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Here, we show that calcium sulfate dihydrate (gypsum) can be directly, rapidly and reversibly converted to calcium sulfate hemihydrate (bassanite) in high salinity solutions (brines). The optimum conditions for the efficient production of bassanite in a short time (<5 min) involve the use of brines with c(NaCl) > 4 M and maintaining a temperature, T > 80 °C. When the solution containing bassanite crystals is cooled down to around room temperature, eventually gypsum is formed. When the temperature is raised again to T > 80 °C, bassanite is rapidly re-precipitated. This contrasts with the better-known behaviour of the bassanite phase in low-salt environments. In low-salinity aqueous solutions, bassanite is considered to be metastable with respect to gypsum and anhydrite, and therefore gypsum-to-bassanite conversion does not occur in pure water. Interestingly, the high-salinity transformation of gypsum-to-bassanite has been reported by many authors and used in practice for several decades, although its very occurrence actually contradicts numerical thermodynamic predictions regarding solubility of calcium sulfate phases. By following the evolution of crystalline phases with in situ and time-resolved X-ray diffraction/scattering and Raman spectroscopy, we demonstrated that the phase stability in brines at elevated temperatures was inaccurately represented in the thermodynamic databases. Most notably for c(NaCl) > 4 M, and T > 80 °C gypsum becomes readily more soluble than bassanite, which induces the direct precipitation of the latter from gypsum. The fact that these transformations are controlled by the solution provides extensive opportunities for precise manipulation of crystal formation. Our experiments confirmed that bassanite remained the sole crystalline phase for many hours before reverting into gypsum. This property is extremely advantageous for practical processing and efficient crystal extraction in industrial scenarios.
In the quest for finding the ideal synchrotron-radiation-induced imaging method for the investigation of trace element distributions in human bone samples, experiments were performed using both a scanning confocal synchrotron radiation micro X-ray fluorescence (SR-mXRF) (FLUO beamline at ANKA) setup and a full-field color X-ray camera (BAMline at BESSY-II) setup. As zinc is a trace element of special interest in bone, the setups were optimized for its detection. The setups were compared with respect to count rate, required measurement time and spatial resolution. It was demonstrated that the ideal method depends on the element of interest. Although for Ca (a major constituent of the bone with a low energy of 3.69 keV for its K alpha XRF line) the color X-ray camera provided a higher resolution in the plane, for Zn (a trace element in bone) only the confocal SR-µXRF setup was able to sufficiently image the distribution.
The gold finds from Bernstorf, in the Freising district of Bavaria, were discovered in 1998, in the area of a Bronze Age settlement. First analyses with X-ray fluorescence (XRF) revealed gold of an unusually high purity grade, which was explained by the use of cementation techniques. A newer analysis with laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) indicated an even higher purity. The analytical results were the starting point of an ongoing discussion. In this study, we re-analysed 11 gold samples with Synchrotron radiation–induced X-ray fluorescence at the BAMline at BESSY. In a thorough analysis, different excitation and detection conditions were applied to confirm or disprove the previous results. It was shown that the purity of the gold from the specimen is higher than 99.9%. The main impurities are silver in a range between 20 and 200 μg/g and copper between 1 and 10 μg/g. The results are in very good agreement with the LA–ICP–MS measurements and provide basic information for discussions about provenance, processing techniques or considerations of authenticity.
The gold finds from Bernstorf, in the Freising district of Bavaria, were discovered in 1998, in the area of a Bronze Age settlement. First analyses with X-ray fluorescence (XRF) revealed gold of an unusually high purity grade, which was explained by using cementation techniques.
A newer analysis with laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) indicated an even higher purity. These analytical results were the starting point of an ongoing discussion. The amount and type of the detected contaminants were highly controversial and led to contradictory interpretations.
We reanalysed 11 gold samples with synchrotron radiation induced X-ray fluorescence (SRXRF) at the BAMline at BESSY-II. To reach the desired detection limits a thorough analysis with three different excitation energies and detection conditions were applied to confirm or disprove the previous results.
In this contribution we will get into the details for the need of the different measurement conditions and the virtues of the use of synchrotron radiation. The use and effectiveness of cementation techniques will be addressed. Finally we will present the achieved results and their impact on the discussion.
