ANSTO :: Browsing by Author "Webster, NAS"

Browsing by Author "Webster, NAS"

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Anatomy of a complex mineral replacement reaction: Role of aqueous redox, mineral nucleation, and ion transport properties revealed by an in-situ study of the replacement of chalcopyrite by copper sulfides
(Elsevier, 2021-10-20) Chaudhari, A; Webster, NAS; Xia, F; Frierdich, AJ; Ram, R; Etschmann, BE; Liu, WH; Wykes, JL; Brand, HEA; Brugger, J
The fluid-driven transformation of chalcopyrite (CuFeS2) into Cu-rich sulfides (e.g., digenite, Cu1.8S; covellite, CuS; and chalcocite, Cu2S) is a complex mineral replacement reaction where the reaction pathway is controlled by the interplay between evolving mineral make-up, texture/porosity, and solution chemistry. This trans-formation was investigated in CuCl2 +H2SO4 solutions under mild hydrothermal conditions (180 to 300 ◦C); the reaction kinetics, nature of minerals formed, and oxidation states of aqueous Fe and Cu were followed in-situ in real-time using synchrotron powder X-ray diffraction (PXRD) and X-ray absorption spectroscopy (XAS). These results are corroborated by an analysis of the textures of reaction products from comparative ex-situ quench experiments. The in-situ and ex-situ experiments revealed that: (i) aqueous Cu2+quickly reduced to Cu+ during chalcopyrite replacement in all experiments, and Fe dissolved as Fe2+; (ii) covellite was the first mineral to form, followed by digenite-high with delayed nucleation; and (iii) a non-quenchable hydrated Fe sulfate mineral (szomolnokite, FeSO4.H2O) formed at 240 ◦C at relatively low concentrations of added CuCl2, which supressed the formation of digenite-high. The quantitative mineral phase evolution retrieved using in-situ PXRD was modelled using a novel dual power law (dual Avrami approach). Avrami exponents revealed that chalcopyrite replacement proceeded initially via a 3-dimensional growth mechanism, followed by diffusion-controlled growth. This is consistent with initial formation of a porous covellite rim around chalcopyrite, confirmed by the observation of the ex-situ reaction products, followed by a second reaction stage where the transport properties of aqueous Fe (released from the chalcopyrite) and aqueous Cu (added from the initial solution) to and from the reaction front become the rate-limiting step; and these two kinetic stages exist even where covellite was the only replacement product. The activation energies calculated for these two kinetic stages were 42.9 ±7.4 kJ mol −1 and 39.3 ± 13.1 kJ mol−1, respectively. We conclude that (i) the replacement of chalcopyrite by covellite and digenite proceeds via an interface coupled dissolution and reprecipitation mechanism; (ii) availabilities of aqueous Cu+ and of Fe2+ play a critical role in covellite nucleation and on the sequence of mineral precipitation during chalcopyrite replacement; the Cu+ to Cu2+ ratio is controlled by the kinetics of Cu2+ to Cu+ reduction, which increases with increasing temperature, and by the transport of Cu2+ through the daughter mineral to the reaction front, while Fe2+ availability is limited at high temperature by the formation of insoluble ferrous sulfate; and (iii) this reaction evolves from a bulk fluid-chemistry controlled reaction (initial formation of covellite) to an interface-controlled reaction (digenite-high or further transformation to covellite). The current findings highlight the complex feedback between Cu2+/Cu+ aqueous redox, mineral nucleation, and ion transport properties during replacement reactions, and the applicability of combined in-situ PXRD and XAS techniques in deciphering complex fluid-driven mineral replacement reactions. © 2021 Elsevier B.V
Effect of oxygen partial pressure on the formation mechanisms of complex Ca-rich ferrites
(The Iron and Steel Institute of Japan Keidanren Kaikan, 2013-01-01) Webster, NAS; Pownceby, MI; Madsen, IC; Kimpton, JA
The formation mechanisms of the complex Ca-rich ferrite iron ore sinter bonding phases SFCA and SFCA-I, during heating of a synthetic sinter mixture in the range 298-1623 K and at pO(2) = 0.21, 5 x 10(-3) and 1 x 10(-4) atm, were determined using in situ X-ray diffraction. SFCA and, in particular, SFCA-I are desirable bonding phases in iron ore sinter, and improved understanding of the effect of parameters such as pO(2) on their formation may lead to improved ability to maximise their formation. in industrial sintering processes. SFCA-I and SFCA were both observed to form at pO(2) = 0.21 and 5 x 10-3 atm, with the formation of SFCA-I preceding SFCA formation in each case, but via distinctly different mechanisms at each pO(2). No SFCA-I was observed at pO(2) = 1 x 10-4 atm; instead, a Ca-rich phase designated CFAlSi, formed at 1 420 K. By 1 456 K, CFAlsi had decomposed to form melt and a small amount of SFCA. Such a low pO(2) during heating of industrial sinter mixtures is, therefore, undesirable, since it would not result in the formation of an abundance of SFCA and SFCA-I bonding phases. In addition, CFA phase, which was determined by Webster et al. (Metall. Mater. Trans. B, 43(2012), 1344) to be a key precursor phase in the formation of SFCA at pO(2) = 5 x 10(-3) atm, was also observed to form at pO(2) = 0.21 and 1 x 10(-4) atm, with the amount decreasing with increasing pO(2). Copyright © The Iron and Steel Institute of Japan 2013.
