Comparing laboratory and field samples of lime-cement improved Norwegian clay

acceptedVersio

Orientational mapping of minerals in Pierre shale using X-ray diffraction tensor tomography

Shales have a complex mineralogy with structural features spanning several length scales, making them notoriously difficult to fully understand. Conventional attenuation-based X-ray computed tomography (CT) measures density differences, which, owing to the heterogeneity and sub-resolution features in shales, makes reliable interpretation of shale images a challenging task. CT based on X-ray diffraction (XRD-CT), rather than intensity attenuation, is becoming a well established technique for non-destructive 3D imaging, and is especially suited for heterogeneous and hierarchical materials. XRD patterns contain information about the mineral crystal structure, and crucially also crystallite orientation. Here, we report on the use of orientational imaging using XRD-CT to study crystallite-orientation distributions in a sample of Pierre shale. Diffraction-contrast CT data for a shale sample measured with its bedding-plane normal aligned parallel to a single tomographic axis perpendicular to the incoming X-ray beam are discussed, and the spatial density and orientation distribution of clay minerals in the sample are described. Finally, the scattering properties of highly attenuating inclusions in the shale bulk are studied, which are identified to contain pyrite and clinochlore. A path forward is then outlined for systematically improving the structural description of shales.publishedVersio

Quantitative Polychromatic X-Ray Computed Tomography - Experiments and Simulations

X-ray Computed Tomography (CT) is an extensively used technique conventionally utilizing either absorption-contrast or phase-contrast to non-destructively image the internal structures of objects. While CT instruments using polychromatic source spectra might provide qualitative information about a sample, quantitative results are limited due to tomographic artifacts such as beam hardening. Beam hardening may be alleviated through energy filtration or using dual energy CT, however, quantitative CT is usually restricted to measurements using a monochromatic source. This thesis has focused on two dimensional monochromatic and polychromatic CT simulations based on absorption-contrast. The polychromatic simulations aim to replicate a Nikon XT H 225 ST CT instrument by implementing models for the X-ray source and the X-ray detector, the focal spot size and the noise. Simulated tomograms of three homogeneous and cylindrical samples consisting of polyoxymethylene, polytetrafluoroethylene and Al were compared to experimental data to verify the models used in the simulations. The results indicate that the Poisson noise applied to the simulated projections accurately describes the noise present in the experimental tomograms. Moreover, a larger amount of beam hardening was observed in the simulations compared to the measured tomograms, especially for the high-attenuating sample Al. The discrepancy was arguably due to differences between the real and the simulated source spectra. A sample consisting of two Si wafers bonded together by a Ni layer and a Ni3Sn2 phase layer was further studied. The simulations were performed with a high magnification using a pixel size of 4 µm and a tube voltage of 180 kV. Using a current of 100 µA it was found that the Ni3Sn2 layer had to be 64 µm thick in order to be resolved. By decreasing the current to 10 µA the thickness of the Ni3Sn2 layer could be resolved at 56 µm, at the expense of increased noise. As the focal spot size used in the simulations is larger than the real focal spot size, real CT measurements should have a better physical resolution than presented here. A sample consisting of a PZT material and a Tungsten Carbide (WC) material bonded together by various Au-Sn phases was measured with a Nikon CT instrument and tomographic images were presented. The presence of beam hardening, ring artifacts and the anode heel effect in the tomograms was discussed. Lastly, a sample of Si wafers bonded together by Ni-Sn phases was measured at the ID-19 beamline at the European Synchrotron Radiation Facility in Grenoble, France. Due to the partial coherence of the beam giving propagation phase-contrast, the measured projections were preprocessed prior to reconstruction using the Paganin approximation. However, the tomograms still contained traces of phase-contrast, especially between air and sample materials. It was argued that the constants, δ and β, had been optimized such that the phase contrast in the bond layer was minimized. Inspection of the bond layer revealed the presence of a high attenuating structure and a low attenuating structure. Simulations using monochromatic, incoherent X-rays were compared to the measured tomograms, indicating that the low attenuating structure consisted of Ni with the possibility of a distribution of voids with a micrometer size or smaller. Moreover, it was demonstrated that the high attenuating structure could consist of a Ni3Sn2 phase, however, it could not be excluded that other phases could be present in the structure as well. It was argued that more reliable results could be obtained if the phase contrast observed in the measured tomograms could be implemented into the simulations

High-energy X-ray Tomography for 3D Void Characterization in Au–Sn Solid-Liquid Interdiffusion (SLID) Bonds

Au-Sn SLID bonding is a technique originally developed for harsh environment applications. The technology has recently shown promising results for ultrasound transducer fabrication. Characterizing the spatial and size distributions of voids is crucial for developing a fabrication process that satisfies acoustic requirements. This measurement is traditionally done by optical or electron cross-section microscopy that gives the void distribution in a randomly selected physically cut plane. X-ray micro computed tomography is a powerful tool for non-destructive three-dimensional imaging of void distributions, but is challenging to use in high-density materials like the ones used in ultrasound transducers. We demonstrate that monochromatic, high-energy synchrotron X-ray tomography can give 3D images of such a challenging sample, resolving μm-sized voids in the bondline. The void distribution is highly non-uniform, implying that traditional cross-section microscopy would give different results depending on the plane of sectioning. Computed tomography allows the voids to be parametrized and treated statistically, revealing a wide distribution of void sizes, a tendency to form oblate voids with size-dependent orientation, as well as porous networks