The BAMline at the synchrotron BESSY II in Berlin supplies users with up to date analytical x-ray methods for the energy range between 5 and 50 keV. Additional to XRF with micron Resolution it provides amongst other things the possibility to use TXRF and XANES. Especially the use of
the so-called Color X-Ray Camera (CXC) opens the possibility to use new and effective detection schemes, which allow to measure simultaneously distributions of elements or Absorption spectra in a motionless mode.
In this talk the analytical possibilities at the BAMline for samples with biological Background will be introduced. The available methods will be presented and discussed for various examples.
A perspective for the future use for XANES in grazing emission and TXRF geometries for plant materials will be given.
Die Eigenschaften und die Verlässlichkeit von Materialien jeglicher Art sind seit jeher die Grundlagen der Technik einer Gesellschaft. Tiefgreifende Kenntnisse über sie sind deshalb eine Voraussetzung um neue Produkte zu entwickeln, Verlässlichkeit zu gewährleisten, oder aber auch, wie in der Archäometrie, Kenntnisse über die Vergangenheit zu gewinnen. Ein Schlüssel zum Verständnis ist das Wissen über die chemische Zusammensetzung und die Struktur von Materialien Die Analyse mit Synchrotronstrahlung bietet hierfür herausragende Werkzeuge an, die zerstörungsfrei und hochsensitiv sind. Mit Röntgenfluoreszenzanalyse kann die elementare Zusammensetzung in winzigen Proben bis auf μg/g bestimmt werden. Anwendungsbeispiele aus verschiedenen Themengebieten, aber besonders von archäologischen Fragestellungen wie z.B. dem Goldfund von Bernstorf werden im Vortrag vorgestellt.
News from the BAMline
(2017)
Airborne particulate matter is an issue of growing concern in industrialized countries. Particles with diameters of less than 10 μm (especially those smaller than 2.5 μm) can enter the human respiratory system and contribute to various diseases depending on their chemical composition and the chemical bonding state, in which elements are present. This chemical speciation can be obtained using X-ray absorption near-edge structure analysis (XANES), which requires a tunable excitation source and therefore has to be carried out at synchrotron facilities. Our special interest lies on the analysis of indoor airborne particulate matter, as particle composition and health effects of outdoor particles have been studied abundantly. For this work, samples were collected in various office rooms in the Atominstitut (ATI) building.
The BAMline at BESSYII features a double-multilayer monochromator (DMM) and a double-crystal monochromator (DCM). The DCM offers an energy resolution E/ΔE of around 103, which makes it suitable for XANES applications. The ATI SR-TXRF vacuum chamber, formerly located at HASYLAB, Beamline L, is now available at the BAMline. The chamber offers a sample changer for up to 8 quartz reflectors and a 30 mm² silicon drift detector (SDD) was used. Aerosol samples were produced using a modified three-stage Dekati™ impactor. For this work, only the coarse (2.5 to 10 μm) and the fine particle fraction (1 to 2.5 μm), were of interest. XANES results of Cr, Cu and Zn will be presented on this poster.
The X-ray Fluorescence beamline at ELETTRA operates in partnership with the IAEA an ultra-high vacuum instrument with a 7-axis manipulator suitable for a variety of X-ray analytical techniques, such as grazing incidence and total reflection X-ray fluorescence analysis (GI-XRF and TXRF), X-ray reflectometry (XRR) and XANES. Samples were produced using a four-stage Sioutas Personal Cascade Impactor. With this impactor, it is possible to produce size-fractionated samples down to the sub-μm range (Stages: A > 2.5 μm, B 1 to 2.5 μm, C 0.5 to 1 μm and D 0.25 to 0.5 μm). Direct sampling was performed on siliconized 25 mm Si wafers suitable for TXRF. Cu-K edge SR-TXRF-XANES analysis was carried out for samples of all impactor stages. Results of these experiments will be shown.
Examples of XRF and PIXE imaging with few microns resolution using SLcam® a color X-ray camera
(2015)
We present results of recent development of the color X-ray camera, type SLcam®, allowing detection of X-ray images with few microns resolution. Such spectral resolution is achieved with the use of high-quality polycapillary optics combined with sub-pixel resolution. Imaging of Siemens star resolution test chart reveals that the resolution limit of SLcam® can go down to nearly 5µm. Several real sample examples of measurements carried out at the laboratory, synchrotron, and particle-induced X-ray emission beamlines are shown. This is the first time SLcam® is used as particle-induced X-ray emission detector.