ANSTO :: Browsing by Author "Hanna, JV"

Browsing by Author "Hanna, JV"

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Anomalous lattice parameter increase in alkali earth aluminium substituted tungsten defect pyrochlores
(Elsevier, 2009-03) Thorogood, GJ; Kennedy, BJ; Peterson, VK; Elcombe, MM; Kearley, GJ; Hanna, JV; Luca, V
The structures of the defect pyrochlores AAl(0.33)W(1.67)O(6) where A = K, Rb or Cs have been investigated using X-ray and neutron powder diffraction methods as well as the ab initio modelling program VASP The three cubic pyrochlores exhibit a non-linear increase in lattice parameter with respect to ionic radius of the A cation as a consequence of displacive disorder of the A-type cations. Solid state Al-27 MAS NMR studies of this pyrochlore system reveal shifts in the delta-21-22 ppm range that are indicative of pseudo-5 coordinate Al environments and emanate frorn distorted Al octahedral with one abnormally long Al. O bond. Solid state K-39, Rb-85, Rb-87 and Cs-133 MAS and static NMR Studies reflect the local cation disorder demonstrated in the structural Studies. © 2008, Elsevier Ltd.
Aqueous 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
Aqueous 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, D
The 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.
Biodegradability of sol-gel silica microparticles for drug delivery
(Springer, 2009-01) Finnie, KS; Waller, DJ; Perret, FL; Krause-Heuer, AM; Lin, HQ; Hanna, JV; Barbé, CJ
The biodegradability of porous sol–gel silica microparticles in physiological buffers has been investigated using a USP4 flow-through dissolution tester. In the open configuration, which most closely models in-vivo conditions, the particles dissolved rapidly at pH 7.4, with a rate dependent on the surface area and media flow rate. In the closed configuration, the fastest dissolving 4 mg silica sample was almost completely dissolved in 100 mL of buffer after 36 h. The initial dissolution rates appeared relatively linear but dropped off as dissolved SiO2 concentrations approached 20–25 ppm. Addition of serum proteins acted to slow dissolution by 20–30%, suggesting a slower degradation in vivo. Silica microparticles administered for controlled release drug delivery would therefore be expected to be eliminated relatively rapidly from the body, depending on the sample size and local fluid flow conditions. © 2009, Springer. The original publication is available at www.springerlink.com
Cation disorder in NaW2O6+δ·nH2−zO post-ion exchange with K, Rb, Sr, and Cs
(Pergamon-Elsevier Science Ltd, 2011-06-01) Thorogood, GJ; Kennedy, BJ; Avdeev, M; Peterson, VK; Hanna, JV; Luca, V
The structure of the defect pyrochlore NaW2O6+delta center dot nH(2-z)O after ion exchange with K, Rb, Sr or Cs for Na has been investigated using thermal analysis, solid-state nuclear magnetic resonance, laboratory X-ray and neutron diffraction methods. Neutron diffraction studies show that both the A-type cations (Na+, K+, Rb+, and/or Cs+) and the water molecules reside within the channels that form in the 111 direction of the W2O6 framework and that these strongly interact. The analytical results suggest that the water and A-type cations compete for space in the tunnels within the W2O6 pyrochlore framework, with the total number of water molecules and cations being approximately constant in the six samples investigated. The interplay between the cations and water explains the non-linear dependence of the a lattice parameter on the choice of cation. It appears that the ion-exchange capacity of the material will be controlled by the amount of water initially present in the sample. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
Cation order/disorder and local structures in alkaline earth pyrochlores
(International Union of Crystallography (IUCr), 2008-08-23) Thorogood, GJ; Kennedy, BJ; Peterson, VK; Elcombe, MM; Kearley, GJ; Hanna, JV
Materials that form the A2-yB2O7-x pyrochlore structure have various applications including use as catalysts, fuel cells, piezoelectrics, ferroelectric devices and ferro-magnets; have a wide range of electrical and ionic conductivities, including metallic, semi and super; can be used in nuclear-waste immobilisation due to radiation toughness, and have ion exchange properties. The degree of disorder of the A-cation is important and may play the major role in the effectiveness of these materials ion exchange properties; and contribute to the high relative permittivities displayed by (Bi,Zn)2(Zn,Nb)2O7. Previous Neutron and X-ray diffraction studies suggest that the disorder involves displacement of the A-cation along the six <112> or <110> directions. Our observation of diffuse scattering in electron diffraction patterns of CsTi0.5W1.5O6 pyrochlores suggests there are strong local correlations among the disordered ions. Movement of O at 48f away from 0.375 reduces the interaction between the two networks and so may increase the amount of disorder of the A-cation. The structures of the defect pyrochlores AAl0.33W1.67O6 where A= K, Rb or Cs have been investigated using an array of advanced structural probes; X-ray and neutron diffraction methods, NMR spectroscopy as well as the ab-initio modeling using VASP. The structures do not show a simple correlation between the radius of the A-type cation and the cubic lattice parameter. Our structural studies suggest that this may reflect the degree of local disorder of the A-cation. The results of these studies will be presented in this presentation. © 2008 International Union of Crystallography
Crystal chemistry of vanadium-bearing ellestadite waste forms
