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The present work describes some new improvements concerning the analysis of cement hydration processes using `pencil-beam' synchrotron X-ray diffraction tomography. (i) A new filtering procedure, applied to the diffraction images, has been developed to separate the powder-like contribution from that of the grains in the diffraction images. (ii) In addition to improving the quality of the diffraction images for the subsequent analysis and tomographic reconstruction, the filtering procedure can also be used to perform a qualitative analysis of the crystallite size distribution, whenever the more standard approaches cannot be applied. (iii) Given the importance of the calcium silicate hydrate phase (C-S-H) in cements, a procedure to obtain its spatial distribution using the diffraction signal has been successfully applied, even though C-S-H is a highly disordered phase, almost amorphous to X-ray diffraction. (iv) The main result of this study has been to show that, in spite of the long measurement times required, it is possible to use in situ experiments at different aging times of cement pastes to monitor the cement evolution. This allowed the evolution of the microstructure during the acceleration and deceleration periods of the hydration process to be checked with unprecedented detail, since the quantitative spatial distribution of each phase (including C-S-H) dissolved or precipitated in the sample has been obtained. The reported approach opens up a range of opportunities for the investigation of complex multiphase systems and processes, including hydration and microstructural development in cements. [ABSTRACT FROM AUTHOR]

The systematic presence of the ternary phases U6Mo4Al43 and UMo2Al20 is reported in a U–Mo/Al interaction layer grown by thermal annealing. This work shows, therefore, the low Mo solubility in UAl3 and UAl4 binary phases; it contradicts the hypothesis of the formation of (U,Mo)Al3 and (U,Mo)Al4 solid solutions often admitted in the literature. Using µ-XAS (micro X-ray absorption spectroscopy) at the Mo K edge and µ-XRD (micro X-ray diffraction), the heterogeneity of the interaction layer obtained on a γ-U0.85Mo0.15/Al diffusion couple has been precisely investigated. The UMo2Al20 phase has been identified at the closest location from the Al side. Moreover, µ-XRD mapping performed on an annealed fuel plate enabled the characterization of the four phases resulting from the γ-U0.85Mo0.15/Al and (U2Mo + α-U)/Al interactions. A strong correlation between the concentrations of UAl4 and UMo2Al20 and those of UAl3 and U6Mo4Al43 has been shown. [ABSTRACT FROM AUTHOR]

The dynamical theory was used to model X-ray diffraction by the YZ-cut of an LiNbO3 crystal modulated by surface acoustic waves (SAWs). It includes both the calculation of the crystal lattice deformation, induced by a surface wave of Rayleigh type, and the simulation of X-ray wavefields in the crystal based on Takagi-Taupin equations. A detailed discussion is included on the effect of peak splitting occurring at high acoustic amplitudes. The developed theory entirely describes this effect and proves to be a powerful tool for understanding X-ray diffractometry and topography measurements by SAW-modulated crystals. [ABSTRACT FROM AUTHOR]

When subjected to plastic deformation, grains within ductile face-centred cubic polycrystals fragment into “soft”, low dislocation density cells separated by “hard”, dislocation-rich walls. Using a narrow-bandwidth, sub-micrometre X-ray beam, we have mapped the deformation structure inside a single grain within a deformed Ni polycrystal. Dislocation multiplication and entanglement was found to vary depending on the physical dimensions of the grain. The method we use overcomes current limitations in classical X-ray topography allowing topographic images to be formed from small, highly deformed grains. [ABSTRACT FROM AUTHOR]