Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (42)
- Beitrag zu einem Sammelband (30)
- Beitrag zu einem Tagungsband (28)
- Vortrag (8)
- Sonstiges (7)
- Posterpräsentation (3)
- Buchkapitel (1)
Sprache
- Englisch (119) (entfernen)
Schlagworte
- Computed tomography (22)
- X-ray refraction (18)
- Reconstruction algorithm (8)
- Synchrotron radiation (6)
- Composites (5)
- Electron tomography (5)
- Refraction (5)
- Computed Tomography (4)
- Diffuse background (4)
- Fluorescent screen (4)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (8)
Non-destructive evaluation of advanced materials by synchrotron radiation refraction topography
(2002)
High performance composites and other light weight materials are generally a comple problem to the performance of nondestructive testing methods. X-ray refraction provide unconventional X-ray scattering techniques to meet the actual demand for improve nondestructive characterization of these advanced materials. Scanning the samples across collimated narrow incident X-ray beam permits to image integral micro-structures (a present) with a resolution of 10 µm. Investigations of samples after strain-induced micro cracks and fibre debonding in impact damaged epoxy are shown.
The physics of X-ray refraction are analogous to the well known refraction of light b optical lenses and prisms, governed by Snell's law. The special feature is the deflection a very small angles of few minutes of arc, as the refractive index of X-rays in matter i nearly one. Due to the density differences at inner surfaces most of the incident X-rays ar deflected. As the scattered intensity of refraction is proportional to the specific surface of sample, a reference standard gives a quantitative measure for analytical determinations.
Figure 1 represents a two-dimensional damage distribution of an impact in a 0/90° CFR laminate of 3 mm, thickness. Unlike in ultrasonic testing, there is no shadowing effect o the successive layers. By use of X-ray refraction the exact concentration of debonde fibres is calculated for each position. Additionally the refraction allows the selection of th fibre orientation.
Micro damage structures of fiber reinforced polymers (FRP) can be characterized nondestructively by X-ray refraction topography, which images inner surfaces. The damage accumulation after fatigue treatment of short glass fiber reinforced polybutylene terephthalate (PBT-GF) is correlated to the applied load and the number of cycles. Micro cracks and fiber/matrix debonding during fatigue can be detected separately due to their different direction of X-ray small angle scattering. The residual strength over the crack surface decreases by a linear decay as 30 %, 60 % and 90 % of the materials lifetime is passed.
HYJECT
(2002)
Quantitative X-ray refraction topography is applied for improved nondestructive evaluation of advanced high performance ceramics. The method is based on X-ray small angle scattering by refraction of X-rays due to density differences of microstructures in heterogeneous materials. It determines the amount of inner surfaces and interfaces within the range of µm to nm dimensions. As the scattered refraction intensity is proportional to the inner surface density of a sample, a reference standard gives a quantitative measure for analytical requirements. X-ray refraction scanning topography visualizes integral interface properties at 10 µm spatial resolution by two-dimensional computer images. Characteristic microstructure parameters, i.e. density fluctuation, porosity and pore size distribution of several examples of SiO[2]-and SiC ceramics at different stages of sintering are presented.
Non-destructive Inspection of Ceramic/Composite Materials using Non-classical X-Ray Techniques
(1999)
The first hard X-ray beamline at BESSY II will be installed by BAM and PTB at a superconducting 7 T wavelength shifter. The main optical elements of the beamline are a Double-Multilayer-Monochromator and a Double-Crystal-Monochromator. The two devices can be used separately or in-line. Main applications of monochromatic radiation with photon energies up to 50 keV are X-ray fluorescence analysis, micro-computed tomography, X-ray topography, detector calibration and reflectometry. Calculable undispersed radiation up to 200 keV will be available for radiometric applications.
