Analytische Chemie
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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 a topic of growing interest. Particles with aerodynamic diameters less than 10 μm (PM 10) and especially the fine fraction below 2.5 μm (PM2.5) are of particular importance, as they can enter the human respiratory system and cause acute and
chronic respiratory or cardiovascular diseases. The mass distribution of airborne particles in dependence of their diameters is well-known, but also the abundance and temporal variation of trace elements in air (mass concentrations down to the pg/m³ range) are crucial.
These elements originate from various natural (abrasion, erosion) and anthropogenic sources (combustion, road traffic), which complicate the discrimination between harmless and toxic emissions. Some new methods of investigation are therefore needed and X-ray fluorescence spectroscopy has ascertained ist huge potential in this matter, thanks to the possibility to determine simultaneously, in a time-resolved manner, the mass concentrations of critical elements which can be considered as markers of a potential toxic source. A method for the quantitative Analysis of airborne particles directly collected on sample substrates (30 mm quartz reflectors and 1" Si wafers suited for total-reflection X-ray fluorescence analysis (TXRF) will be presented.
Samplings were performed using a three- stage Dekati™ PM10 impactor (>10 μm, 2.5 to 10 μm and 1 to 2.5 μm) and a four-stage Sioutas Personal Cascade Impactor (>2.5 μm, 1 to 2.5 μm,0.5 to 1 μm and 0.25 to 0.5 μm) at indoor and outdoor sites at the Atominstitut (Vienna, Austria). Quantitative results of two outdoor test sampling campaigns (July 2016 and January 2017) will be presented and discussed. Low detection limits were assessed via TXRF and range from several 10 to several 100 pg/m³ depending on the element and particle size fraction.
Absorptionskantentomographie, auch bekannt als differentielle Tomographie an Kanten, ist ein Verfahren, bei dem ausgenutzt wird, dass sich die Schwächung von Röntgenstrahlen beim Übergang der Photonenenergie über die Absorptionskanten sprunghaft ändert. Die Verwendung von Synchrotronstrahlung ermöglicht die Anwendung der Absorptionskantentomographie für nahezu jedes Element, da sie eine intensive, durchstimmbare Strahlenquelle mit kleiner Bandbreite darstellt. Der Mikrotomographieaufbau der BAM am Elektronenspeicherring BESSY II eignet sich mit einem Energiebereich von 5 keV bis über 60 keV und einer Ortsauflösung besser als 0.5 µm zur differentiellen Tomographie an den K-Kanten der Elemente von Chrom bis zu den Lanthaniden, bei Einbeziehung der L-Kante bis zu Uran.
In dieser Arbeit wird die Absorptionskantentomographie ausgenutzt, um das Gefüge von Legierungen dreidimensional und nichtdestruktiv zu vermessen. Als Beispiel wird eine Legierung zwischen Magnesium, Yttrium und Zink analysiert, die sich gegenüber unlegiertem Magnesium durch größere Festigkeit und geringere Korrosionsanfälligkeit auszeichnet. Der Grund dafür liegt in der Bildung einer kristallographisch hochgeordneten Phase (long period stacking ordered - LPSO) der Legierungsbestandteile, die die Matrix in Form von Fasern durchzieht. Anhand ihres Yttriumgehaltes wird die dreidimensionale Verteilung der LPSO-Phase in der Matrix für verschiedene Proben bestimmt und mit Schnittbildern und Korrosionstests verglichen. Die Absorptionskantentomographie erweist sich als eine geeignete Methode, um die dreidimensionale Mikrostruktur von Legierungen zu charakterisieren.
Gold ist eines der sieben schon im Altertum bekannten Metalle und wurde wg. seines Glanzes und seiner Seltenheit von alters her als Tauschmittel und zur Herstellung von Schmuck benutzt. Außerdem ist es einfach bearbeitbar und weitestgehend gegen chemische Einflüsse resistent. Die Untersuchungen von Gold mit synchrotronstrahlungsangeregter Röntgenfluoreszenzanalyse sind zerstörungsfrei und geben Auskunft über die in der untersuchten Probe vorhandenen chemischen Elemente. Bei den hier vorgestellten Untersuchungen an der BAMline stehen Fragestellungen wie Herkunft, Herstellungsverfahren und Zusammengehörigkeit von Goldfunden im Vordergrund. Die verschiedenen Fragestellungen werden an einer Reihe von Beispielen erläutert die vom Wikingerschatz aus Hiddensee über die Himmelsscheibe von Nebra bis hin zu Funden aus Ägypten langen. Zusätzlich werden die modernen Messmethoden vorgestellt, die am Synchrotron heutzutage zur Verfügung stehen.
Absorption edge tomography, also known as differential tomography at absorption edges, is a method which exploits the sudden change of the attenuation coefficient, when the photon energy crosses the absorption edge of an element. Synchrotron radiation is the best source for absorption edge tomography, because of its small bandwidth, high intensity and easily adjustable photon energy. The synchrotron beamline BAMline at the synchrotron radiation facility BESSY II in Berlin, which is operated by the Bundesanstalt für Materialforschung und -prüfung (BAM), provides a monochromatized beam in a photon energy range from 5 keV up to 80 keV with a bandwidth of 2%, when the double multilayer monochromator is used. Together with the microtomography setup, this enables differential tomography with submicron resolution at the K edge of the elements from chromium up to the lanthanides, and up to uranium, when the L edges are used as well.
