I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[24092]
Open Access
Abstract: Marine archaeological artefacts contain unexpected compounds due to prolonged exposure to the sea. These can remain dormant and embedded within materials until a change in their surrounding environment, such as exposure to oxygen, prompts a transformation. These changes can pose a problem, as acidic compounds are formed which disintegrate the material, or crystals form which physically break the artefact apart. The extent of these transformations is highly heterogeneous due to its dependence on the ability for oxygen to reach and catalyse these reactions. Additionally, these transformations are heavily dependent on the environment the artefact is exposed to, and the pathways available for ingress, either naturally or through previous degradation. This results in materials with a range of different compounds which are often co-located on the macro, micro and nano-scale. Trying to de-convolute these compounds is challenging, and usually requires a suite of complementary techniques to achieve. Here we report on damaging salts found within marine archaeological bricks and show how it is only possible to qualitatively and quantitatively understand what is present by employing a range of analytical techniques, such as XRD, SEM-EDS and SR-XPD. The marine archaeological bricks studied were found to contain a range of different sulfate-based salts, which had grown crystals in preferred orientations. This provides information which will guide further conservation strategies such as how these bricks are stored, conserved and protected in the future.
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May 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[18533, 23341]
Abstract: Energy-dispersive X-ray diffraction (EDXRD) is extremely insensitive to sample morphology when implemented in a back-reflection geometry. The capabilities of this non-invasive technique for cultural heritage applications have been explored at high resolution at the Diamond Light Source synchrotron. The results of the XRD analysis of the pigments in 40 paints, commonly used by 20th century artists, are reported here. It was found that synthetic organic pigments yielded weak diffraction patterns at best, and it was not possible to unambiguously identify any of these pigments. In contrast, the majority of the paints containing inorganic pigments yielded good diffraction patterns amenable to crystallographic analysis. The high resolution of the technique enables the extraction of a range of detailed information: phase identification (including solid solutions), highly accurate unit cell parameters, phase quantification, crystallite size and strain parameters and preferred orientation parameters. The implications of these results for application to real paintings are discussed, along with the possibility to transfer the technique away from the synchrotron and into the laboratory and museum through the use of state-of-the-art microcalorimeter detectors. The results presented demonstrate the exciting potential of the technique for art history and authentication studies, based on the non-invasive acquisition of very high quality crystallographic data.
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Nov 2021
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[16328]
Open Access
Abstract: Data analysis methods for iron X-ray Absorption Spectroscopy (XAS) can provide extensive information about the oxidation state and co-ordination of an Fe-species. However, the extent to which techniques developed using a single-phase iron sample may be applied to complex, mixed-phase samples formed under real-world conditions is not clear. This work uses a combination of pre-edge fitting and linear combination analysis (LCA) to characterise the near edge region of the X-ray absorption spectrum (XANES) for a set of archaeological iron corrosion samples from a collection of cast iron cannon shot excavated from the Mary Rose shipwreck and compares the data with phase compositions determined by Synchrotron X-ray Powder Diffraction (SXPD). Archaeological powder and cross-section samples were compared to a library of iron standards and diffraction data. The XANES are consistent with previous observations that generation of the chlorinated phase akaganeite, β-FeO(OH,Cl), occurs in those samples which have been removed form passive storage and subjected to active conservation. However, the results show that if any metallic species is present in the sample, the contribution from Fe(0) to the spectral region containing a pre-edge for oxidised iron – Fe(II) and Fe(III) – causes the analysis to be less effective and the conclusions unreliable. Consequently, while the pre-edge fitting methodology may be applied to a mixture of iron oxides or oxyhydroxides, the procedure is inappropriate for a mixed metal-oxide sample without the application of a complimentary technique, such as SXPD.