Different very dilute suspensions of magnetic nanoparticles (magnetite surrounded by an organic shell) in water (ferrofluids) were investigated using small-angle X-ray scattering. It is shown that the scattering originates not only from noncorrelated coreshell nanoparticles, but also from larger structures. By modelling, these structures can be identified as close-packed clusters consisting of coreshell particles (core diameter ~10 nm). The analysis of the radial distance distribution function, obtained by Fourier transformation of the scattered intensity, reveals a lower bound of the mean cluster size of about 40 nm. The formation of clusters is persistent, even in very dilute suspensions.
The morphology and thermal behaviour of polypropylenegraftmaleic anhydride (PPgMA) layered silicate (montmorillonite) nanocomposites were investigated using X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and thermogravimetry. The study focuses on the influence of the presence of oxygen during the preparation of PPgMAnanocomposite using two different modified clays. The nanocomposites show tactoid, intercalated and exfoliated structures side by side with different dominant states depending on the clay used and on the processing conditions. The systems are described as multi-component blends rather than binary blends since the organic ions do not only change the mixing behaviour, but also influence material properties. Beside the physical barrier property of the clay layers also chemical processes were found to play an important role.
For the first time Metal Matrix Composites (MMC) have been investigated by 3D Computed Tomography combined with enhanced interface contrast due to X-ray refraction. X-ray refraction is a relatively new approach for the characterization of advanced materials. The related techniques of Refraction Topography and Refraction Computed Tomography have been developed and applied at our laboratory during the last decade to meet the actual demand for improved nondestructive characterization of high performance composites, ceramics and other low density materials and components. X-ray refraction occurs, when X-rays crosses interfaces of spherical or cylindrical shape (e.g. pores or fibres) in the same way as visible light is refracted by lenses. These X-ray optical effects can be observed at small scattering angles of few minutes of arc as the refractive index n of X-rays is nearly unity (n = 1 10-6). Due to the short X-ray wavelength of about 0.1 nm the technique determines the amount of inner surfaces and interfaces of nanometer dimensions. The technique is expected to solve many problems in understanding the meaning of micro and sub micro structures in materials science. With the results of the CT investigation, some questions could be clarified for a better understanding of fatigue failure mechanisms under cyclic loading conditions. The specimens for the test programme have been provided by MTU Aero Engines. They consist of a titanium matrix (Ti6242) reinforced by SiC fibres (SCS6). The investigations have been performed at the materials research station of BAM (BAMline) at the Synchrotron Facility BESSY in Berlin, Germany.
Precise Measurements of Fibre Direction, Type and Content in CFRP by X-Ray Rotation Topography
(2003)
C-fibre degradation debonding and lamella buckling measurement in CMC by new X-ray topography
(1993)
The employment of synchrotron radiation for refraction topography of materials has considerable advantages over standard x-ray sources. The much higher beam intensity and the parallel and monochromatic radiation provide faster measurements and better angular and spatial resolution. X-ray refraction techniques image the inner surface and interface concentration of micro-structured materials. This effect of x-ray optics is additional to small-angle scattering by diffraction, when the scattering objects reach micrometre dimensions. We have developed x-ray refraction techniques within the last decade in order to meet the growing demands for improved non-destructive characterization of high-performance composites, ceramics and other low-density materials. Sub-micron particle dimensions, the pore size of ceramics, the crack density distribution and single fibre debonding within damaged composites can be measured and visualized by computer-generated interface topographs. For this purpose investigations are now being performed at the new hard x-ray beamline of the Federal Institute for Materials Research and Testing (BAM) at BESSY, Berlin. This BAMline provides monochromatic radiation of photon energies from 5 to 60 keV from a double multilayer and/or a double-crystal monochromator. A separate instrument is dedicated to the further development and application of synchrotron radiation refraction (SRR) topography. Different from conventional small-angle scattering cameras with collimating slits and pinholes, scattering angles down to a few seconds of arc are selected by a single-crystal analyser, similar to a Bonse-Hart diffractometer. A 20 µm spatial resolution of the scattering micro-structures is achieved by a CCD camera with a fluorescent converter. First SRR topographs of aircraft composites [carbon fibre-reinforced plastics (CFRP), carbon fibre-reinforced ceramics (C/C), metal matrix ceramics (MMC)] will be reported.
