sub>2</sub>O<sub>2</sub> and U<sub>3</sub>O<sub>3</sub> rings in it.<ref> |
|
There is a high-pressure solid form with U<sub>2</sub>O<sub>2</sub> and U<sub>3</sub>O<sub>3</sub> rings in it.<ref>{{cite journal|vauthors=Siegel S, Hoekstra HR, Sherry E |year=1966 |title=The crystal structure of high-pressure UO<sub>3</sub>|journal=Acta Crystallographica|volume=20|issue=2|pages=292–295 |doi=10.1107/S0365110X66000562|bibcode=1966AcCry..20..292S }}</ref> |
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{{cite journal| author=Siegel S, Hoekstra HR, Sherry E |year=1966 |title=The crystal structure of high-pressure UO<sub>3</sub>|journal=Acta Crystallographica |volume=20| issue=2 |pages=292–295 |doi=10.1107/S0365110X66000562}}</ref> |
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|
<ref>''Gmelin Handbuch'' (1982) '''U-C1,''' 129–135.</ref> |
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<ref>''Gmelin Handbuch'' (1982) '''U-C1,''' 129–135.</ref> |
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====Hydrates==== |
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==== Hydrates ==== |
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<gallery> |
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] |
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Uranium Trioxides.jpg|Hydrous and anhydrous forms of UO<sub>3</sub> |
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Several ] of uranium trioxide are known, e.g., UO<sub>3</sub>·6H<sub>2</sub>O.<ref name="wheeler" /> |
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UO3 Anhydrous.jpg|Anhydrous forms of UO<sub>3</sub> |
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</gallery> |
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Several ] of uranium trioxide are known, e.g., UO<sub>3</sub>·6H<sub>2</sub>O, which are commonly known as "uranic acid" in older literature due to their similarity in formula to various metal ], although they are not in fact particularly acidic.<ref name="wheeler" /> |
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===Bond valence parameters=== |
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It is possible by ] calculations<ref>. Kristall.uni-mki.gwdg.de. Retrieved on 2011-07-19.</ref> to estimate how great a contribution a given oxygen atom is making to the assumed valence of uranium.<ref>{{cite journal|author=Zachariasen|journal=J. Less Common Metals|year=1978|volume=62|pages= 1–7|doi=10.1016/0022-5088(78)90010-3|title=Bond lengths in oxygen and halogen compounds of d and f elements}}</ref> Bond valence calculations use parameters which are estimated after examining a large number of crystal structures of uranium oxides (and related uranium compounds), note that the oxidation states which this method provides are only a guide which assists in the understanding of a crystal structure. |
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=== Molecular forms === |
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The formula to use is |
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<center> |
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<math> |
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s = e^{-\frac{R-R_O}{B}} |
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</math> |
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</center> |
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The sum of the ''s'' values is equal to the oxidation state of the metal centre. |
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For uranium binding to oxygen the constants R<sub>O</sub> and B are tabulated in the table below. For each oxidation state use the parameters from the table shown below. |
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{| style="margin:auto;" |
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|- |
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!Oxidation state!!R<sub>O</sub>!!B |
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|U(VI)||2.08 Å||0.35 |
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|- |
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|U(V)||2.10 Å||0.35 |
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|- |
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|U(IV)||2.13 Å||0.35 |
