Incorporation of uranium in zirconolite (CaZrTi2O7)

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dc.contributor.authorVance, ERen_AU
dc.contributor.authorLumpkin, GRen_AU
dc.contributor.authorCarter, MLen_AU
dc.contributor.authorCassidy, DJen_AU
dc.contributor.authorBall, CJen_AU
dc.contributor.authorDay, RAen_AU
dc.contributor.authorBegg, BDen_AU
dc.date.accessioned2022-11-04T04:49:00Zen_AU
dc.date.available2022-11-04T04:49:00Zen_AU
dc.date.issued2002-07en_AU
dc.date.statistics2022-10-21en_AU
dc.description.abstractUp to 0.15 formula unit (f.u.) of U4+ incorporated in the Zr site of zirconolite by firing CaUxZr(1−x)Ti2O7 compositions in argon at 1400°C allows retention of the 2M polytype. Further U4+ substitution for Zr, up to 0.4 f.u., produces the 4M polytype (containing ∼0.4 f.u. of U) plus the 2M polytype containing 0.15 f.u. of U. The pyrochlore structure (containing 0.6 f.u. of U) forms in conjunction with the 4M polytype at U contents of 0.4 f.u. up to 0.7 f.u. Higher U contents give the pyrochlore structure, but the solid-state reactivity of even alkoxide-based preparations becomes increasingly poor for x > ∼0.7 and hot pressing in graphite dies at ∼1250°C is necessary to achieve near single-phase pyrochlore structures for x= 1. When samples of CaUxZr1−xTi2O7 stoichiometry (x= 0.1 and 0.2) are oxidized at 1400°C in air, diffuse reflectance spectroscopy (DRS) shows evidence for U5+ formation at the expense of U4+ via enhanced absorption bands, ∼50 nm in half-width, near 970 and 1500 nm and correspondingly weakened absorption at 1150 and 1660 nm. Weight gains consistent with complete oxidation of U4+ to U5+ are observed when finely powdered argon-fired samples with x= 0.1 and 0.4 are heated in air to 1200°C. Evidence for U valence states higher than +4 in both argon- and air-heated materials containing charge compensators to encourage U5+ or U6+ formation was also derived from DRS (showing U5+ in particular), and XANES. DRS shows weak absorption bands attributable to U4+ in zirconolites containing ∼0.2 f.u. of U incorporated in the Ca site via Mg or Al substitutions in the Ti sites, with the spectrum being closely but not exactly similar to that attributed to U4+ in the Zr site. Zirconolite and pyrochlore compositions which are melted at 1500° or 1550°C in argon and furnace-cooled yield broadly similar phase assemblages to the corresponding sintered materials, but there is evidence of incongruent melting in all materials. © 2002 The American Ceramic Societyen_AU
dc.description.sponsorshipThis work was supported in part by the Environmental Management Science Program of the U.S. Department of Energy.en_AU
dc.identifier.citationVance, E. R., Lumpkin, G. R., Carter, M. L., Cassidy, D. J., Ball, C. J., Day, R. A., & Begg, B. D. (2002). Incorporation of uranium in zirconolite (CaZrTi2O7). Journal of the American Ceramic Society, 85(7), 1853-1859. doi:10.1111/j.1151-2916.2002.tb00364.xen_AU
dc.identifier.issn1551-2916en_AU
dc.identifier.issue7en_AU
dc.identifier.journaltitleJournal of the American Ceramic Societyen_AU
dc.identifier.pagination1853-1859en_AU
dc.identifier.urihttps://doi.org/10.1111/j.1151-2916.2002.tb00364.xen_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/13991en_AU
dc.identifier.volume85en_AU
dc.language.isoenen_AU
dc.publisherJohn Wiley & Sons, Incen_AU
dc.subjectUraniumen_AU
dc.subjectUranium compoundsen_AU
dc.subjectZirconiumen_AU
dc.subjectZirconium compoundsen_AU
dc.subjectZirconoliteen_AU
dc.subjectSpectroscopyen_AU
dc.subjectPyrochloreen_AU
dc.titleIncorporation of uranium in zirconolite (CaZrTi2O7)en_AU
dc.typeJournal Articleen_AU
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