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Browsing by Author "Grosvenor, Andrew"

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    Assessing the oxidation states and structural stability of the Ce analogue of brannerite
    (Wiley, 2017) Aluri, Esther Rani; Bachiu, Lisa; Grosvenor, Andrew; Forbes, Scott; Greedan, John
    The Ce‐containing analogue of brannerite (ie, UTi2O6) was previously considered to be stoichio- metric (ie, CeTi2O6); however, it has recently been determined that the material is O deficient. This oxygen‐deficient material has been suggested to be charged balanced by the presence of a minor concentration of Ce3+ or by the A‐site being cation deficient with the Ce oxidation state being 4+. A variety of Ti‐containing oxides (including brannerite) have been investigated as potential nuclear wasteforms, and it is necessary to understand the electronic structure of a proposed nuclear wasteform material as well as how the structure responds to radiation from incorporated waste elements. The radiation resistance of a material can be simulated by ion implantation. The objective of this study was to confirm the Ce oxidation state in the cation‐ and oxygen‐deficient material (ie, Ce0.94Ti2O6 − δ) and to determine how radiation damage affects this material. X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near‐edge spectros- copy were used to study Ce0.94Ti2O6 − δ before and after being implanted with 2 MeV Au− ions. Analysis of the Ce 3d XPS spectra from the as‐synthesized samples by using a previously developed fitting method has unequivocally shown that Ce adopts both 4+ (major) and 3+ (minor) oxidation states, which was confirmed by examination of magnetic susceptibility data. Analysis of XPS and X‐ray absorption near‐edge spectroscopy spectra from ion‐implanted materials showed that both Ce and Ti were reduced because of radiation damage and that the local coordination environments of the cations are greatly affected by radiation damage.
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    Identifying calcium-containing mineral species in the JEB Tailings Management Facility at McClean Lake, Saskatchewan
    (Elsevier, 2016) Blanchard, Peter; Grosvenor, Andrew; Rowson, John; Hughes, Kebbi; Brown, Caitlin
    The JEB Tailings Management Facility (TMF) is central to reducing the environmental impact of the McClean Lake uranium mill facility that is operated by AREVA Resources Canada. This facility has been designed around the idea that elements of concern (e.g., U, As, Ni, Se, Mo) will be controlled through equilibrium with precipitants. Confirming the presence of calcium-containing carbonates in the JEB TMF is the first step in determining if gypsum (CaSO4$2H2O) controls the concentration of HCO 3 (aq), limiting the formation of soluble uranyl bicarbonate complexes. A combination of X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), and microprobe X-ray fluorescence (XRF) mapping was used to analyze a series of tailings samples from the JEB TMF. Calcium carbonate in the form of calcite (CaCO3), aragonite (CaCO3), and dolomite (CaMg(CO3)2) were identified by analysing Ca K-edge m-XANES spectra coupled with microprobe XRF mapping. This is the first observation of these phases in the JEB TMF. The combination of m-XANES and XRF mapping provided a greater sensitivity to low concentration calcium species compared to the other techniques used, which were only sensitive to the major species present (e.g., gypsum).
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    Investigating the Geochemical Model for Molybdenum Mineralization in the JEB Tailings Management Facility at McClean Lake, Saskatchewan: An X‐ray Absorption Spectroscopy Study
    (American Chemical Society, 2015) Blanchard, Peter; Hayes, John; Grosvenor, Andrew; Rowson, John; Hughes, Kebbi; Brown, Caitlin
    The geochemical model for Mo mineralization in the JEB Tailings Management Facility (JEB TMF), operated by AREVA Resources Canada at McClean Lake, Saskatchewan, was investigated using X-ray Absorption Near-Edge Spectroscopy (XANES), an elemental-specific technique that is sensitive to low elemental concentrations. Twenty five samples collected during the 2013 sampling campaign from various locations and depths in the TMF were analyzed by XANES. Mo K-edge XANES analysis indicated that the tailings consisted primarily of Mo6+ species: powellite (CaMoO4), ferrimolybdite (Fe2(MoO4)3·8H2O), and molybdate adsorbed on ferrihydrite (Fe(OH)3 − MoO4). A minor concentration of a Mo4+ species in the form of molybdenite (MoS2) was also present. Changes in the Mo mineralization over time were inferred by comparing the relative amounts of the Mo species in the tailings to the independently measured aqueous Mo pore water concentration. It was found that ferrimolybdite and molybdate adsorbed on ferrihydrite initially dissolves in the TMF and precipitates as powellite.