Fundamentals of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter bonding phase formation: effects of CaO:SiO2 ratio
(Springer Link, 2014-07-22) Webster, NAS; Pownceby, MI; Madsen, IC; Studer, AJ; Manuel, JR; Kimpton, JA
Effects of basicity, B (CaO:SiO2 ratio) on the thermal range, concentration, and formation mechanisms of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated using an in situ synchrotron X-ray diffraction-based methodology with subsequent Rietveld refinement-based quantitative phase analysis. SFCA and SFCA-I phases are the key bonding materials in iron ore sinter, and improved understanding of the effects of processing parameters such as basicity on their formation and decomposition may assist in improving efficiency of industrial iron ore sintering operations. Increasing basicity significantly increased the thermal range of SFCA-I, from 1363 K to 1533 K (1090 °C to 1260 °C) for a mixture with B = 2.48, to ~1339 K to 1535 K (1066 °C to 1262 °C) for a mixture with B = 3.96, and to ~1323 K to 1593 K (1050 °C to 1320 °C) at B = 4.94. Increasing basicity also increased the amount of SFCA-I formed, from 18 wt pct for the mixture with B = 2.48 to 25 wt pct for the B = 4.94 mixture. Higher basicity of the starting sinter mixture will, therefore, increase the amount of SFCA-I, considered to be more desirable of the two phases. Basicity did not appear to significantly influence the formation mechanism of SFCA-I. It did, however, affect the formation mechanism of SFCA, with the decomposition of SFCA-I coinciding with the formation of a significant amount of additional SFCA in the B = 2.48 and 3.96 mixtures but only a minor amount in the highest basicity mixture. In situ neutron diffraction enabled characterization of the behavior of magnetite after melting of SFCA produced a magnetite plus melt phase assemblage. © 2014, The Minerals, Metals & Materials Society and ASM International.