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|} |
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It is possible to do these calculations on paper or software.<ref>. Ccp14.ac.uk. Retrieved on 2011-07-19.</ref><ref>. Ccp14.ac.uk (2001-08-13). Retrieved on 2011-07-19.</ref> |
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===Molecular forms=== |
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While uranium trioxide is encountered as a polymeric solid under ambient conditions, some work has been done on the molecular form in the gas phase, in matrix isolations studies, and computationally. |
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While uranium trioxide is encountered as a polymeric solid under ambient conditions, some work has been done on the molecular form in the gas phase, in matrix isolations studies, and computationally. |
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====Gas phase==== |
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==== Gas phase ==== |
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At elevated temperatures gaseous UO<sub>3</sub> is in ] with solid ] and molecular ]. |
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At elevated temperatures gaseous UO<sub>3</sub> is in ] with solid ] and molecular ]. |
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::2 U<sub>3</sub>O<sub>8</sub>(s) + O<sub>2</sub>(g) {{eqm}} 6 UO<sub>3</sub>(g) |
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::2 U<sub>3</sub>O<sub>8</sub>(s) + O<sub>2</sub>(g) {{eqm}} 6 UO<sub>3</sub>(g) |
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With increasing temperature the equilibrium is shifted to the right. This system has been studied at temperatures between 900 °C and 2500 °C. The vapor pressure of monomeric UO<sub>3</sub> in equilibrium with air and solid U<sub>3</sub>O<sub>8</sub> at ambient pressure, about 10<sup>−5</sup> mbar (1 mPa) at 980 °C, rising to 0.1 mbar (10 Pa) at 1400 °C, 0.34 mbar (34 Pa) at 2100 °C, 1.9 mbar (193 Pa) at 2300 °C, and 8.1 mbar (809 Pa) at 2500 °C.<ref>{{cite journal|author= Ackermann RJ, Gilles PW, Thorn RJ|title= High-Temperature Thermodynamic Properties of Uranium Dioxide|journal= Journal of Chemical Physics|year= 1956|volume= 25|issue= 6| page= 1089|doi= 10.1063/1.1743156}}</ref><ref>{{cite journal|author= Alexander CA|title= Volatilization of urania under strongly oxidizing conditions|journal= Journal of Nuclear Materials|year= 2005|volume= 346|issue= 2–3|pages= 312–318| doi= 10.1016/j.jnucmat.2005.07.013}}</ref> |
|
With increasing temperature the equilibrium is shifted to the right. This system has been studied at temperatures between 900 °C and 2500 °C. The vapor pressure of monomeric UO<sub>3</sub> in equilibrium with air and solid U<sub>3</sub>O<sub>8</sub> at ambient pressure, about 10<sup>−5</sup> mbar (1 mPa) at 980 °C, rising to 0.1 mbar (10 Pa) at 1400 °C, 0.34 mbar (34 Pa) at 2100 °C, 1.9 mbar (193 Pa) at 2300 °C, and 8.1 mbar (809 Pa) at 2500 °C.<ref>{{cite journal|vauthors=Ackermann RJ, Gilles PW, Thorn RJ|title=High-Temperature Thermodynamic Properties of Uranium Dioxide|journal=Journal of Chemical Physics|year= 1956|volume=25|issue=6|page=1089|doi=10.1063/1.1743156|bibcode=1956JChPh..25.1089A}}</ref><ref>{{cite journal|author=Alexander CA|title=Volatilization of urania under strongly oxidizing conditions|journal=Journal of Nuclear Materials|year=2005|volume=346|issue=2–3|pages=312–318|doi=10.1016/j.jnucmat.2005.07.013|bibcode=2005JNuM..346..312A}}</ref> |
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====Matrix isolation==== |
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==== Matrix isolation ==== |
|
Infrared spectroscopy of molecular UO<sub>3</sub> isolated in an argon matrix indicates a T-shaped structure (] ''C<sub>2v</sub>'') for the molecule. This is in contrast to the commonly encountered ''D<sub>3h</sub>'' ] exhibited by most trioxides. From the force constants the authors deduct the U-O bond lengths to be between 1.76 and 1.79 ] (176 to 179 ]).<ref>{{cite journal|author= Gabelnick SD, Reedy GT, Chasanov MG| title= Infrared spectra of matrix-isolated uranium oxide species. II: Spectral interpretation and structure of UO<sub>3</sub>|journal= Journal of Chemical Physics|year= 1973|volume= 59|issue= 12|pages= 6397–6404|doi= 10.1063/1.1680018}}</ref> |
