I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[585]
Abstract: Combined microfocus XAS and XRD analysis of alpha-particle radiation damage haloes around thorium-containing monazite in Fe-rich biotite reveals changes in both short- and long-range order. The total alpha-particles flux derived from the Th and U in the monazite over 1.8 Ga was 0.022 alpha particles per atomic component of the monazite and this caused increasing amounts of structural damage as the monazite emitter is approached. Short-range order disruption revealed by Fe K-edge EXAFS is manifest by a high variability in Fe-Fe bond lengths and a marked decrease in coordination number. XANES examination of the Fe K-edge shows a decrease in energy of the main absorption by up to 1 eV, revealing reduction of the Fe3+ components of the biotite by interaction with the He-4(2)2+, the result of low and thermal energy electrons produced by the cascade of electron collisions. Changes in d spacings in the XRD patterns reveal the development of polycrystallinity and new domains of damaged biotite structure with evidence of displaced atoms due to ionization interactions and nuclear collisions. The damage in biotite is considered to have been facilitated by destruction of OH groups by radiolysis and the development of Frenkel pairs causing an increase in the trioctahedral layer distances and contraction within the trioctahedral layers. The large amount of radiation damage close to the monazite can be explained by examining the electronic stopping flux.
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Aug 2013
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[22876]
Abstract: Fly ash represents a promising alternative source of rare earth elements (REE). However, information on REE containing mineral phases and their association with other fly ash components, vital for REE recovery from fly ash, is currently lacking. Herein, the mass fraction, distribution, crystallography and solid-state chemistry of REE, U and Th in Nigerian simulated fly ash samples were characterised using a range of laboratory and synchrotron x-ray based analytical techniques to underpin future extraction methodologies. Inductively coupled plasma mass spectrometry following full-acid digest of forty-five samples revealed recoverable average total REE content which ranged between 442 mgkg−1and 625 mgkg−1, comprising over 30 wt% of the critical REE Nd, Eu, Tb, Dy, Y and Er. These REE within the fly ash samples were found to be most frequently associated with discrete monazite, xenotime and Y-bearing zircon mineral particles, with the former the most detected, which could be beneficiated through gravity separation. Analysis of monazite particles isolated from the composite samples through a complimentary suite of analytical synchrotron radiation techniques revealed a core-shell pattern, with the shell rich in colocalised Ce, Nd and La, and the core enrich in both U and Th. Ce in monazite was found to exist in a mixed trivalent and tetravalent oxidation state, with the monazite structure amorphized due to the high temperature combustion process. Such results demonstrate the strong co-association and physical distribution of REE, U and Th within monazite in fly ash; knowledge of which can subsequently be used to optimise or develop a more selective, cost-effective and environmentally friendly solvent extraction methodology, by targeting the strongly colocalised and surface bound REE in fly ash monazite particles.
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Aug 2020
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I18-Microfocus Spectroscopy
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Abstract: A factory in Colonie (NY, USA) emitted c. 4.8 ± 1 tonnes of depleted uranium (DU) particulates into a suburban environment during 1958 – 1984. These particulates were initially dispersed by prevailing winds. Quadrupole inductively coupled plasma mass spectrometry (ICP-MS), laser ablation multicollector (LA-MC-) ICP-MS, scanning electron microscopy (SEM) and microfocus extended X-ray absorption fine structure (?EXAFS) spectroscopy have been used to characterise soils, dusts, vegetation, and individual particles. The concentration range of natural uranium in Colonie soils is 0.7 — 2.1 ?g g-1; with total uranium up to 500 ± 40 ?g g-1 in DU contaminated soils. Bioturbation can account for dispersal of contaminant from the soil surface. Primary morphologies are described for uraniferous particles from soils and dusts. Polycrystalline, often hollow microscopic uranium oxide spheres are similar to particles produced by DU munitions impacting armoured targets. These survive as UO2+x and U3O8, the least bioaccessible oxides of uranium. Fruit and wood samples were contaminated by DU, demonstrating limited bioavailability. Deviation of 235U/238U from the natural isotope ratio allows detection of DU in soils to at least 5.6 km from site. The average DU ‘end-member’ composition aggregated in soil samples comprises (2.05 ± 0.06) x10-3 235U/238U, (3.2 ± 0.1) x10-5 236U/238U, and (7.1 ± 0.3) x10-6 234U/238U. Individual uranium oxide grains were analysed by LA-MC-ICP-MS, all of which were from DU, with variable isotopic compositions (236U/238U, 235U/238U & 234U/238U). There is no evidence of enriched uranium in Colonie soils and dusts. The isotopic compositions of the Colonie particles can be explained by the inhomogeneous mixing of at least seven batches of tails from the Paducah gaseous diffusion plant, which are identified as the origins of the DU feedstocks used by National Lead Industries at Colonie. LA-MC-ICP-MS is recommended for nuclear forensic applications. This case-study is an attractive analogue for battlefield contamination.
