Corrosion of UO2 and ThO2: A quantum-mechanical investigation

Skomurski, Frances N.; Shuller, Lindsay C.; Ewing, Rodney C.; Becker, Udo

doi:10.1016/j.jnucmat.2007.12.007

Cited by 61 publications

(54 citation statements)

References 64 publications

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“…The surface was prepared using deoxygenated aqueous solutions, and no effort was made to remove bound hydroxyl or water [29], which would require heating in UHV. Previous theoretical studies predict surface U-OH and U-OH 2 bond lengths of 2.2 and 2.6 Å, respectively [22,28], consistent with the CTR results. Given that the binding energy difference between Slab 2 and Slab 3 interstitials for a hydroxylated surface is very small (Fig.…”

Section: +supporting

confidence: 84%

“…These findings differ from those of ultrahigh vacuum (UHV) experiments, which indicate incomplete U coordination and outward relaxation of U atoms [15]. DFT calculations indicate that an O-terminated surface should have a U-O adatom bond length of ~1.8 Å regardless of whether subsurface interstitials are present, and the surface U should be fully oxidized to U(VI), producing a surface species that resembles half of the uranyl cation [22,23]. Our calculations indicate this "hemi-uranyl" termination energetically favors incorporation of the first oxygen interstitial layer into Slab 3, as observed with CTR, whereas hydroxyl termination slightly favors Slab 2 (Fig.…”

Section: +contrasting

confidence: 67%

“…The surface U atoms are relaxed into the bulk, broadly consistent with theoretical predictions of surface behavior under oxygen [22,23]. These findings differ from those of ultrahigh vacuum (UHV) experiments, which indicate incomplete U coordination and outward relaxation of U atoms [15].…”

Section: +supporting

confidence: 65%

“…Single crystal surface structures and oxidation have been studied under vacuum [10,11,[13][14][15][16][17][18][19][20][21], and by computational methods [22,23], but little is known about atomic level oxidation mechanisms under atmospheric conditions, especially in the earliest stages of oxidation.…”

Section: +mentioning

confidence: 99%

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UO2Oxidative Corrosion by Nonclassical Diffusion

et al. 2015

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Using x-ray scattering, spectroscopy, and density-functional theory we determine the structure of the oxidation front when a UO 2 (111) surface is exposed to oxygen at ambient conditions. In contrast to classical diffusion and previously reported bulk UO 2+x structures, we find oxygen interstitials order into a nanoscale superlattice with three-layer periodicity and uranium in three oxidation states: IV, V, and VI. This oscillatory diffusion profile is driven by the nature of the electron transfer process, and has implications for understanding the initial stages of oxidative corrosion in materials at the atomistic level. Main textOxidative corrosion is a key cause of material failure. This is especially true of uranium dioxide, which is the most economically important uranium mineral [1], the primary constituent of most nuclear fuels [2], and the desired product of many bioremediation strategies for uranium contamination [3]. UO 2 is an end-member in a complex metal-oxide system that is fundamentally important to experimental and computational actinide science [e.g., 4-7]. Despite more than 60 years of UO 2 oxidation research [8], moving beyond a macroscopic or empirical description to an understanding of the underlying atomistic processes has been difficult due to experimental challenges and the complex oxidation behavior of uranium oxides.Uranium dioxide exhibits a broad range of structural transformations due to oxidation. The UO 2 lattice readily incorporates interstitial oxygen atoms up to a stoichiometry near UO 2.25 (U 4 O 9 ) with minimal unit cell distortion [9]. Further oxidation to U 3 O 8 leads to structural rearrangement, volume expansion, and material failure [10,11]. When U(IV) in UO 2 is oxidized to U(VI) under water, dissolution occurs since U(VI) readily forms soluble uranyl (UO 2 2+) that can be released into the environment, although surfaces can be passivated [12]. Single crystal surface structures and oxidation have been studied under vacuum [10,11,[13][14][15][16][17][18][19][20][21], and by computational methods [22,23], but little is known about atomic level oxidation mechanisms under atmospheric conditions, especially in the earliest stages of oxidation.We have combined crystal truncation rod (CTR) x-ray diffraction -an in situ method that is sensitive to surface atomic structure [24,25] -with density functional theory (DFT) and x-ray photoelectron spectroscopy (XPS) to detail the initial stages of UO 2 oxidation via the (111) surface, which is the natural cleavage plane and predicted to be the most stable when dry [26][27][28]. We show that the oxidation front does not follow classical diffusion, but instead exhibits complex self-organization behavior, with interstitial oxygen atoms preferentially occupying every third layer below the surface.A freshly polished surface was measured with CTR (time 0), exposed to ~1 atm dry oxygen gas, and re-measured several times up to 21 days (504 hours) of exposure [29]. As the surface oxidizes, broad, bulk-forbidden peaks develop at L valu...

