B18-Core EXAFS
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Diamond Proposal Number(s):
[9621, 10163, 12767]
Open Access
Abstract: Understanding interactions between radionuclides and mineral phases underpins site environmental clean-up and waste management in the nuclear industry. Transport and fate of radionuclides in many subsurface environments are controlled by adsorption, redox and mineral incorporation processes. Interactions of iron (oxyhydr)oxides with uranium have been extensively studied due to the abundance of uranium as an environmental contaminant and ubiquity of iron (oxyhydr)oxides in engineered and natural environments. Despite this, detailed mechanistic information regarding the incorporation of uranium into Fe(II) bearing magnetite and green rust is sparse. Here, we present a co-precipitation study where U(VI) was reacted with environmentally relevant iron(II/III) (oxyhydr)oxide mineral phases. Based on diffraction, microscopic, dissolution and spectroscopic evidence, we show the reduction of U(VI) to U(V) and stabilisation of the U(V) by incorporation within the near-surface and bulk of the particles during co-precipitation with iron (oxyhydr)oxides. U(V) was stable in both magnetite and green rust structures and incorporated via substitution for octahedrally coordinated Fe in a uranate-like coordination environment. As the Fe(II)/Fe(III) ratio increased, a proportion of U(IV) was also precipitated as surface associated UO2. These novel observations have significant implications for the behaviour of uranium within engineered and natural environments.
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Sep 2017
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I18-Microfocus Spectroscopy
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Anna
Di Laura
,
Paul D.
Quinn
,
Vasiliki C.
Panagiotopoulou
,
Harry S.
Hothi
,
Johann
Henckel
,
Jonathan J.
Powell
,
Fitim
Berisha
,
Fernanda
Amary
,
J. Fred W.
Mosselmans
,
John A.
Skinner
,
Alister J.
Hart
Diamond Proposal Number(s):
[8779, 12646]
Open Access
Abstract: The mechanisms of metal release from the articulation at the head cup bearing and the tapered
junctions of orthopaedic hip implants are known to differ and the debris generated varies in size,
shape and volume. Significantly less metal is lost from the taper junction between Cobalt-Chromium-
Molybdenum (CoCrMo) and Titanium (Ti) components (fretting-corrosion dominant mechanism),
when compared to the CoCrMo bearing surfaces (wear-corrosion dominant mechanism). Corrosion
particles from the taper junction can lead to Adverse Reactions to Metal Debris (ARMD) similar to
those seen with CoCrMo bearings. We used synchrotron methods to understand the modes underlying
clinically significant tissue reactions to Co, Cr and Ti by analysing viable peri-prosthetic tissue. Cr was
present as Cr2O3 in the corroded group in addition to CrPO4 found in the metal-on-metal (MoM) group.
Interestingly, Ti was present as TiO2 in an amorphous rather than rutile or anatase physical form. The
metal species were co-localized in the same micron-scale particles as result of corrosion processes and
in one cell type, the phagocytes. This work gives new insights into the degradation products from metal
devices as well as guidance for toxicological studies in humans.
