Browsing by Author "Vance, ER"
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- ItemActinides in gology, energy, and the environment. Quantification of α-particle radiation damage in zircon.(GeoScienceWorld, 2014-10-01) Smye, KM; Brigden, C; Vance, ER; Farnan, IAnalysis of radiation damage in natural mineral analogs such as zircon is important for the evaluation of the long-term behavior of nuclear waste forms and for geochronology. Here we present results of experiments to determine the partitioning of radiation damage due to the heavy nuclear recoil of uranium and thorium daughters and the α-particles ejected in an α-decay event in zircon. Synthetic polycrystalline zircon ceramics were doped with 10B and irradiated in a slow neutron flux for 1, 10, and 28 days to achieve the reaction 10B + n → 7Li + α (+2.79 MeV), creating an α event without a heavy nuclear recoil. The 7Li atoms produced in the nuclear reaction were directly detected by NMR “spin-counting”, providing a precise measurement of the α-dose applied to each sample. The amount of damage (number fraction and volume fraction) created by each α-event (one α-event being a 7Li + α-particle) has been quantified using radiological nuclear magnetic resonance and X-ray diffraction data. The number of permanently displaced atoms in the amorphous fraction was determined by 29Si NMR to be 252 ± 24 atoms for the 10B(n,α) event when the heavy recoil is absent, which is broadly in agreement with ballistic Monte Carlo calculations. The unit-cell swelling of the crystalline fraction, determined by X-ray diffraction, is small and anisotropic. The anisotropy is similar to that observed in ancient natural samples and implies an initial anisotropic swelling mechanism rather than an anisotropic recovery mechanism occurring over geological timescales. The small unit-cell volume swelling is only ~6% of the expansion frequently attributed to α-particles associated with an actinide α-decay event. The lattice parameters indicate a volume increase as α function of a dose of 0.21 A3/1018 α-events/g, which is significantly less than the increase of 3.55 A3/1018 α-events/g seen in Pu-doped zircon and 2.18 A3/1018 α-events/g seen in natural zircon. It is concluded that the heavy recoil plays a more important role in unit-cell swelling than previously predicted. The likely mechanism for such an effect is the rapid, and thus defect-rich, recrystallization of material initially displaced by the heavy recoil. © 2014, Mineralogical Society of America.
- ItemAlternative Synroc formulations(Cambridge University Press/Springer Nature, 2011-02-25) Vance, ER; Smith, KL; Thorogood, GJ; Begg, BD; Moricca, SA; Angel, PJ; Stewart, MWA; Ball, CJPerovskite is the least durable of the resistate minerals comprising Synroc-C and it is desirable to reduce its abundance in Synroc. Kinetic limitations and competition with Csapparently affect the incorporation of Sr into hollandite during hot-pressing at 1200°C/20 MPa so that ~ 10% of perovskite (a value below the percolation limit) is probably an optimum target. Zirconolite-rich Synroc formulations have been prepared for actinide-rich wastes. Background XRD and TEM studies have also been performed to study the crystal-chemical behaviour of Nd (a simulant of trivalent actinides) in zirconolite. Either rare-earth compensated perovskite or freudenbergite in Synroc can evidently be used to immobilise Na-bearing HLW. © 1992 Materials Research Society
- ItemAqueous dissolution and immobilisation potential of geopolymers for radioactive ions(Materials Australia, 2007-07-02) Vance, ER; Perera, DS; Aly, Z
- ItemAqueous leachability of geopolymers containing cations Ag, Cd, and Co(The Italian Ceramic Society, 2008-06-29) Perera, DS; Aly, Z; Davis, J; Kurlapski, I; Vance, ER
- ItemAqueous leachability of metakaolin-based geopolymers with molar ratios of Si/Al=1.5-4(Elsevier, 2008-08-31) Aly, Z; Vance, ER; Perera, DS; Hanna, JV; Griffith, CS; Davis, J; Durce, DThe leachability in water of metakaolin based geopolymers with molar ratios of Na/Al = 1 and Si/Al = 1.5-4.0 has been investigated in order to optimise the composition for the immobilisation of nuclear waste. Formulations with Si/Al of around 2 are the most suitable using the ASTM/PCT leach test method. The variability of the leach results is discussed with reference to the microstructure, compressive strength and the degree of polymerisation of the geopolymers as observed here by solid state nuclear magnetic resonance, XRD and infrared measurements. © 2008, Elsevier Ltd.
