User:LossIsNotMore/Uranium trioxide

There are three methods to generate uranium trioxide. As noted below, two are used industrially in the reprocessing of nuclear fuel and uranium enrichment.

1. U₃O₈ can be oxidized at 500°C with oxygen.{{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 | pages= 2172-2173 | doi= 10.1021/ja01161a082 }} Note that above 750°C even in 5 Atm O₂ UO₃ decomposes into U₃O₈.{{cite journal | author= Wheeler VJ, Dell RM, Wait E| title= Uranium trioxide and the UO₃ hydrates | journal= J. Inorganic Nuclear Chemistry| year= 1964 | volume= 26 | pages= 1829-1845 | doi= 10.1016/0022-1902(64)80007-5 }}
2. Uranyl nitrate, (UO₂(NO₃)₂·6H₂O) can be heated to yield UO₃. This occurs during the reprocessing of nuclear fuel. Fuel rods are dissolved in HNO₃ to separate uranyl nitrate from plutonium and the fission products (the PUREX method). The pure uranyl nitrate is converted to solid UO₃ by heating at 400 °C. After reduction with hydrogen (with other inert gas present) to uranium dioxide, the uranium can be used in new MOX fuel rods.
3. Ammonium diuranate or sodium diuranate (Na₂U₂O₇·6H₂O) may be decomposed. Sodium diuranate, also known as yellowcake, is converted to uranium trioxide in the enrichment of uranium. Uranium dioxide and uranium tetrafluoride are intermediates in the process which ends in uranium hexafluoride.{{cite journal | author= Dell RM, Wheeler VJ | title= Chemical Reactivity of Uranium Trioxide Part 1. — Conversion to U₃O₈, UO₂ and UF₄| journal= Transactions of the Faraday Society | year= 1962 | volume= 58 | pages= 1590-1607 | doi= 10.1039/TF9625801590}}

Image:Uranium-trioxide-formation.png

Uranium trioxide is shipped between processing facilities in the form of a gel.

Cameco Corporation, which operates at the world's largest uranium refinery at Blind River, Ontario, produces high-purity uranium trioxide.

Like all hexavalent uranium compounds, UO₃ is hazardous by inhalation, ingestion, and through skin contact. It is a poisonous, radioactive substance, which may cause shortness of breath, coughing, acute arterial lesions, and changes in the chromosomes of white blood cells and gonads leading to congenital malformations if inhaled.{{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 }} [http://www.bovik.org/du/Sutton04.pdf full text]

During nuclear fuel fabrication or reprocessing stages of a nuclear fuel cycle, it is possible for small particles of uranium oxides including UO₃ to escape into the environment.{{cite journal | author= Schuenemana RA, Khaskelisa AI, Eastwooda D, van Ooijb WJ, Burggraf LW | title= Uranium oxide weathering: spectroscopy and kinetics| journal= Journal of Nuclear Materials | year= 2003 | volume= 323 | pages=8-17 | doi= 10.1016/j.jnucmat.2003.07.003 }} The extent of immediate inhalation intake of uranium oxides is inversely proportional to the size of particles inhaled; uranium oxide gases are absorbed immediately into the bloodstream.{{cite journal | author= Chazel V | title=Effect of U₃O₈ specific surface area on in vitro dissolution, biokinetics, and dose coefficients | journal=Radiation Protection Dosimetry | year= 1998 | volume=79 | pages=39-42}} [http://www.bovik.org/du/Chazel98.pdf full text] Urine assay for UO₃ exposure can be useful, provided that measurements are made soon after a known acute intake.{{cite journal | author= Ansoborlo E | title= Exposure implications for uranium aerosols formed at a new laser enrichment facility: application of the ICRP respiratory tract and systemic model | journal= Radiation Protection Dosimetry| year=1998 | volume= 79| pages=23-27}} [http://www.bovik.org/du/Ansoborlo98.pdf full text]{{cite journal | author= Stradling N | title= Optimising monitoring regimens for inhaled uranium oxides | journal= Radiation Protection Dosimetry| year= 2003 | volume=105 | pages=109-114}} [http://www.bovik.org/du/Stradling03a.pdf full text] Treatment for UO₃ inhalation primarily involves decorporation therapy.{{cite journal | author= Stradling GN | title= Treatment for Actinide-bearing Industrial Dusts and Aerosols | journal= Radiation Protection Dosimetry | year= 2000 | volume= 87| pages=41-50}} [http://intl-rpd.oxfordjournals.org/cgi/content/abstract/87/1/41 abstract], [http://www.bovik.org/du/Stradling2000.pdf full text]

