Uranium dioxide: Difference between revisions

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 446398737

| = Uranium dioxide

| ImageFile = UO2lattice.jpg

| IUPACName = Uranium dioxide<br/>Uranium(IV) oxide

| OtherNames = Urania<br/>Uranous oxide

| SystematicName =

| Section1 = {{Chembox Identifiers

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = L70487KUZO

| PubChem = 10916

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| ChemSpiderID = 10454

| EC_number = 215-700-3

| StdInChI=1S/2O.U

| StdInChIKey = FCTBKIHDJGHPPO-UHFFFAOYSA-N

| SMILES = O=[U]=O

| Section2 = {{Chembox Properties

| = 2865

| MeltingPt_notes =

| Section3 = {{Chembox Structure

| CrystalStruct = [[Fluorite]] (cubic), [[Pearson symbol|''cF12'']]

| Coordination = Tetrahedral (O); cubic (U^IV)

| LattConst_a = 547.1 pm <ref name=lp>{{cite journal |doi=10.1016/j.jnucmat.2015.01.029 |title=Accurate lattice parameter measurements of stoichiometric uranium dioxide |journal=Journal of Nuclear Materials |volume=459 |pages=135–42 |year=2015 |last1=Leinders |first1=Gregory |last2=Cardinaels |first2=Thomas |last3=Binnemans |first3=Koen |last4=Verwerft |first4=Marc |bibcode=2015JNuM..459..135L |s2cid=97183844 | url=https://zenodo.org/record/884499}}</ref>

| = {{Chembox

| DeltaHf = −1084&nbsp;kJ·mol⁻¹<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 = 78&nbsp;J·mol⁻¹·K⁻¹<ref name=b1/>

}}

| Section5 =

| Section6 =

| Section7 = {{Chembox Hazards

| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics1251.htm ICSC 1251]

| GHSPictograms = {{GHS06}}{{GHS08}}{{GHS09}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|300|330|373|410}}

| PPhrases = {{P-phrases|260|264|270|271|273|284|301+310|304+340|310|314|320|321|330|391|403+233|405|501}}

| NFPA-H = 4

| NFPA-F = 0

| NFPA-R = 0

| NFPA-S =OX

| FlashPt = N/A

| Section8 = {{Chembox Related

| OtherAnions =

| = [[ ]]<br>[[ ]]

| OtherFunction = [[Triuranium octoxide]]<br/>[[Uranium trioxide]]

| OtherFunction_label = [[uranium]] [[oxide]]s

| OtherCompounds =

'''Uranium dioxide''' or '''uranium(IV) oxide ({{}})''', also known as '''urania''' or '''uranous oxide''', is an [[oxide]] of [[uranium]], and is a black, radioactive, powder that naturally occurs in the mineral [[uraninite]]. It is used in [[nuclear fuel]] rods in [[nuclear reactors]]. A mixture of uranium and [[plutonium]] dioxides is used as [[MOX fuel]]. Prior to 1960 it was used as yellow and black color in [[ ceramic ]] and glass.

Uranium dioxide is produced by [[reducing]] [[uranium trioxide]] with [[hydrogen]].

:UO₃ + H₂ → UO₂ + H₂O at 700&nbsp;°C (&nbsp;K)

This reaction part in the [[ nuclear ]] and [[ enrichment]].