|
Infrared spectroscopy of molecular UO<sub>3</sub> isolated in an argon matrix indicates a T-shaped structure (] ''C<sub>2v</sub>'') for the molecule. This is in contrast to the commonly encountered ''D<sub>3h</sub>'' ] exhibited by most trioxides. From the force constants the authors deduct the U-O bond lengths to be between 1.76 and 1.79 ] (176 to 179 ]).<ref>{{cite journal|vauthors=Gabelnick SD, Reedy GT, Chasanov MG | title=Infrared spectra of matrix-isolated uranium oxide species. II: Spectral interpretation and structure of UO<sub>3</sub>|journal= Journal of Chemical Physics|year=1973|volume=59|issue=12|pages=6397–6404|doi=10.1063/1.1680018| bibcode=1973JChPh..59.6397G}}</ref> |
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====Computational study==== |
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==== Computational study ==== |
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] |
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] |
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Calculations predict that the point group of molecular UO<sub>3</sub> is ''C<sub>2v</sub>'', with an axial bond length of 1.75 Å, an equatorial bond length of 1.83 Å and an angle of 161 ° between the axial oxygens. The more symmetrical ''D<sub>3h</sub>'' species is a saddle point, 49 kJ/mol above the ''C<sub>2v</sub>'' minimum. The authors invoke a second-order ] as explanation.<ref>{{cite journal|author= Pyykkö P, Li J|title= Quasirelativistic pseudopotential study of species isoelectronic to uranyl and the equatorial coordination of uranyl|journal= Journal of Physical Chemistry|year= 1994|volume= 98|issue= 18|pages= 4809–4813|doi = 10.1021/j100069a007}}</ref> |
|
Calculations predict that the point group of molecular UO<sub>3</sub> is ''C<sub>2v</sub>'', with an axial bond length of 1.75 Å, an equatorial bond length of 1.83 Å and an angle of 161° between the axial oxygens. The more symmetrical ''D<sub>3h</sub>'' species is a saddle point, 49 kJ/mol above the ''C<sub>2v</sub>'' minimum. The authors invoke a second-order ] as explanation.<ref>{{cite journal|vauthors=Pyykkö P, Li J |title= Quasirelativistic pseudopotential study of species isoelectronic to uranyl and the equatorial coordination of uranyl|journal= Journal of Physical Chemistry|year= 1994|volume= 98|issue= 18|pages= 4809–4813|doi = 10.1021/j100069a007}}</ref> |
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=== Cubic form of uranium trioxide === |
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==Reactivity== |
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|
The crystal structure of a uranium trioxide phase of composition UO<sub>2·82</sub> has been determined by X-ray powder diffraction techniques using a Guinier-type focusing camera. The unit cell is cubic with a = 4·138 ± 0·005 kX. A uranium atom is located at (000) and oxygens at (View the MathML source), (View the MathML source), and (View the MathML source) with some anion vacancies. The compound is isostructural with ReO<sub>3</sub>. The U-O bond distance of 2·073 Å agrees with that predicted by Zachariasen for a bond strength S = 1.<ref>{{cite journal|doi=10.1016/0022-1902(55)80036-X|volume=1|issue=4–5|title=A cubic form of uranium trioxide|journal=Journal of Inorganic and Nuclear Chemistry|pages=309–312|year=1955|last1=Wait|first1=E.}}</ref> |
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Uranium trioxide reacts at 400 °C with ] to form ], ], ] and ]. The freon-12 can be replaced with ] which forms ] instead of carbon dioxide. This is a case of a hard perhalogenated ] which is normally considered to be inert being converted chemically at a moderate temperature.<ref>{{cite journal|author= Booth HS, Krasny-Ergen W, Heath RE| title= Uranium Tetrafluoride|journal= ]|year= 1946|volume= 68|issue= 10|pages= 1969–1970| doi= 10.1021/ja01214a028}}</ref> |
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== Reactivity == |
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|
