Jj X-Ray

Crystallite size distributions and particle size distributions were determined by transmissions electron microscopy (TEM), X-ray powder diffraction (XRD), and small-angle X-ray scattering (SAXS) for three commercially available TiO2 powders (P25, UV100, and TiO2_5 nm) and one SSEC produced powder (SSEC78). The theoretical Guinier model was fitted to the experimental obtained XRD data and compared to analytical expressions. Modeling of the XRD spectra showed a difference between the analytical size dependent expressions and the theoretical Guinier model. Primary particle size distributions were extracted from SAXS measurements by the hard sphere model including an interparticle interference factor. The sizes obtained from SAXS were smaller than the sizes obtained from the XRD experiments; however, a good agreement was obtained between the two techniques. Electron microscopy confirmed the primary particle sizes and the shapes obtained by XRD and SAXS. The SSEC78 powder and the commercially available powders showed different morphologies, but SSEC78, UV100, and TiO2_5 nm all consisted of both primary particles as well as a secondary structure comprised of nanosized primary particles agglomeration into larger clusters. P25 showed the largest primary particle size, but did not show a secondary structure.

Sol–gel chemistry can be performed in minutes instead of hours in a supercritical fluid, a process that has now been monitored in situ by a combination of small- and wide-angle X-ray scattering (SAXS and WAXS) with high-energy synchrotron radiation. The setup used to monitor the growth of TiO2 nanoparticles, seeded by polypropylene fibers, in supercritical CO2 is shown schematically in the picture. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2007/z603386_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Minuten statt Stunden: Sol-Gel-Prozesse laufen in einer überkritischen Flüssigkeit schneller ab. Das Wachstum von TiO2-Nanopartikeln auf Polypropylenfasern als Keimen in überkritischem CO2 wurde in situ durch eine Kombination von Kleinwinkel- und Großwinkelröntgenstreuung (SAXS bzw. WAXS) mit energiereicher Synchrotronstrahlung beobachtet (siehe Bild).

Beam conditioning CRL transfocator optics implemented at the Materials Imaging and Dynamics (MID) instrument of the European XFEL are described. Two CRL transfocator units are equipped with beryllium parabolic refractive lenses of large radii of curvature to provide collimated or focused x-ray beam in the 5–25 keV photon energy range. Optical schemes, design and performance of the CRL units, which were recently installed at the SASE2 photon tunnels, are presented.

Recently some successful design strategies employ host molecules possessing special molecular symmetries, often coupled to the ideas of rigidity and to bulk. Crystal engineering also often touches upon the molecular symmetry theme[1] as mediated by prime intermolecular actions [2]. If one considers that symmetries must bring about operator-(and of course van der Waals radii) dependent forbidden volumes in crystals then incorporation of symmetries into molecules may lead to interesting consequences. Several crystal structures from our laboratory will be enumerated in which host molecules have two-, three-, four-and even six-fold molecular symmetry. These symmetries are employed more or less efficiently in building crystal structures of the associate molecular crystals in a range of space groups such as mainly from the trigonal, from tetragonal and from the hexagonal crystal systems. In going through these examples several interesting phenomena will be encountered such as Pasteur resolution, success and failure of chiral molecular recognition and like. We relate presence of the specific molecular symmetry to the macroscopic phenomenon in question. Discriminating effects as reflected by distances will be analyzed. Exploring into the CSD [3] V5.25 indicated over 38.000 crystal structures complying with the Z' < 1 AND No. of entities > 1 criteria thus indicating further research possibilities into the issues of molecular symmetry, space group symmetry and associate formation