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High-pressure high-temperature syntheses that involve volatile-bearing aqueous fluids are typically accomplished by enclosing the samples in gas-tight welded shut noble-metal capsules, from which the bulk volatile content must be extracted to be analyzed with mass spectroscopy, hence making the analysis non-replicable. Here we describe a novel non-destructive method that ensures the identification and the quantitative estimate of the volatiles directly in the sealed capsule, focusing on fluid H2O–CO2 mixtures equilibrated with graphite at conditions of geological interest (1 GPa, 800 °C). We used a high-energy (77 keV) synchrotron X-ray radiation combined with a cryostat to produce X-ray diffraction patterns and X-ray diffraction microtomographic cross-sections of the volatile-bearing samples down to –180 °C, thus encompassing the conditions at which crystalline phases-solid CO2 and clathrate (CO2 hydrate)-form. The uncertainty of the method is < 15 mol%, which reflects the difference between the volatile proportion estimated by both Rietveld refinement of the diffraction data and by image analysis of the microtomograms, and the reference value measured by quadrupole mass spectrometry. Therefore, our method can be reliably applied to the analysis of frozen H2O–CO2 mixtures and, moreover, has the potential to be extended to experimental fluids of geological interest containing other volatiles, such as CH4, SO2 and H2S. [ABSTRACT FROM AUTHOR]

Semiconducting indium sulfide (In2S3) has recently attracted considerable attention as a buffer material in the field of thin film photovoltaics. Compared with this growing interest, however, detailed characterizations of the crystal structure of this material are rather scarce and controversial. In order to close this gap, we have carried out a reinvestigation of the crystal structure of this material with an in situ X-ray diffraction study as a function of temperature using monochromatic synchrotron radiation. For the purpose of this study, high quality polycrystalline In2S3 material with nominally stoichiometric composition was synthesized at high temperatures. We found three modifications of In2S3 in the temperature range between 300 and 1300 K, with structural phase transitions at temperatures of 717 K and above 1049 K. By Rietveld refinement we extracted the crystal structure data and the temperature coefficients of the lattice constants for all three phases, including a high-temperature trigonal γ-In2S3 modification. [ABSTRACT FROM AUTHOR]

This article reports the creation of tomographic reconstructions giving three-dimensional data on the distribution of various structural features for SAPO-34 zeolite catalyst beds used in the commercially important methanol to olefin conversion process. The data were processed using parametric Rietveld refinement to treat entire slices of the tomograph as single refined data sets, allowing extraction of real structural parameters from all voxels of the reconstruction. This has the advantage over more traditional methods of X-ray diffraction computed tomography using peak intensities, that the structural parameters are independent of the intensity, meaning that information can still be extracted from poor data sets: an example is shown where part of the sample was no longer in the beam during data collection. Reconstructions using several structural parameters are presented and the results compared. Analysis of the variation of the catalyst c axis (linked to the degree of deactivation in earlier work) shows small but significant three-dimensional variations in the degree of deactivation with patterns which depend on the silicon content of the catalyst. Average data for the tomographic slices compare well with the results of earlier operando two-dimensional reactor scanning experiments. [ABSTRACT FROM AUTHOR]

Semiconducting indium sulfide (In2S3) has recently attracted considerable attention as a buffer material in the field of thin film photovoltaics. Compared with this growing interest, however, detailed characterizations of the crystal structure of this material are rather scarce and controversial. In order to close this gap, we have carried out a reinvestigation of the crystal structure of this material with an in situ X-ray diffraction study as a function of temperature using monochromatic synchrotron radiation. For the purpose of this study, high quality polycrystalline In2S3 material with nominally stoichiometric composition was synthesized at high temperatures. We found three modifications of In2S3 in the temperature range between 300 and 1300 K, with structural phase transitions at temperatures of 717 K and above 1049 K. By Rietveld refinement we extracted the crystal structure data and the temperature coefficients of the lattice constants for all three phases, including a high-temperature trigonal γ-In2S3 modification. [ABSTRACT FROM AUTHOR]