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Section: +supporting

confidence: 84%

Section: +contrasting

confidence: 67%

Section: +supporting

confidence: 65%

Section: +mentioning

confidence: 99%

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UO2Oxidative Corrosion by Nonclassical Diffusion

et al. 2015

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“…(B.1) (e.g., Wu and Nancollas, 1998). The surface energy value of 0.73 J/m 2 for UO 2 was estimated starting from a value computed by Skomurski et al (2006) (1.194 J/m 2 for the (100) face, consistent with cubic UO 2 ) then lowered to consider hydration based on the same average ratio of anhydrous to hydrous surface energies reported by Mazeina and Navrotsky (2007) for Fe (hydr)oxides (on the basis of similar enthalpies of water adsorption; Skomurski et al, 2008). This value is in the range of mean surface energies at 25°C ($0.85 ± 0.6 J/m 2 ) obtained from correlations presented by Hall and Mortimer (1987), and yields a solubility consistent with that given by Guillaumont et al (2003) for UO 2(am) at a particle size of about 3 nm when surface stress is neglected (and thus assumed to be compensated by hydration) (Fig.…”

Section: Appendix Bmentioning

confidence: 99%

Biogenic uraninite precipitation and its reoxidation by iron(III) (hydr)oxides: A reaction modeling approach

Spycher

Issarangkun

Stewart

et al. 2011

Geochimica et Cosmochimica Acta

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Giant Radiolytic Dissolution Rates of Aqueous Ceria Observed in Situ by Liquid‐Cell TEM

2017

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The dynamics of cerium oxide nanoparticle aqueous corrosion are revealed in situ. We use innovative liquid-cell transmission electron microscopy (TEM) combined with deliberate high-intensity electron-beam irradiation of nanoparticle suspensions. This enables life video-recording of materials reactions in liquid, with nm resolution. We introduce image quantification to measure detailed rates of dissolution as a function of time and particle size to be compared with literature data. Giant dissolution rates, exceeding any previous reports for chemical dissolution rates at room temperature by many orders of magnitude, are discovered. The reasons for this accelerated dissolution are outlined, including the importance of the radiolysis of water preceding the ceria attack. Electron-water interaction generates radicals, ions, and hydrated electrons, which assist in hydration and reductive dissolution of oxide minerals. The presented methodology has the potential to become a novel accelerated testing procedure to compare multiple nanoscale materials for relative aqueous durability. The ceria-water system is of crucial importance for the fields of catalysis, abrasive polishing, environmental remediation, and as simulant for actinide oxide behaviour in contact with liquid for nuclear engineering.

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Corrosion of UO2 and ThO2: A quantum-mechanical investigation

Cited by 61 publications

References 64 publications

UO2Oxidative Corrosion by Nonclassical Diffusion

UO2Oxidative Corrosion by Nonclassical Diffusion

Biogenic uraninite precipitation and its reoxidation by iron(III) (hydr)oxides: A reaction modeling approach

Giant Radiolytic Dissolution Rates of Aqueous Ceria Observed in Situ by Liquid‐Cell TEM

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