I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1215]
Abstract: The luminescence emission of quartz is used in optically stimulated luminescence dating (OSL), however the precise origins of the emission are unclear. A suite of quartz samples were analysed using X-ray excited optical luminescence (XEOL). Radiation dose effects were observed whereby the UV emissions (3.8 and 3.4 eV) were depleted to the benefit of the red emission (1.9–2.0 eV). Samples were excited at ?7 keV. Understanding why some quartz emit light more brightly than others will increase the efficiency and precision of OSL analyses.
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Oct 2011
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I18-Microfocus Spectroscopy
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Oct 2011
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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):
[1205]
Abstract: This thesis reports a study of the sulfur problem which is the production of sulfuric acid via the oxidation of iron sulfide in the timbers of the Mary Rose a flagship of Henry VIII 's navy which sunk in 1535 and was raised in 1982. The work has involved a range of chemical and physical techniques with particular use of synchrotron sources to measure the iron and sulfur speciation in the timbers with X-ray absorption spectroscopy (XAS) measurements. XAS measurements are almost unique in providing the speciation of atoms in a sample via the XANES. They are particularly useful for sulfur, which has a wide range of oxidation states. However, the current work has shown the need to use the bulk and microfocus XAS measurements in parallel, particularly for archaeological samples. It is clear that the iron and sulfur contents and speciation can vary widely from sample to sample of the Mary Rose timbers. In the study on the effectiveness of chelating agents in the removal of iron species from the timbers care was taken, wherever possible, to ensure that the same samples and sample positions were used for the before and after treatment measurements. The nature of the iron and su~ur species is of extreme importance because it is assumed that it is Fe" that gives rise to the production of su~uric acid. The current study has shown that in the timbers that had not been PEG treated contained iron in the surface regions that was predominantly Fe", similar to the findings of other workers. Most of the work in this thesis used samples close to the surface of the timbers. It was only in samples taken deep into the timbers experiments that there were significant concentrations of Fe". A range of sulfur species were found in the samples. The predominant species were reduced sulfur species, elemental sulfur and sulfate. Very little pyrite was found -in the timbers studied, but it should be noted that these timbers had not been PEG treated. Some pyrite was found in the cell walls. The present studies were predominantly on the surface regions of the timbers and the conclusion is that the bulk of the pyrite which may have been present had oxidised in the moist, oxygen containing environment in which they had been stored after recovery from the sea bed. A key finding of the present study is the co-location of iron and sulfate in the timbers. This had been suggested but had not been experimentally verified. The production of sulfuric acid in the timbers is thought to involve the oxidation of iron sulfides in the presence of water to produce is iron sulfate and sulfuric acid. The fact that the present experiments show iron and sulfate in the same positions i'] the XANES maps strongly supports the proposed oxidation mechanism of iron sulfides. The bulk and microfocus XAS experiments show that a large fraction of the iron in the current samples was in the form of an oxide. This is most likely to be goethite (FeO(OH)). The XANES analysis and the fitting of the EXAFS are consistent with this identification. All the four chelating agents used in this work (EDTA, DTPA, ammonium citrate and calcium phytate) were effective in removing iron from the timbers. However, the more efficient are DTPA and calcium phytate in terms of amount removed at fixed molarity. For samples that had been treated with PEG the current work showed that the chelating agents were less effective. This is presumably due to the PEG blocking the penetration of the solutions of the chelating agents into the wood.
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Oct 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[4861]
Abstract: The deposition of gold at the interface between immiscible electrolyte solutions has been investigated using reduction of tetrachloroaurate or tetrabromoaurate in 1,2-dichloroethane, with aqueous phase hexacyanoferrate as reducing agent. In a clean environment without defects present at the interface, the Au(III) complex was reduced to the Au(I) complex, but no solid phase formation could be observed. A deposition process could only be observed through the addition of artificial nucleation sites in the form of palladium nanoparticles at the interface. This process could be associated with the reduction of the Au(I) halide complex to metallic gold, by determining the gold reduction potentials in 1,2-dichloroethane. XANES measurements indicate that tetrachloroaurate ion transfers intact into the organic phase, with the central Au atom retaining its oxidation state of +3 and the overall anion remaining charged at −1.
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Aug 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[614]
Abstract: We report R2 and R2* in human hippocampus from five unfixed post-mortem Alzheimer's disease (AD) and three age-matched control cases. Formalin-fixed tissues from opposing hemispheres in a matched AD and control were included for comparison. Imaging was performed in a 600 MHz (14 T) vertical bore magnet at MR microscopy resolution to obtain R2 and R2* (62 ?m × 62 ?m in-plane, 80 ?m slice thickness), and R1 at 250 ?m isotropic resolution. R1, R2 and R2* maps were computed for individual slices in each case, and used to compare subfields between AD and controls. The magnitudes of R2 and R2* changed very little between AD and control, but their variances in the Cornu Ammonis and dentate gyrus were significantly higher in AD compared for controls (p < 0.001). To investigate the relationship between tissue iron and MRI parameters, each tissue block was cryosectioned at 30 ?m in the imaging plane, and iron distribution was mapped using synchrotron microfocus X-ray fluorescence spectroscopy. A positive correlation of R2 and R2* with iron was demonstrated. While studies with fixed tissues are more straightforward to conduct, fixation can alter iron status in tissues, making measurement of unfixed tissue relevant. To our knowledge, these data represent an advance in quantitative imaging of hippocampal subfields in unfixed tissue, and the methods facilitate direct analysis of the relationship between MRI parameters and iron. The significantly increased variance in AD compared for controls warrants investigation at lower fields and in-vivo, to determine if this parameter is clinically relevant.