The solid is [[isostructural]] with (has the same structure as) [[fluorite]] ([[calcium fluoride]]), where each U is surrounded by eight O nearest neighbors in a cubic arrangement. In addition, the dioxides of [[Cerium(IV) oxide|cerium]], [[thorium]], and the [[Transuranium element|transuranic]] elements from [[neptunium]] through [[californium]] have the same structures.<ref>{{Cite journal |last1=Petit |first1=L. |last2=Svane |first2=A. |last3=Szotek |first3=Z. |last4=Temmerman |first4=W. M. |last5=Stocks |first5=G. M. |date=2010-01-07 |title=Electronic structure and ionicity of actinide oxides from first principles |url=https://link.aps.org/doi/10.1103/PhysRevB.81.045108 |journal=Physical Review B |volume=81 |issue=4 |pages=045108 |doi=10.1103/PhysRevB.81.045108|arxiv=0908.1806 |bibcode=2010PhRvB..81d5108P |s2cid=118365366 }}</ref> No other elemental dioxides have the fluorite structure. Upon melting, the measured average U-O coordination reduces from 8 in the crystalline solid (UO₈ cubes), down to 6.7±0.5 (at 3270 K) in the melt.<ref name = "Skinner2014">{{cite journal |doi=10.1126/science.1259709 |pmid=25414311 |title=Molten uranium dioxide structure and dynamics |journal=Science |volume=346 |issue=6212 |pages=984–7 |year=2014 |last1=Skinner |first1=L. B. |last2=Benmore |first2=C. J. |last3=Weber |first3=J. K. R. |last4=Williamson |first4=M. A. |last5=Tamalonis |first5=A. |last6=Hebden |first6=A. |last7=Wiencek |first7=T. |last8=Alderman |first8=O. L. G. |last9=Guthrie |first9=M. |last10=Leibowitz |first10=L. |last11=Parise |first11=J. B. |bibcode=2014Sci...346..984S |osti=1174101 |s2cid=206561628 |url=https://www.osti.gov/biblio/1174101 }}</ref> Models consistent with these measurements show the melt to consist mainly of UO₆ and UO₇ polyhedral units, where roughly {{frac|2|3}} of the connections between polyhedra are corner sharing and {{frac|1|3}} are edge sharing.<ref name = "Skinner2014"/>

<gallery>

UO2 Powder.jpg|Uranium dioxide

UO2 Pellet.jpg|Sintered uranium dioxide pellet

</gallery>

:3 UO₂ + O₂ → U₃O₈ at 700&nbsp;°C (&nbsp;K)

The [[electrochemistry]] of uranium dioxide has been investigated in detail as the [[galvanic corrosion]] of uranium dioxide controls the rate at which used [[nuclear fuel]] dissolves. See [[spent nuclear fuel]] for further details. [[Water]] increases the oxidation rate of [[plutonium]] and uranium metals.<ref>{{cite |url=http://www.osti.gov/bridge/servlets/purl/756904-DrPADO/webviewable/756904.pdf| title =Reactions of Plutonium Dioxide with Water and Oxygen-Hydrogen Mixtures: Mechanisms for Corrosion of Uranium and Plutonium| =2009-06-06}}</ref>

===Carbonization===

Uranium dioxide is [[Carbonization|carbonized]] in contact with [[carbon]], forming [[uranium carbide]] and [[carbon monoxide]].

:<chem>UO2 \ + \ 4C -> UC2 \ + \ 2CO</chem>.

This process must be done under an [[inert gas]] as uranium carbide is easily oxidized back into [[uranium oxide]].

UO₂ is used mainly as [[nuclear fuel]], specifically as UO₂ or as a mixture of UO₂ and PuO₂ ([[plutonium dioxide]]) called a mixed oxide ([[MOX fuel]]), in the form of [[fuel rod]]s in [[nuclear reactor]]s.

The [[thermal conductivity]] of uranium dioxide is very low when compared with [[uranium]], [[uranium nitride]], [[uranium carbide]] and [[zirconium]] cladding material. This low thermal conductivity can result in localised overheating in the centres of fuel pellets. The graph below shows the different temperature gradients in different fuel compounds. For these fuels, the thermal power density is the same and the diameter of all the pellets are the same.{{citation needed|date=January 2017}}

:ZrUthermalcond.png|The thermal conductivity of zirconium metal and uranium dioxide as a function of temperature

<gallery class="center">

FuelPellet1.jpg|Uranium oxide fuel pellet

RIAN archive 132609 Uranium dioxide fuel pellet starting material.jpg|Starting material containers for uranium dioxide fuel pellet production at a plant in Russia

===Color for glaze===

[[File:FiestaWare Velleman-K2645 GeigerCounter.ogv|thumb|right|Geiger counter (kit without housing) audibly reacting to an orange Fiestaware shard.]]

Uranium oxide (urania) was used to color glass and ceramics prior to World War II, and until the applications of radioactivity were discovered this was its main use. In 1958 the military in both the US and Europe allowed its commercial use again as depleted uranium, and its use began again on a more limited scale. Urania-based ceramic glazes are dark green or black when fired in a reduction or when UO₂ is used; more commonly it is used in oxidation to produce bright yellow, orange and red glazes.<ref>{{Cite book|url=http://www.uranglasuren.com/|title=Uran in der Keramik. Geschichte - Technik - Hersteller|last=Örtel|first=Stefan}}</ref> Orange-colored [[Fiestaware]] is a well-known example of a product with a urania-colored glaze. [[Uranium glass]] is pale green to yellow and often has strong fluorescent properties. Urania has also been used in formulations of [[Vitreous enamel|enamel]] and [[porcelain]]. It is possible to determine with a [[Geiger counter]] if a glaze or glass produced before 1958 contains urania.