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    Investigating the local structure of B-site cations in (1-x) BaTiO3exBiScO3 and (1-x)PbTiO3exBiScO3 using X-ray absorption spectroscopy
    (Elsevier, 2018) Blanchard, Peter; Grosvenor, Andrew
    The structural properties of (1-x)BaTiO3exBiScO3 and (1-x)PbTiO3exBiScO3 were investigated using powder X-ray diffraction and X-ray absorption spectroscopy. Diffraction measurements confirmed that substituting small amounts of BiScO3 into BaTiO3 initially stabilizes a cubic phase at x 1⁄4 0.2 before im- purity phases begin to form at x 1⁄4 0.5. BiScO3 substitution also resulted in noticeable changes in the local coordination environment of Ti4þ. X-ray absorption near-edge spectroscopy (XANES) analysis showed that replacing Ti4þ with Sc3þ results in an increase in the off-centre displacement of Ti4þ cations. Sur- prisingly, BiScO3 substitution has no effect on the displacement of the Ti4þ cation in the (1-x)PbTiO3 exBiScO3 solid solution.
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    Investigation of CeTi2O6- and CaZrTi2O7-containing glass–ceramic composite materials
    (NRC Research Press, 2017) Paknahad, Elham; Grosvenor, Andrew
    Glass–ceramic composite materials are being investigated for numerous applications (i.e., textile, energy storage, nuclear waste immobilization applications, etc.) due to the chemical durability and flexibility of these materials. Borosilicate and Fe–Al–borosilicate glass–ceramic composites containing brannerite (CeTi2O6) or zirconolite (CaZrTi2O7) crystallites were synthe- sized at different annealing temperatures. The objective of this study was to understand the interaction of brannerite or zirconolite-type crystallites within the glass matrix and to investigate how the local structure of these composite materials changed with changing synthesis conditions. Powder X-ray diffraction (XRD) and Backscattered electron (BSE) microprobe images have been used to study how the ceramic crystallites dispersed in the glass matrix. X-ray absorption near edge spectros- copy (XANES) spectra were also collected from all glass–ceramic composite materials. Examination of Ti K-, Ce L3-, Zr K-, Si L2,3-, Fe K-, and Al L2,3-edge XANES spectra from the glass–ceramic composites have shown that the annealing temperature, glass composition, and the loading of the ceramic crystallites in the glass matrix can affect the local environment of the glass–ceramic composite materials. A comparison of the glass–ceramic composites containing brannerite or zirconolite crystallites has shown that similar changes in the long range and local structure of these composite materials occur when the synthesis conditions to form these materials or the composition are changed.
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    Investigation of NdxY0.25–xZr0.75O1.88 inert matrix fuel materials made by a co-precipitation synthetic route
    (NRC Research Press, 2016) Hayes, John; Grosvenor, Andrew
    Yttria-stabilized zirconia (YSZ) is a material that is being considered for use as an inert matrix fuel in nuclear reactors, but a complete characterization of these materials is required for them to be licensed for use. A series of NdxY0.25–xZr0.75O1.88 materials have been synthesized using a co-precipitation method, and the thermal stability of these materials has been studied by annealing them at 1400 and 1500 °C. (Nd was used as surrogate for Am.) The long-range and local structures of the materials were characterized via powder X-ray diffraction, scanning electron microscopy, wavelength dispersive spectroscopy, and X-ray absorption spectroscopy at the Zr K- and Y K-edges. These results were compared with the previous characterization of Nd-YSZ materials synthesized using a ceramic method. The results indicated that the ordering in the local metal–oxygen polyhedral remains relatively unaffected by the synthetic method, but there was increased long-range disorder in the materials prepared by the co-precipitation method. Further, it was found that the materials produced by the co-precipitation method were unexpect- edly unstable when annealed at high temperature. This study highlights the importance of determining the effect of synthetic method on material properties and demonstrates how the co-precipitation route could be used to produce inert matrix fuels.