The only well characterized binary trioxide of any actinide is UO₃, of which several polymorphs are known. Solid UO₃ loses O₂ on heating to give green-colored U₃O₈: reports of the decomposition temperature in air vary from 200–650 °C. Heating at 700 °C under H₂ gives dark brown uranium dioxide (UO₂), which is used in MOX nuclear fuel rods.

There is a high-pressure solid form with U₂O₂ and U₃O₃ rings in it.Siegel S, Hoekstra HR, Sherry E (1966) Acta Crystallographica 20, 292-295.Gmelin Handbuch (1982) U-C1, 129-135.

Several hydrates of uranium trioxide are known, e.g., UO₃•6H₂O.

While uranium trioxide is mostly encountered as a polymeric solid, work has been done on molecular forms in inert gas matrices and in the vapor phase, too.

Uranium trioxide is produced when uranium burns.Rostker, B. (2000) [http://www.deploymentlink.osd.mil/du_library/du_ii/du_ii_refs/n52en017/mr1018_7_chap1.html "Depleted Uranium in the Gulf (II)"] Environmental Exposure Reports Tech. Rep. No. 2000179-2 (Washington, DC: Special Assistant for Gulf War Illnesses, Department of Defense)Army Environmental Policy Institute (June, 1995) Health and Environmental Consequences of Depleted Uranium Use in the US Army, Champaign, Illinois, June 1995.U.S. Army Center for Health Promotion and Preventive Medicine (1998) Interim Summary, Total Uranium and Isotope Uranium Results, Operation Southern Watch, CHPPM Project No. 47-EM-8111-98. Uranyl ion contamination in uranium oxides has been detected in the residue of depleted uranium munitions fires.Salbu, B. et al. (2005) [http://www.bovik.org/du/Salbu-uranyl-detected.pdf "Oxidation states of uranium in depleted uranium particles from Kuwait,"] Journal of Environmental Radioactivity, 78, 125–135.

At elevated temperatures gaseous UO₃ and O₂ are in equilibrium with solid U₃O₈.{{cite journal | author= Ackermann RJ, Thorn RJ, Alexander C, Tetenbaum M | title= Free Energies of Formation of Gaseous Uranium, Molybdenum, and Tungsten Trioxides | journal=Journal of Physical Chemistry | year= 1960 | volume=64 | pages=350-355| doi= 10.1021/j100832a016}} ([http://www.bovik.org/du/scans/a60-350.jpg page 350], [http://www.bovik.org/du/scans/a60-351.jpg 351], [http://www.bovik.org/du/scans/a60-352.jpg 352], [http://www.bovik.org/du/scans/a60-353.jpg 353], [http://www.bovik.org/du/scans/a60-354.jpg 354], [http://www.bovik.org/du/scans/a60-355.jpg 355]){{cite journal | author= Wilson WB | title= High-Pressure High-Temperature Investigation of the Uranium-Oxygen System | journal=Journal Inorganic Nuclear Chemistry | year= 1961 | volume=19 | pages=212-222| doi= 10.1016/0022-1902(61)80109-7 }} [http://www.bovik.org/du/Wilson61.pdf full text]{{cite journal | author= Chatillion C, Defoort F, Froment K | title= Mass spectrometric critical assessment of thermodynamic data for UO₃(g) | journal= Journal of Physics and Chemistry of Solids | year= 2005 | volume=66 | pages=379-383 | doi= 10.1016/j.jpcs.2004.06.077 }}H. Wanner and I. Forest, eds. (2004) "Gaseous uranium oxides" [http://www.nea.fr/html/dbtdb/pubs/uranium.pdf Chemical Thermodynamics of Uranium] (Paris: OECD and French Nuclear Energy Agency) pp. 97-98