In situ diffraction studies of iron ore sinter bonding phase formation: QPA considerations and pushing the limits of laboratory data collection
(Cambridge University Press, 2014-11-17) Webster, NAS; Pownceby, MI; Madsen, IC; Studer, AJ
The formation and decomposition of silico-ferrite of calcium and aluminium (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated using in situ synchrotron and laboratory X-ray diffraction (XRD) and neutron diffraction (ND). An external standard approach for determining absolute phase concentrations via Rietveld refinement-based quantitative phase analysis is discussed. The complementarity of in situ XRD and ND in characterising sinter phase formation and decomposition is also shown, with the volume diffraction afforded by the neutron technique reducing errors in the quantification of magnetite above ~1200 °C. Finally, by collecting 6 s laboratory XRD datasets and using a heating rate of 175 °C min−1, phase formation and decomposition have been monitored under heating rates more closely approximating those encountered in industrial iron ore sintering.© 2014 International Centre for Diffraction Data
In situ formation of reactive sulfide precursors in the one-pot, multigram synthesis of Cu2ZnSnS4 nanocrystals
(American Chemical Society, 2013-03-05) Chesman, ASR; van Embden, J; Duffy, NW; Webster, NAS; Jasieniak, JJ
Herein we outline a general one-pot method to produce large quantities of compositionally tunable, kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) through the decomposition of in situ generated metal sulfide precursors. This method uses air stable precursors and should be applicable to the synthesis of a range of metal sulfides. We examine the formation of the ligands, precursors, and particles in turn. Direct reaction of CS2 with the aliphatic primary amines and thiols that already constitute the reaction mixture is used to produce ligands in situ. Through the use of 1H and 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy, and optical absorption spectroscopy, we elucidate the formation of the resulting oleyldithiocarbamate and dodecyltrithiocarbonate ligands. The decomposition of their corresponding metal complexes at temperatures of ∼100 °C yields nuclei with a size of 1–2 nm, with further growth facilitated by the decomposition of dodecanethiol. In this way the nucleation and growth stages of the reaction are decoupled, allowing for the generation of NCs at high concentrations. Using in situ X-ray diffraction, we monitor the evolution of our reactions, thus enabling a real-time glimpse into the formation of Cu2ZnSnS4 NCs. For completeness, the surface chemistry and the electronic structure of the resulting CZTS NCs are studied. © 2013, American Chemical Society.
In situ x-ray diffraction investigation of the formation mechanisms of silico-ferrite of calcium and aluminium-I-type (SFCA-I-type) complex calcium ferrites
(The Iron and Steel Institute of Japan, 2013-01-01) Webster, NAS; Pownceby, MI; Madsen, IC
The formation mechanisms of the complex Ca-rich ferrite phase SFCA-I, an important bonding material in iron ore sinter, during heating of synthetic sinter mixtures in the temperature range 298-1623 K in air and at pO(2) = 5 x 10(-3) atm, were determined using in situ X-ray powder diffraction. In air, the initial formation of SFCA-I at similar to 1438 K (depending on composition) was associated with reaction of precursor phases Fe2O3, CaO center dot Fe2O3, SiO2, amorphous AI-oxide and a CFA phase of approximate composition 71.7 mass% Fe2O3, 12.9 mass% CaO, 0.3 mass% SiO2 and 15.1 mass% Al2O3. At temperatures above similar to 1453 K, the decomposition of another phase, gamma-CFF, resulted in the formation of additional SFCA-I. At lower oxygen partial pressure the initial formation of SFCA-I occurred at similar temperatures and was associated with reaction between similar phases as its formation in air. However, the decomposition of gamma-CFF did not result in the formation of additional SFCA-I, with the maximum SFCA-I concentration (25 mass%) lower than the values attained in air (54 and 34 mass%). Hence, more oxidising conditions appear to favour the formation of the desirable SFCA-I phase. Copyright © The Iron and Steel Institute of Japan 2013.
In situ XRD investigation of the evolution of surface layers on Pb-alloy anodes
(Cambridge University Press, 2017-08-22) Clancy, M; Styles, MJ; Beetles, CJ; Birbilis, N; Kimpton, JA; Webster, NAS
