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In-situ synchrotron x-ray experiments have been used to follow the evolution of the diffraction peaks for crystalline dendrites embedded in a bulk metallic glass matrix subjected to a compressive loading-unloading cycle. We observe irreversible diffraction-peak splitting even though the load does not go beyond half of the bulk yield strength. The chemical analysis coupled with the transmission electron microscopy mapping suggests that the observed peak splitting originates from the chemical heterogeneity between the core (major peak) and the stiffer shell (minor peak) of the dendrites. A molecular dynamics model has been developed to compare the hkl-dependent microyielding of the bulk metallic-glass matrix composite. The complementary diffraction measurements and the simulation results suggest that the interface, as Maxwell damper, between the amorphous matrix and the (211) crystalline planes relax under prolonged load that causes a delay in the reload curve which ultimately catches up with the original path. [ABSTRACT FROM AUTHOR]

Abstract: The features associated with modern synchrotron radiation machines (intense and coherent beams) result in a substantial extension of X-ray imaging capabilities in terms of spatial and temporal resolution, phase contrast and 3D images. This allows crystal growth-related information to be obtained which is not available otherwise. After briefly describing the main synchrotron radiation based imaging techniques of interest, we give original examples illustrating the new capabilities for crystal growth: characterisation of crystals grown for applications, such as ice tri-crystals produced for mechanical deformation studies; SiC; crystalline silicon for solar photovoltaic cells; in situ and in real time studies of quasicrystal growth (AlPdMn); and ultrafast tomography for the study of the growth of dendrites in metallic alloys. [Copyright &y& Elsevier]

At the High Energy Beamline ID15A at the European Synchrotron Radiation Facility we have developed a fast three-dimensional x-ray microtomography system, which acquires a complete dataset in typically less than 10 s. This unprecedented speed is achieved by combining a high efficiency phosphor screen, a reflecting microscope objective and a fast charge coupled device detector with the very intense high-energy white beam radiation provided by a wiggler source. The achieved spatial resolution is 2 μm. The available x-ray energy spectrum spans from 20 to 250 keV and can therefore be used for low and high Z materials. The spectrum can be modified by inserting different filters into the x-ray beam in order to optimize the signal-to-noise ratio and to avoid beam-hardening artifacts. Different phosphors with different energy sensitivity can be used. The very high speed allows in situ studies of systems evolving on the time scale of a few seconds or minutes. Three examples are given on sintering of metallic powders, solidification of binary alloys and liquid front propagation in granular materials. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the working principles of heterogeneous catalysts represents one of the great challenges in the field of materials science today. Ex situ bulk and surface science techniques provide information on such systems; however it is difficult to know whether any observed change in the physicochemical state of the catalyst would occur under the real working conditions. To counter this operando gap, the last decade has witnessed research efforts pushing towards more operando-like experimental setups to investigate ‘catalysis in action’. The advances in this field have been considerable so that it is now feasible to observe catalytic materials using a variety of techniques (sometimes combined into a single experiment) under conditions approaching those used for commercial operation. There still remain, however, some key differences between the conditions under which the experiments and the measurements are performed and with those required to fully understand a catalyst material in an industrial setting. In this paper we aim to show how multiple high energy techniques can be employed to further close the operando gap and meet the relevant criteria of replicating industrially relevant conditions and gleaning useful high quality data, whilst minimizing sample effects. For this purpose, a new high energy source experimental setup is described. We present results from high energy X-ray experiments on a simple model parent oxide, molybdenum oxide (MoO3) used for the selective oxidation of methanol as well as a new characterization study on the more complex iron molybdate (Fe2(MoO4)3) catalyst. The advantages and limitations of high energy X-ray experiments will be discussed. [ABSTRACT FROM AUTHOR]

This Note presents a few selected results of an experimental testing program carried out at the ESRF in Grenoble, France. X-ray microtomography (with a spatial resolution of 14 μm) has been used to evaluate the onset and evolution of shear banding in a fine-grained stiff soil under deviatoric loading. It allowed detailed observations of strain localization in a specimen during the test, including the presence of more than one shear zone and a varying degree of dilatancy and/or crack opening. To cite this article: G. Viggiani et al., C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]