Microstructural characterization of porous materials by two-dimensional X-ray refraction topography
(2004)
X-ray refraction topography determines the internal surfaces and interfaces of non-metallic porous materials within the range of namometer to micrometer dimensions. The method is based on refraction of X-rays caused by interfaces of microstructures in heterogeneous materials.
Generally, it permits a non-destructive full volume characterization of the pore topology. The X-ray refraction scanning technique make possible to visualize integral interface properties up to 10 μm spatial resolution by two-dimensional topographic images. It detects the spatially resolved internal surfaces of both, open and closed pores. Comparison to a certified powder reference of uniform grain size and known packing density reveals a quantitative measure for calibration requirements. An investigation on SiC- and Al2O3-ceramics illustrate the quantitative characterization of the internal surface density, pore sizes and their spatial distribution as well as local porosity fluctuations.
Neutron tomography was applied to study the 3D water distribution in full polymer electrolyte membrane fuel cell (PEMFC) stacks. The water distribution after switch-off of the fuel cell was analyzed over a period of 36 h. We found a slowly increasing water amount in the fuel cell, but only few changes within a time period of 5 h, which is about the time necessary for neutron tomography. In this way, the requirement for successful tomography was obtained. It is demonstrated how the quasi in-situ tomography technique enables us to study the water content in individual flow field channels of three-fold stacks. Flow field as well as stack design issues are addressed by this visualization method showing weak points due to a non-uniform water distribution that can be identified by means of neutron imaging.
A novel approach is suggested to strongly suppress artifacts in radiography and computed tomography caused by the effect of diffuse background signals 'backlighting' of 2D X-ray detectors. Depending on the detector geometry the mechanism may be different. Either based on the optical scattering of the fluorescent screen materials into the optical detection devices or Compton or X-ray fluorescence scattering by the detector components. Consequently, these erroneous intensity portions result in locally different violations of Lambert Beer's law in single projections (radiographs) as a function of the detector area coverage and the magnitude of the attenuation. The absorption of multiple metal sheets is investigated by monochromatic synchrotron radiation, thus excluding beam hardening. The proposed correction procedure simply requires the individual subtraction of one and the same fraction of the primary and transmitted mean intensity, as a constant (non-local) scattering mechanism is assumed.
Tomography data obtained from transmission electron microscopes are especially attractive due to their unrivaled spatial resolution in the nanometer range or even less, but they require enormous efforts in sample preparation and suffer from a diverse accumulation of experimental restrictions, which unavoidably result in fundamental reconstruction artifacts. These restrictions refer to: partial opacity, a limited view (limited angle or missing wedge), very few angles (with respect to the detector size), limited to a region of interest (ROI; due to the sample size), variable angular increments as well as sample degradation due the interactions with the electron beam. An advanced version of the DIRECTT (Direct Iterative Reconstruction of Computed Tomography Trajectories) algorithm proves to cope with most of these severe deviations from ideal CT measuring conditions. However, careful data preprocessing is required in order to exploit the capabilities of the algorithm.
Nanometer sized Ruthenium catalyst particles for fuel cell applications are 3D imaged at a few Ångström resolution in order to estimate their partial free surface on carbon black supports, which rule the efficiency of the catalytic activity.
Comparisons of DIRECTT reconstructions to the conventional filtered back projection, prove the significant improvements.
A novel approach to strongly suppress artifacts in radiography and computed tomography caused by the effect of diffuse background Signals (backlight) of 2D X-ray detectors is suggested. Depending on the detector geometry the mechanism may be different, either based on the optical scattering of the fluorescent screen materials into optical detection devices or Compton or X-ray fluorescence scattering by the detector components. Consequently, these erroneous intensity portions result in locally different violations of Lambert Beers law in single projections (radiographs).
When used as input data for computed tomography these violations are directly observed via modulation of the projected mass as a function of the rotation Phase and the samples aspect ratio (dynamics). The magnitude of the diffuse Background signal depends on the detector area covered by the projected sample. They are more pronounced the smaller the shaded area and the stronger the total attenuation.