(American Chemical Society, 2018-07-16) Fang, Y; Page, SJ; Rees, GJ; Avdeev, M; Hanna, JV; White, TJ
Vanadate ellestadites Ca10(SiO4)x(VO4)6–2x(SO4)xCl2, serving as prototype crystalline matrices for the fixation of pentavalent toxic metals (V, Cr, As), were synthesized and characterized by powder X-ray and neutron diffraction (PXRD and PND), electron probe microanalysis (EPMA), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (SS-NMR). The ellestadites 0.19 < x < 3 adopt the P63/m structure, while the vanadate endmember Ca10(VO4)6Cl2 is triclinic with space group P1̅. A miscibility gap exists for 0.77 < x < 2.44. The deficiency of Cl in the structure leads to short-range disorder in the tunnel. Toxicity characteristic leaching testing (TCLP) showed the incorporation of vanadium increases ellestadite solubility, and defined a waste loading limit that should not exceed 25 atom % V to ensure small release levels. © 2018 American Chemical Society
Fe 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, M
The 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.
Geopolymers for low-level waste immobilization
(American Ceramic Society, 2006-10-15) Vance, ER; Blackford, MG; Hanna, JV; Aly, Z; Perera, DS
Hybrid inorganic-organic adsorbents, Part 1: synthesis and characterization of mesoporous zirconium titanate frameworks containing coordinating organic functionalities
(American Chemical Society, 2010-12-22) Griffith, CS; Reyes, MDL; Scales, N; Hanna, JV; Luca, V
A series of functional hybrid inorganic−organic adsorbent materials have been prepared through postsynthetic grafting of mesoporous zirconium titanate xerogel powders using a range of synthesized and commercial mono-, bis-, and tris-phosphonic acids, many of which have never before been investigated for the preparation of hybrid phases. The hybrid materials have been characterized using thermogravimetric analysis, diffuse reflectance infrared (DRIFT) and 31P MAS NMR spectroscopic techniques and their adsorption properties studied using a 153Gd radiotracer. The highest level of surface functionalization (molecules/nm2) was observed for methylphosphonic acid (3 molecules/nm2). The level of functionalization decreased with an increase in the number of potential surface coordinating groups of the phosphonic acids. Spectral decomposition of the DRIFT and 31P MAS NMR spectra showed that each of the phosphonic acid molecules coordinated strongly to the metal oxide surface but that for the 1,1-bis-phosphonic acids and tris-phosphonic acids the coordination was highly variable resulting in a proportion of free or loosely coordinated phosphonic acid groups. Functionalization of a porous mixed metal oxide framework with the tris-methylenephosphonic acid (ATMP-ZrTi-0.33) resulted in a hybrid with the highest affinity for 153Gd3+ in nitric acid solutions across a wide range of acid concentrations. The ATMP-ZrTi-0.33 hybrid material extracted 153Gd3+ with a Kd value of 1 × 104 in 0.01 M HNO3 far exceeding that of the other hybrid phases. The unfunctionalized mesoporous mixed metal oxide had negligible affinity for Gd3+ (Kd < 100) under identical experimental conditions. It has been shown that the presence of free or loosely coordinated phosphonic acid groups does not necessarily translate to affinity for 153Gd3+. The theoretical cation exchange capacity of the ATMP-ZrTi-0.33 hybrid phase for Gd3+ has been determined to be about 0.005 mmol/g in 0.01 M HNO3. This behavior and that of the other hybrid phases suggests that the surface-bound ATMP ligand functions as a chelating ligand toward 153Gd3+ under these acidic conditions. © 2010, American Chemical Society
Hydrolysis and dpeciation of Al bound to pectin and plant cell wall material and its reaction with the dye chrome Azurol S
(American Chemical Society, 2010-05-12) Wehr, JB; Blamey, FPC; Hanna, JV; Kopittke, PM; Kerven, GL; Menzies, NW
Hydrolysis of aluminum (Al) in solution increases at pH ≥ 4 and with an Al concentration. Pectin, an important anionic polysaccharide of plant cell walls, adsorbs Al, but this phenomenon is poorly understood. This study showed that Al3+ hydrolysis results in binding of Al to pectin in excess of the stoichiometric equivalent, leading to oversaturation of the pectin with Al. However, the degree of pectin methyl-esterification did not affect the extent of Al hydrolysis. Binding of Al to purified cell wall material also resulted in Al hydrolysis in a pH- and soluble Al concentration-dependent manner, but the source of cell wall material had no effect at fixed pH. Staining of Al-treated pectin and cell wall material from wheat (Triticum aestivum L.) and sunflower (Helianthus annuus L.) with the Al-specific dye, chrome azurol S (CAS), resulted in the formation of a purple color, with the intensity related to the extent of Al hydrolysis. © 2010, American Chemical Society
Microcrystalline hexagonal tungsten bronze. 1. Basis of ion exchange selectivity for cesium and strontium
(American Chemical Society, 2009-07-06) Griffith, CS; Luca, V; Hanna, JV; Pike, KJ; Smith, ME; Thorogood, GJ