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Mar 2010
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[12907]
Abstract: The complex tribochemical nature of lubricated tribological contacts is inaccessible in real
time without altering their initial state. To overcome this issue, a new design of a pin-ondisc
tribological apparatus was developed and combined with synchrotron X-ray absorption
spectroscopy (XAS). Using the designed apparatus it is possible to study in-situ the transient
decomposition reactions of various oil additives on different surfaces under a wide range of
realistic operating conditions of contact pressure (1.0 - 3.0 GPa), temperature (25 - 120
oC) and sliding speed (30 - 3000 rpm or 0.15 - 15 m/s). To test the apparatus, several
tribological tests were performed at different shearing times ranging from 2.5 to 60 minutes.
These tests were carried out under Helium atmosphere at a temperature of 80 oC, contact
pressure of 2.2 GPa and sliding speed of 50 rpm. The XAS experiments showed that the zinc
dialkyldithiophosphate (ZDDP) antiwear additive decomposes in the oil to form a tribofilm
on the iron surface at different reaction kinetics from the ones of the thermal film. This
confirmed the findings of several previous studies that the formation of the tribofilm is a
thermally activated mechanically assisted process, which is faster than the one involved the
thermal film that is only thermally activated. Furthermore, the results indicated that the
sulfur of the formed film, whether a tribofilm or a thermal film, appears initially in the form
of sulfate, with some sulfide, which under heat or shear is reduced into mainly sulfide.
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Jan 2017
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I18-Microfocus Spectroscopy
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Jan 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[10358]
Open Access
Abstract: Methane (CH4) represents one of the key compounds in the global carbon (C) cycle. A major proportion of the CH4 in the Earth system is produced in marine sediments by methanogenesis, the final step in the gradual fermentation of organic matter deposited on the seafloor. Once emitted to the atmosphere, CH4 acts as a powerful greenhouse gas. Despite high rates of methanogenesis in continental shelf and slope environments, the ocean today contributes only a relatively small amount of this potent greenhouse gas to the global atmospheric budget. The low atmospheric CH4 efflux from the ocean is largely due to the effective biological removal of dissolved CH4 through anaerobic oxidation with sulfate (SO42-) in marine sediments. This removal of pore water CH4 occurs within a distinct sulfate/methane transition zone (SMTZ), preventing the large amounts of CH4 generated in marine sediments from escaping to the water column. The relevant pathways and the environmental factors that control the rates of CH4 oxidation in marine sediments are, however, still incompletely understood. In some settings, for example, pore water CH4 is found throughout the SO42--bearing zone, pointing towards an inefficient CH4 oxidation by SO42- in certain marine environments. Other more recent findings further indicate that nitrate and nitrite, as well as metal oxides (e.g. manganese and iron (Fe) oxides) can enhance the conversion of CH4 to CO2 in the absence of oxygen. Sulfate may thus not be the only electron acceptor used by microorganisms to oxidize CH4 in anoxic sediments, but knowledge about the significance of additional electron acceptors for the global CH4 cycle is still lacking. In addition, little is known about how CH4 oxidation may impact the marine cycling of Fe and phosphorus (P), both key nutrients for oceanic phytoplankton. This thesis aims to refine our understanding of the potential impacts and controls of CH4 oxidation in marine sediments. In particular, it discusses how anaerobic oxidation of CH4 affects the sequestration and sedimentary records of Fe and P, using a wide range of geochemical tools. The results presented here also demonstrate that climate change and anthropogenic nutrient loading may alter the position and efficiency of the CH4 oxidation barrier in coastal sediments, which in turn could lead to increased atmospheric CH4 emissions from the coastal ocean.
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Jun 2016
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[13690]
Open Access
Abstract: Using the data we have gathered at I18 on micron-size grains returned by Stardust from Comet Wild2, we hypothesise that this comet has affinities to CO and CR carbonaceous chondrites. For instance, the abundance of magnetite (Fe3O4) grains that we identified in previous I18 experiments [1] demonstrates the action of liquid water on the parent body. By analysing CR chondrite powder shot into aerogel at 6 kms-1, and also newly harvested Wild2 aerogel tracks we made accurate comparisons between chondrites and the comet. This demonstrates that the mineral assemblages preserved in the Stardust tracks were formed from carbonaceous chondrite like material. We also conducted a pilot XRD, XANES study on newly discovered martian meteorites also analyse recently discovered martian meteorites in order to characterise the mineralogical effects of water-rock reaction. We will complete the latter study in a future planned experiment.