- ItemAqueous leachability of metakaolin-based geopolymers with molar ratios of Si/Al=1.5-4(Materials Australia, 2007-07-04) Aly, Z; Davis, J; Vance, ER; Perera, DS; Durce, D; Hanna, JV
- ItemCation antisite disorder in uranium-doped gadolinium zirconate pyrochlores(Elsevier, 2014-09-01) Gregg, DJ; Zhang, ZM; Thorogood, GJ; Kennedy, BJ; Kimpton, JA; Griffiths, GJ; Guagliardo, PR; Lumpkin, GR; Vance, ERThe incorporation of uranium into gadolinium zirconate (Gd2Zr2O7) is investigated by synchrotron X-ray powder diffraction and X-ray absorption near-edge structure (XANES) spectroscopy. The results suggest that the uranium cation is largely located on the pyrochlore B-site instead of the targeted A-site. Cation disorder in Gd2Zr2O7 and U-doped Gd2Zr2O7 is investigated by positron annihilation lifetime spectroscopy (PALS) which demonstrates the absence of cation vacancies in these systems. This work provides direct evidence for cation antisite (A- and B-site mixing) disorder in U-doped and off-stoichiometric Gd2Zr2O7 pyrochlore. © 2014, Elsevier B.V.
- ItemCell parameters and the orthorhombic to cubic transformation in strontium substituted perovskite (CaTiO3)(Australian and New Zealand Institutes of Physics, 1994-02-10) Ball, CJ; Begg, BD; Vance, ERThe departure of the orthorhombic unit cell of perovskite (CaTiO3) from the cubic symmetry can be characterised by the angle of shear, ∅ of the pseudo-cubic sub-cell. We have determined ∅ for a series of strontium-substituted perovskites, of general formula Cai-xSrxTiO3, at room temperature. ∅ decreases linearly with increases in x and extrapolates to zero at x ≈ 0.4, in fair agreement with previous work. For x > 0.4 the structure is cubic, contrary to previous reports.
- ItemCeramic waste forms(Elsevier, 2012-02-01) Vance, ERFor nearly 40 years, ceramics have been commonly seen to be competitors to the baseline borosilicate glass option for the immobilization of high- and intermediate-level nuclear waste. However, it is now increasingly clear that the wide variety of extant nuclear wastes will ensure that both glasses and ceramics will have very significant roles to play in the immobilization of nuclear wastes and thus confirm one of the criteria of sustainability for nuclear power production. Currently, hot isostatic pressing technology is making a strong impression as a very advantageous processing technique for the consolidation of ceramics and glass–ceramics for nuclear waste immobilization. Copyright © 2012, Elsevier
- ItemCharacterisation of metakaolin-based geopolymers using beam-based and conventional PALS(Institute of Physics, 2010-08-01) Guagliardo, P; Roberts, J; Vance, ER; Weed, R; Sergeant, AD; Howie, A; Wilkie, P; Went, M; Sullivan, J; Williams, J; Samarin, S; Buckman, SJThe nano-porosity of metakaolin-based geopolymers and the effect of heat-treatment on porosity have been studied with conventional and beam-based positron annihilation lifetime spectroscopy (PALS). Conventional PALS found significant nano-porosity in the geopolymers, as indicated by the presence in the PALS spectrum of two long lifetime components, τ3 = 1.58 ns and τ4 = 47 ns, associated with pore diameters of approximately 0.5 and 3 nm respectively. The lifetime of the shorter component was found to decrease monotonically with successive heat treatments of 300°C and 600°C. Beam-based PALS, conducted at 5 keV, also indicated two long lifetime components, τ3 = 4.84 ns and τ4 = 54.6 ns. These are significantly longer than those observed by conventional PALS and the monotonic decrease of τ3 with successive heat treatments was not observed. As the beam-based PALS probed only the near-surface region, with an average implantation depth of about 350 nm, these results suggest that the near-surface structure may vary significantly from that of the bulk. This could be an inherent property of the samples or an artefact caused by surface effects or sample outgassing. © Copyright 2020 IOP Publishing
