Browsing by Author "Glover, CJ"
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- ItemFerric iron geometry and coordination during hydrolysis and ferrihydrite precipitation(Mineralogical Society of Great Britain & Ireland, 2011-10-01) Collins, RN; Rose, AL; Glover, CJ; Boland, DD; Payne, TE; Waite, TDDefinitive structural characterisation of ferrihydrite has challenged scientists primarily due to its nanosized particles and inherent long-range structural disorder which challenges analytical methodology (and modelling) typically employed to determine the structure of minerals. Here we report on the application of a synchrotron quick-scanning X-ray absorption spectroscopy (XAS) approach, which allows the collection of Extended X-ray Absorption Fine Structure (EXAFS) spectral data to k = 15 Å-1 in < 1 minute, to obtain unparalleled iron Kedge data on the hydrolysis of FeIII(H2O)6 and ferrihydrite precipitation. Modelling of the pre-edge and EXAFS data: 1) supports theoretical studies which have suggested the existence of a monomeric penta-coordinated FeIII hydrolysis species and; 2) corroborates recently proposed structural models of ferrihydrite that contain tetrahedral FeIII. Modelling results indicate that ferrihydrite consists of 15 to 25 % tetrahedral FeIII and suggest that this geometry must be included in any comprehensive structural model of ferrihydrite and, furthermore, should be considered when evaluating the reactivity, stability and other structure-property relationships of this mineral. © 2011 The Authors.
- ItemIon-irradiation-induced porosity in GaSb and InSb(Australian Institute of Physics, 2005-01-31) Kluth, SM; Johannessen, B; Kluth, P; Glover, CJ; Foran, GJ; Ridgway, MCIon irradiation of crystalline GaSb and InSb can yield not only amorphisation, as commonly observed in semiconductors, but also porosity. Extended x-ray absorption fine structure spectroscopy, electron microscopy and Rutherford backscattering spectrometry have been used to determine the exact nature of and relationship between these two transformations. In both materials, low dose, room temperature implantation produces spherical voids yet the material remains crystalline. With increasing implant dose, the porous layer eventually evolves into a network of straight rods 15nm in diameter. We suggest the porosity arises from preferential clustering of interstitials into extended defects and vacancies agglomerating to form voids.
- ItemKinetics of coupled Fe(II)-catalysed ferrihydrite transformation and U(VI) reduction(Mineralogical Society of Greate Britian & Ireland, 2011-10-01) Boland, DD; Collins, RN; Glover, CJ; Payne, TE; Waite, TDAntimony is released into the environment in some natural and man-induced processes. . Yet, its impact on the transformation processes of heavy metal-adsorbing minerals remains poorly understood. In acid-mine drainage systems and shooting ranges, the adsorption of antimony by iron oxides such as ferrihydrite can play a major role. The poorly crystalline 2-line ferrihydrite represents one of the most common Fe oxides in these settings and can transform to goethite (,-FeOOH) or hematite (,-Fe2O3) with time . The rate of transformation depends on the pH, temperature, and on the ions and molecules present during the transformation process . This study focuses on the transformation of synthetic ferrihydrite to crystalline iron oxides in the presence of Sb(V). Transformations were carried out for 1-16 days at 70 ºC and at pH 4, 7 and 12, with different concentrations of Sb(V) (0.00, 0.23, 0.75, 2.25 and 6.00 mM Sb). Samples taken from aqueous suspensions were washed, dried, and characterized by X-ray diffraction (XRD) and atomic absorption spectroscopy (AAS). At pH 12, goethite (Sb concentrations up to 3.7 mg Sb/g) is favored and the transformation is completed after one day. Only a concentration of 6 mM Sb retarded the transformation, where even after 8 days only 50 % of the ferrihydrite was transformed into goethite. Transformations at pH 7 led to a mixture of 75 % hematite and 25 % goethite (4.3 mg Sb/g). However, at concentrations of 6 mM Sb, feroxyhyte (!-FeOOH) (9.1 mg Sb/g) was favored instead. At pH 4, hematite (32.3 mg Sb/g) was favored except for concentrations of 6 mM Sb, were again feroxyhyte (141.1 mg Sb/g) occurred. We assume that increased Sb concentrations favor feroxyhyte and indicate the incorporation of Sb into the structure of feroxyhyte. © The Authors