The structural basis of selectivity for cesium and strontium of microcrystalline hexagonal tungsten bronze (HTB) phase NaxWO3+x/2·zH2O has been studied using X-ray and neutron diffraction techniques, 1D and 2D 23Na magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and radiochemical ion exchange investigations. For the HTB system, this study has shown that scattering techniques alone provide an incomplete description of the disorder and rapid exchange of water (with tunnel cations) occurring in this system. However, 1D and 2D 23Na MAS NMR has identified three sodium species within the HTB tunnels—species A, which is located at the center of the hexagonal window and is devoid of coordinated water, and species B and C, which are the di- and monohydrated variants, respectively, of species A. Although species B accords with the traditional crystallographic model of the HTB phase, this work is the first to propose and identify the anhydrous species A and monohydrate species C. The population (total) of species B and C decreases in comparison to that of species A with increasing exchange of either cesium or strontium; that is, species B and C appear more exchangeable than species A. Moreover, a significant proportion of tunnel water is redistributed by these cations. Multiple ion exchange investigations with radiotracers 137Cs and 85Sr have shown that for strontium there is a definite advantage in ensuring that any easily exchanged sodium is removed from the HTB tunnels prior to exchange. The decrease in selectivity (wrt cesium) is most probably due to the slightly smaller effective size of Sr2+; namely, it is less of a good fit for the hexagonal window, ion exchange site. The selectivity of the HTB framework for cesium has been shown unequivocally to be defined by the structure of the hexagonal window, ion exchange site. Compromising the geometry of this window even in the slightest way by either (1) varying the cell volume through changes to hydration or sodium content or (2) introducing disorder in the a−b plane through isomorphous substitution of molybdenum is sufficient to reduce the selectivity. Indeed, it is our hypothesis that this applies for all cations which are strongly bound by the HTB framework. © 2009, American Chemical Society
Microcrystalline hexagonal tungsten bronze. 2. Dehydration dynamics
(American Chemical Society, 2009-07-06) Luca, V; Griffith, CS; Hanna, JV
Low-temperature (25−600°C) thermal transformations have been studied for hydrothermally prepared, microcrystalline hexagonal tungsten bronze (HTB) phases AxWO3+x/2·zH2O as a function of temperature, where A is an exchangeable cation (in this case Na+ or Cs+) located in hexagonal structural tunnels. Thermal treatment of the as-prepared sodium- and cesium-exchanged phases in air were monitored using a conventional laboratory-based X-ray diffractometer, while thermal transformations in vacuum were studied using synchrotron X-ray and neutron diffraction. Concurrent thermogravimetric, diffuse reflectance infrared (DRIFT), and 23Na and 133Cs magic angle spinning (MAS) NMR spectroscopic studies have also been undertaken. For the cesium variant, cell volume contraction occurred from room temperature to about 350°C, the regime in which water was “squeezed” out of tunnel sites. This was followed by a lattice expansion in the 350−600°C temperature range. Over the entire temperature range, a net thermal contraction was observed, and this was the result of an anisotropic change in the cell dimensions which included a shortening of the A−O2 bond length. These changes explain why Cs+ ions are locked into tunnel positions at temperatures as low as 400°C, subsequently inducing a significant reduction in Cs+ extractability under low pH (nitric acid) conditions. The changing Cs+ speciation as detected by 133Cs MAS NMR showed a condensation from multiple Cs sites, presumably associated with differing modes of Cs+ hydration in the tunnels, to a single Cs+ environment upon thermal transformation and water removal. While similar lattice contraction was observed for the as-prepared sodium variant, the smaller radius of Na+ caused it to be relatively easily removed with acid in comparison to the Cs+ variant. From 23Na MAS NMR studies of the parent material, complex Na+ speciation was observed with dehydrated and various hydrated Na+ species being identified, and a subsequent dynamic interchange within this speciation was observed upon thermal treatment. © 2009, American Chemical Society
Structural evolution and stability of sol-gel biocatalysts
(Elsevier, 2006-11-15) Rodgers, LE; Knott, RB; Holden, PJ; Pike, KJ; Hanna, JV; Foster, LJR; Bartlett, JR
Immobilisation strategies for catalytic enzymes are important as they allow recovery and reuse of the biocatalysts. In this work, sol-gel matrices have been used to immobilise Candida antarctica lipase B (CALB), a commonly used industrial enzyme. The sol-gel bioencapsulate is produced through fluoride-catalysed hydrolysis of mixtures of tetramethylorthosilicate (TMOS) and methyltrimethoxysilane (MTMS) in the presence of CALB, yielding materials with controlled pore sizes and surface chemistries. Sol-gel matrices prolong the catalytic life and enhance the activity of CALB, although the molecular basis for this effect has yet to be elucidated due to the limitations of analytical techniques applied to date. Small angle neutron scattering (SANS) allows such multi-component systems to be characterised through contrast matching. In the sol-gel bioencapsulate system at the contrast match point for silica, residual scattering intensity is due to the CALB and density fluctuations in the matrix. A SANS contrast variation series found the match point for the silica matrix, both with and without enzyme present, to be around 35%. The model presented here proposes a mechanism for the interaction between CALB and the surrounding sol-gel matrix, and the observed improvement in enzyme activity and matrix strength. Essentially, the inclusion of CALB modulates silicate speciation during evolution of the inorganic network, leading to associated variations in SANS contrast. The SANS protocol developed here may be applied more generally to other encapsulated enzyme systems. © 2006, Elsevier Ltd.