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    Investigation of the stability of glass-ceramic composites containing CeTi2O6 and CaZrTi2O7 after ion implantation
    (Elsevier, 2017) Paknahad, Elham; Grosvenor, Andrew
    Glass-ceramic composite materials have been investigated for nuclear waste sequestration applications due to their ability to incorporate large amounts of radioactive waste elements. A key property that needs to be understood when developing nuclear waste sequestration materials is how the structure of the material responds to radioactive decay of nuclear waste elements, which can be simulated by high en- ergy ion implantation. Borosilicate glass-ceramic composites containing brannerite-type (CeTi2O6) or zirconolite-type (CaZrTi2O7) oxides were synthesized at different annealing temperatures and investi- gated after being implanted with high-energy Au ions to mimic radiation induced structural damage. Backscattered electron (BSE) images were collected to investigate the interaction of the brannerite crystallites with the glass matrix before and after implantation and showed that the morphology of the crystallites in the composite materials were not affected by radiation damage. Surface sensitive Ti K-edge glancing angle XANES spectra collected from the implanted composite materials showed that the structures of the CeTi2O6 and CaZrTi2O7 ceramics were damaged as a result of implantation; however, analysis of Si L2,3-edge XANES spectra indicated that the glass matrix was not affected by ion implantation.
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    Investigation of the Thermal Stability of NdxScyZr1−x−yO2−δ Materials Proposed for Inert Matrix Fuel Applications
    (American Chemical Society, 2016) Hayes, John; Grosvenor, Andrew; Saoudi, Mouna
    Inert matrix fuels (IMF) consist of transuranic elements (i.e., Pu, Am, Np, Cm) embedded in a neutron transparent (inert) matrix and can be used to “burn up” (transmute) these elements in current or Generation IV nuclear reactors. Yttria-stabilized zirconia has been extensively studied for IMF applications, but the low thermal conductivity of this material limits its usefulness. Other elements can be used to stabilize the cubic zirconia structure, and the thermal conductivity of the fuel can be increased through the use of a lighter stabilizing element. To this end, a series of NdxScyZr1−x−yO2−δ materials has been synthesized via a co-precipitation reaction and characterized by multiple techniques (Nd was used as a surrogate for Am). The long-range and local structures of these materials were studied using powder X-ray diffraction, scanning electron microscopy, and X-ray absorption spectroscopy. Additionally, the stability of these materials over a range of temperatures has been studied by annealing the materials at 1100 and 1400 °C. It was shown that the NdxScyZr1−x−yO2−δ materials maintained a single cubic phase upon annealing at high temperatures only when both Nd and Sc were present with y ≥ 0.10 and x + y > 0.15.
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    An investigation of the thermal stability of NdxYyZr1 x yO2 d inert matrix fuel materials
    (Elsevier, 2015) Hayes, John; Grosvenor, Andrew; Saoudi, Mounda
    An important step in achieving a closed uranium fuel cycle is to develop new inert matrix fuel (IMF) materials for use in the burn-up of transuranic species (TRU; i.e., Pu, Np, Am, Cm). Cubic fluorite zirconia (ZrO2) has ideal properties for use in IMF applications, but it is not stable at room temperature and must be stabilized through the addition of small amounts of dopants such as Y. While Y-substituted zirconia (YSZ) has been extensively studied, relatively little work has been done to investigate how the addition of an actinide to the YSZ system affects the properties of these materials. To this end, the long-range and local structures of a series of NdxYyZr1 x yO2 d compounds (Nd was used as a surrogate for Am) were studied using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray absorption spectroscopy (XAS) at the Zr K-, Zr L3-, Y K-, and Nd L3-edges. The thermal stability of Nd–YSZ materials was also investigated by annealing the materials at temperatures ranging between 600 and 1400 °C. These studies showed that the thermal stability of the NdxYyZr1-x-yO2-d system was improved by the addition of small amounts of Y (i.e. 5 at.%) to the system. Additionally, the XAS results showed that the local structure around Zr remained relatively constant; only changes in the second coordination shell were observed when the materials were annealed. These results strongly suggest that the addition of Y can significantly improve the thermal stability of zirconia-based IMFs. This study has also confirmed the importance and value of using advanced characterization techniques that are sensitive to the local struc- tures of a material (i.e., XAS).
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    Probing the effect of radiation damage on the structure of rare-earth phosphates
    (Elsevier, 2015) Rafiuddin, Mohamed Ruwaid; Grosvenor, Andrew
    Synthetic analogues of naturally occurring monazite (REPO4; RE = La to Gd) and xenotime (RE0PO4; RE0 = Tb to Lu and Y) minerals have been identified as potential wasteforms for nuclear waste. High energy ion-implantation of crystalline materials simulates radiation-induced structural damage and allows for the radiation resistance of a crystal structure to be probed. The structural stability of Au ion- implanted La1-xYbxPO4 materials was investigated using micro-X-ray diffraction (m-XRD) and glancing angle X-ray absorption near-edge spectroscopy (GA-XANES) in this study. The long- and short-range order of La1-xYbxPO4 (x = 0, 0.3, 0.7, 1.0) is affected by ion-implantation and, thus, the materials are prone to structural damage. The structures of some members of the La1-xYbxPO4 series (x = 0.7 and 1.0) were observed to partially recover after being implanted with Au ions to a high dose. The structures of all members of the La1-xYbxPO4 series were observed to recover from damage resulting from ion- implantation after annealing the materials at temperatures >300 C.
