A comparison of the KOSSEL and the X-ray Rotation-Tilt Technique

Constrained geometrical analysis of complete K-line patterns for calibrationless auto-indexing

Indexing of Kikuchi and Kossel lines is a crucial step in K-line pattern analysis. Previous approaches mostly rely on the knowledge of unit-cell parameters and experimental geometry. An auto-indexing procedure is introduced that is able to find the unknown lattice, its orientation and the indices of the lines. To achieve this, the unbiased extraction of the precise conical geometrical information from the patterns is combined with existing auto-indexing procedures developed in the field of crystallography. A subsequent lattice-constrained refinement of all lines to the experimental pattern yields reliable lattice and experimental parameters simultaneously. Beyond providing detailed mathematical formulae, the procedure is also demonstrated on an experimental Kossel line pattern.

A high pressure cell for supercritical CO₂ on-line chemical reactions studied with X-ray techniques

A versatile high pressure X-ray sample cell has been developed for conducting in situ time-resolved X-ray scattering experiments in the pressure and temperature regime required (pressures up to 210 bars and temperatures up to 120 °C) for chemical reactions in supercritical fluids. The large exit opening angle of the cell allows simultaneous performance of SAXS-WAXS experiments. Diamond windows are used in order to benefit from the combination of maximum strength, minimal X-ray absorption and chemical inertia. The sample cell can also be utilised for X-ray spectroscopy experiments over a wide range of photon energies. Results of the online synthesis of a block copolymer, poly(methyl methacrylate-block-poly(benzyl methacrylate), by Reversible Addition-Fragmentation Chain Transfer (RAFT) in a supercritical CO2 dispersion polymerisation will be discussed. The contribution of the density fluctuations, as function of temperature, to the X-ray scattering signal has been quantified in order to allow appropriate background subtractions.