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Jun 2021
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I18-Microfocus Spectroscopy
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Thomas
Christiansen
,
Marine
Cotte
,
Wout
De Nolf
,
Elouan
Mouro
,
Juan
Reyes-Herrera
,
Steven
De Meyer
,
Frederik
Vanmeert
,
Nati
Salvado
,
Victor
Gonzalez
,
Poul Erik
Lindelof
,
Kell
Mortensen
,
Kim
Ryholt
,
Koen
Janssens
,
Sine
Larsen
Diamond Proposal Number(s):
[23348]
Open Access
Abstract: A hitherto unknown composition is highlighted in the red and black inks preserved on ancient Egyptian papyri from the Roman period (circa 100 to 200 CE). Synchrotron-based macro–X-ray fluorescence (XRF) mapping brings to light the presence of iron (Fe) and lead (Pb) compounds in the majority of the red inks inscribed on 12 papyrus fragments from the Tebtunis temple library. The iron-based compounds in the inks can be assigned to ocher, notably due to the colocalization of Fe with aluminum, and the detection of hematite (Fe2O3) by micro–X-ray diffraction. Using the same techniques together with micro-Fourier transform infrared spectroscopy, Pb is shown to be associated with fatty acid phosphate, sulfate, chloride, and carboxylate ions. Moreover, micro-XRF maps reveal a peculiar distribution and colocalization of Pb, phosphorus (P), and sulfur (S), which are present at the micrometric scale resembling diffused “coffee rings” surrounding the ocher particles imbedded in the red letters, and at the submicrometric scale concentrated in the papyrus cell walls. A similar Pb, P, and S composition was found in three black inks, suggesting that the same lead components were employed in the manufacture of carbon-based inks. Bearing in mind that pigments such as red lead (Pb3O4) and lead white (hydrocerussite [Pb3(CO3)2(OH)2] and/or cerussite [PbCO3]) were not detected, the results presented here suggest that the lead compound in the ink was used as a drier rather than as a pigment. Accordingly, the study calls for a reassessment of the composition of lead-based components in ancient Mediterranean pigments.
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Oct 2020
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[18676]
Abstract: The in-situ formation of lead-sulfur inorganic compounds in historical oil paintings can have a strong detrimental effect on an artwork’s physical and visual integrity. In this paper, paint micro-samples collected from several paintings from the Rijksmuseum (Amsterdam) and Mauritshuis (The Hague) collections were probed at the micro-scale using a combination of synchrotron micro-XRD and XRD-CT. This permitted to precisely identify the chemical nature of the in-situ formed crystalline compounds as well as to chart their distribution within paint layers at the microscopic level. This provided new information on the origin of the ions involved in the crystallization of the various newly formed mineral lead-sulfur products. The formation of palmierite K2Pb(SO4)2, anglesite PbSO4 and lanarkite Pb2(SO4)O in historical samples can thus be connected to paint stratigraphic build-up, environmental conditions and potential past restoration treatments.
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Jul 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[10104]
Open Access
Abstract: Determining the nature, evolution, and impact of acid‐generating sulfur deposits in the Mary Rose wooden hull is crucial for protecting Henry VIII's famous warship for generations to come. Here, a comprehensive X‐ray absorption near‐edge spectroscopy (XANES) and X‐ray fluorescence (XRF) study sheds vital light on the evolution of complex sulfur‐based compounds lodged in Mary Rose timbers as a function of drying time. Combining insights from infrared spectroscopy correlates the presence of oxidized sulfur species with increased wood degradation via the loss of major wood components (holocellulose). Intriguingly, zinc is found to co‐exist with iron and sulfur in the most degraded wood regions, indicating its potential contributing role to wood degradation. This study provides crucial information on the degradation processes and resulting products within the wood, which can be used to develop remediation strategies to save the Mary Rose.