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    A Structural Investigation of Hydrous and Anhydrous Rare-Earth Phosphates
    (American Chemical Society, 2016) Rafiuddin, Mohamed Ruwaid; Grosvenor, Andrew
    Rhabdophane- (REPO4·nH2O; RE = La to Dy), monazite- (REPO4; RE = La to Gd), and xenotime-type (REPO4 and RE′PO4·nH2O; RE = Tb to Lu and Y; RE′ = Ho to Lu and Y) rare-earth phosphate materials are being considered for a number of applications including as photonic materials, for biolabeling studies, and as potential nuclear wasteforms. Structural studies of hydrous rare-earth phosphates are rather limited when compared to anhydrous rare-earth phosphates. In this study, rhabdophane- (REPO4·nH2O; RE = La, Nd, Sm, Gd, and Dy) and xenotime-type (REPO4·nH2O; RE = Y and Yb) materials were synthesized by a precipitation-based method and investigated using X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES). Examination of the powder XRD data from rhabdophane-type materials has confirmed that the rhabdophane structure crystallizes in the monoclinic crystal system rather than the hexagonal structure that has most often been reported. Materials adopting the rhabdophane- or xenotime-type structure were studied as a function of temperature to understand how the structure varies with increasing annealing temperature. Local structural information was obtained by collecting P K- and RE L1-edge XANES spectra. Examination of P K-edge XANES spectra from rhabdophane- and xenotime-type materials revealed changes in the local environment around P as a function of temperature. These changes were attributed to the removal of water from these structures as a result of high temperature annealing.
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    A study of the electronic structure and structural stability of Gd2Ti2O7 based glass-ceramic composites
    (the Royal Society of Chemistry, 2015) Aluri, Esther Rani; Grosvenor, Andrew
    Glass-ceramic composite materials have been investigated for nuclear waste sequestration applications due to their ability to incorporate large amounts of radioactive waste elements. Borosilicate- and Fe–Al–borosilicate glass-ceramic composites containing pyrochlore-type Gd2Ti2O7 crystallites were synthesized at different annealing temperatures and investigated by multiple techniques. Backscattered electron (BSE) images were collected to investigate the interaction of the pyrochlore crystallites with the glass matrix. Examination of the X-ray absorption near edge spectroscopy (XANES) spectra from the composite materials has shown how the glass composition, pyrochlore loading, and annealing temperature affects the chemical environment around the metal centers. These investigations have shown that the Gd2Ti2O7 crystallites can dissolve in the glass matrix depending on the glass composition and annealing temperature. The borosilicate glass composite materials were implanted with high-energy Au ions to mimic radiation induced structural damage. Surface sensitive glancing angle XANES spectra collected from the implanted composite materials have shown that structural damage of Gd2Ti2O7 occurs as a result of implantation, and that these materials show a similar response to ion implantation as Gd2Ti2O7 alone.
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    XPS and EELS characterization of Mn2SiO4, MnSiO3 and MnAl2O4
    (Elsevier, 2016) Grosvenor, Andrew; Bellhouse, Erika; Korinek, A.; Bugnet, M.; McDermid, Joseph
    X-ray Photoelectron Spectroscopy (XPS) and Electron Energy Loss Spectroscopy (EELS) are strong candi- date techniques for characterizing steel surfaces and substrate-coating interfaces when investigating the selective oxidation and reactive wetting of advanced high strength steels (AHSS) during the continuous galvanizing process. However, unambiguous identification of ternary oxides such as Mn2SiO4, MnSiO3, and MnAl2O4 by XPS or EELS, which can play a significant role in substrate reactive wetting, is difficult due to the lack of fully characterized standards in the literature. To resolve this issue, samples of Mn2 SiO4 , MnSiO3 and MnAl2O4 were synthesized and characterized by XPS and EELS. The unique features of the XPS and EELS spectra for the Mn2 SiO4 , MnSiO3 and MnAl2 O4 standards were successfully derived, thereby allowing investigators to fully differentiate and identify these oxides at the surface and subsurface of Mn, Si and Al alloyed AHSS using these techniques.