The penetration power of hard X-rays together with the energy the selectivity of third generation synchrotron radiation sources such as ESRF (European Synchrotron Radiation Facility) offer new experimental possibilities for through-thickness quantitative analyses of bulk samples and structural analyses of minor phases.
By using the anomalous scattering of X-rays near an absorption edge, the difference of scattering factors between two atoms with close atomic numbers Z can be enhanced and a combined diffraction and spectroscopic information can be obtained in a single experiment. Thus by performing sequential diffraction experiments on the same sample at different energies close to the absorption edge of a given atom, it is possible to obtain differential diffraction spectra influenced primarily by the absorbing atom. When the absorbing atom segregates preferentially to a given precipitate, specific structural (and compositional) information about this precipitate can be obtained.
To check the sensitivity of anomalous scattering and experimental conditions during high energy experiments, we have realized powder diffraction measurements in the vicinity of the Pt K edge (78.4 keV). Two different powder samples have been chosen for experiments: a CeO$_{2}$ standard sample for calibration of experimental conditions (peak shape, 2Q resolution, signal/noise ratio, background level ... ) and a Bi$_{1.67}$Pb$_{0.33}$PtO$_{4}$ powder for anomalous diffraction investigations. We have used the Debye-Scherrer geometry. The complete Debye rings have been recorded by using a 2D imaging plate detector. The anomalous scattering factor f'(E) of platinum has been refined at 27 energies by a multi-wavelength refinement procedure using Bragg reflections with large platinum contributions. The results demonstrate the potentialities of high energy anomalous diffraction experiments.
By performing through-thickness powder diffraction experiments with hard X-ray beam and two dimensional detectors, we can record complete Debye rings containing at the same time information on both texture and grain distribution. The analysis of intensity variations along the circumference of rings (azimuthal analysis) gives the average texture information. The radial analysis of rings gives a through-thickness information on crystallographic texture, recrystallization fraction and grain size distribution.
We have carried out powder diffraction experiments using hard X-rays (60 keV) on aluminium alloys submitted to different thermo-mechanical treatments. Imaging plates were used as 2D detectors to record complete Debye rings. In order to obtain the information on texture and grain distribution, we have performed a data extraction process by applying a geometrical "unrolling" transformation of the Debye rings.
The straight lines so produced have been integrated along the azimuthal angle while conserving the angular relationship between rings.
The 2D imaging plate detectors have been used during all these experiments. Comparing with 1D detectors they offer the possibility of recording a large number of reflections without any energy shift in a relatively short time. These high energy experiments show other conveniences of "imaging plates" such as a relatively good signal to noise ratio and low background level even after the absorption edge. On the other hand, the quantitative 2D data analysis is a time consuming process (aberrations corrections, integration procedure over the whole Debye rings).