In this work, metal organic frameworks (MOFs) embedded in polymer are characterized using differential tomography. MOFs are microporous structures of metal ions, coordinated by organic linker molecules, that can be used in a broad field of applications, especially in gas storage and catalysis. In this work, polymer embedded MOFs were extruded into filaments, which could be used for 3d-printing to profit from the specific properties of the MOFs in polymeric materials combined with the arbitrary shapes provided by 3d-printing. For the extrusion, different polymer classes like ABS, polyester- and polyetherurethanes, as well as different MOFs (ZIF-8, ZIF-67, HKUST-1) were used to create MOF containing filaments with a nominal diameter of 3.0 mm. Differential tomography at the edges of the Zn, Co, and Cu was then used to find the distribution of the corresponding MOF in the filament and to analyze the shape of the inclusions.
XAFS@BAMline
(2018)
X-ray Absorption fine structure spectroscopy (XAFS) is a frequently employed technique in order to investigate structural composition and Change of chemical compounds such as catalytic species or corrosion processes. These structural properties are essential (i) to understand underlying reaction mechanism and (ii) to further improve the design of materials.
While XAFS measurements are usually performed with ionization Chambers or simple fluorescence detectors, we at BAMline specialize in measurements with innovative set-ups that meet Specialrequirements such as time resolution, (3D-) spatial Resolution or demanding sample environments.
This contribution presents various available XAFS configurations with their corresponding applications. In particular, these comprise single -shot XAFS for time- resolved measurements, grazing-exit XAFS with energy and a spatially resolved detector for the characterization of thin films and an in situ grazing incidence Setup for the characterization of corrosion layers.
Additionally,the possibility of analyzing Minute samples in total-reflection geometry is demonstrated.
X-ray absorption fine structure spectroscopy (XAFS) is a frequently employed technique in order to investigate structural composition and change of chemical compounds such as catalytic species. These structural properties are essential (i) to understand underlying reaction mechanism and (ii) to further improve the design of efficient catalysts.
This investigation is based on a newly developed XAFS setup comprising both time- and lateral-resolved XAFS information simultaneously in a single-shot (S2XAFS). The primary broadband beam is generated by a filter/X-ray-mirror combination (bandpass). The transmitted beam through the sample is diffracted by a convexly bent Si (111) crystal, producing a divergent beam. This, in turn, is collected by an area sensitive detector with a theta to 2 theta geometry. This facile, stable and scanningless setup was tested at the BAMline @ BESSY-II (Berlin, Germany).
This contribution focuses on further experimental optimizations allowing the characterization of supported vanadium oxide (VOx) based catalysts at the lower hard X-ray regime (5 to 6 keV). First S2XAFS measurements of these catalysts are presented herein. Supported VOx catalysts show promising results in the oxidation of methane to formaldehyde.
S2XAFS allows determining the structural composition of the metal (i.e. vanadium) based on a fast and smart setup. It is therefore an ideal tool to identify crucial roles of chemical compounds in catalytic reactions.
The Color X-ray Camera CXC or SLcam® is an energy-resolving X-ray camera capable of energy- and space-resolved measurements. It consists of a high-speed CCD detector coupled to a polycapil-lary optic that conducts the X-ray photons from the probe to distinct pixels onto the detector. The camera is capable of fast acquisition of spatially and energy resolved fluorescence images. A dedicated software enables the acquisition and the online processing of the spectral data for all 69696 pixels, leading to a real-time visualization of the elements distribution in a sample. It was developed in a joint project with BAM, IFG Berlin and PN Sensors. In this contribution we will mainly discuss the use of the CXC at our beamline, the BAMline at BESSY II and imaging applications of the CXC from different areas, like biology and archaeometry. Additionally new developments for the use of the detector without optics, like wavelength dispersive detection or 1shot-XANES, will be presented.
Synchrotron radiation sources with their unique properties in terms of intensity, polarization and adjustability offer a wide range of possibilities in materials research. A basic introduction about the creation and special properties of synchrotron radiation will be given. Examples of current work at BAMline, the high-energy measuring facility of the Federal Institute for Materials Research and Testing at the synchrotron BESSY, are used to illustrate the possibilities and limitations of existing measuring methods. It will be shown how the formation of corrosion layers can be tracked, how the abrasion of implants leads to the introduction of heavy metals into the surrounding bone matrix and how the detection of smallest impurities in gold is possible by optimizing the measuring conditions. Finally, an outlook at the hardware and software developments to be expected in the coming years is given.
In X-ray fluorescence (XRF), a sample is excited with X-rays, and the resulting characteristic radiation is detected to detect elements quantitatively and qualitatively. Quantification is traditionally done in several steps:
1. Normalization of the data
2. Determination of the existing elements
3. Fit of the measured spectrum
4. Calculation of concentrations with fundamental parameters / MC simulations / standard based
The problem with standard based procedures is the availability of corresponding standards. The problem with the calculations is that the measured intensities for XRF measurements are matrix-dependent. Calculations must, therefore, be performed iteratively (= time consuming) in order to determine the chemical composition.
First experiments with gold samples have shown the feasibility of machine learning based quantification in principle. A large number of compositions were simulated (> 10000) and analyzed with a deep learning network. For first experiments, an ANN (Artificial Neural Network) with 3 hidden layers and 33x33x33 neurons was used. This network learned the mapping of spectra to concentrations using supervised learning by multidimensional regression. The input layer was formed by the normalized spectrum, and the output layer directly yielded the searched values. The applicability for real samples was shown by measurements on certified reference materials.