::¹/₃ U₃O₈(s) + ¹/₆ O₂(g) $\backslash overrightarrow\{\backslash gets\}$ UO₃(g)

With increasing temperature the equilibrium is shifted to the right. This system has been studied at temperatures between 900 °C and 2200 Kelvin. The vapor pressure of monomeric UO₃ is low but appreciable, about 10⁻⁵ mbar (1 mPa) at 980 °C, rising to 0.1 mbar (10 Pa) at 1400 °C, 0.34 mbar (34 Pa) at 1800 K, 1.9 mbar (193 Pa) at 2000 K, and 8.1 mbar (809 Pa) at 2200 K.{{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| pages= 1089 | doi= 10.1063/1.1743156 }}{{cite journal | author= Alexander CA | title= Volatilization of urania under strongly oxidizing conditions | journal= Journal of Nuclear Materials | year= 2005 | volume= 346 | pages= 312-318| doi= 10.1016/j.jnucmat.2005.07.013}} [http://www.bovik.org/du/Alexander2005.pdf full text] Small pieces of uranium burn at temperatures exceeding 2500 Kelvin.{{cite journal | author=Mouradian and Baker | title= Burning Temperatures of Uranium and Zirconium in Air| journal= Nuclear Science and Engineering | year= 1963 | volume= 15| pages=388-394 }}

Image:Uranium-trioxide-3D-vdW.png

Infrared spectroscopy of molecular UO₃ isolated in an argon matrix indicates a T-shaped structure (point group C_2v) for the molecule. This is in contrast to the commonly encountered D_3h symmetry exhibited by most trioxides. From the force constants the authors deduct the U-O bond lengths to be between 1.76 and 1.79 angstroms (176 to 179 picometers).{{cite journal | author= Gabelnick SD, Reedy GT, Chasanov MG| title= Infrared spectra of matrix-isolated uranium oxide species. II: Spectral interpretation and structure of UO₃ | journal= Journal of Chemical Physics | year= 1973 | volume= 59 | pages= 6397-6404 | doi= 10.1063/1.1680018 }}

Calculations indicate that the point group of gaseous UO₃ is C_2v, 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_3h species is a saddle point, 49 kJ/mol above the C_2v minimum. The authors invoke a second-order Jahn-Teller effect as explanation.{{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 | pages= 4809-4813 }}

Uranium trioxide reacts at 400 °C with freon-12 to form chlorine, phosgene, carbon dioxide and uranium(IV) fluoride. The freon-12 can be replaced with freon-11 which forms carbon tetrachloride instead of carbon dioxide. This is a case of a hard perhalogenated freon which is normally considered to be inert being converted chemically at a moderate temperature.{{cite journal | author= Booth HS, Krasny-Ergen W, Heath RE| title= Uranium Tetrafluoride | journal= Journal of the American Chemical Society | year= 1946 | volume= 68 | pages= 1969-1970| doi= 10.1021/ja01214a028 }}

2 CF₂Cl₂ + UO₃ → UF₄ + CO₂ + COCl₂ + Cl₂

4 CF₂Cl₂ + UO₃ → UF₄ + 3COCl₂ + CCl₄ + Cl₂

Uranium trioxide can be dissolved in a mixture of tributyl phosphate and thenoyltrifluoroacetone in supercritical carbon dioxide, ultrasound was employed during the dissolution.{{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 | pages= 129-130 | doi= 10.1070/MC2001v011n04ABEH001468 }}

It has been reported that the corrosion of uranium in a silica rich aqueous solution forms both uranium dioxide and uranium trioxide.Trueman ER, Black S, Read D, Hodson ME (2003) "Alteration of Depleted Uranium Metal" Goldschmidt Conference Abstracts, p. A493 [http://www.the-conference.com/2003/Gold2003/abstracts/A493.pdf abstract] Reports on the corrosion of uranium metal have been published by the Royal Society.Ander L, Smith B (2002) "[http://www.royalsoc.ac.uk/downloaddoc.asp?id=1182 Annexe F: Groundwater transport modelling]" The health hazards of depleted uranium munitions, part II (London: The Royal Society)Smith B (2002) "[http://www.royalsoc.ac.uk/downloaddoc.asp?id=1183 Annexe G: Corrosion of DU and DU alloys: a brief discussion and review]" The health hazards of depleted uranium munitions, part II (London: The Royal Society)

