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Abstract: In this study, the polymorphic transitions of mefenamic acid (MA) were studied by synchrotron X-ray powder diffraction combined with differential scanning calorimetry (XRD-DSC). The initial material was found to be phase-pure form I which, when heated, produces two endotherms that can be observed by DSC at 162.72 and 219.55°C. The former was found to correspond to a solid–solid enantiotropic transition from form I to a mixture of forms II and III. The latter is the melting point of form II. As form I is heated, significantly greater unit-cell expansion is seen in the a direction than in b and c, which can be explained by the stronger intermolecular interactions in the bc plane. Refinements of the reported MA structures against the patterns collected during heating revealed that at 175°C there exists a mixture of forms I, II and III, whereas only forms II and III remain at 205°C. However, reflections are observed at both temperatures which cannot be fitted with the known forms of MA. It is hypothesized that a new form of MA is produced upon heating. The stability of MA after the enantiotropic transition temperature is II > III > I, which differs from the previously reported II > I > III.

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Abstract: Changes in crack growth rate associated with overload events during fatigue are poorly understood, especially for materials with anisotropic microstructures. Here overload fatigue tests are reported for compact tension samples cut in two different orientations from high pressure torsion disc samples. During growth the crack planes reoriented either slightly, or significantly, to align with the elongated grain structure leading to low, and high, levels of mixed mode fatigue loading respectively. In both cases the ultrafine grained microstructure led to macroscopically flat crack faces. The fatigue crack growth rate was around 3.4 times slower for the case with the high mode II component than for the low. A 100% overload was then introduced and synchrotron X-ray diffraction and digital image correlation (DIC) were applied in-situ to map the bulk crack-tip elastic strain field (plane strain) and surface displacement field (plane stress) respectively prior to, during and after overload. The high mode II case displayed a larger degree of retardation after overload. Residual stress and plasticity-induced crack closure were found to be the primary causes for the retardation as the crack grows into the overload plastic zone. Significant crack face contact was observed for the high mode II case along with significant levels of compressive stress transferred across the crack faces at minimum load. Compared with conventional (coarse) grain Ni, the ultrafine grained Ni is less retarded by overload, because of its relatively flatter crack path and higher yield stress and thus less plasticity and residual stress induced closure.

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Abstract: We present new results on solid (monolithic) synthetic C-S-H made at room temperature from easily obtainable calcium sources (calcium oxide, calcium hydroxide) and nanosilica (w/s = 2) with a 2 minute mixing time. Using synchrotron X-ray diffraction combined with TGA/DSC, 29Si NMR and synchrotron pair distribution function (PDF) data we show that the solid C-S-H is crystallographically similar to the more conventionally made synthetic C-S-H slurry. We show that C-S-H is present after 1 day curing (C/S = 0.81) and no X-ray visible portlandite is present at day 3. PDF data shows that the ordered domain size is 2.5 – 4.5 nm, depending on the fit chosen.

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Abstract: A study of a transition from conventional multicomponent alloys to high-entropy alloys (HEAs) is important both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of conventional alloys. We report the main result of such a study performed on (TiZrNbNi)1−xCux metallic glasses (MG) over a broad concentration range x ≤ 0.52 encompassing both high entropy-MGs and Cu-based MGs. A comprehensive study of the composition, homogeneity, thermal stability, atomic structure, electronic structure, and magnetic susceptibility of 11 alloys has been performed. Thermal analysis revealed a rather weak variation of thermal parameters and glass forming ability with x. The study of the atomic structure showed a linear variation of average interatomic distances and atomic volumes close to those predicted by Vegard’s law. The coordination numbers and atomic packing fractions were constant throughout the explored concentration range. The electronic density of states (DOS) showed a split-band structure with DOS close to the Fermi level dominated with d-states of Ti, Zr, and Nb. Accordingly, magnetic susceptibility decreased linearly with x and extrapolated to that of Cu. Thus, the studied alloys show ideal solution behavior similar to that of binary Cu-Ti, Zr, and Hf MGs. The results are compared with those for (TiZrNbCu)1−xNix MGs and (CrMnFeCo)1−xNix alloys and their impact on understanding the transition from high-entropy-MGs to conventional MGs with the same composition is briefly discussed.

Open Access

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Abstract: X-Ray parallel-beam micro-tomography systems at synchrotron facilities are mainly bespoke designs. Technical problems from a detector system can strongly affect the quality of reconstruction results. Radial lens distortion in the visible light optics causes streak artifacts which get stronger towards the edge of the image. The irregular response of the detector gives rise to a variety of stripe artifacts in the sonogram; full stripes, partial stripes, fluctuating stripes, and unresponsive stripes. These give rise to ring artifacts of different kinds in the reconstructed image. The scattering of the scintillation photons can cause artifacts which are similar to beam hardening artifacts and reduce the resolution of the image. Here we present our practical approaches to tackle each such problem. These approaches are easy to implement and have low computational cost. The algorithms are freely available as open-source software.