- ItemMedium Energy Spectroscopy (MEX) - sample environments and supporting infrastructure(Australian Nuclear Science and Technology Organisation, 2021-11-26) Lamb, K; Glover, CJ; James, S; Finch, E; Wykes, JLThe Medium Energy Spectroscopy (MEX) beamline aims to facilitate a wide variety of ex- and in-situ experimental work from a variety of research areas. As such, we will provide a number of sample environments as standard set-up, in addition to ancillary equipment that can be used with custom or BYO sample environments. Sample environments will likely include; room temperature cell, electrochemical flow cell, micro-fluidic cell, flammable gas cell, furnace with gas environments,and a battery testing cell. In addition, supporting infrastructure and ancillary equipment will likely include; flammable and toxic gas handling (flow and pressure control), gas and vapor ventilation, electrochemical testing station (Autolab or similar), fluid (gas or vapour) syringe pumps with pressure monitoring. Most, if not all, of the sample environments and supporting infrastructure will be controlled with the beamline systems, enabling integration and triggering for maximum achievable automation of experiments.© 2021 The Authors
- ItemPreferential amorphisation of Ge nanocrystals in a silica matrix(Australian Institute of Physics, 2005-01-31) Ridgway, MC; Azevedo, GDM; Elliman, RG; Wesch, W; Glover, CJ; Miller, R; Llewellyn, DJ; Foran, GJ; Hansen, JL; Nylandsted Larsen, ARelative to bulk crystalline material, Ge nanocrystals in a silica matrix exhibit subtle structural perturbations including a non-Gaussian inter-atomic distance distribution. We now demonstrate such nanocrystals are extremely sensitive to ion irradiation. Using transmission electron microscopy, Raman spectroscopy and extended x-ray absorption fine structure spectroscopy, the crystalline-to-amorphous phase transformation in -8 nm diameter nanocrystals and bulk crystalline material has been compared. Amorphisation of Ge nanocrytals in a silica matrix was achieved at an ion dose -100 times less than that required for bulk crystalline standards. This rapid amorphisation of Ge nanocrystals is attributed to the preferential nucleation of the amorphous phase at the nanocrystal/matrix interface, the pre-irradiation, higher-energy structural state of the nanocrystals themselves and an enhanced nanocrystal vacancy concentration due to the more effective trapping of irradiation-induced interstitials at the nanocrystal/matrix interface and inhibited Frenkel pair recombination when Ge interstitials are recoiled into the matrix. To demonstrate the significance of the latter, we show ion irradiation of -2 nm diameter nanocrystals yields their dissolution when the range of recoiled Ge atoms exceeds the nanocrystal bounds.
- ItemPreferential amorphisation of Ge nanocrystals in a silica matrix(Elsevier, 2004-09-05) Ridgway, MC; Azevedo, GDM; Elliman, RG; Wesch, W; Glover, CJ; Miller, R; Llewellyn, DJ; Foran, GJ; Hansen, JL; Nylandsted Larsen, AExtended X-ray absorption fine structure and Raman spectroscopies have been used to compare the crystalline-to-amorphous phase transformation in nanocrystalline and polycrystalline Ge. We demonstrate Ge nanocrystals are extremely sensitive to ion irradiation and are rendered amorphous at an ion dose ∼40 times less than that required to amorphise bulk, crystalline standards. This rapid amorphisation is attributed to the higher-energy nanocrystalline structural state prior to irradiation, inhibited Frenkel pair recombination when Ge interstitials are recoiled into the matrix and preferential nucleation of the amorphous phase at the nanocrystal/matrix interface. © 2005 Elsevier B.V
- ItemReduction of U (VI) by Fe (II) during the Fe (II) - accelerated transformation of ferrihydrite(American Chemical Society, 2014-08-19) Boland, DD; Collins, RN; Glover, CJ; Payne, TE; Waite, TDX-ray absorption spectroscopy has been used to study the reduction of adsorbed U(VI) during the Fe(II)-accelerated transformation of ferrihydrite to goethite. The fate of U(VI) was examined across a variety of pH values and Fe(II) concentrations, with results suggesting that, in all cases, it was reduced over the course of the Fe(III) phase transformation to a U(V) species incorporated in goethite. A positive correlation between U(VI) reduction and ferrihydrite transformation rate constants implies that U(VI) reduction was driven by the production of goethite under the conditions used in these studies. This interpretation was supported by additional experimental evidence that demonstrated the (fast) reduction of U(VI) to U(V) by Fe(II) in the presence of goethite only. Theoretical redox potential calculations clearly indicate that the reduction of U(VI) by Fe(II) in the presence of goethite is thermodynamically favorable. In contrast, reduction of U(VI) by Fe(II) in the presence of ferrihydrite is largely thermodynamically unfavorable within the range of conditions examined in this study. © 2014, American Chemical Society.