Structure and dehydration of the pyrochlore system NaW2−yMoyO6+δ·nH2−zO between 10 and 675 K
(Elsevier, 2008-07) Thorogood, GJ; Kennedy, BJ; Luca, V; Blackford, MG; van de Geeste, SK; Finnie, KS; Hanna, JV; Pike, KJ
The temperature dependence of the structure of the pyrochlore NaW2−yMoyO6+δ·nH2−zO has been investigated using a variety of diffraction and spectroscopic methods. The positions of OH−/H2O molecules in the structure have been determined. Increases in temperature induce small lattice parameter changes, which are thought to result from movement of the H2O molecules in the pyrochlore lattice. Crown Copyright © 2008 Published by Elsevier Ltd.
Structure and phase transformations in the titanosilicate, sitinakite. The importance of water
(American Chemical Society, 2010-07-27) Thorogood, GJ; Kennedy, BJ; Griffith, CS; Elcombe, MM; Avdeev, M; Hanna, JV; Thorogood, SK; Luca, V
Synchrotron X-ray diffraction and neutron diffraction have been used to investigate the phase changes that the titanosilicate mineral sitinakite undergoes when dehydrated. Refinements of the powder diffraction data of the material before and after heating to 573K indicate a phase change from space group P42/mcm to P42/mbc. Upon exposure to normal atmospheric conditions for an extended period the material transforms back to P42/mcm with a reduced lattice parameter. If the material is heated in a sealed capillary, it is possible to get the two phases coexisting. The coexistence of these two phases in sealed system suggests that it is only the loss of H2O that is driving the reversible phase transformation. © 2010, American Chemical Society
Tungstate-based glass-ceramics for the immobilization of radio cesium
(Elsevier, 2009-02-15) Drabarek, E; McLeod, TI; Hanna, JV; Griffith, CS; Luca, V
The preparation of tungstate-containing glass–ceramic composites (GCC) for the potential immobilization of radio cesium has been considered. The GCC materials were prepared by blending two oxide precursor compositions in various proportions. These included a preformed Cs-containing hexagonal tungsten bronze (HTB) phase (Cs0.3Ti0.2W0.8O3, P63/mcm) and a blend of silica and other oxides. The use of the HTB phase was motivated on the assumption that a HTB-based adsorbent could be used to remove cesium directly from aqueous high level liquid waste feeds. In the absence of the HTB, glass–ceramics were relatively easily prepared from the Cs-containing glass-forming oxide blend. On melting the mixture a relative complex GCC phase assemblage formed. The principal components of this phase assemblage were determined using X-ray powder diffraction, 133Cs MAS-NMR, and cross-sectional SEM and included glass, various zeolites, scheelite (CaWO4) and a range of other oxide phases and Cs-containing aluminosilicate. Importantly, under no circumstance was cesium partitioned into the glass phase irrespective of whether or not the composition included the preformed Cs-containing HTB compound. For compositions containing the HTB, cesium was partitioned into one of four major phases including zeolite; Cs–silica–tungstate bronze, pollucite (CsAlSi2O6), and an aluminosilicate with an Al/Si ratio close to one. The leach resistance of all materials was evaluated and related to the cesium distribution within the GCC phase assemblages. In general, the GCCs prepared from the HTB had superior durability compared with materials not containing tungsten. Indeed the compositions in many cases had leach resistances comparable to the best ceramics or glass materials. © 2009, Elsevier Ltd.

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