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Jul 2016
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I18-Microfocus Spectroscopy
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Carolin
Schultz
,
Kathryn
Powell
,
Alison
Crossley
,
Kerstin
Jurkschat
,
Peter
Kille
,
A. John
Morgan
,
Daniel
Read
,
William
Tyne
,
Elma
Lahive
,
Claus
Svendsen
,
David
Spurgeon
Diamond Proposal Number(s):
[7837]
Abstract: Initiatives to support the sustainable development
of the nanotechnology sector have led to rapid growth
in research on the environmental fate, hazards and risk of
engineered nanoparticles (ENP). As the field has matured
over the last 10 years, a detailed picture of the best
methods to track potential forms of exposure, their uptake
routes and best methods to identify and track internal fate
and distributions following assimilation into organisms has
begun to emerge. Here we summarise the current state of
the field, focussing particularly on metal and metal oxide
ENPs. Studies to date have shown that ENPs undergo a
range of physical and chemical transformations in the
environment to the extent that exposures to pristine well
dispersed materials will occur only rarely in nature.
Methods to track assimilation and internal distributions
must, therefore, be capable of detecting these modified
forms. The uptake mechanisms involved in ENP assimilation
may include a range of trans-cellular trafficking and
distribution pathways, which can be followed by passage to
intracellular compartments. To trace toxicokinetics and
distributions, analytical and imaging approaches are
available to determine rates, states and forms. When used
hierarchically, these tools can map ENP distributions to
specific target organs, cell types and organelles, such as
endosomes, caveolae and lysosomes and assess speciation
states. The first decade of ENP ecotoxicology research,
thus, points to an emerging paradigm where exposure is to
transformed materials transported into tissues and cells via
passive and active pathways within which they can be
assimilated and therein identified using a tiered analytical
and imaging approach.
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Mar 2015
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1205]
Abstract: Synchrotron-based techniques are becoming increasingly important in heritage science and the aim of this article is to describe how recently developed microfocus methods can probe the elemental composition, speciation and structure at the micron level in samples from structures. Firstly an outline is given of the major techniques that are used, namely x-ray fluorescence, diffraction and absorption spectroscopy, and the information that they can provide. This is followed by a description of the experimental set-up and procedures. The application of the methods is exemplified by case studies of the degradation of three types of historic structural materials; marble, glass and ship timbers. The results of the studies and their role in developing conservation strategies are described.
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Oct 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[8211]
Open Access
Abstract: The neutral, distorted octahedral complex [TiCl4(SenBu2)2] (1), prepared from the reaction of TiCl4 with the neutral SenBu2 in a 1:2 ratio and characterized by IR and multinuclear (1H, 13C{1H}, 77Se{1H}) NMR spectroscopy and microanalysis, serves as an efficient single-source precursor for low-pressure chemical vapor deposition (LPCVD) of titanium diselenide, TiSe2, films onto SiO2 and TiN substrates. X-ray diffraction patterns on the deposited films are consistent with single-phase, hexagonal 1T-TiSe2 (P3̅m1), with evidence of some preferred orientation of the crystallites in thicker films. The composition and structural morphology was confirmed by scanning electron microscopy (SEM), energy dispersive X-ray, and Raman spectroscopy. SEM imaging shows hexagonal plate crystallites growing perpendicular to the substrate, but these tend to align parallel to the surface when the quantity of reagent is reduced. The resistivity of the crystalline TiSe2 films is 3.36 ± 0.05 × 10–3 Ω·cm with a carrier density of 1 × 1022 cm–3. Very highly selective film growth from the reagent was observed onto photolithographically patterned substrates, with film growth strongly preferred onto the conducting TiN surfaces of SiO2/TiN patterned substrates. TiSe2 is selectively deposited within the smallest 2 μm diameter TiN holes of the patterned TiN/SiO2 substrates. The variation in crystallite size with different diameter holes is determined by microfocus X-ray diffraction and SEM, revealing that the dimensions increase with the hole size, but that the thickness of the crystals stops increasing above ∼20 μm hole size, whereas their lengths/widths continue to increase.
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Nov 2013
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