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Sep 2017
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1175]
Abstract: The relationships between the composition of hibonite with the general formula CaAl12-2x-yMgxTi4 +xTi3 +yO19, the oxidation state of Ti (Ti3 +/ΣTi, where ΣTi = Ti3 + + Ti4 +), and oxygen fugacity (fO2) were investigated experimentally. It was found that hibonite can be synthesised with a range of Ti3 +/ΣTi values at constant fO2 and with a constant Ti3 +/ΣTi value for a range of fO2s. It was also found that if hibonite with the formula CaAl12-yTi3 +yO19 (Ti3 +/ΣTi = 1) is equilibrated with a melt of CAI composition at fO2s below the iron-wüstite buffer then the resulting hibonite contained Mg, with Mg per formula unit (pfu) ~ 0.8 Ti pfu, and Ti3 +/ΣTi ~ 0.2, irrespective of the fO2. These results suggest that the availability of Mg, rather than fO2, is the key factor that determines Ti3 +/ΣTi of hibonite. The structures of synthetic samples of hibonite with the general formula CaAl12-2xMgxTi4 +xO19, where 0 ≤ X < 1, were determined by Rietveld refinement of X-ray powder diffraction data. The predominant site occupied by Ti4 + was found to change from M2 to M4 with increasing Ti content. The range of Ti concentrations over which the site occupancy changed corresponds to that observed in meteoritic hibonite. This change in the Ti4 + site produces changes in the Ti K-edge XANES spectra, particularly in the intensity of the pre-edge feature, for constant Ti3 +/ΣTi. The observed dependence of the pre-edge on the Ti4 + site was reproduced by ab initio simulations of the XANES spectra. The XANES spectra of natural hibonite with variable Ti content from the Murchison carbonaceous chondrite closely match the spectra of the synthetic samples with similar Ti contents. These differences in the spectra of meteoritic hibonite could be misinterpreted as being due to changes in Ti3 +/ΣTi, but are instead due to differences in ΣTi, which relate to the petrogenetic history. Crystal chemistry exerts a first order control on the Ti site occupancy and Ti3 +/ΣTi value of hibonite. As a result, no simple relationship between Ti3 +/ΣTi and fO2 should be expected. It is unlikely that hibonite will be useful as an oxybarometer for solar processes without Ti3 +/ΣTi standards that are compositionally matched to the unknown.
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Apr 2017
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[10242, 12064, 12499, 12601, 14440]
Open Access
Abstract: Although we often understand empirically what constitutes an active catalyst, there is still much to be understood fundamentally about how catalytic performance is influenced by formulation. Catalysts are often designed to have a microstructure and nanostructure that can influence performance but that is rarely considered when correlating structure with function. Fischer-Tropsch synthesis (FTS) is a well-known and potentially sustainable technology for converting synthetic natural gas (“syngas”: CO + H2) into functional hydrocarbons, such as sulfur- and aromatic-free fuel and high-value wax products. FTS catalysts typically contain Co or Fe nanoparticles, which are often optimized in terms of size/composition for a particular catalytic performance. We use a novel, “multimodal” tomographic approach to studying active Co-based catalysts under operando conditions, revealing how a simple parameter, such as the order of addition of metal precursors and promoters, affects the spatial distribution of the elements as well as their physicochemical properties, that is, crystalline phase and crystallite size during catalyst activation and operation. We show in particular how the order of addition affects the crystallinity of the TiO2 anatase phase, which in turn leads to the formation of highly intergrown cubic close-packed/hexagonal close-packed Co nanoparticles that are very reactive, exhibiting high CO conversion. This work highlights the importance of operando microtomography to understand the evolution of chemical species and their spatial distribution before any concrete understanding of impact on catalytic performance can be realized.
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Mar 2017
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B18-Core EXAFS
I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[11865]
Abstract: Endochondral ossification is the process by which bone is deposited during development, growth and repair of the skeleton. The regulation of endochondral ossification is extremely important as developmental flaws can result in severe skeletal abnormalities. However, until recently the limitations of available methodologies have restricted our understanding of this fundamental physiological process. The analysis of chemical elements that are intimately associated with discrete biochemical stages of ossification within bone could provide new insight to such processes at the atomic level. In this study we present detailed characterisation of the elemental inventory within actively ossifying bone during development in mice using synchrotron microfocus X-ray techniques. X-ray fluorescence imaging showed differential distributions of Zn, Sr and Ca, which may be correlated with the processes of cartilage replacement (Zn), active ossification (Sr) and fully ossified tissues (Ca). Quantification of these trace elements confirmed their relative distributions. These results represent the first detailed visualisation of local endochondral ossification processes using trace elemental mapping. Such studies have far reaching applications not only in the medical field, but to our understanding of the evolution of the bony skeleton given that trace element inventories have been shown to be preserved through deep time (millions of years).
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Mar 2017
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I18-Microfocus Spectroscopy
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Open Access
Abstract: With the development of fourth-generation high-brightness synchrotrons on the horizon, the already large volume of data that will be collected on imaging and mapping beamlines is set to increase by orders of magnitude. As such, an easy and accessible way of dealing with such large datasets as quickly as possible is required in order to be able to address the core scientific problems during the experimental data collection. Savu is an accessible and flexible big data processing framework that is able to deal with both the variety and the volume of data of multimodal and multidimensional scientific datasets output such as those from chemical tomography experiments on the I18 microfocus scanning beamline at Diamond Light Source.