Moreover, the local intensity mismatch depends on the attenuation of the sample.
We present very basic reference data measured with multiple metal foils at a synchrotron radiation source. Beam hardening artifacts can be excluded due to the monochromatic radiation. The proposed correction procedure assumes a constant (non-local) scattering mechanism.
We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells.
Beyond classical X-ray techniques are used for the purpose of preferably short-term applications, but some supplementary X-ray and synchrotron techniques for higher resolution microdiagnostics take advantage of scattering effects. In contrast to directly imaging methods their resolution is only limited by the diffraction limit of the X-ray wavelength, far below the atomic dimensions. These techniques of scanning topography and refraction synchrotron tomography may permit the systematic diagnostics for finding and exploiting structure/property relations like correlations among atomic, nano and microstructures with macroscopic properties. Their basic advantage over microscopic techniques is their potential for the non-destructive characterisation of materials, far from invasive sample treatments. They combine scattering and spatial resolution.
A novel approach to strongly suppress artifacts in radiography and computed tomography caused by the effect of diffuse background signals ('backlighting') of 2D X-ray detectors is suggested. Depending on the detector geometry the mechanism may be different, either based on the optical scattering by the fluorescent screen materials into optical detection devices or Compton or X-ray fluorescence scattering by the detector components. Consequently, these erroneous intensity portions result in locally different violations of Lambert–Beer's law in single projections (radiographs). When used as input data for computed tomography these violations are directly observed via modulation of the projected mass as a function of the rotation phase and the samples aspect ratio (dynamics). The magnitude of the diffuse background signal depends on the detector area covered by the projected sample. They are more pronounced the smaller the shadowed area and the stronger the total attenuation. This implies that the reconstruction suffers from additional anisotropic artifacts caused by elongated sample structures. This issue is studied simply by absorption of flat plates in a conventional laboratory radiography set-up and at a synchrotron radiation facility. In the latter case beam hardening artifacts can be excluded due to the monochromatic radiation. The proposed correction procedure requires simple integral intensity offsets as a constant (non-local) light scattering mechanism is assumed.
The use of high brilliance and partial coherent synchrotron light for radiography and computed tomography (CT) allows to image micro-structured, multi-component specimens with different contrast modes and resolutions up to submicrometer range. This is of high interest for materials research, life science and non-destructive evaluation applications. An imaging setup for microtomography and radiography installed at BESSY II (a third generation synchrotron light source located in Berlin, Germany) as part of its first hard X-ray beamline (BAMline) can now be used for absorption, refraction as well as phase contrast dedicated to inhouse research and applications by external users. Monochromatic synchrotron light between 6 keV and 80 keV is attained via a fully automated double multilayer monochromator. For imaging applications the synchrotron beam transmitted by the sample is converted with a scintillator into visible light. By use of microscope optics this luminescence image is then projected onto, e.g., a CCD chip. Several scintillating materials are used in order to optimise the performance of the detector system. Different optical systems are available for imaging ranging from a larger field of view and moderate resolutions (macroscope up to 14 mm x 14 mm field of view) to high resolution (microscope down to 0.35 μm pixel size), offering magnifications from 1.8× to 40×. Additionally asymmetric cut Bragg crystals in front of the scintillator can be used for a further magnification in one dimension by a factor of about 20. Slow and fast cameras are available, with up to 16 bit dynamic range. We show the suitability of the setup for numerous applications from materials research and life science.
X-ray refraction topography techniques are based on ultra-small angle scattering by micro-structural elements causing phase-related effects such as refraction and total reflection at a few minutes of arc as the refractive index of X-rays is nearly unity. The refraction contrast is several times higher than true absorption and results in images of cracks, pores and fibre debonding separations below the spatial resolution of the detector. In most cases the investigated inner surface and interface structures correlate to mechanical properties. For the exploration of micro structured materials the refraction technique has been improved by a 3D Synchrotron Refraction Computed Tomography test station. The specimen is placed in an X-ray beam between two single crystals, which suppresses all sample scattering. In addition, an asymmetric cut second crystal can magnify the image up to 50 times revealing nano meter resolution. The technique is an alternative to other attempts on raising the spatial resolution of CT machines.