The electrochemical behaviour of a number of Pb-based anode alloys, under simulated electrowinning conditions, in a 1.6 M H2SO4 electrolyte at 45 °C was studied. Namely, the evolution of PbO2 and PbSO4 surface layers was investigated by quantitative in situ synchrotron X-ray diffraction (S-XRD) and subsequent Rietveld-based quantitative phase analysis (QPA). In the context of seeking new anode alloys, this research shows that the industry standard Pb-0.08Ca-1.52Sn (wt%) anode, when exposed to a galvanostatic current and intermittent power interruptions, exhibited poor electrochemical performance relative to select custom Pb-based binary alloys; Pb–0.73Mg, Pb–5.05Ag, Pb–0.07Rh, and Pb–1.4Zn (wt%). The in situ S-XRD measurements and subsequent QPA indicated that this was linked to a lower proportion of β-PbO2, relative to PbSO4, on the Pb-0.08Ca-1.52Sn alloy at all stages of the electrochemical cycling. The best performing alloy, in terms of minimisation of overpotential during normal electrowinning operation and minimising the deleterious effects of repeated power interruptions – both of which are significant factors in energy consumption – was determined to be Pb–0.07Rh. © Cambridge University Press 2022
An investigation of goethite-seeded Al(OH)(3) precipitation using in situ x-ray diffraction and rietveld-based quantitative phase analysis
(Wiley-Blackwell, 2010-06) Webster, NAS; Madsen, IC; Loan, MJ; Knott, RB; Naim, F; Wallwork, KS; Kimpton, JA
An in situ X-ray diffraction investigation of goethite-seeded Al(OH)3 precipitation from synthetic Bayer liquor at 343 K has been performed. The presence of iron oxides and oxyhydroxides in the Bayer process has implications for alumina reversion, which causes significant process losses through unwanted gibbsite precipitation, and is also relevant for the nucleation and growth of scale on mild steel process equipment. The gibbsite, bayerite and nordstrandite polymorphs of Al(OH)3 precipitated from the liquor; gibbsite appeared to precipitate first, with subsequent formation of bayerite and nordstrandite. A Rietveld-based approach to quantitative phase analysis was implemented for the determination of absolute phase abundances as a function of time, from which kinetic information for the formation of the Al(OH)3 phases was determined. © 2010, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
An investigation of the mechanisms of goethite, hematite and magnetite-seeded Al(OH)(3) precipitation from synthetic Bayer liquor
(Elsevier, 2011-09-01) Webster, NAS; Loan, MJ; Madsen, IC; Knott, RB; Kimpton, JA
The precipitation of Al(OH)3 from synthetic Bayer liquor at 70 degrees C seeded with goethite, hematite and magnetite particles was investigated in order to gain insight into the nucleation and growth mechanisms in the presence of these materials. A combination of characterisation techniques was employed including conductivity analysis, particle size analysis, electron microscopy and in situ synchrotron X-ray diffraction. The magnetite seed was less active for promoting Al(OH)(3) precipitation than the goethite and hematite, based on a comparison of the induction time before the onset of measurable precipitation. For each seed material, the early stages of precipitation were characterised by relatively slow deposition of gibbsite on the seed particles. Precipitation then proceeded via a two-stage mechanism, where gibbsite and small amounts of bayerite and nordstrandite precipitated concurrently. The outcomes of this investigation have implications for the nucleation and growth of scale on mild steel process equipment, and are also relevant for alumina reversion which causes significant process losses through uncontrolled precipitation. (C) 2011 Elsevier B.V.
Kinetics of the thermally-induced structural rearrangement of γ-MnO2
(ACS Publications, 2014-09-17) Dose, WM; Sharma, N; Webster, NAS; Peterson, VK; Donne, SW
This work presents a temperature-dependent and time-resolved X-ray and neutron diffraction study of the thermally induced structural rearrangement of γ-MnO2. Here, we study electrochemically prepared γ-MnO2, the manganese dioxide phase used in the majority of battery applications, which we find to be ∼64% ramsdellite [a = 4.4351(6) Å, 9.486(2) Å, c = 2.8128(7) Å, and V = 118.33(3) Å3] and ∼36% pyrolusite [a = 4.718(3) Å, c = 2.795(2) Å, and V = 62.22(8) Å3]. Taking a deeper look at the kinetics of the structural rearrangement, we find two steps: a fast transition occurring within 4–8 min with a temperature-dependent ramsdellite to pyrolusite transformation (rate constant 0.11–0.74 min–1) and a slow transition over 4 h that densifies (with changes in unit cell and volume) the ramsdellite and pyrolusite phases to give structures that appear to be temperature-independent. This effectively shows that γ/β-MnO2 prepared in the range of 200–400 °C consists of temperature-independent structures of ramsdellite, unit cell a = 4.391(1) Å, b = 9.16(5) Å, c = 2.847(1) Å, and V = 114.5(6) Å3, and pyrolusite, unit cell a = 4.410(2) Å, c = 2.869(2) Å, and V = 55.79(4) Å3, with a temperature-dependent pyrolusite fraction between 0.45 and 0.77 and increasing with temperature. Therefore, we have linked the temperature and time of heat treatment to the structural evolution of γ-MnO2, which will aid the optimization of γ/β-MnO2 as used in Li-primary batteries. © 2014, American Chemical Society.
