Evidence for 6‐Coordinated Zirconium in Inactive Nuclear Waste Glasses

Galoisy, Laurence; Pelegrin, E.; Arrio, Marie‐Anne; Ildefonse, Philippe; Calas, Georges; Ghaleb, D.; Fillet, C.; Pacaud, François

doi:10.1111/j.1151-2916.1999.tb02065.x

Cited by 112 publications

(118 citation statements)

References 17 publications

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“…This slightly distorted [ZrO 6 ] octahedral are consistent with experimental observations. [44][45][46] BAD of O-Na-O shows a higher/sharper peak at~60°and a lower/broader peak at 110°for all compositions, which is consistent with a previous study on soda-lime silicate glasses. 53 Interestingly, BADs of O-Ca-O exhibit higher intensity of the peak~60°as compared to the peak~90°.…”

Section: Discussionsupporting

confidence: 92%

“…The study of Zr in both simplified and simulant borosilicate glasses using EXAFS 44,57,60,61 dates back to the late 1990s and has consistently shown that Zr is in 6-fold coordination, with evidence for 7-fold coordinated Zr only appearing at very high ZrO 2 contents. 61 In contrast, the composition of the second shell has not been unequivocally resolved from EXAFS due in large part to the large number of degrees of freedom (elements, distances, coordination numbers, Debye-Waller factors) in the traditional shell-by-shell EXAFS fitting approach.…”

Section: Discussionmentioning

confidence: 99%

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Structural role of ZrO2 and its impact on properties of boroaluminosilicate nuclear waste glasses

Deng

Kerisit

et al. 2018

npj Mater Degrad

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Addition of zirconia (ZrO 2 ) to nuclear waste glasses, even in small amount, significantly affects physical properties such as chemical durability, density, viscosity, and glass transition temperature. Hence ZrO 2 plays an important role in the development of nuclear waste glass compositions. It was found recently that addition of zirconia decreases the initial dissolution rate but increases longterm dissolution by changing the protective properties such as porosity of alteration layers. In this study, the International Simple Glass (ISG) with different amounts of ZrO 2 /SiO 2 substitution was simulated using classical molecular dynamics (MD) simulations and recently developed composition-dependent potential sets. Local structural descriptors such as bond distances, bond angle distributions, and coordination numbers were systematically studied and compared with experimental values. Zr K-edge extended X-ray absorption fine structure spectra were also calculated and compared with experiment to resolve the local coordination environment around Zr. Medium-range structural information (e.g., Q n distribution, network connectivity, and ring-size distribution) showed that ZrO 2 /SiO 2 substitution increases the overall network connectivity and the amount of smaller sized rings, which will decrease the initial dissolution rate by strengthening the glass network and limiting water diffusivity. Finally, diffusion and dynamic properties of the ions were studied and discussed to develop a better understanding of the chemical durability of these glasses.

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Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Structural role of ZrO2 and its impact on properties of boroaluminosilicate nuclear waste glasses

Deng

Kerisit

et al. 2018

npj Mater Degrad

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“…The spectrum resembles that of BaZrO 3 with a sixfold coordinated Zr 4+ (Dixit et al 2004). Data, mostly X-ray-based, from Zr-bearing silicate glasses have been interpreted to indicate that Zr 4+ is in sixfold coordination with oxygen (Farges et al 1991, Galoisy et al 1999Farges and Rossano 2000). From this limited information, we conclude that Zr 4+ in ZrO 2 - Fig.…”

Section: Raman Spectroscopymentioning

confidence: 92%

An in situ experimental study of Zr4+ transport capacity of water-rich fluids in the temperature and pressure range of the deep crust and upper mantle

Mysen

2015

Prog. in Earth and Planet. Sci.