Analyser-based imaging expands the performance of X-ray imaging by utilizing not only the absorption properties of X-rays but also the refraction and scatter rejection (extinction) properties. In this study, analyser-based computed tomography has been implemented on imaging an articular cartilage sample, depicting substructural variations, without overlay, at a pixel resolution of 3.6 µm.
Erstmals wurden MMCs mit Hilfe der Interface-Kontrast verstärkenden Röntgen-Refraktions-Technik in Kombination mit der 3D-CT-Technik untersucht. Die Methode der Röntgen-Refraktions-Topography sowie der Röntgen-Refraktions-Tomography wurden in den letzten Jahren speziell für die zerstörungsfreie Charakterisierung von Leichtbau-Hochleistungs-Werkstoffen wie Verbund-Werkstoffen und Keramiken entwickelt. Die Technik basiert auf der Refraktion von Röntgenlicht an Grenzflächen zwischen Bereichen unterschiedlicher Elektronendichte wie z.B. Faser- und Matrix-Werkstoff. Auf Grund der kurzen Röntgen-Wellenlänge hat der Brechungsindex einen Wert dicht bei eins, sodass der Streuwinkel nur wenige Bogenminuten beträgt. Der Vorteil der kurzen Wellenlänge besteht jedoch darin, dass Poren und Risse detektiert werden können, deren Größe im Nanometerbereich liegen. Damit kann die Refraktions-Technik zum besseren Verständnis von Mikro- und Submikro-Strukturen in der Materialwissenschaft eingesetzt werden. Mit der hier vorgestellten Refraktions-CT wurden Ermüdungsmechanismen an MMCs, bestehend aus SiC-Faser verstärktem Titan (Ti6242) untersucht. Die Messungen wurden am Röntgen-Messplatz der BAM (BAMline) am Synchrotron-Speicherring-BESSY in Berlin Adlershof durchgeführt.
X-Ray Refraction Techniques
(2005)
Enhanced Spatial Resolution in 2D CT-Reconstruction without Filtered Back Projection: DIRECTT
(2008)
Microstructural aspects of composites such as reinforcement particle size, shape, and distribution play important roles in deformation behavior. In addition, Fe-rich inclusions and porosity also influence the behavior of these composites, particularly under fatigue loading. Three-dimensional (3-D) visualization of porosity and Fe-rich inclusions in three dimensions is critical to a thorough understanding of fatigue resistance of metal matrix composites (MMCs), because cracks often initiate at these defects. In this article, we have used X-ray synchrotron tomography to visualize and quantify the morphology and size distribution of pores and Fe-rich inclusions in a SiC particle-reinforced 2080 Al alloy composite. The 3-D data sets were also used to predict and understand the influence of defects on the deformation behavior by 3-D finite element modeling.
The presence of elongation, streak and blurring artifacts in tomograms recorded under a missing wedge of rotation angles presents a major challenge for the quantitative analysis of tomographic image data. We show that the missing wedge artifacts of standard reconstruction algorithms may be reduced by the innovative reconstruction technique DIRECTT. For the comparison of missing wedge artifacts we apply techniques from spatial statistics, which have been specifically designed to investigate the shape of phase boundaries in tomograms.
In order to demonstrate the challenging tasks in current R&D applications in the field of renewable energy
sources experimental neutron and electron tomographic data sets of PEM fuel cell components are processed by
an advanced version of the DIRECTT algorithm. The neutron measurements of the water distribution suffer from
several intrinsic limitations such as massive position dependent focal smearing due to the large primary neutron
beam aperture. Electron (TEM) tomography allows characterisation of nanometre sized catalyst particles but is
hampered by the following restrictions: partial opacity, a limited sector of projections (missing wedge), very few
projections, samples exceeding the detector size (region of interest) and improper angular alignment. Beyond the
capabilities of other algorithms DIRECTT proves to overcome these essential reconstruction problems, in
comparison to FBP and SIRT. Nevertheless, careful data pre-processing is an inevitable requirement in order to
fully exploit the algorithm's potentials.
