User:Stone/Uraniumtrioxide

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Stone/Uraniumtrioxide
solid γ-UO3
(gamma polymorph)
oxygen diameters sharply
reduced for visibility
General
Systematic name Uranium trioxide
Uranium(VI) oxide
Other names Uranyl oxide
Uranic oxide
Molecular formula UO3
Molar mass 286.03 g/mol1 g/mol
Appearance  ?
CAS number [1344-58-7]
Properties
Density and phase 5.5-8.7 g/cm3
Solubility in water  ? g/100 ml (? °C)
Melting point ca. 500 °C decomp.
Acidity (pKa)  ?
Basicity (pKb)  ?
Chiral rotation [α]D  ?°
Viscosity  ? cP at ? °C
Structure
Molecular shape  ?
Coordination
geometry		 γ-UO3:UO2]2+[UO4]2 
Crystal structure [ I41/amd
Dipole moment  ? D
Hazards
MSDS UO3-MSDS
Main hazards  ?
NFPA 704
Flash point  ? °C
R/S statement R: ?
S: ?
RTECS number  ?
Supplementary data page
Structure and
properties		 n, εr, etc.
Thermodynamic
data		 Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other anions  ?
Other cations  ?
Related ?  ?
Related compounds  ?
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references


Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is the hexavalent oxide of uranium. The toxic, teratogenic, and radioactive solid may be obtained by heating uranyl nitrate to 400 °C. The gas is produced when uranium burns in oxygen or air, and condenses at standard temperature and pressure. Its most commonly encountered polymorph, γ-UO3, is a yellow-orange powder.

Contents

[edit] Health and safety hazards

Like all hexavalent uranium compounds (also called uranium(VI) 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.

See also: Depleted uranium#Health concerns

[edit] Production and Use

There are several methods to obtain uranium trioxide, one is heating uranyl nitrate to 400 °C, an other is oxidation of U3O8 with oxygen at 500°C and an other by decomposition of ammonium diuranate. [1]

The starting point of the reprocessing of nuclear fuel is the dissolution of the fuel rods in HNO3. After separating the uranyl nitrate (UO2(NO3)2·6H2O) from the plutonium and the fission products, for example the PUREX method, the pure uranyl nitrate is converted to solid UO3 by heating at 400 °C. After reduction to uranium dioxide it can be used in new MOX fuel rods.

Uranium trioxide is also an intermediary compound in the enrichment of uranium. The process starts from sodium diuranate yellowcake (Na2U2O7·6H2O) ending with uranium hexafluoride. The uranium dioxide and the uranium tetrafluoride are other intermediates in this process. [2] The uranium trioxide is shipped between processing facilities in the form of a UO3 gel. In the jargon of the uranium refining industry, the chemical solution containing the concentrated uranium trioxide is called "OK liquor". Upon heating, this material liberates ammonia, giving

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

[edit] Chemistry

[edit] Chemical and structural properties

At 800-900 °C, UO3 releases some O2 to give green-colored U3O8. Heating at 700 °C under H2 gives dark brown uranium dioxide (UO2), which is used in MOX nuclear fuel rods. [3][4][5]

[edit] Structural properties

One of the best characterized binary trioxide of any actinide is UO3, of which several polymorphs are known. At standard conditions the yellow rhombic gamma UO3 is the most stable on.[6] At higher oxygen pressure and temperatures above 500°C it can be transformed into the red beta UO3.[7]. Several crystalline and amorph high temperature and high pressure modifications are known. [8][9]↑ 

[edit] Solid state

the γ (gamma) form, with the different uranium enviroments in green and yellow
Enlarge
the γ (gamma) form, with the different uranium enviroments in green and yellow
the enviroment of the uranium atoms shown as yellow in the gamma form
Enlarge
the enviroment of the uranium atoms shown as yellow in the gamma form
The chains of U2O2 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 a octahedral enviroment which are distorted towards square planar by an elongation of the axial oxygen-uranium bonds.
Enlarge
The chains of U2O2 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 a octahedral enviroment which are distorted towards square planar by an elongation of the axial oxygen-uranium bonds.

The most frequently encountered polymorph is γ-UO3, whose x-ray structure has been solved from powder diffraction data. The compound crystallizes in the space group I41/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 [UO2]2+[UO4]2 , that is uranyl uranate. ([10].

The structures of β-UO3 and δ-UO3 can be found in the Supplementary data page.

The geometry of the uranyl ion has been the subject of much debate. The close approach of two oxygen atoms to uranium, with each linear O-U-O bond from 1.7 to 1.9 Å, prevents the close approach of a third or more. Bond angles are 90 and 180 degrees. d-p and f-p bonding have been suggested to explain the short U-O bonds. [11]

Infrared spectroscopy of molecular UO3 isolated in an argon matrix indicates a T-shaped structure (point group C2v) for the molecule. This is in contrast to the commonly encountered D3h symmetry exhibited by most trioxides. One could think of the compound as "uranyl monoxide", [UO2]2+O2−. From the force constants the authors deduct the U-O bond lengths to be between 1.76 and 1.79 angstroms. The authors did not attempt to deduce bond angles. (Gabelnick, Reedy, Chasanov, 1970)

[edit] Related anions and cations

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 (NH4U2O7), sodium diuranate (Na2U2O7) and magnesium diuranate (MgU2O7), which forms part of some yellowcakes. [12]

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)2?6H2O) 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. [13]

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.