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Aug 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1493]
Abstract: Highly alkaline (pH 12.2) chromate contaminated leachate (990 ?mol L?1) has been entering soils below a chromite ore processing residue disposal (COPR) site for over 100 years. The soil immediately beneath the waste has a pH of 11 ? 12.5, contains 0.3 ? 0.5% (w/w) chromium, and 45 ? 75% of the microbially available iron is Fe(II). Despite elevated pH, a viable microbial consortium of Firmicutes dominated iron reducers was isolated from this COPR affected soil. Soil pH and Cr concentration decrease with distance from the waste. XAS analysis of soil samples indicated that Cr is present as a mixed Cr(III)–Fe(III) oxy-hydroxide phase, suggesting that the elevated soil Cr content is due to reductive precipitation of Cr(VI) by Fe(II). Microcosm results demonstrate the capacity of COPR affected soil to abiotically remove all Cr(VI) from the leachate within 40 days. In air oxidation experiments less than 2% of the total Cr in the soil was remobilised despite significant Fe(II) oxidation. XAS analysis after air oxidation showed no change in Cr-speciation, indicating the Cr(III)-containing phase is a stable long term host for Cr. This work suggests that reductive precipitation of Cr(VI) is an effective method of contaminant immobilisation in soils where microbially produced Fe(II) is present.
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Aug 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[6769]
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Aug 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1828]
Open Access
Abstract: The Fischer
-Tropsch Synthesis (FTS) is an alternative route
to produce liquid fuels from a variety of
carbon feedstocks including coal and biomass. Typically iron and cobalt based catalysts have been
used for the FTS reaction, in which a mixture of CO and H
2
(syn
-gas) reacts to form hydrocarbons.
Enhanced performa
nce has been reported for iron
-based systems doped with alkali metals and
chalcogenides. Sulfides are considered a poison for most catalytic processes, but sul
fur in the form of
sul
fates (S
VI
) is found to enhance the performance of iron based catalysts tow
ards the FTS when
present at low levels.
In this study a wide range of iron based catalysts w
as
prepared
under varying synthesis conditions and
with
different dopants. The standard methods of preparation used were co-
precipitation and incipient
wetness
impregnation. A
structural
study
of
a wide range of iron based catalysts
was
carried out using
characterisation methods
such as
X-ray Absorption Fine Structure (XAFS) spectroscopy, X
-ray
Photoelectron Spectroscopy (XPS), Powder X
-ray Diffraction (PXRD),
Scanning
Electron
Microscopy (SEM), Energy Dispersive X
-ray (EDX) and
Brunner
-Emmett
-Taller surface area
determination (BET). The characterisation was performed before and after reduction of the catalysts
(under H
2
) to form the catalytically active material
s.
Before reduction, PXRD
, XPS
and quantitative analysis
identified a ha
ematite iron oxide structure (
α
-
Fe
2
O
3
) for all samples. The crystallinity of the iron o
xide materials varied
between samples
prepared
in various conditions
. The highest crystallinity
was observed for the samples synthesised at pH7, fast
titrant addition rate, at room temperature.
The same techniques
revealed changes in the iron oxide
structure after reduction. T
he catalyst
s activated
at 400
o
C were
mainly composed of
Fe
3
O
4
and
those
activated at 450
o
C were a
mixture of Fe
2+
, Fe
3+
oxides and metallic iron Fe
0
. Moreover
, the
study of
the role of alkali metals show
ed that some of the alkali promoters (K, Rb) may decrease
the effective
iron oxide reduction
temperature.
The
nitrogen adsorp
tion experiment was used to establish that iron
oxide
doped
with different promoters
had a mesopor
ous structure
with
a narrow pore size
distribution
.
The SEM analysis indicated two different types of surface
: irregularly shaped agglomerates with
smaller ro
und edged particles attached to their surface and homogenous agglomerates surfaces with
sharp edges for the samples with different promot
ers. The most homogenous were the samples with
Rb. All samples had small particles attached to the surface of larger ag
glomerates.
An
increase of the alkali metals on the su
rface after the
activation process and migration of the alkalis
to the surface with ris
ing reduction temperature
were observed using bulk and surface techniques
(XRF, EDX and XPS)
. The
differences i
n K K
-edge shape of the XANES
spectrum indicated changes
in the local structure of K
corresponding to
changes
of
coordination number around K
+
during
activation.
It was also observed that reduction influenced the sulfur species in
iron oxide catalyst.
For
all the samples prior to reduction sulfates
(SO
4
2-
) were
detected by XPS and XAFS. After
the
reduction
at 400
o
C and 450
o
C, characteristic XPS
S 2p peaks for both sulfate and sulf
ide,
were
noticed.
The sulf
ate/sulfide ratio was higher for the catalyst sam
ples
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Aug 2011
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I18-Microfocus Spectroscopy
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Open Access
Abstract: The preservation of waterlogged archaeological wooden finds, such as Henry VIII's flagship the Mary Rose[1], [2] and [3], is complicated by the biological, chemical, and mechanical changes induced from prolonged exposure to a marine environment. Of particular concern are sulfur species that form acidic compounds that attack wood4. Here we show that different sulfur compounds do not form acids at the same rate or pathway and propose a preservation strategy of applying SrCO3 nanoparticles. These nanoparticles not only neutralize problematic sulfuric acid, but also reduced sulfur compounds, such as sulfur and pyrite, which pose a long term threat. This is the first treatment that eliminates acidification at the root. Although this strategy was devised for the Mary Rose, it could be employed to preserve any archaeological organic artifact rich in problematic sulfur, from sunken ships and silk tapestries to ancient texts and parchments.
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Jul 2011
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