New quenched-in fluorite-type materials in the Bi2O3-La2O3-PbO system: synthesis and complex phase behaviour up to 750 degrees C
(Pergamon-Elsevier Science Ltd, 2011-04-01) Webster, NAS; Hartlieb, KJ; Saines, PJ; Ling, CD; Lincoln, FJ
New quenched-in fluorite-type materials with composition (BiO1.5)(0.94-x)(LaO1.5)(0.06)(PbO)(x), x = 0.02, 0.03, 0.04 and 0.05, were synthesised by solid state reaction. The new materials undergo a number of phase transformations during heating between room temperature and 750 degrees C, as indicated by differential thermal analysis. Variable temperature X-ray diffraction performed on the material (BiO1.5)(0.92)(LaO1.5)(0.06)(PbO)(0.02) revealed that the quenched-in fcc fluorite-type material first undergoes a transformation to a beta-Bi2O3-type tetragonal phase around 400 degrees C. In the range 450-700 degrees C, alpha-Bi2O3-type monoclinic, Bi12PbO19-type bcc and beta(1)/beta(2)-type rhombohedral phases, and what appeared to be a epsilon-type monoclinic phase, were observed, before a single-phase fluorite-type material was regained at 750 degrees C. (C) 2010 Elsevier Ltd.
Non-injection synthesis of Cu2ZnSnS4 nanocrystals using a binary precursor and ligand approach
(Royal Society of Chemistry, 2012-11-23) Chesman, ASR; Duffy, NW; Peacock, S; Waddington, L; Webster, NAS; Jasieniak, JJ
We present a non-injection, one-pot synthesis of kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) that allows for multi-gram yields with precise control of the NCs’ metal composition. This is enabled through the selective use of a binary sulfur precursor and ligand reaction mixture, which acts to decouple the nucleation and growth stages. © 2013, The Royal Society of Chemistry.
Proceedings of the 2014 Australian X-ray Analytical Association Workshops, Conference, and Exhibition
(Cambridge University Press, 2014-12-18) Peterson, VK; Webster, NAS
This special issue of Powder Diffraction offers a selection of contributions presented at the Australian X-ray Analytical Association (AXAA) Workshops, Conference, and Exhibition on 9–13th February 2014 (AXAA-2014) in Perth, Australia. The AXAA is a not-for-profit organisation comprised of a diverse group of scientists and technologists employed in mining and manufacturing industries, research and educational organisations, as well as instrument manufacturers throughout Australia and the Asia Pacific region. Details on AXAA can be found at www.axaa.org The AXAA holds a National Conference and Workshop event every 3 years that provides a forum for technical meetings, discussions, and information interchange between workers in the fields of X-ray analysis, including X-ray diffraction (XRD), X-ray fluorescence (XRF), as well as synchrotron and neutron-based techniques of analysis. AXAA-2014 encompassed a rich variety of topics ranging from XRF studies of iron ore to in situ XRD and neutron diffraction studies of batteries, in keeping with the theme of the conference, “From minerals to materials.” The approximately 200 registered participants were from over a dozen countries, including Papua New Guinea, India, China, and Japan. Plenary talks were given by the IUCr's Commission on Powder-Diffraction Chair Dr. Pamela Whitfield (Oak Ridge National Laboratory), Professor David Bish (Indiana University), Professor Bill David (ISIS and Oxford University), Dr. Bob von Dreele (Argonne National Laboratory), and Dr. John Fowler (Intertek). For the first time in the event's history, a public lecture was held, “The Mars Science Laboratory Experience,” given by Professor David Bish as a new and exciting opening. Students and early-career researchers are the key to the continued vitality of the AXAA community, and student prizes are a feature of the AXAA Conference and Workshop. AXAA-2014 provided the opportunity for four postgraduate students to attend the Denver X-ray Conference through prizes for the best oral and poster presentations in both the minerals and materials categories. These prizes were provided through the ICDD's own Bob Snyder travel grants, and were also sponsored by PANalytical, Initiative Scientific Products, the Australian Nuclear Science and Technology Organisation (ANSTO), and the Commonwealth Scientific and Industrial Research Organisation (CSIRO). Thanks also go to Microanalysis Australia for providing the opportunity for student attendance at AXAA-2014 through bursaries. AXAA-2014 also saw the introduction of a new award, the AXAA Award for Excellence in Analysis by an Early-Career Scientist (< 5 years since Ph.D. conferral). The inaugural award was given to Dr. Joel O'Dwyer (CSIRO) for his work developing a new XRD system, which uses energy-dispersive XRD for online analysis of mineral slurries in mineral processing, for the purpose of process optimisation and control. AXAA-2014 demonstrated a continued interest in X-ray and related analytical methods, applications, and research in Australia and surrounds. The next AXAA Conference event will take place in 2017 (AXAA-2017). The guest editors of this special issue of Powder Diffraction: Vanessa K. Peterson, Bragg Institute, ANSTO, Lucas Heights, Australia; Nathan A.S. Webster, Mineral Resources Flagship, CSIRO, Clayton, Australia. © 2022 Cambridge University Press
Proceedings of the 2017 Australian X-ray Analytical Association workshops, conference, and exhibition
(Cambridge University Press, 2018-01-13) Webster, NAS; Peterson, VK
This special issue of Powder Diffraction offers a selection of contributions from the Australian X-ray Analytical Association (AXAA) workshops, conference, and exhibition held on 5–9th February 2017 (AXAA-2017) in Melbourne, Australia. The AXAA (http://www.axaa.org) is a not-for-profit organisation formed of a diverse group of scientists and technologists employed in mining and manufacturing industries, research and educational organisations, as well as instrument manufacturers throughout Australia, the Asia Pacific, and beyond. The AXAA holds an event every 3 years as a forum for scientific and technical discussion and information interchange between workers in the fields of X-ray analysis, including X-ray diffraction and fluorescence (XRD and XRF), which are the traditional focus areas of AXAA, as well as in small angle X-ray scattering, X-ray absorption spectroscopy, XRF mapping and tomography, and neutron scattering, which form a significant part of the event as Australia's synchrotron and neutron facilities mature. At AXAA-2017, nearly one-quarter of the 200 delegates travelled from outside of Australia, from New Zealand, Canada, USA, Germany, Netherlands, France, Italy, Denmark, Sweden, Finland, Switzerland, Italy, Singapore, Hong Kong, Japan, Mongolia, China, Malaysia, and Pakistan. The theme for AXAA-2017 was “Innovation from Characterisation”, reflecting the current drive of Australia to be an innovation nation. The importance and utility of characterization to innovation in Australia was presented in talks covering a wide range of topics, from Dr. Kathy Ehrig's Plenary presentation on the role of XRF and XRD on BHP's Olympic Dam mining and processing operations, to an invited presentation on biomimetic mineralisation of metal-organic frameworks at the surface of living cells, and to the talk by a Student Bursary Award recipient on trapping CO2 and toxic metals. Plenary presentations were also given by Dr. Thomas Proffen (Director Neutron Data Analysis and Visualisation at Oak Ridge National Laboratory, USA) “Structural Characterization of Complex Materials”, Dr. Bridget Ingham (Senior Scientist at Callaghan Innovation, New Zealand) “Innovation from X-ray Characterisation in Materials and Energy Research”, Dr. Chris Ryan (Senior Principal Research Scientist, CSIRO Mineral Resources) “Super High-Definition Synchrotron XRF Element Imaging: A Catalyst for Innovative Research”, and Prof. Andrew Peele (Director, Australian Synchrotron) “Innovation From Characterisation at The Australian Synchrotron”. Continuing on from the success of the inaugural AXAA-2014 Public Lecture, “The Mars Science Laboratory Experience”, by Prof. David Bish (Indiana State University), two Public Lectures were given as an exciting opening to AXAA-2017: “Journeying to the Centres of the Planets” by Dr. Helen Maynard-Casely (Planetary and Beamline Scientist, Australian Centre for Neutron Scattering, ANSTO) and “When Art and