Incomplete tomographic data sets such as limited view (missing wedge) data represent a well-known challenge
for reconstruction algorithms, since they unavoidably lead to substantial image artefacts. Such data sets may
occur in industrial computed tomography of limited access (e.g. extended components, fixed objects), directional
opacity, limited sample life time or laminographic set-up. We present strategies to effectively suppress the
typical elongation artefacts (e.g. lemon-like deformed pores) by our iterative algorithm DIRECTT which offers
the opportunity to vary the versatile reconstruction parameters within each cycle. Those strategies are applied to
experimental data obtained from metallic foams as well as model simulations. Comparison is drawn to state-ofthe-
art techniques (filtered backprojection and algebraic techniques). Further reference is made to reconstructions
of complete data sets serving as gold standards. For quantitative assessment of the reconstruction
quality adapted techniques based on spatial statistics are introduced.
A novel approach to strongly suppress artifacts in radiography and computed tomography caused by the effect of
diffuse background signals ('backlighting') of 2D X-ray detectors is suggested. Depending on the detector
geometry the mechanism may be different, either based on the optical scattering of the fluorescent screen
materials into optical detection devices or Compton or X-ray fluorescence scattering by the detector components.
Consequently, these erroneous intensity portions result in locally different violations of Lambert Beers law in
single projections (radiographs) as function of the detector area coverage and the magnitude of the attenuation.
The absorption of multiple metal sheets is investigated by monochromatic synchrotron radiation, thus excluding
beam hardening. The proposed correction procedure simply requires the individual subtraction of one and the
same fraction of the primary and transmitted mean intensity, as a constant (non-local) scattering mechanism is
assumed.
The relevance of nano sized structures and interfaces in upcoming technologies requires new non-destructive Xray
techniques exploiting attenuation as well as scattering. In the course of driving the resolution and the contrast
of modern radiography into micro and nano metre dimension the inevitable scattering effects require increased
attention. Several radiologists interpret the observed edge artefacts simply by 'phase contrast' due to different
X-ray path lengths within the sample and others refer to Fresnel scattering. The ultra small angle scattering is of
high intensity and may reach the level of the primary beam. We present monochromatic synchrotron
measurements on rather simply shaped objects (such as plates and cylinders) which prove clearly the dominance
of refraction intensity over total reflection and coherent small angle scattering. The refraction conditions hold for
angles of incidence of several degrees to the surface, but typical deflection angles range from several seconds to
minutes of arc. Additionally to the concept of 'phase contrast' of the primary beam its deflection becomes the
essential issue. The appropriate removal of the attenuation contribution enables the imaging of inner surfaces and
interfaces by refraction scanning topography. The presented measurements of reference particles demonstrate the
reliability of laboratory refraction scanners applying X-ray tubes.
Evaluating porosity in cordierite diesel particulate filter materials, part 1 X-ray refraction
(2013)
Bi-continuous porous ceramics for filtration applications possess a particularly complicated microstructure, with porosity and solid matter being intermingled. Mechanical, thermal, and filtration properties can only be precisely estimated if the morphology of both solid matter and porosity can be quantitatively determined. Using x-ray absorption and refraction, we quantitatively evaluate porosity and pore orientation in cordierite diesel particulate filter ceramics. Porosity values turn out to agree with mercury intrusion measurements, while pore orientation factors agree with published crystallographic texture data.