[edit] Phase behaviour

[edit] Monomolecular UO3

At elevated temperatures gaseous UO3 and O2 are in equilibrium with solid U3O8. These Uranium trioxide gas molecules are a known intermediate in the chemical transition reactions forming U3O8 crystals from combustion products including uranium oxides:

1/3 U3O8(s) + 1/6 O2(g) → UO3(g) at T1;
UO3(g) → 1/3 U3O8 + 1/6 O2(g) at T2;
where T2 < T1.

With increasing temperature the equilibrium is shifted to the right. This system has been studied at temperatures between 900 and 1500 °C. The vapor pressure of UO3 is low but appreciable, about 10−8 bar at 980 °C, rising to 10−4 bar at 1400 °C (in the presence of 1 bar oxygen). At these partial pressures, uranium trioxide is monomeric.

Volatility of UO3(g) in dry air
Temperature Partial pressure
1800 K 0.34% atm
2000 1.9%
2200 8.1%
from Alexander (2005) Table 6, p. 317

[14]

[edit] Uranium oxide in ceramics

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, glass, and porcelain. #bastarache

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 with UO3 as colour.

[edit] References

Peer-reviewed
  1. ↑ Depets PC (1966). "The Structure of beta- UO3". Acta Cryst 21: 589.
  2. ↑ Engmann R, de Wolff PM (1963). "". Acta Cryst 16: 993.
  3. ↑ Neumüller O-A (1988). Römpps Chemie-Lexikon, 6, Stuttgart: Frankh'sche Verlagshandlung. ISBN 3-440-04516-1.
  4. ↑  (1977) Gmelin Handbook of Inorganic Chemistry, 8.
  5. ↑  (1977) Gmelin Handbuch der anorganischen Chemiek, 8.
  6. ↑ Ackermann RJ, Thorn RJ, Alexander C, Tetenbaum M (1960). "Free Energies of Formation of Gaseous Uranium, Molybdenum, and Tungsten Trioxides". J Phys Chem 64: 350-355.
  7. ↑ Mouradian EM, Baker L jr (1963). "Burning Temperatures of Uranium and Zirconium in Air". Nucl Sci Engen 15: 388-394.
  8. ↑ Ackermann RJ, Chang AT (1973). Thermodynamic Characterization of U3O8-z Phase, 5.
  9. ↑ Wilson WB (1961). "High-Pressure High-Temperature Investigation of the Uranium-Oxygen System". J Inorg Nuclear Chem 19: 212-222.
  10. ↑ Morrow (1972). "Inhalation studies of uranium trioxide". Health Physics 23: 273-280.
  11. ↑ Holleman AF, Wiberg E, Wiberg N (1985). Lehrbuch der Anorganische Chemie, 91-100, Berlin, New York: Walter de Gruyter. ISBN 3-11-07511-3.
  12. ↑ Gilchrist RL, Glissmyer JA, Mishima J (1979). "Characterization of Airborne Uranium from Test Firings of XM774 Ammunition," Technical report no. PNL-2944 Richland, WA: Battelle Pacific Northwest Laboratory".
  13. ↑ Stuart (1979). "Solubility and Hemolytic Activity of Uranium Trioxide". Environmental Research 18: 385-396.
  14. ↑ Green DW (1980). "Relationship between spectroscopic data and thermodynamic functions; application to uranium, plutonium, and thorium oxide vapor species". J Nuclear Materials 88: 51-63.
  15. ↑ Chapman AT, Meadows RE (1964). "Volatility of UO2+/-x and Phase Relations in the System Uranium Oxygen". J Am Ceramic Soc 47: 614-621.
  16. ↑ Drowart J, Pattoret A, Smoes S (1964). "Heat of sublimation of uranium and consistency of thermodynamic data for uranium compounds". J Nuclear Materials 12: 319-322.
  17. ↑ Roberts LEJ, Walter AJ (1961). "Equilibrium Pressures and Phase Relations in the Uranium Oxide System". J Inorg Nuclear Chem 22: 213-229.
  18. ↑ Hoekstra HR, Siegel (1970). "Uranium-Oxygen System at high pressure". J Inorg Nuclear Chem 32: 3237-3248.
  19. ↑ Dell RM, Wheeler V J (1962). "Chemical Reactivity of Uranium Trioxide Part 1.conversion to U3O8, U02 and UF4". Trans Farad Soc: 1590-1607.
  20. ↑ Sheft I, Fried S, Davidson N (1950). "Preparation of Uranium Trioxide". J Am Chem Soc 72: 2172-2173.
  21. ↑ Hutchings, G. J. (1996). "AUranium-Oxide-Based Catalysts for the Destruction of Volatile Chloro-Organic compounds". Nature 384: 341-343.
  22. ↑ Berkowitz J, Chupka WA . (1957). "". J Chem Phys 25: 842.
  23. ↑ Ackermann RJ, Gilles PW, Thorn RJ (1956). "". J Chem Phys 25: 1089.