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An in situ experimental study of Zr 4+ transport capacity of water-rich fluids in the temperature and pressure range of the deep crust and upper mantle Bjorn MysenAbstract Throughout the Earth's history, mass transport involved fluids. In order to address the circumstances under which Zr 4+ may have been transported in this manner, its solubility behavior in aqueous fluid with and without NaOH and SiO 2 in equilibrium with crystalline ZrO 2 was determined from 550 to 950°C and 60 to 1200 MPa. The measurements were carried out in situ while the samples were at the temperatures and pressures of interest. In ZrO 2 -H 2 O and ZrO 2 -SiO 2 -H 2 O fluids, the Zr 4+ concentration ranges from ≤10 to~70 ppm with increasing temperature and pressure. Addition of SiO 2 to the ZrO 2 -H 2 O system does not affect these values appreciably. In these two environments, Zr 4+ forms simple oxide complexes in the H 2 O fluid with ΔH~40 kJ/mol for the solution equilibrium, ZrO 2 (solid) = ZrO 2 (fluid). The Zr 4+ concentration in aqueous fluid increases about an order of magnitude upon addition of 1 M NaOH, which reflects the formation of zirconate complexes. The principal solution mechanism is ZrO 2 + 4NaOH = Na 4 ZrO 4 + 2H 2 O with ΔH~200 kJ/mol. Addition of both SiO 2 and NaOH to ZrO 2 -H 2 O enhances the Zr 4+ by an additional factor of about 5 with the formation of partially protonated alkali zircon silicate complexes in the fluid. The principal solution mechanism is 2ZrO 2 + 2NaOH + 2SiO 2 = Na 2 Zr 2 Si 2 O 9 + H 2 O with ΔH~40 kJ/mol. These results, in combination with other published experimental data, imply that fluid released during high-temperature/high-pressure dehydration of hydrous mineral assemblages in the Earth's interior under some circumstances may carry significant concentrations of Zr and probably other high field strength elements (HFSEs). This suggestion is consistent with the occurrence of Zr-rich veins in high-grade metamorphic eclogite and granulite terranes. Moreover, aqueous fluids transported from dehydrating oceanic crust into overlying mantle source rocks of partial melting also may carry high-abundance HFSE of fluids released from dehydrating slabs and transported to the source rock of partial melting in the overlying mantle wedge. These processes may have been operational in the Earth's history within which subduction resembling that observed today was operational.

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“…These techniques complement x-ray diffraction (XRD) measurements. The XANES is able to determine the chemical surrounding (e.g., crystal field, density of unoccupied states, and the orientation of the specimen with respect to the polarization of the photon) 27,28 . Typically, measurements are made in transmission mode if attenuation length of the photon in the material being analysed is sufficiently long; however, in the soft X-ray region, due to small attenuation length, XANES measurements are made by detecting total electron yield (TEY), which is surface sensitive 29 .…”

Section: Introductionmentioning

confidence: 99%

Fingerprints of short-range and long-range structure in BaZr_1−xHf_xO₃ solid solutions: an experimental and theoretical study

Fassbender

Lilge

Cava

et al. 2015

Phys. Chem. Chem. Phys.

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Microwave-assisted hydrothermal method was applied to synthesize BaZr 1−x Hf x O 3 , (BZHO) solid solutions at low temperature, 140 • C, and relative short times, 160 min. The detailed features of the crystal structure, at both short and long ranges, as well as the crystal chemistry doping process, are extensively analysed. X-ray diffraction measurements and Raman spectroscopy have been used to confirm that pure and Hf-doped BZO materials present a cubic structure. Extended X-ray absorption fine structure (EXAFS) indicate that Hf 4+ ions has replaced the Zr 4+ ions on the 6-fold coordination and a subsequent change on the Ba 2+ 12-fold coordination can be sensed. X-ray absorption near-edge spectroscopy (XANES) measurements reveal a local symmetry breaking process, associated to overlap of the 4d -2p and 5d -2p orbitals of Zr-O and Hf-O bonds, respectively. Field emission gun (FE-SEM) and high resolution transmission electron microscope (HRTEM) show the mesocrystalline nature of self-assembled BZHO nanoparticles under dodecahedron shape. In addition were performed first principle calculations to complement experimental data. The analysis of the band structures and density of states of undoped BZO and doped BZHO host lattice allow a deep insight on the main electronic features. The theoretical results help us to find a correlation between simulated and experimental Raman modes and allow a more substantial interpretation of crystal structure.

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Evidence for 6‐Coordinated Zirconium in Inactive Nuclear Waste Glasses

Cited by 112 publications

References 17 publications

Structural role of ZrO2 and its impact on properties of boroaluminosilicate nuclear waste glasses

Structural role of ZrO2 and its impact on properties of boroaluminosilicate nuclear waste glasses

An in situ experimental study of Zr4+ transport capacity of water-rich fluids in the temperature and pressure range of the deep crust and upper mantle

Fingerprints of short-range and long-range structure in BaZr_1−xHf_xO₃ solid solutions: an experimental and theoretical study

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Evidence for 6‐Coordinated Zirconium in Inactive Nuclear Waste Glasses

Cited by 112 publications

References 17 publications

Structural role of ZrO2 and its impact on properties of boroaluminosilicate nuclear waste glasses

Structural role of ZrO2 and its impact on properties of boroaluminosilicate nuclear waste glasses

An in situ experimental study of Zr4+ transport capacity of water-rich fluids in the temperature and pressure range of the deep crust and upper mantle

Fingerprints of short-range and long-range structure in BaZr1−xHfxO3 solid solutions: an experimental and theoretical study

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Fingerprints of short-range and long-range structure in BaZr_1−xHf_xO₃ solid solutions: an experimental and theoretical study