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Abstract: Analyses of the degraded mordant gilding on two early fourteenth-century paintings by Pietro Lorenzetti were undertaken at the UK synchrotron facility Diamond Light Source. Previous studies revealed a complex orpiment-tinted mordant and its application for adhering two separate layers of silver and gold leaf and demonstrated degradation of the original materials. A new study involving synchrotron radiation (SR) microfocus X-ray fluorescence (µ-XRF) maps on cross-sections of the discolored mordant allowed imaging of the extent of migration of mobile As-Ag-S bearing species and provided ideal positions from which to collect microfocus X-ray absorption near edge structure (µ-XANES) maps of As, Ag, and S for oxidation state analysis. SR µ-XANES indicates that arsenolite (As2O3) is present throughout the mordant suggesting light-induced photooxidation of orpiment. Both As3+ (as oxide) and As5+ have been detected and these are known signs for orpiment degradation. SR microfocus X-ray diffraction (µ-XRD) was used to reveal the nature of altered phases in the mordant layer and identified the presence of acanthite Ag2S, xanthoconite Ag3AsS3, and arsenolite As2O3. The analysis confirmed that the darkening of the mordant is most probably caused by finely dispersed grey-colored Ag + -bearing acanthite particles (Ag2S). The results are discussed in the context of analysis of contemporary paintings and recent studies on the alteration of orpiment.

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Abstract: Coal fly ash is an industrially useful by-product of coal combustion, with millions of tonnes held in repositories globally. This fine and cheaply-available waste material, is proven to sometimes be enriched in valuable elements/compounds, such as rare earth element (REE) minerals and actinides, alongside heavy toxic elements such as Cr, Pb, As and Cd, making coal fly ash both a potential unconventional source of valuable minerals and a hazardous material depending on the elemental trace chemistry of the parent coal body. The importance of REE and actinides for use in advanced electronics technologies and the nuclear industry, alongside concerns over geopolitics and instability in the global supply market, means there is now a renewed incentive for countries to secure native sources of economically-sustainable rare earth elements through research and development efforts. Unconventional sources of REE, such as coal fly ash, represent a potentially interesting value proposition, especially for developing countries. The work presented in this thesis provides a study of rare earth elements and actinides in Nigerian simulant coal fly ash from the perspective of resource recovery and environmental protection. A suite of advanced analytical laboratory techniques and novel synchrotron radiation techniques, alongside micromanipulation methods, were used in this study to understand the amounts and mineralogical association of REE and actinides in 3 different Nigerian coal deposits. Bulk and micro mineralogical analyses were first performed on the simulant coal fly ash using x-ray diffraction and scanning electron microscopy / with energy dispersive x-ray fluorescence and spectroscopy used for elemental analysis. It was observed that the Nigerian simulant coal fly ash samples were less complex in mineralogy than conventional rare earth ores (with quartz, mullite, haematite and cristobalite as the major mineral phases), composed of discrete micron-scale particles of rare earth mineral monazite ([Ce,La,Nd,Th]PO4), xenotime (YPO4) and zircon (ZrSiO4), alongside uraninite (UO2) and thorite (ThSiO4). Subsequent bulk elemental analysis performed using inductively-coupled plasma mass spectrometry, showed the simulant coal fly ash to be enriched in the rare earth elements, being more enriched in the higher-valued critical rare earth elements Nd, Eu, Tb, Dy, Y and Er, compared to conventional rare earth ores. Sequential extraction analysis of the simulant fly ash materials showed significant recoverability of rare earth elements in the acid-soluble fraction using cheap and environmentally-friendly ethanoic acid; the toxic heavy metals Cd and As were also significantly recovered in the acid-soluble fraction. Synchrotron radiation analysis of individual micro-particles of monazite and uraninite using micro-x-ray fluorescence mapping, micro-x-ray fluorescence tomography, micro-x-ray absorption near edge spectroscopy and micro-x-ray diffraction showed a zonation pattern in the monazite particles, with the rims rich in the rare earth elements, and the core rich in U and Th but depleted in the rare earth elements. In the uraninite particles, U was homogeneously-distributed, existing in the chemically reduced IV oxidation state. Gamma-ray spectrometry analysis of the bulk coal and simulant coal fly ash was also performed using a high-purity Ge gamma-ray detector. Compared to World mean levels, the radioactivity and associated hazard associated with the parent coal samples were insignificantly-low. However, the equivalent activity concentration and radiological hazard levels associated with the simulant coal fly ashes were significantly-high, above United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) World mean and recommended levels.