We present a synchrotron X-ray tomographic study on the morphology of carbon fiber-based gas diffusion layer (GDL) material under compression. A dedicated compression device is used to provide well-defined compression conditions. A flat compression punch is employed to study the fiber geometry at different degrees of compression. Transport relevant geometrical parameters such as porosity, pore size and tortuosity distributions are calculated. The geometric properties notably change upon compression which has direct impact on transport conditions for gas and fluid flow. The availability of broad 3D paths, which are most important for the transport of liquid water from the catalyst layer through the GDL, is markedly reduced after compression. In a second experiment, we study the influence of the channel-land-pattern of the flow-field on shape and microstructure of the GDL. A flow-field compression punch is employed to reproduce the inhomogeneous compression conditions found during fuel cell assembly. While homogenously compressed underneath the land the GDL is much less and inhomogeneously compressed under the channel. The GDL material extends far into the channel volume where it can considerably influence gas and fluid flow. Loose fiber endings penetrate deeply into the channel and form obstacles for the discharge of liquid water droplets.
Complementary to Part 1 of this work, the bi-continuous microstructure of porous synthetic cordierite ceramics for filtration applications was investigated using 3D x-ray computed tomography at different resolutions. Applying both Fast Fourier Transform and a newly developed image analysis algorithm, we quantitatively evaluated porosity and pore orientation. The statistical approach allows extraction of spatially resolved or average values. Porosity values based on x-ray absorption agree with mercury intrusion measurements, while pore orientation factors agree with x-ray refraction data (Part 1 of this work), and with published crystallographic texture data.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread holds equally for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated. We shall show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. We will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Bi-continuous porous ceramics for filtration applications possess a particularly complicated microstructure, whereby porosity and solid matter are intermingled. Mechanical, thermal, and filtration properties can only be precisely estimated if the morphology of both solid matter and porosity can be quantitatively determined. Using 3D computed tomography (CT) at different resolutions, and several X-ray refraction-based techniques, we quantitatively evaluated porosity and pore orientation in cordierite diesel particulate filter ceramics.Moreover, applying both Fast Fourier Transform (FFT) and a newly developed image analysis algorithm (directional interface variance analysis, DIVA), we quantitatively evaluated porosity and pore orientation. Both the experimental techniques and the statistical approach allow extraction of spatially resolved or average values.Porosity values from synchrotron computed tomography used turn out to agree with mercury intrusion measurements, while pore orientation factors agree with published crystallographic texture data. This latter point also implies that the study of the pore/matter interface is sufficient to describe the morphological properties of these materials.
X-ray compton tomography
(2014)
The potentials of incoherent X-ray Scattering (Compton) tomography are investigated. Imaging materials of very different density or atomic number at once is a perpetual challenge for X-ray tomography or radiography, in general. In a basic laboratory set-up for simultaneous perpendicular Compton Scattering and direct beam attenuation tomographic scans are conducted by single channel photon counting. This results in asymmetric distortions of the projection profiles of the scattering CT-data set. ln a first approach corrections of Compton scattering data by taking advantage of rotational symmetry yield tomograms without major geometric artefacts.
A cylindrical sample composed of PE, PA, PVC, glass and wood demonstrates similar Compton contrast for all the substances, while the conventional absorption tomogram only reveals the two high order materials.
Compärison to neutron tomography reveals astonishing similarities except for the glass component (without hydrogen). Therefore, Compton CT bears the potential to replace neutron tomography, which requires much more efforts.
For the first time we present direct 2D imaging of refracted X-rays without any discrimination of the Primary radiation. X-refraction works in analogy to visible light optics: X-rays are entirely deflected at interfaces where discontinuities of (electron) density occur. This is demonstrated at the example of inner and outer surfaces of model samples of well-defined geometry (fibres, capillaries, and monodisperse micro particles). The samples are scanned through a 50 μm monochromatic (20 keV) pencil beam. In order to warrant a sufficient angular resolution a 2D detector (pixel size 7 μm) is placed 3 m downstream of the sample. Scanning the sample in micron steps allows for detecting local changes of interface / surface orientation directly in two dimensions. At the actual angular resolution of about 3 seconds of arc (scattering vector increments Δk = 10-3 nm-1) and 50 μm spatial resolution (scanning) the material’s inner surfaces (with nanometer separation) can be characterized even at sampling rates below 1 second per frame. Moreover, our technique is suited to directly determine particle diameters of up to 250 nm by means of diffraction fringes. Some potential applications to technical submicron structures are discussed.