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May 2020
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Abstract: We present experimental results and FLUKA Monte-Carlo simulations reproducing the counting efficiency and the energy resolution of the cerium-activated yttrium-aluminium-perovskite photon detectors installed on the VESUVIO neutron spectrometer at the ISIS Pulsed Neutron and Muon Source. In particular, we investigate the performance of these detectors in the energy range between 100 keV and 300 keV. In this range, the
-emission of the 197Au resonant analyser foils, installed on VESUVIO to select the energy of scattered neutrons, is predominant. Such photons are currently discarded by the low-level discrimination threshold of the acquisition electronics set to 600 keV. Here, we model the detector crystals for a series of thickness values, and we discuss how 2-cm-thick crystals would significantly reduce the acquisition times with respect to the 6-mm-thick crystals employed at present. Additionally, we show how the signal-to-background ratio can be substantially enhanced by shielding the scintillators with 0.5-mm-thick Pb foils. We finally discuss the improved detection performance on a model sample of interest for Cultural-Heritage applications.
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Apr 2020
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Open Access
Abstract: Advances in research in Cultural Heritage see increasing application of a multidisciplinary approach and the combined use of physical and chemical characterization of artefacts that can be used to define their structure and their state of conservation, also providing valuable information in selecting the most suitable microclimatic conditions for the exhibition environment. This approach provides a platform for a synergic collaboration amongst researchers, restorers, conservators, and archaeologists. Existing state-of-the-art technologies for neutron-based methods are currently being applied to the study of objects of historical and cultural interest in several neutron-beam facilities around the world. Such techniques are non-invasive and non-destructive and are, therefore, ideal to provide structural information about artefacts, such as their composition, presence of alterations due to the environmental conditions, inclusions, structure of the bulk, manufacturing techniques, and elemental composition, which provide an overall fingerprint of the object's characteristics, thanks to the nature of the interaction of neutrons with matter. Here, we present an overview of the main neutron methods for the characterization of materials of interest in Cultural Heritage and we provide a brief introduction to the sensors and detectors that are used in this framework. We conclude with some case studies underlining the impact of these applications in different archaeological and historical contexts.
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Jan 2020
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[16863, 16328]
Abstract: A combination of X-ray analytical techniques has been used to study the microstructure and corrosion of a 450-year-old cast-iron cannonball fragment from the Mary Rose shipwreck. Using a 3D approach, it has been shown that akaganeite, β-FeO(OH, Cl), starts to appear ˜1.5 mm below the outer surface of the object, occurring selectively around non-contiguous graphite flakes in the microstructure, with no corrosion in graphite-free regions. This spatial analysis has given a new look inside a 450-year-old system, to see how metallographic features interact with local chemical environments to give complex corrosion products, centuries in the making.
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Aug 2019
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I11-High Resolution Powder Diffraction
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Abstract: Pure anhydrous Cu(CH3COO)2 was obtained both, by thermal dehydration of Cu(CH3COO)2·H2O and by drying a commercially purchased mixture of Cu(CH3COO)2·H2O and Cu(CH3COO)2 in a nitrogen atmosphere using P2O5 as drying agent. The crystal structure was solved ab initio from synchrotron X‐ray powder diffraction (XRPD) data at 150 °C and from laboratory XRPD data at ambient conditions and found to be isotypic to anhydrous chromium(II), molybdenum(II) and rhodium(II) acetate. Cu(CH3COO)2 crystallizes in space group P1 (no. 2) with lattice parameters of a = 5.1486(3) Å, b = 7.5856(6) Å, c = 8.2832(6) Å, α = 77.984(4)°, β = 75.911(8)°, γ = 84.256(6)° at ambient conditions. Cu2(CH3COO)4 paddle wheels with short (2.6 Å) Cu–Cu distances form chains in a direction, which is the main motif in the crystal structure. Due to their identical structural main motif Cu(CH3COO)2·H2O and Cu(CH3COO)2 exhibit a similar bluish‐green color, almost identical UV/Vis spectra and comparable magnetic properties. The temperature dependent magnetic susceptibility also indicates only weak inter‐dimer spin exchange between neighbouring Cu2(CH3COO)4 paddle wheels.
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Jul 2019
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