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Abstract: Objectives: Yttria Partially Stabilised Zirconia (YPSZ) is a high strength ceramic which has become widely used in porcelain veneered dental copings due to its exceptional toughness. Within these components the residual stress and crystallographic phase of YPSZ close to the interface are highly influential in the primary failure mode; near interface porcelain chipping. In order to improve present understanding of this behaviour, characterisation of these parameters is needed at an improved spatial resolution. Methods: In this study transmission micro-focus X-ray Diffraction, Raman spectroscopy, and focused ion beam milling residual stress analysis techniques have, for the first time, been used to quantify and cross-validate the microscale spatial variation of phase and residual stress of YPSZ in a prosthesis cross-section. Results: The results of all techniques were found to be comparable and complementary. Monoclinic YPSZ was observed within the first 10 μm of the YPSZ-porcelain interface with a maximum volume fraction of 60%. Tensile stresses were observed within the first 150μm of the interface with a maximum value of ≈300MPa at 50μm from the interface. The remainder of the coping was in mild compression at ≈ − 30 MPa, with shear stresses of a similar magnitude also being induced by the YPSZ phase transformation. Significance: The analysis indicates that the interaction between phase transformation, residual stress and porcelain creep at YPSZ-porcelain interface results in a localised porcelain fracture toughness reduction. This explains the increased propensity of failure at this location, and can be used as a basis for improving prosthesis design.

Open Access

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Abstract: Heterogeneous functional materials, like catalytic solids, batteries and fuel cells tend to usually possess complex structures where the 3D spatial distribution of the various components of these materials is rarely uniform. Such materials are known to change with time under operating conditions. In order to gain an insight into the structure-function relationships, it is essential to study them in situ with spatially-resolved techniques. The work presented in this thesis focuses on the development and application of synchrotron X-ray tomographic imaging methods to study various catalytic materials in real time and under real process conditions. The main X-ray tomographic imaging technique used in this study is X-ray diffraction computed tomography (XRD-CT) which couples powder diffraction with “pencil” beam computed tomography. Chapters 3 and 4 of this thesis outline some of the technical achievements accomplished in this work. More specifically, Chapter 3 outlines the development of a new data processing strategy used to remove line or “streak” artefacts generated in reconstructed XRD-CT images due to the presence of large crystallites in the sample; a common problem in XRD-CT measurements. Chapter 4 introduces a new data collection strategy, termed interlaced XRD-CT, which allows, post experiment, choice between temporal and spatial resolution. This data collection strategy can in principle be applied to all pencil beam CT techniques. The results from the first multi-length scale chemical imaging experiments of an unpromoted and a La-promoted Mn-Na-W/SiO2 catalyst for the oxidative coupling of methane are presented in Chapter 5. The spatially-resolved chemical signals obtained from these operando experiments provided new chemical information that can lead to the rational design of improved OCM catalysts. In Chapter 6, the results from, the first ever reported, XRD-CT experiments of working catalytic membrane reactors are presented. It is shown that the pertinent changes in the physicochemical state of these integrated reactor systems can be spatially-resolved. The results from Rietveld analysis of a 5D diffraction imaging (>106 diffraction patterns) redox experiment of a Ni-Pd/CeO2-ZrO2/Al2O3 catalyst and the first XRD-CT study of this catalyst during partial oxidation of methane are presented in Chapter 7.

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Abstract: Relevant mineral fibres of social and economic importance (chrysotile UICC, crocidolite UICC and a fibrous erionite from Jersey, Nevada, USA) were put in contact with cultured diploid human nontumorigenic bronchial epithelial (Beas2B) and pleural transformed mesothelial (MeT5A) cells to test their cytotoxicity. Slides of each sample at different contact times up to 96 h were studied in situ using synchrotron XRF, m-XRD and m-XAS (I18 beamline, Diamond Light Source, UK) and TEM investigations. XRF maps of samples treated for 96 h evidenced that iron is still present within the chrysotile and crocidolite fibres and retained at the surface of the erionite fibres, indicating its null to minor mobilization in contact with cell media; this picture was confirmed by the results of XANES pre-edge analyses. m-XRD and TEM data indicate greater morphological and crystallinity modifications occurring in chrysotile, whereas crocidolite and erionite show to be resistant in the biological environment. The contact of chrysotile with the cell cultures seems to lead to earlier amorphization, interpreted as the first dissolution step of these fibres. The formation of such silica-rich fibre skeleton may prompt the production of HO
in synergy with surface iron species and could indicate that chrysotile may be much more reactive and cytotoxic in vitro in the (very) short term whereas the activity of crocidolite and erionite would be much more sluggish but persistent in the long term.