Uranium trioxide reacts at 400 °C with ] to form ], ], ] and ]. The freon-12 can be replaced with ] which forms ] instead of carbon dioxide. This is a case of a hard perhalogenated ] which is normally considered to be inert being converted chemically at a moderate temperature.<ref>{{cite journal|vauthors=Booth HS, Krasny-Ergen W, Heath RE |title=Uranium Tetrafluoride|journal=]|year=1946|volume=68|issue=10|pages=1969–1970|doi=10.1021/ja01214a028|bibcode=1946JAChS..68.1969B }}</ref> |
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:2 CF<sub>2</sub>Cl<sub>2</sub> + UO<sub>3</sub> → UF<sub>4</sub> + CO<sub>2</sub> + COCl<sub>2</sub> + Cl<sub>2</sub> |
|
:2 CF<sub>2</sub>Cl<sub>2</sub> + UO<sub>3</sub> → UF<sub>4</sub> + CO<sub>2</sub> + COCl<sub>2</sub> + Cl<sub>2</sub> |
| Line 200: |
Line 162: |
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:4 CFCl<sub>3</sub> + UO<sub>3</sub> → UF<sub>4</sub> + 3 COCl<sub>2</sub> + CCl<sub>4</sub> + Cl<sub>2</sub> |
|
:4 CFCl<sub>3</sub> + UO<sub>3</sub> → UF<sub>4</sub> + 3 COCl<sub>2</sub> + CCl<sub>4</sub> + Cl<sub>2</sub> |
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Uranium trioxide can be dissolved in a mixture of ] and ] in ], ultrasound was employed during the dissolution.<ref>{{cite journal|author= Trofimov TI, Samsonov MD, Lee SC, Myasoedov BF, Wai CM|title= Dissolution of uranium oxides in supercritical carbon dioxide containing tri-''n''-butyl phosphate and thenoyltrifluoroacetone|journal= Mendeleev Communications|year= 2001|volume= 11|issue= 4|pages= 129–130|doi= 10.1070/MC2001v011n04ABEH001468}}</ref> |
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Uranium trioxide can be dissolved in a mixture of ] and ] in ], ultrasound was employed during the dissolution.<ref>{{cite journal|vauthors=Trofimov TI, Samsonov MD, Lee SC, Myasoedov BF, Wai CM |title=Dissolution of uranium oxides in supercritical carbon dioxide containing tri-''n''-butyl phosphate and thenoyltrifluoroacetone|journal=Mendeleev Communications|year=2001|volume=11|issue=4|pages=129–130|doi=10.1070/MC2001v011n04ABEH001468}}</ref> |
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===Electrochemical modification=== |
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=== Electrochemical modification === |
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The reversible insertion of ] cations into the ] of uranium trioxide by ] using a ] electrode modified with microscopic particles of the uranium oxide has been investigated. This experiment has also been done for U<sub>3</sub>O<sub>8</sub>. This is an example of ] of a solid modified ], the experiment which used for uranium trioxide is related to a ] experiment. It is also possible to reduce uranium trioxide with ] metal to form sodium uranium oxides.<ref>{{cite journal|doi=10.1149/1.2221232|title=Investigation of the Mechanism of Formation of Insertion Compounds of Uranium Oxides by Voltammetric Reduction of the Solid Phase after Mechanical Transfer to a Carbon Electrode|year=1992|last1=Dueber|first1=R. E.|journal=Journal of the Electrochemical Society|volume=139|issue=9|pages=2363}}</ref> |
|
The reversible insertion of ] cations into the ] of uranium trioxide by ] using a ] electrode modified with microscopic particles of the uranium oxide has been investigated. This experiment has also been done for U<sub>3</sub>O<sub>8</sub>. This is an example of ] of a solid modified ], the experiment which used for uranium trioxide is related to a ] experiment. It is also possible to reduce uranium trioxide with ] metal to form sodium uranium oxides.<ref>{{cite journal|doi=10.1149/1.2221232|title=Investigation of the Mechanism of Formation of Insertion Compounds of Uranium Oxides by Voltammetric Reduction of the Solid Phase after Mechanical Transfer to a Carbon Electrode|year=1992|last1=Dueber|first1=R. E.|journal=Journal of the Electrochemical Society|volume=139|issue=9|pages=2363–2371|bibcode=1992JElS..139.2363D}}</ref> |
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It has been the case that it is possible to insert ]<ref>{{cite journal|title =Insertion compounds of uranium oxides| author = Dickens PG, Lawrence SD, Penny DJ, Powell AV| year= 1989| volume= 32–33| doi=10.1016/0167-2738(89)90205-1|pages =77–83|journal =Solid State Ionics}} |