===Other uses===

Prior to the realisation of the harmfulness of radiation, uranium was included in false teeth and dentures, as its slight fluorescence made the dentures appear more like real teeth in a variety of lighting conditions.{{fact|date= November 2023}}

[[Depleted uranium|Depleted]] UO₂ (DUO₂) can be used as a material for [[radiation shielding]]. For example, [[DUCRETE]] is a "heavy [[concrete]]" material where [[gravel]] is replaced with uranium dioxide aggregate; this material is investigated for use for [[cask]]s for [[radioactive waste]]. Casks can be also made of DUO₂-[[steel]] [[cermet]], a [[composite material]] made of an [[aggregate (composite)|aggregate]] of uranium dioxide serving as radiation shielding, [[graphite]] and/or [[silicon carbide]] serving as [[neutron radiation]] absorber and moderator, and steel as the matrix, whose high thermal conductivity allows easy removal of decay heat.{{citation needed|date=January 2017}}

Depleted uranium dioxide can be also used as a [[catalyst]], e.g. for degradation of [[volatile organic compound]]s in gaseous phase, [[oxidation]] of [[methane]] to [[methanol]], and removal of [[sulfur]] from [[petroleum]]. It has high efficiency and long-term stability when used to destroy VOCs when compared with some of the commercial [[catalyst]]s, such as [[precious metal]]s, [[titanium dioxide|TiO₂]], and [[cobalt oxide|Co₃O₄]] catalysts. Much research is being done in this area, DU being favoured for the uranium component due to its low radioactivity.<ref>{{cite journal|= |title=Uranium-- for the of - compounds journal=Nature |volume= |issue=6607 pages= |= .|last2=Heneghan|first2=Catherine S.|last3=Hudson|first3=Ian D.|last4= |first4=Stuart H. |bibcode=1996Natur.384..341H }}</ref>

The use of uranium dioxide as a material for [[rechargeable battery|rechargeable batteries]] is being investigated. The batteries could have high [[power density]] and potential of 4.7 V per cell. Another investigated application is in [[photoelectrochemical cell]]s for solar-assisted hydrogen production where UO₂ is used as a [[photoanode]]. In earlier times, uranium dioxide was also used as heat conductor for current limitation (URDOX-resistor), which was the first use of its semiconductor properties.

Uranium dioxide displays strong [[piezomagnetism]] in the [[antiferromagnetic]] state, observed at cryogenic temperatures below 30 [[kelvin]]s. Accordingly, the linear [[magnetostriction]] found in UO₂ changes sign with the applied magnetic field and exhibits magnetoelastic memory switching phenomena at record high switch-fields of 180,000 Oe.<ref>{{cite journal |doi=10.1038/s41467-017-00096-4 |title=Piezomagnetism and magnetoelastic memory in uranium dioxide. |journal=Nature Communications |volume=8 |pages=99 |year=2017 |last1=Jaime |first1=Marcelo |last2=Saul |first2=Andres |last3=Salamon |first3=Myron B. |last4=Zapf |first4=Vivien |last5=Harrison |first5=Neil |last6=Durakiewicz |first6=Tomasz |last7=Lashley |first7=Jason C. |last8=Andersson |first8=David A. |last9=Stanek |first9=Christopher R. |last10=Smith |first10=James L. |last11=Gofryk |first11=Krysztof|issue=1 |pmid=28740123 |pmc=5524652 |bibcode=2017NatCo...8...99J }}</ref> The microscopic origin of the material magnetic properties lays in the face-centered-cubic crystal lattice symmetry of uranium atoms, and its response to applied magnetic fields.<ref>{{cite journal |doi=10.1038/s43246-021-00121-6 |bibcode=2021CoMat...2...17A |title=Piezomagnetic switching and complex phase equilibria in uranium dioxide. |journal=Communications Materials |volume=2 |issue=1 |pages=17 |year=2021 |last1=Antonio |first1=Daniel J. |last2=Weiss |first2=Joel T. |last3=Shanks |first3=Katherine S. |last4=Ruff |first4=Jacob P.C. |last5=Jaime |first5=Marcelo |last6=Saul |first6=Andres |last7=Swinburne |first7=Thomas |last8=Salamon |first8=Myron B. |last9=Lavina |first9=Barbara |last10=Koury |first10=Daniel |last11=Gruner |first11=Sol M. |last12=Andersson |first12=David A. |last13=Stanek |first13=Christopher R. |last14=Durakiewicz |first14=Tomasz |last15=Smith |first15=James L. |last16=Islam |first16=Zahir |last17=Gofryk |first17=Krysztof|arxiv=2104.06340 |s2cid=231812027 }}</ref>