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Jan 2017
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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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Diamond Proposal Number(s):
[490, 1175]
Abstract: The Al-rich oxide hibonite (CaAl12O19) is modelled to be the second mineral to condense from a gas of solar composition and is found within calcium-aluminum-rich inclusions and the matrix of chondritic meteorites. Both Ti3+ and Ti4+ are reported in meteoritic hibonite, so hibonite has been proposed as a single mineral oxybarometer that could be used to elucidate conditions within the first 0.2 Myrs of the Solar System.
Synthetic hibonites with Ti3+/(Ti3++Ti4+) (hereafter Ti3+/ΣTi) ranging between 0 and 1 were prepared as matrix-matched standards for meteoritic hibonite. The largest yield of both Ti-free and Ti-bearing hibonite at ∼1300 and ∼1400 °C was obtained by a single sinter under reducing conditions.
In situ micro-beam Ti K-edge X-ray absorption near edge structure (XANES) spectra were collected from the synthetic hibonites, as well as from terrestrial hibonite. Spectral features in the post-crest region were shown to correlate with the Ti4+ content. Furthermore, Ti4+ on the M2 trigonal bipyramidal and the adjoining M4 octahedral sites appears to cause variability in the post-crest region as a function of orientation. For this suite of synthetic hibonites it was observed that the pre-edge peak region is not influenced by orientation, but is controlled by Ti3+/ΣTi, site geometry and/or Ti concentration. In particular, the pre-edge peak intensities reflect Ti coordination environment and distortion of the M4 octahedral site. Therefore, although pre-edge peak intensities have previously been used to determine Ti3+/ΣTi in meteoritic minerals, we excluded use of the pre-edge peak intensities for quantifying Ti valence states in hibonite.
The energy of the absorption edge at a normalized intensity of 0.8 (E0.8) and the energy of the minimum between the pre-edge region and the absorption edge (Em1) were found to vary systematically with Ti3+/ΣTi. Ti3+/ΣTi in hibonite as a function of Em1 was modelled by a quadratic function that may be used to quantify Ti3+/ΣTi in meteoritic hibonite when the synthetic hibonite standards are crystal-chemically matched to the natural samples and are measured during the same analytical session as the meteoritic hibonites.
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Jun 2016
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1205]
Abstract: We report a microfocus X-ray absorption (XAS) investigation of a thin film sample from an iron contaminated wooden arrow tip raised from the seabed with the Mary Rose. The XAS studies were combined with optical and scanning electron microscopy measurements. The arrow tip had been treated with polyethylene glycol (PEG) soon after it had been raised and stored in a controlled environment. The measurements revealed a significant concentration of iron sulfide nanoparticles. This indicates that in this sample there was a reduction of the oxidative effects of the normal ambient atmosphere that is usually seen in untreated timbers. The film was treated overnight with an aqueous solution of diethylenetriaminepentaacetic acid (DTPA), which is normally very effective in sequestering iron. This had little effect in terms of removing iron from the film and possible explanations are discussed.
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Jun 2016
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[9044, 11703, 12064]
Open Access
Abstract: The development of complementary imaging techniques at beamline I18 at Diamond
Light Source (Didcot, UK) to investigate the microstructure of inorganic materials is
described. In particular, the use of X-ray micro-imaging techniques to understand the
effect of alpha radiation on phyllosilicates, and the nature of individual catalytic par-
ticles are reported. Micro X-ray diffraction (
m
XRD) studies of the former materials
have shown structural changes that will affect their adsorption properties, while the
chemistry of the catalyst particles has been investigated using micro X-ray fluorescence,
m
XRD and
m
X-ray absorption near-edge structure mapping. The distribution of a Mo-
promoted Pt nitrobenzene hydrogenation catalyst has shown that some of the Pt pene-
trated to the core of the particle and has the same chemistry as the bulk of the Pt located
on the outside of the particle. The phase distribution in an as-prepared Re-Ti-promoted
Co Fischer-Tropsch catalyst is reported.
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Jun 2016
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