No abstract

The local structure and the electronic properties of the active Ti sites in heterogeneous Ziegler–Natta catalysts, generated in situ by interaction of the precatalyst with different Al‐alkyl activators, were investigated by combining X‐ray absorption and valence‐to‐core X‐ray emission spectroscopy (XAS and vtc‐XES), coupled with UV/Vis, FTIR, and DFT theoretical calculations. Irrespective of the activator used, the active system was found to be a highly dispersed TiCl3‐like phase in which the Ti sites are surrounded, not only by bridged chlorine ligands (with the same bond length of bulk TiCl3), but also by terminal chlorine ligands, at a much shorter distance. These results set Ziegler–Natta catalysts in the category of complex nanomaterials. Despite the observation that the investigated catalysts polymerize ethylene, cutting‐edge XAS and XES techniques do not yet offer unequivocal proof for the presence of any alkyl chain attached to the Ti sites, as a consequence of the small fraction of the active sites.

We present a high-resolution in situ imaging and localization method of energetic particle beams. Recording of the scattered radiation from a thin featureless foil, placed in the path of the beam, and taken with a pinhole or coded aperture camera arrangement magnifies beam movements at the sensor. At the same time, a magnified image of the beam is available with an exceptional signal-to-noise ratio. We show measurement results of the level of precision that can be achieved and compare them to theoretical limits based on the signal-to-noise levels.

SynopsisDual loop active feedback stabilisation of the position and monochromatic flux of the beam at the output of the double crystal monochromator is described. The efficacy of the proposed stabilisation system is demonstrated in EXAFS spectroscopy measurements on inhomogeneous diluted Ti containing samples. AbstractWe report on the simultaneous and active feedback stabilisation of x-ray beam position and monochromatic beam flux during EXAFS scans at the Titanium K-edge as produced by a double crystal monochromator beam line. The feedback is generated using two independent feedback loops using separate beam flux and position measurements. The flux is stabilized using a fast extremum-searching algorithm that is insensitive to changes in the synchrotron ring current and energy dependent monochromator output. Corrections of beam height are made using an innovative transmissive beam position monitor instrument. We demonstrate the efficacy of the feedback stabilisation method by comparing the measurements of EXAFS spectra on inhomogeneous diluted Ti containing samples with and without feedback applied.

A novel plug-and-play setup based on polycapillary X-ray optics enables three-dimensional (3D) confocal X-ray fluorescence (XRF) and X-ray absorption spectroscopy down to 8 × 8 × 11 μm (17 keV) at the European Synchrotron Radiation Facility Collaborative Research Group Dutch-Belgian Beamline, BM26A. A complete description and analytical characterization is presented, together with two recently performed experimental cases. In Deep Earth diamond São Luiz-Frankfurt am Main 16, an olivine-rich inclusion was mapped with full 3D XRF elemental imaging. The preliminary tests on Iron Gall ink contained in an historical document, a letter from the court of King Philip II of Spain, reveal both the delicate nature of Iron Gall ink and the lack of Fe-Ni chemical bonding.