The reversible insertion of magnesium cations into the lattice of uranium trioxide by cyclic voltammetry using a graphite electrode modifed with microscopic particles of the uranium oxide has been investigated. This experiment has also been done for U₃O₈. This is an example of electrochemistry of a solid modifed electrode, the experiment which used for uranium trioxide is related to a carbon paste electrode experiment. It is also possible to reduce uranium trioxide with sodium metal to form sodium uranium oxides.Dueber RE, Bond AM, Dickens PG (1992) Journal of the Electrochemical Society 139, 2363-2371. The [http://link.springer.de/link/service/journals/10008/index.htm Journal of Solid State Electrochemistry] is devoted to this type of electrochemistry.

It has been the case that it is possible to insert lithium ions and protons into the uranium trioxide lattice by electrochemical means, this is similar to the way that some rechargeable lithium ion batteries work. In these rechargeable cells one of the electrodes is a metal oxide which contains a metal such as cobalt 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. Dickens PG, Lawrence SD, Penny DJ, Powell AV (1989) Solid State Ionics 32/33, 77-83.P.G. Dickens, S.D Lawrence and M.T. Weller (1985) Mat. Res. Bull. 20, 635.(Li+) P.G. Dickens, S.V. Hawke and M.T. Weller (1984) Mat. Res. Bull. 19, 543.(H+)

UO₃-based ceramics become green or black when fired in a reducing atmosphere and yellow to orange when fired with oxygen. Orange-coloured Fiestaware is a well-known example of a product with a uranium-based glaze. UO₃-has also been used in formulations of enamel, uranium glass, and porcelain.

Prior to 1960, UO₃ was used as an agent of crystallization in crystalline coloured glazes. It is possible to determine with a Geiger counter if a glaze or glass was made from UO₃.

Uranium oxide is amphoteric and reacts as acid and as a base, depending on the conditions.

;As an acid:

:UO₃ + H₂O → UO₄²⁻ + H⁺

Dissolving uranium oxide in a strong base like sodium hydroxide forms the doubly negatively charged

uranate anion (UO₄²⁻). Uranates tend to agglomerate, forming diuranate,

U₂O₇²⁻, or other poly-uranates.

Important diuranates include ammonium diuranate ((NH₄)₂U₂O₇), sodium diuranate (Na₂U₂O₇) and

magnesium diuranate (MgU₂O₇), which forms part of some yellowcakes. It is worth noting that uranates of the form M₂UO₄ do not contain UO₄²⁻ ions, but rather flattened UO₆ octahedra, containing a uranyl group and bridging oxygens.{{cite book | last= Cotton | first= Simon | year = 1991 | title = Lanthanides and Actinides | publisher= Oxford University Press | location = New York | pages= 128 }} ([http://www.bovik.org/du/scans/Cotton126.jpg page 126], [http://www.bovik.org/du/scans/Cotton127.jpg 127], [http://www.bovik.org/du/scans/Cotton128.jpg 128])

;As a base:

:UO₃ + H₂O → UO₂²⁺ + OH⁻

Dissolving uranium oxide in a strong acid like sulfuric or nitric acid forms the double positive charged uranyl cation. The uranyl nitrate formed (UO₂(NO₃)₂ˑ6H₂O) is soluble in ethers, alcohols, ketones and esters; for example, tributylphosphate. This solubilty is used to separate uranium from other elements in nuclear reprocessing, which begins with the dissolution of nuclear fuel rods in nitric acid. The uranyl nitrate is then converted to uranium trioxide by heating.

From nitric acid one obtains uranyl nitrate, trans-UO₂(NO₃)₂·2H₂O, consisting of eight-coordinated uranium with two bidentate nitrato ligands and two water ligands as well as the familiar O=U=O core.