- ItemCharge compensation mechanisms for aliovalent impurities in perovskite and zirconolite(Australian and New Zealand Institutes of Physics, 1994-02-10) Vance, ER; Day, RA; Begg, BD; Blackford, MGAs part of the chemical design of Synroc-type ceramics for the immobilisation of different high-level radioactive wastes from nuclear fuel reprocessing, it is necessary to understand the various possible charge compensation mechanisms which occur when up to tens of atomic percent of rare earths and actinides are incorporated in solid solution in perovskite (CaTiO3) and zirconolite (CaZrTi2O7). In particular the solid solution of Gd in the Ca site of perovskite and the incorporation of Nd, Ce, U, Np and Pu in the Ca and Zr sites of zirconolite have been studied by XRD, SEM, TEM, and XANES. The essential conclusions are that in formulations where charge compensating ions are made available, then this is the preferred mechanism for incorporation of these cations in Ca and Zr sites. However in formulations where such compensators are not made available, it is possible for charge compensation to take place via significant abundances of cation vacancies, or by the appearance of unexpected valence states stabilised by crystal-chemical forces. An example of the latter is the probable stabilisation of Ti3+ in Ti sites, and of trivalent Ce and actinides in Ca and Zr sites, even under quite oxidising conditions. A complication in these studies is the effect of prevailing or inherited redox conditions. Redox conditions influence phase abundances and compositions as they control the valencies of cations capable of more than one oxidation state. There is also an indication that reducing conditions can promote oxygen site deficiencies in some formulations. Other complicating factors relate to sample fabrication, arising from the need to make extremely chemically uniform phases having the desired composition. This requires prolonged heating at high temperatures to achieve complete solid-state reaction that may result in selective losses due to volatilisation. Incipient melting due to localised eutectic formation and the apparently straightforward task of efficient stoichiometric mixing on a 1 to 10 um scale are other problems which have had to be overcome in sample fabrication.
- ItemComparative study of Synroc-c ceramics produced by hot-pressing and inductive melting(Materials Research Society, 1997) Sobolev, IA; Stefanovsky, SV; Omelianenko, BI; Ioudintsev, SV; Vance, ER; Jostsons, AThree Synroc-C samples, containing simulated high level waste were studied. One was produced by the conventional hot-pressing method at ANSTO, Australia, and the others were obtained using cold crucible technology at Radon, Russia. One of the melted samples was prepared using the Australian sol-gel precursor and the second one was obtained from an oxide-nitrate mixture. It was established that the specimens have closely similar mineral compositions, with major hollandite, perovskite, zirconolite, and rutile. Small amounts of hibonite were also found. Unlike the hot-pressed Synroc containing metallic alloy particles, melted Synrocs contain molybdates. An investigation of mineral compositions and elemental distribution in the samples was carried out. Features of hot-pressed and melted ceramics were compared. Unit cell parameters of the Synroc phases were determined and preliminary results on durability of the melted Synroc are presented. © Materials Research Society 1997
- ItemComparison of measured aqueous leachabilities of Cs- and Sr- containing metakaolin-based geopolymers using regulatory leaching test protocols(The Italian Ceramic Society, 2008-06-29) Aly, Z; Vance, ER; Perera, DS