Science Collide: X-ray Fluorescence Elemental Mapping of Nineteenth Century Paintings From The National Gallery of Victoria” by Michael Varcoe-Cocks (Head of Conservation, National Gallery of Victoria). A new addition to AXAA-2017 was the Career Path Panel Discussion session, of particular value to students and early career researchers, and live demonstrations showcasing the latest developments in X-ray instrumentation and equipment. Following AXAA-2017 delegates had the opportunity to tour the Australian Synchrotron, Australia's major X-ray characterisation and research facility, as well as the conservation facilities at the National Gallery of Victoria. Diversity was forefront in the AXAA-2017 conference policy, and in the area of gender diversity, the proportion of female delegates was substantially higher than in previous events, with 43% of plenary, 38% of invited, and 53% of conference committee members female. AXAA-2017 demonstrated a continued high level of interest and engagement in X-ray and related analytical methods, applications and research in Australia and surrounds. The next AXAA conference event will be in 2020 (AXAA-2020). © Cambridge University Press 2022
Silico-ferrite of calcium and aluminum (SFCA) iron ore sinter bonding phases: new insights into their formation during heating and cooling
(Springer nature, 2012-12-01) Webster, NAS; Pownceby, MI; Madsen, IC; Kimpton, JA
The formation of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter phases during heating and cooling of synthetic iron ore sinter mixtures in the range 298 K to 1623 K (25 A degrees C to 1350 A degrees C) and at oxygen partial pressure of 5 x 10(-3) atm has been characterized using in situ synchrotron X-ray diffraction. SFCA and SFCA-I are the key bonding phases in iron ore sinter, and an improved understanding of their formation mechanisms may lead to improved efficiency of industrial sintering processes. During heating, SFCA-I formation at 1327 K to 1392 K (1054 A degrees C to 1119 A degrees C) (depending on composition) was associated with the reaction of Fe2O3, 2CaO center dot Fe2O3, and SiO2. SFCA formation (1380 K to 1437 K [1107 A degrees C to 1164 A degrees C]) was associated with the reaction of CaO center dot Fe2O3, SiO2, and a phase with average composition 49.60, 9.09, 0.14, 7.93, and 32.15 wt pct Fe, Ca, Si, Al, and O, respectively. Increasing Al2O3 concentration in the starting sinter mixture increased the temperature range over which SFCA-I was stable before the formation of SFCA, and it stabilized SFCA to a higher temperature before it melted to form a Fe3O4 + melt phase assemblage (1486 K to 1581 K [1213 A degrees C to 1308 A degrees C]). During cooling, the first phase to crystallize from the melt (1452 K to 1561 K [1179 A degrees C to 1288 A degrees C]) was an Fe-rich phase, similar in composition to SFCA-I, and it had an average composition 58.88, 6.89, 0.82, 3.00, and 31.68 wt pct Fe, Ca, Si, Al, and O, respectively. At lower temperatures (1418 K to 1543 K [1145 A degrees C to 1270 A degrees C]), this phase reacted with melt to form SFCA. Increasing Al2O3 increased the temperature at which crystallization of the Fe-rich phase occurred, increased the temperature at which crystallization of SFCA occurred, and suppressed the formation of Fe2O3 (1358 K to 1418 K [1085 A degrees C to 1145 A degrees C]) to lower temperatures. © 2012, Springer Nature
Structural and conductivity evolution of fluorite-type Bi2O3-Er2O3-PbO solid electrolytes during long-term annealing
(Elsevier, 2008-08) Webster, NAS; Ling, CD; Raston, CL; Lincoln, FJ
Quenched-in fcc fluorite-type materials in the Bi2O3-Er2O3-PbO system were annealed in air at 500 and 600 degrees C for up to 2000 h. Each material experienced a conductivity-lowering structural transformation, thus making them unsuitable for use in SOFCs. For example, the materials (BiO1.5)(0.80)(ErO1.5)(0.20-x)(PbO)(x), x = 0.03, 0.06 and 0.09, underwent a fluorite-type to tetragonal transformation during annealing at 500 degrees C due to (100) oxide-ion vacancy ordering, and the rate of conductivity decay at 500 degrees C increased with increasing Pb2+/Er3+ ratio. © 2008, Elsevier Ltd.