The [[band gap]] of uranium dioxide is comparable to of [[silicon]] and [[gallium arsenide]], near the optimum for efficiency vs band gap curve for absorption of solar radiation, suggesting its possible use for very efficient [[solar cell]]s based on [[Schottky diode]] structure; it also absorbs at five different wavelengths, including infrared, further enhancing its efficiency. Its intrinsic conductivity at room temperature is about the same as of [[single crystal]] silicon.<ref>{{cite journal|=.. |title=Ultrafast Hopping Dynamics of Electrons in the Mott Insulator UO2 Studied by Femtosecond Pump-Probe Spectroscopy|journal= |volume=|issue=20|pages=207402|=...| = 2011PhRvL.106t7402A }}</ref>

The [[dielectric constant]] of uranium dioxide is about 22, which is almost twice as high as of silicon (11.2) and GaAs (14.1). This is an advantage over Si and GaAs in construction of [[integrated circuit]]s, as it may allow higher density integration with higher [[breakdown voltage]]s and with lower susceptibility to the [[CMOS]] [[quantum |]] breakdown.

The [[Seebeck coefficient]] of uranium dioxide at room temperature is about 750 /K, a value significantly higher than the 270 /K of [[thallium tin telluride]] (Tl₂SnTe₅) and [[thallium germanium telluride]] (Tl₂GeTe₅) and of [[bismuth]]-[[tellurium]] alloys, other materials promising for [[]] applications and [[Peltier element]]s.

The [[radioactive decay]] impact of the²³⁵U and²³⁸U on its semiconducting properties was not measured {{as of|2005|lc=on}}. Due to the slow decay rate of these isotopes, it should not meaningfully influence the properties of uranium dioxide solar cells and thermoelectric devices, but it may become an important factor for [[very-large-scale integration|VLSI]] chips. Use of [[depleted uranium]] oxide is necessary for this reason. The capture of alpha particles emitted during radioactive decay as helium atoms in the crystal lattice may also cause gradual long-term changes in its properties.

The [[stoichiometry]] of the material dramatically influences its electrical properties. For example, the electrical conductivity of UO_1.994 is orders of magnitude lower at higher temperatures than the conductivity of UO_2.001.

Uranium dioxide, like U₃O₈, is a [[ceramic]] material capable of withstanding high temperatures (about 2300°C, in comparison with at most 200&nbsp;°C for silicon or GaAs), making it suitable for high-temperature applications like thermophotovoltaic devices.

A [[Schottky diode]] of [[yellowcake|U₃O₈]] and a [[p-n-p transistor]] of UO₂ were successfully manufactured in a laboratory.

Uranium dioxide is known to be absorbed by [[phagocytosis]] in the lungs.<ref>Principles of Biochemical Toxicology. Timbrell, John. PA 2008 ISBN </ref>

*[[Uranium oxide]]

*[[Uranium glass]]

*[[Uranium tile]]

*{{cite journal|= |title=The preparation and structure of barium uranium oxide +x|journal=Acta Crystallographica B|= 1982|= |= | = |= . }}

* [http://web.ead.anl.gov/uranium/pdf/WM01Semicond.pdf Semiconducting properties of uranium oxides]

* The <span class="plainlinks">[http://www.ibilabs.com/Uranium%20Oxide,%20di.htm Uranium dioxide] {{Webarchive|url=https://web.archive.org/web/20130916230607/http://ibilabs.com/Uranium%20Oxide,%20di.htm |date=2013-09-16 }}</span> International Bio-Analytical Industries, Inc.

{{Uranium compounds}}

{{Oxides}}

[[Category: ]]

[[Category:Uranium(IV) compounds]]

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[[Category:Fluorite crystal structure]]