- ItemComparison of sodium zirconium phosphate-structured HLW forms and Synroc for high-level nuclear waste immobilization(Materials Research Society, 1997) Zyryanov, VN; Vance, ERThe incorporation of (a) Cs and Sr as; (b) simulated actinides, and (c) simulated Purex waste in sodium zirconium phosphate (NZP) has been studied. The samples were prepared by sintering, by hot pressing and by hot isostatic pressing in metal bellows containers. The short-term chemical durability of the phosphate-based material containing Purex waste was within an order of magnitude ofthat for Synroc-C, as measured by 7-day MCC-1 tests at 90°C. The dissolution behaviour showed evidence of re-precipitation phenomena, even after times as short as 28 days. Potential for improvement of NZP-based ceramics for HLW management is discussed. © Materials Research Society 1997
- ItemCrystal chemistry and phase manipulation in Synroc(Trans Tech Publications Ltd, 1991) Vance, ER; Moricca, SA; Thorogood, GJ; Lumpkin, GRSynroc is a multi-phase ceramic designed for geological immobilisation of radioactive waste produced by reprocessing nuclear fuel from power reactors [1]. The main crystalline phases are hollandite, perovskite, zirconolite, and reduced titanium oxide. The compositions of these phases and the nuclides they can incorporate in solid solution are shown in Table 1. Table 1. Principal Phases comprising Synroc Phase Nominal Composition Waste nuclides incorporated Estimated wt%* [2] Hollandite Ba1.14(Al, Tr3+)2.28Ti6O16 Cs, Sr, Rb 25 Perovskite CaTio3 Sr, RE, An 20 Zirconolite CaZrTi2O7 RE, An 20 Titanium Oxide TinO2n-1 - 35 *No HLW present RE = rare earths, An = actinides. The main (Synroc-C) formulation is designed for Purex reprocessing waste and the standard composition is wt%: Al2O3(4.3); BaO(4.4); CaO(8.8); ZrO2(5.6); TiO2(57.9); waste oxides (20). The loading of high-level waste (HLW) oxides can be varied if desired, but probably cannot exceed a value of 30-35% [2]. Several variants of this composition have been formulated at the laboratory scale, with Synroc-D, E and F being directed towards Savannah River (U.S.A.) military waste, encapsulation of high-level nuclear reprocessing waste and unreprocessed spent fuel respectively. © 1991 Trans Tech Publications Ltd.
- ItemCrystal chemistry and structures of (Ca,U) titanate pyrochlores(Wiley-Blackwell, 2010-10-01) James, M; Carter, ML; Zhang, ZM; Zhang, YJ; Wallwork, KS; Avdeev, M; Vance, ERAnalysis of multiphase (Ca,U) titanate pyrochlore samples produced under argon or in air, using laboratory X-ray powder diffraction (XRD) and electron microscopy revealed discrete pyrochlore phase compositions, together with either perovskite or rutile impurities. Investigations of these samples using diffuse reflectance and X-ray photoelectron spectroscopies revealed mixed U4+/U5+ oxidation states for argon-annealed samples and U5+/U6+ oxidation states for air-annealed samples. Single-phase (Ca1.25U4+0.25U5+0.50)Ti2O7 (argon) and (Ca1.40U5+0.60)(Ti1.90U6+0.10)O7 (air) compositions were synthesized and characterized using a combination of synchrotron X-ray and neutron powder diffraction. Severe intensity reduction of hkl odd XRD peaks from the sample produced in air was found to be the result of U6+ sharing the Ti site. The refined crystal structures for both single-phase samples were found to be consistent with the compositions and mixed oxidation states observed by the above spectroscopic measurements. Although the normalized uranium leach rate of the argon-annealed sample was found to be approximately twice that of the air-annealed sample, in 7-day Product Consistency Test the durability of both compounds with respect to leaching by water was found to be excellent. Ca releases were in the range of 0.01–0.03 g/L and U releases were <3 × 10−5 g/L. © 2010, Wiley-Blackwell.