Structure and conductivity of new fluorite-type Bi2O3-Er2O3-PbO materials
(Elsevier, 2007-10) Webster, NAS; Ling, CD; Raston, CL; Lincoln, FJ
Fluorite-type fcc phases have been synthesised in the system Bi2O3-Er2O3-PbO by solid state reaction, and a partial air-quenchable domain of the fluorite-type phase has been established. Some of these materials display high oxide ion conductivities, notably (BiO1.5)(0.80)(ErO1.5)(0.11)(PbO)(0 09) and (BiO1.5)(0.85)(ErO1.5)(0.12)(PbO)(0.03), which have conductivities of 0.49 and 0.72 S cm(-1) at 750 degrees C, respectively, placing them among the most conductive Bi2O3-based materials. Conductivity was found to increase with increasing Pb2+/Er3+ ratio and decreasing (Er3+ + Pb2+)/Bi3+ ratio. Positional disorder in the oxide ion sublattice was characterised by neutron powder diffraction. At room temperature, the oxide ion sublattice appeared to be completely disordered, with oxide ions only in 32f and 48i sites, and changes in occupancy with increasing Pb2+/Er3+ and (Er3+ + Pb2+)/Bi3+ ratios were not significant. At 700 degrees C, there appeared to be oxide ions in 8c sites for the material (BiO1.5)(0.80)(ErO1.5)(0.11)(PbO)(0 09), with a correspondingly smaller occupancy of the 32f sites, whilst the occupancy of the 48i sites had not changed significantly. © 2007, Elsevier Ltd.
Studying electrical double layers in ionic liquids using neutron and x-ray reflectometry
(Australian Institute of Physics, 2010-02-05) Lauw, Y; Nelson, A; Horne, MD; Rodopoulos, T; Minofar, B; Webster, NAS; Hamilton, WA
Ionic liquids are typically defined as salts that exist in a liquid state at, or near, room temperature. Due to their favourable properties (e.g., good thermal stability, low volatility, and wide electrochemical window), ionic liquids have potential use in many industrial applications, such as catalysis, lubrication, batteries, and metal electrodeposition. Despite recent advances in the field, ionic liquid research is still in its infancy. Additional fundamental studies are needed to explore the properties of ionic liquids and to allow the full potential of these properties in particular applications to be exploited. Electrical double layers (EDL) are well known in aqueous colloidal systems where the potential field from a charged surface affects many properties of the particle. The structure of the EDL at a conductive surface is of prime importance to electrochemistry because it strongly affects the transport of reactants and products within the region where electrochemical reactions take place. The understanding of the EDL in ionic liquids is not nearly as advanced as aqueous systems and even a description of how it responds to changes in the conductor potential is yet to be agreed. Here we present some recent results from simulation and Neutron/X-ray reflectometry measurements that explore the electrical double layer in ionic liquids at the air-liquid and solid-liquid interfaces. The effect of water impurities within the (EDL) of an ionic liquid is of particular interest since they are known to reduce the electrochemical window of ionic liquids, decrease their density and viscosity, and anomalously decrease their surface tension.
X-ray reflectometry studies on the effect of water on the surface structure of [C(4)mpyr][NTf2] ionic liquid
(Royal Society of Chemistry, 2009-10-21) Lauw, Y; Horne, MD; Rodopoulos, T; Webster, NAS; Minofar, B; Nelson, A
The effect of water on the surface structure of 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonylimide [C(4)mpyr][NTf2] ionic liquid was investigated using X-ray reflectometry. The measured reflectivity data suggests a significant amount of water is adsorbed at the surface, with the first layer from the gas (nitrogen)-liquid phase boundary mainly occupied by a mixture of cations and water. Beyond the cation + water layer, the scattering length density increases towards the bulk value, indicating a decreasing amount of water and cations, and/or an increasing amount of anions. The orientation of the butyl chain of cation at the phase boundary and the population of water at the surface were described based on results from an independent molecular dynamics (MD) simulation. We show that the presence of water in the ionic liquid has a non-monotonic effect on the overall thickness of the surface. At low water content, the addition of water does not change the surface thickness since water is mainly present in the bulk. As the water content increases, the surface swells before eventually shrinking down close to the solubility limit of water. The non-monotonic surface thickness is used to explain the anomalous trend of surface tension in ionic liquid-water mixtures reported in the literature. © 2009, Royal Society of Chemistry

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