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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.
Simulation becomes more and more important in modern CT imaging. It is increasingly used to optimize techniques for complex applications, to support the preparation of written procedures, and for educational purposes. The radiographic simulator aRTist is a modelling tool which simulates X-ray imaging using a hybrid analytical and Monte Carlo method to efficiently model the radiation transport. In addition to the relevant physical effects such as absorption, scattering and fluorescence, simplified fast models are employed to describe the characteristics of the X-ray source and the detector. aRTist is well equipped to model realistic X-ray imaging setups due to the ability to load exported CAD object descriptions. A simple CT scan module is contained in aRTist which allows the simulation of standard (circular cone beam) scanning trajectories.
TomoSynth is a module for aRTist which allows to set up more complex scanning trajectories by attaching geometrical modification functions to the objects in the radiographic scene. In this way, advanced scanning modes can be realized, for instance helical CT as an overlay of a rotation and a linear motion, or laminography as a motion of the source point. In addition to deterministic motion, also random variations can be introduced. By combining random variations with deterministic motion, non-ideal (realistic) CT scan geometries can be simulated, e.g. focal spot drift and mechanical instability of the axis of rotation. The TomoSynth module conveniently allows to construct these scenarios in a graphical interface and provides a preview before starting the (potentially long running) batch job. Therefore, deviations from ideal CT scan trajectories can be easily adjusted which is a necessary step towards uncertainty determination from simulation.
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.
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 BundesanstaltfürMaterialforschung 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 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, the absorption edge tomography is employed to perform a non-destructive, three-dimensional characterization of the microstructure of metallic alloys. As an example, a high strength Mg-Y-Zn alloy containing long period stacking ordered (LPSO) phases is analysed. The alloy with a nominal composition of Mg97Y2Zn1 was synthesized by melting highly pure magnesium, zinc and a Mg-22%Y master alloy and casting an ingot, which was homogenised at 350 °C and then extruded using an extrusion ratio of 18:1.
The results demonstrate that synchrotron based absorption edge tomography is a promising technique to perform a 3D characterization of the microstructure of metallic alloys.
This paper describes a novel methodology for quantitative in-situ moisture measurement without tracking agents using X-ray computed tomography (XCT). The high levels of grey-scale precision required for the measurement of moisture without tracking agents resulted in the need for an additional image calibration procedure to correct for water-related X-ray scattering and for equipment-variability related artefacts arising during in-situ testing. This calibration procedure was developed on the basis of existing principles of XCT image cor-rection. Resulting images of moisture distribution exhibit a high level of agreement with expected material behaviour. This research demonstrated that XCT can be successfully used to measure both moisture-front movement over time and changes in 3D moisture distribution within samples. This approach to moisture measurement lays the groundwork for the planned future investigation of the interaction between cracking induced by varying chemical and mechanical processes and water transport in concrete.