- ItemDevelopment and evaluation of an early removal process for the beneficiation of arsenic-bearing copper ores.(Elsevier, 2010-12) Bruckard, WJ; Davey, KJ; Jorgensen, FRA; Wright, S; Brew, DRM; Hague, N; Vance, ERIn conventional flotation flowsheets for treating copper sulphide ores containing small but significant amounts of arsenic, the arsenic is generally concentrated with the copper in final concentrate. Often, a penalty can be imposed by the smelter processing the concentrate, based on the arsenic content. In some cases the arsenic level is such that the smelter will not treat or accept the concentrate. A new approach to address this issue is reported in this paper, which is becoming more significant as the quality of the copper ore bodies currently being mined diminishes. A new flowsheet, based on the early removal of arsenic at the concentrator, has been developed and tested at bench-scale. The proposed flowsheet comprises three key steps: firstly, separation of arsenic and copper minerals using controlled-potential flotation to produce a low-arsenic high-copper concentrate and a high-arsenic low-copper concentrate. The low-arsenic concentrate can be sold without incurring any penalty for arsenic content. In the second stage, the high-arsenic concentrate is subjected to a low temperature roasting, where the arsenic is selectively fumed off into a low-volume stream product. The calcine from the roaster is high in copper and sulphur and can still be smelted directly. In the final stage of the flowsheet, the arsenic in the fume product is immobilised in a low temperature ceramic such that safe disposal back into the ground is possible. The new early removal flowsheet has been sequentially tested in the laboratory at small scale. The technical and economic merits of the flowsheet compared with that of the conventional copper flotation flowsheet show that there is a net benefit. © 2010, Elsevier Ltd.
- ItemDiffuse reflectance and x-ray photoelectron spectroscopy of uranium in ZrO2 and Y2Ti2O7.(Elsevier, 2010-05-01) Vance, ER; Zhang, YJ; Zhang, ZMDiffuse reflectance measurements were made over the wavenumber range of 4000–20,000 cm−1 at room temperature on monoclinic and stabilised ZrO2, together with Y2Ti2O7 having the pyrochlore structure, all of which were doped with U and sintered in various atmospheres. X-ray photoelectron spectroscopy measurements were also carried out on selected samples. In monoclinic and stabilised zirconia, U exhibited valence states of +4 and/or +5, depending on the sintering atmosphere and the presence of appropriate charge compensators. Using both diffuse reflectance and X-ray photoelectron spectroscopy, U was also observed as mainly U4+ and/or U5+ in U-doped Y2Ti2O7 sintered at 1400°C in air or Ar, although a small amount of U6+ also appeared to be present in some U-doped Y2Ti2O7 samples heated in air. © 2010, Elsevier Ltd.
- ItemFe and Mg solubility in the Ca site of zirconolite, CaZrTi2O7(Australian Institute of Physics, 2004-02-04) Vance, ER; Cashio, JG; Hanna, JV; Garrett, Z; Bhati, MThe solid solubility of Fe in the Ca site of zirconolite appears to be approximately the same whether it is incorporated as the divalent or trivalent species. Divalent Fe was encouraged by using an argon firing atmosphere and direct substitution in the Ca site [Ca(1-x)FexZrTi2O7] and trivalent Fe by the use of an air atmosphere and Al compensation in the Ti site [Ca(1-x)FexZrTi(2-x)AlxO7]. The anticipated valences were confirmed by X-ray near-edge, Xray photoelectron and Mossbauer spectroscopies. Changing the firing atmosphere from argon to air and vice versa also changed the Fe valences, but scanning electron microscopy showed that small amounts of second phase, Fe-bearing materials were present. The possible reasons for the apparently similar solid solubilities of divalent and trivalent Fe in the Ca site are discussed. Solid state magic-angle nuclear magnetic resonance was used to study Mg speciation in the Ca and Ti sites of zirconolite.
- ItemFe speciation in geopolymers with Si/Al molar ratio of ~2.(Elsevier, 2007-05-01) Perera, DS; Cashion, JD; Blackford, MG; Zhang, Z; Vance, ERThe speciation of Fe was studied in metakaolin-based geopolymers to which Fe was added as ferric nitrate solution or freshly precipitated ferric hydroxide. From Mössbauer and near-edge X-ray absorption spectroscopies, coupled with X-ray diffraction and electron microscopy, it was concluded that in as-cured geopolymers the Fe was present in octahedral sites, either as isolated ions in the geopolymer matrix or as oxyhydroxide aggregates which had not reacted with the starting geopolymer components. For material to which iron nitrate was added, heating to 900°C allowed the formation of nepheline and a glass, both of which contained tetrahedrally coordinated, substituted Fe3+. © 2007, Elsevier Ltd.