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It has been the case that it is possible to insert ]<ref>{{cite journal|title=Insertion compounds of uranium oxides|vauthors=Dickens PG, Lawrence SD, Penny DJ, Powell AV|year=1989| volume=32–33|doi=10.1016/0167-2738(89)90205-1|pages =77–83|journal=Solid State Ionics}}</ref><ref>{{cite journal|title=Lithium insertion into αUO<sub>3</sub> and U<sub>3</sub>O<sub>8</sub> |vauthors=Dickens PG, Hawke SV, Weller MT | year=1985 |volume=20 |doi=10.1016/0025-5408(85)90141-2 |issue=6 |pages=635–641 |journal =Materials Research Bulletin }}</ref><ref>{{cite journal|title=Hydrogen insertion compounds of UO<sub>3</sub>|vauthors=Dickens PG, Hawke SV, Weller MT|year=1984|volume=19|doi=10.1016/0025-5408(84)90120-X|issue=5|pages=543–547|journal =Materials Research Bulletin}}</ref> into the uranium trioxide lattice by electrochemical means, this is similar to the way that some ] ] work. In these rechargeable cells one of the electrodes is a metal oxide which contains a metal such as ] which can be reduced, to maintain the electroneutrality for each electron which is added to the electrode material a lithium ion enters the lattice of this oxide electrode. |
|
</ref><ref>{{cite journal|title =Lithium insertion into αUO<sub>3</sub> and U<sub>3</sub>O<sub>8</sub>| author = Dickens, P.G. Hawke, S.V. Weller, M.T.| year= 1985| volume= 20| doi=10.1016/0025-5408(85)90141-2|issue =6|pages =635–641|journal =Materials Research Bulletin}}</ref><ref>{{cite journal|title =Hydrogen insertion compounds of UO<sub>3</sub>|author = Dickens, P.G. Hawke, S.V. Weller, M.T.| year= 1984| volume= 19| doi=10.1016/0025-5408(84)90120-X|issue =5|pages =543–547|journal =Materials Research Bulletin}}</ref> into the uranium trioxide lattice by electrochemical means, this is similar to the way that some ] ] work. In these rechargeable cells one of the electrodes is a metal oxide which contains a metal such as ] which can be reduced, to maintain the electroneutrality for each electron which is added to the electrode material a lithium ion enters the lattice of this oxide electrode. |
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===Amphoterism and reactivity to form related uranium(VI) anions and cations=== |
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=== Amphoterism and reactivity to form related uranium(VI) anions and cations === |
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Uranium oxide is ] and reacts as ] and as a ], depending on the conditions. |
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Uranium oxide is ] and reacts as ] and as a ], depending on the conditions. |
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;As an acid: |
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====As an acid==== |
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:UO<sub>3</sub> + H<sub>2</sub>O → {{chem|UO|4|2−}} + 2 H<sup>+</sup> |
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:UO<sub>3</sub> + H<sub>2</sub>O → {{chem|UO|4|2−}} + 2 H<sup>+</sup> |
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Dissolving uranium oxide in a strong ] like ] forms the doubly negatively charged ] ] ({{chem|UO|4|2−}}). Uranates tend to concatenate, forming ], {{chem|U|2|O|7|2−}}, or other poly-uranates. |
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Dissolving uranium oxide in a strong ] like ] forms the doubly negatively charged ] ] ({{chem|UO|4|2−}}). Uranates tend to concatenate, forming ], {{chem|U|2|O|7|2−}}, or other poly-uranates. |
|
Important diuranates include ] ((NH<sub>4</sub>)<sub>2</sub>U<sub>2</sub>O<sub>7</sub>), ] (Na<sub>2</sub>U<sub>2</sub>O<sub>7</sub>) and |
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Important diuranates include ] ((NH<sub>4</sub>)<sub>2</sub>U<sub>2</sub>O<sub>7</sub>), ] (Na<sub>2</sub>U<sub>2</sub>O<sub>7</sub>) and |
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] (MgU<sub>2</sub>O<sub>7</sub>), which forms part of some ]s. It is worth noting that uranates of the form M<sub>2</sub>UO<sub>4</sub> do ''not'' contain {{chem|UO|4|2−}} ions, but rather flattened UO<sub>6</sub> octahedra, containing a uranyl group and bridging oxygens.<ref>{{cite book|last= Cotton|first= Simon|year = 1991|title = Lanthanides and Actinides|publisher= Oxford University Press|location = New York|page= 128|isbn= 0195073665}}</ref> |