Nakajima K Arai Y (2001). "{{{title}}}". J Nuclear Mater 294: 250-255. Chatillion C, Defoort F, Froment K (2005). "Mass spectrometric critical assessment of thermodynamic data for UO3 (g)". J Phys Chem Solid 66: 379-382.


United Nations invitation-only
  1. ↑ . Hoekstra HR, Siegel S (1958). "Recent Developments in the Chemistry of the Uranium-Oxygen System". Proceedings of the Second International Conference on Peaceful Uses of Atomic Energy (Geneva: UN) 7: 394-400.
Other
  1. ↑  Wanner H, Forest I, eds. (2004) Chemical Termodynamics of Uranium (Paris: OECD and French Nuclear Energy Agency)
  2. ↑  URANIUM and CERAMICS by Edouard Bastarache


Uranium trioxide (UO3), also called uranyl oxide, uranium(VI) oxide, and uranic oxide, is the hexavalent oxide of uranium. The toxic, teratogenic, and radioactive solid may be obtained by heating uranyl nitrate to 400 °C. The gas is produced when uranium burns in oxygen or air, and condenses at standard temperature and pressure.

Its most commonly encountered polymorph, γ-UO3, is a yellow-orange powder.

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

[edit] Health and safety hazards

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.

UO3-Material Safety Data Sheet.

[edit] Chemistry

In addition to the monomeric gas which may be produced by uranium combustion.

[edit] Combustion product of uranium

UO3 gas vapor is produced by combustion of uranium metal in air (Cotton, 1991.) The burning temperature reaches 2800 K (Mouradian and Baker, 1963.) UO3 gas will eventully condense under normal atmospheric conditions.

Uranium-nitrogen salts UN and UN2, form above 700 deg. C. Professor Simon Cotton (1991) Lanthanides and Actinides (New York: Oxford University Press) also writes, on page 127: "Aerial oxidation of any uranium compound eventually results in the formation of a uranyl compound."

Uranium trioxide gas molecules are a known intermediate in the chemical transition reactions forming U3O8 crystals from combustion products including uranium oxides. According to Wilson (1961), Ackermann et al. (1960) show that U3O8 crystals result from the two step process:

1/3 U3O8(s) + 1/6 O2(g) → UO3(g) at T1;
UO3(g) → 1/3 U3O8 + 1/6 O2(g) at T2;
where T2 < T1.

The uptake of oxygen by U3O8 is "not infrequently ignored" (Gmelin vol. U-C1, p. 98.)

Individual UO3 molecules will not decompose below the burning temperature of uranium in air, because uranium monoxide requires additional energy to form, as does the release of O2 by a single UO3 molecule. (Hoekstra and Siegel 1958; Wanner and Forest (2004) p. 98.)


[edit] In the gas phase

At elevated temperatures gaseous UO3 and O2 are in equilibrium with solid U3O8.

1/3 U3O8(s) + 1/6 O2(g) ⇄ UO3(g)

With increasing temperature the equilibrium is shifted to the right. This system has been studied at temperatures between 900 and 1500 °C. The vapor pressure of UO3 is low but appreciable, about 10−8 bar at 980 °C, rising to 10−4 bar at 1400 °C (in the presence of 1 bar oxygen). At these partial pressures, uranium trioxide is monomeric. (Ackermann, 1960)



[edit] See also

Accidental teratogens:

[edit] References

Peer-reviewed


  • S.D. Gabelnick, G.T. Reedy, M.G. Chasanov (1973) "Infrared spectra of matrix-isolated uranium oxide species. II: Spectral interpretation and structure of UO3," J. Chem. Phys., 59, 6397.
  • Rauh, E.G. and R.J. Ackermann (1974) "First ionization potentials of some refractory oxide vapors," J. Chem. Phys., 60, 1396.
United Nations invitation-only
  • H. R. Hoekstra and S. Siegel (1958) "Recent Developments in the Chemistry of the Uranium-Oxygen System," in the Proceedings of the Second International Conference on Peaceful Uses of Atomic Energy, (Geneva: UN) 7, 394-400.
Other
  • H. Wanner and I. Forest, eds. (2004) Chemical Termodynamics of Uranium (Paris: OECD and French Nuclear Energy Agency)
  • Gmelin Handbook of Inorganic Chemistry, 8th ed., English translation, vol. U-C1 (1977), page 98
  • «Gmelin Handbuch der anorganischen Chemiek» 8th ed., vol. U-C2, pp. 118-120
  • Gilchrist, R.L., J.A. Glissmyer, and J. Mishima (1979) "Characterization of Airborne Uranium from Test Firings of XM774 Ammunition," Technical report no. PNL-2944, Richland, WA: Battelle Pacific Northwest Laboratory, November 1979.
  • URANIUM and CERAMICS by Edouard Bastarache
  • Uranium and Insoluble Compounds from the Occupational Safety and Health Administration; note that UO3 is moderately soluble (Morrow, 1972.)
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