- ItemStatus of the x-ray absorption spectroscopy (XAS) beamline at the Australian synchrotron(American Institute of Physics, 2007-02-02) Glover, CJ; McKinlay, J; Clift, M; Barg, B; Boldeman, JW; Ridgway, MC; Foran, GJ; Garrett, RL; Lay, PA; Broadbent, AWe present herein the current status of the X-ray Absorption Spectroscopy (XAS) Beamline at the 3 GeV Australian Synchrotron. The optical design and performance, details of the insertion device (Wiggler), end station capabilities and construction and commissioning timeline are given.
- ItemStructural characterization of ion implanted Au nanocrystals using synchrotron-based analytical techniques(Australian Institute of Physics, 2005-01-31) Kluth, P; Johannessen, B; Glover, CJ; Foran, GJ; Kluth, SM; Ridgway, MCSynchrotron based analytical techniques including extended x-ray absorption fine structure (EXAFS) spectroscopy provide powerful tools for structural characterization of nanocrystalline materials. Combining these techniques with conventional analytical methods such as x-ray diffraction and transmission electron microscopy we have investigated Au nanocrystals formed in thin SiO2 using ion implantation. Furthermore, we have studied their structural evolution following ion irradiation. Non-irradiated nanocrystals show a significant bondlength contraction, essentially retaining the facecentred-cubic structure present in bulk material. In contrast to bulk elemental metals, which cannot be rendered amorphous by ion irradiation, irradiated nanocrystals exhibit a significant structural change consistent with amorphous material.
- ItemStructural perturbations within nanocrystalline Cu probed by EXAFS(Australian Institute of Physics, 2005-01-31) Johannessen, B; Kluth, P; Glover, CJ; Foran, GJ; Ridgway, MCExtended x-ray absorption fine structure (EXAFS) spectroscopy has emerged as an invaluable synchrotron radiation technique for determining the short-range atomic structure in a vast range of diverse materials. Cu nanocrystals (NCs) were synthesised by high-energy ion beam implantation and thermal annealing. We present results of EXAFS measurements determining the first nearest neighbour Cu environment and quantify significant concentration- and annealing-temperature-dependent structural perturbations as compared to a bulk Cu standard. In particular we observe and explain an enhanced structural disorder involving both a suppressed coordination number and bondlength contraction.
- ItemStructure and cation ordering in spinel-type TcCo2O4. An example of a trivalent technetium oxide(Royal Society of Chemistry, 2011-11-11) Thorogood, GJ; Zhang, Z; Hester, JR; Kennedy, BJ; Ting, J; Glover, CJ; Johannessen, BThe structure of TcCo(2)O(4) has been determined using a combination of synchrotron X-ray and neutron powder diffraction methods. It has an inverse spinel structure where the Tc occupies the octahedral sites. Both the refined Tc-O distance and X-ray absorption spectra suggest the Tc is predominantly trivalent. The structure of TcCo(2)O(4) has been determined using a combination of synchrotron X-ray and neutron powder diffraction methods. It has an inverse spinel structure where the Tc occupies the octahedral sites. Both the refined Tc-O distance and X-ray absorption spectra suggest the Tc is predominantly trivalent.© 2011, Royal Society of Chemistry