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] (MgU<sub>2</sub>O<sub>7</sub>), which forms part of some ]s. It is worth noting that uranates of the form M<sub>2</sub>UO<sub>4</sub> do ''not'' contain {{chem|UO|4|2−}} ions, but rather flattened UO<sub>6</sub> octahedra, containing a uranyl group and bridging oxygens.<ref>{{cite book|last= Cotton|first= Simon|year=1991|title=Lanthanides and Actinides|publisher=Oxford University Press|location=New York|page=128|isbn=978-0-19-507366-9}}</ref> |
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;As a base: |
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====As a base==== |
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:UO<sub>3</sub> + H<sub>2</sub>O → {{chem|UO|2|2+}} + 2 OH<sup>−</sup> |
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:UO<sub>3</sub> + H<sub>2</sub>O → {{chem|UO|2|2+}} + 2 OH<sup>−</sup> |
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Dissolving uranium oxide in a strong acid like ] or ] forms the double positive charged ] ]. The ] formed (UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>·6H<sub>2</sub>O) is soluble in ]s, ]s, ]s and ]s; for example, ]. This solubility is used to separate uranium from other elements in ], which begins with the dissolution of ] rods in ]. The ] is then converted to uranium trioxide by heating. |
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Dissolving uranium oxide in a strong acid like ] or ] forms the double positive charged ] ]. The ] formed (UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>·6H<sub>2</sub>O) is soluble in ]s, ], ]s and ]s; for example, ]. This solubility is used to separate uranium from other elements in ], which begins with the dissolution of ] rods in ] to form this salt. The ] is then converted to uranium trioxide by heating. |
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From ] one obtains ], ''trans''-UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>·2H<sub>2</sub>O, consisting of eight-coordinated uranium with two ] nitrato ligands and two water ligands as well as the familiar O=U=O core. |
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From ] one obtains ], ''trans''-UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>·2H<sub>2</sub>O, consisting of eight-coordinated uranium with two ] nitrato ligands and two water ligands as well as the familiar O=U=O core. |
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==Uranium oxides in ceramics== |
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== Uranium oxides in ceramics == |
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UO<sub>3</sub>-based ceramics become green or black when fired in a reducing atmosphere and yellow to orange when fired with oxygen. Orange-coloured ] is a well-known example of a product with a uranium-based glaze. UO<sub>3</sub>-has also been used in formulations of ], ], and ]. |
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UO<sub>3</sub>-based ceramics become green or black when fired in a reducing atmosphere and yellow to orange when fired with oxygen. Orange-coloured ] is a well-known example of a product with a uranium-based glaze. UO<sub>3</sub>-has also been used in formulations of ], ], and ]. |
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Prior to 1960, UO<sub>3</sub> was used as an agent of crystallization in crystalline coloured glazes. It is possible to determine with a ] if a glaze or glass was made from UO<sub>3</sub>. |
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Prior to 1960, UO<sub>3</sub> was used as an agent of crystallization in crystalline coloured glazes. It is possible to determine with a ] if a glaze or glass was made from UO<sub>3</sub>. |
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==References== |
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== References == |
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{{reflist|2}} |
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{{reflist|30em}} |
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{{Uranium compounds}} |
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{{Uranium compounds}} |
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{{Oxides}} |
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] |
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