Open Access

Show Abstract ▼

Abstract: Carbon fibre composites are widely used in low specific stiffness and high strength structures such as airframes. Compressive loading of these assemblies can lead to buckling and localised deformation around defects and imperfections that can hinder performance and lead to overengineering via excessive safety factors. Synchrotron X-Ray Diffraction (SXRD) has recently been shown to be capable of performing lattice strain mapping within carbon fibre composites at the microscale, a previously unprecedented resolution. In this study SXRD and radiography was performed on carbon fibre composite columns produced via two different methods (standard lamination and half square) at a range of different load states: unbuckled, one-third of the buckling load and post buckling. The results provide quantitative insights into the impact of these different production methods on lattice strain and fibre orientation, as well as the influence these factors have on reducing buckling load (by up to 22%). As well as being the first use of SXRD on industrially representative full-size carbon fibre samples, these insights provide invaluable detail into the factors which limit performance and the origins of column failure; crucial factors required to optimise structural design, production and loading capability.

Show Abstract ▼

Abstract: Purpose / Aim: Dentine hypersensitivity (DH) is a commonly occurring dental condition where sharp pain derived from exposed dentine in response to stimuli that cannot be ascribed to any other dental diseases. It is highly prevalent affecting up to 69% of the UK population and has a significant impact on the quality of life. Bioactive glasses that degrade in oral environment and form apatite are thought to be beneficial in occluding the exposed open dentine tubules and have been introduced to toothpastes, e.g. Novamin® (45S5 Bioglass) for Sensodyne by GSK, fluoride containing bioactive glass for BioMin® F by BioMin Technologies Ltd. Post-mortem characterisations evidenced tubule occlusion (Fig.1) but failed in providing dynamic history. Therefore, this study aimed to monitor dentine tubule occlusion with bioactive glasses using an operando time-lapse X-ray diffraction tomography experiment. Materials & Methods: Disinfected Teeth (collected under REC reference 16/SW/0220) were sectioned mesio-distally into discs approximately 500 μm thick using a precision diamond saw, polished down to 300 μm manually. Matchstick specimens (5 mm length x 3 mm width) prepared were brushed for 2 mins with bioactive glasses pastes, housed in a modified Eppendorf tube and positioned on the tomography stage of the Dual Imaging and Diffraction (DIAD) beamline at Diamond Light Source (UK’s national synchrotron). A baseline X-ray tomography (pink beam, 0-180°, detector exposure of 0.01 and 5,000 projections) and X-ray diffraction mapping (matrix scan with 10x10 points, 20 s exposure) were collected before artificial saliva was introduced. Time-lapse X-ray tomography and X-ray diffraction mapping using the same parameters as baseline scan were carried out consecutively for 8 h allowing the visualisation of tubule occlusion and changes of mineral density as well as monitor the phase evolution from glass to apatite. Artificial saliva was manually replenished. Monochromatic beam with an energy of 20 keV was used and calibrations were performed. Results: The collected tomography data allow visualisation of dentine tubule occlusion showing improved occlusion with time. 2D XRD data provide qualitative and quantitative information relates to glass dissolution and apatite formation as a function of time. Conclusions: The Dual Imaging and Diffraction (DIAD) beamline correlates X-ray tomography and X-ray diffraction mapping offers the opportunity to study dentine occlusion by bioactive glasses in a time evolving manner that is not available via other techniques. Although in vitro but clinically relevant. The results will potentially provide a guidance for optimising and designing products for dentine tubule occlusion/treating dentine hypersensitivity – one of the most prevalent global diseases with healthy ageing.

Show Abstract ▼

Abstract: In situations where the stereoregularity of the polymer chains permits, crystals can form in synthetic or natural polymers. These crystals have an immense impact on the properties of the polymeric material. Typically polymers crystallized from a quiescent melt form spherulites, but where the melt exhibits a level of anisotropy, the crystalline morphology, is quite different to the spherulitic structure, although it may well contain chain-folded lamellar crystals. We consider a number of different systems in which the anisotropy has developed in different ways. Despite these differences, there are strong features in common within the semi-crystalline polymer morphology. We consider the strain-induced crystallization in deformed natural rubber, in sheared melts containing both self-assembling nanoparticles and engineered nanoparticles, and during extrusion as part of fused granular deposition-based 3D printing.

Open Access

Show Abstract ▼

Abstract: The overall performance of proton exchange membrane fuel cells is limited by the sluggish kinetics of the oxygen-reduction reaction (ORR). Among the most active PGM-free ORR electrocatalysts are metal-nitrogen-carbon (M-N-C), such as Fe–N–C. The Fe–N4 ensembles in these PGM-free catalysts, present in different configurations, are proposed to be the active sites for the ORR in acid. In this work, we have synthesized a Fe/N/C catalyst via thermal treatment of a polymeric CxNy precursor obtained by the wet-polymerization of melamine (a nitrogen rich molecule) and terephthaldehyde. The materials obtained (Im-FeNC-1HT and Im-FeNC-2HT) display high ORR activity in acid electrolyte compared to other Fe–N–C catalysts prepared with precursors different than 2-methylimidazole or ZIF-8. Characterization data indicate the formation of high- and low-spin Fe-Nx ensembles, with a site density of 4.4·1019 sitesFe·g−1 estimated by electrochemical stripping of NO. The ORR activity was evaluated in a RRDE configuration in 0.1 M HClO4 and in MEA configuration in a single cell.

Open Access

Show Abstract ▼

Abstract: Single-crystal chemical vapour deposition (CVD) diamond detectors are an established transmissive synchrotron beamline diagnostic instrument used for beam position and beam intensity monitoring. A recently commercialized alternative is silicon carbide (4H-SiC) devices. These have the potential to provide the same diagnostic information as commercially available single-crystal CVD diamond X-ray beam position monitors, but with a much larger transmissive aperture. At Diamond Light Source an experimental comparison of the performance of single-crystal CVD diamond and 4H-SiC X-ray beam position monitors has been carried out. A quantitative comparison of their performance is presented in this paper. The single-crystal diamond and 4H-SiC beam position monitors were installed in-line along the synchrotron X-ray beam path enabling synchronous measurements at kilohertz rates of the beam motion from both devices. The results of several tests of the two position monitors' performance are presented: comparing signal uniformity across the surface of the detectors, comparing kHz intensity measurements, and comparing kHz beam position measurements from the detectors. Each test is performed with a range of applied external bias voltages. A discussion of the benefits and limitations of 4H-SiC and single-crystal CVD diamond detectors is included.