High-energy X-ray Tomography for 3D Void Characterization in Au–Sn Solid-Liquid Interdiffusion (SLID) Bonds

Au-Sn SLID bonding is a technique originally developed for harsh environment applications. The technology has recently shown promising results for ultrasound transducer fabrication. Characterizing the spatial and size distributions of voids is crucial for developing a fabrication process that satisfies acoustic requirements. This measurement is traditionally done by optical or electron cross-section microscopy that gives the void distribution in a randomly selected physically cut plane. X-ray micro computed tomography is a powerful tool for non-destructive three-dimensional imaging of void distributions, but is challenging to use in high-density materials like the ones used in ultrasound transducers. We demonstrate that monochromatic, high-energy synchrotron X-ray tomography can give 3D images of such a challenging sample, resolving μm-sized voids in the bondline. The void distribution is highly non-uniform, implying that traditional cross-section microscopy would give different results depending on the plane of sectioning. Computed tomography allows the voids to be parametrized and treated statistically, revealing a wide distribution of void sizes, a tendency to form oblate voids with size-dependent orientation, as well as porous networks

A technique for in situ X-ray computed tomography of deformation-induced cavitation in thermoplastics

Deformation-induced cavitation influences the mechanical response of polymeric materials, but acquiring in situ measurements of the spatial evolution of cavities has typically necessitated the use of synchrotron radiation sources. The objective of this study is to develop and demonstrate a method allowing for in situ measurements of deformation-induced cavitation in axisymmetric polymer specimens, using a home-laboratory X-ray computed tomography setup. The method is demonstrated by assessing deformation-induced cavitation of mineral-filled PVC in a repeated loading-unloading experiment. A temporal resolution of about 3 s is obtained by exploiting the axisymmetry of notched round tensile specimens. The evolution of relative density was captured throughout the experiment, revealing an interplay between void nucleation and void growth. Combined with surface deformation measurements obtained by digital image correlation, the present technique yields data suitable for calibration and validation of material models

Orientational mapping of minerals in Pierre shale using X-ray diffraction tensor tomography

Shales have a complex mineralogy with structural features spanning several length scales, making them notoriously difficult to fully understand. Conventional attenuation-based X-ray computed tomography (CT) measures density differences, which, owing to the heterogeneity and sub-resolution features in shales, makes reliable interpretation of shale images a challenging task. CT based on X-ray diffraction (XRD-CT), rather than intensity attenuation, is becoming a well established technique for non-destructive 3D imaging, and is especially suited for heterogeneous and hierarchical materials. XRD patterns contain information about the mineral crystal structure, and crucially also crystallite orientation. Here, we report on the use of orientational imaging using XRD-CT to study crystallite-orientation distributions in a sample of Pierre shale. Diffraction-contrast CT data for a shale sample measured with its bedding-plane normal aligned parallel to a single tomographic axis perpendicular to the incoming X-ray beam are discussed, and the spatial density and orientation distribution of clay minerals in the sample are described. Finally, the scattering properties of highly attenuating inclusions in the shale bulk are studied, which are identified to contain pyrite and clinochlore. A path forward is then outlined for systematically improving the structural description of shales

Orientational mapping of minerals in Pierre shale using X-ray diffraction tensor tomography

Shales have a complex mineralogy with structural features spanning several length scales, making them notoriously difficult to fully understand. Conventional attenuation-based X-ray computed tomography (CT) measures density differences, which, owing to the heterogeneity and sub-resolution features in shales, makes reliable interpretation of shale images a challenging task. CT based on X-ray diffraction (XRD-CT), rather than intensity attenuation, is becoming a well established technique for non-destructive 3D imaging, and is especially suited for heterogeneous and hierarchical materials. XRD patterns contain information about the mineral crystal structure, and crucially also crystallite orientation. Here, we report on the use of orientational imaging using XRD-CT to study crystallite-orientation distributions in a sample of Pierre shale. Diffraction-contrast CT data for a shale sample measured with its bedding-plane normal aligned parallel to a single tomographic axis perpendicular to the incoming X-ray beam are discussed, and the spatial density and orientation distribution of clay minerals in the sample are described. Finally, the scattering properties of highly attenuating inclusions in the shale bulk are studied, which are identified to contain pyrite and clinochlore. A path forward is then outlined for systematically improving the structural description of shales

Quantifying the hydroxyapatite orientation near the ossification front in a piglet femoral condyle using X-ray diffraction tensor tomography

While a detailed knowledge of the hierarchical structure and morphology of the extracellular matrix is considered crucial for understanding the physiological and mechanical properties of bone and cartilage, the orientation of collagen fibres and carbonated hydroxyapatite (HA) crystallites remains a debated topic. Conventional microscopy techniques for orientational imaging require destructive sample sectioning, which both precludes further studies of the intact sample and potentially changes the microstructure. In this work, we use X-ray diffraction tensor tomography to image non-destructively in 3D the HA orientation in a medial femoral condyle of a piglet. By exploiting the anisotropic HA diffraction signal, 3D maps showing systematic local variations of the HA crystallite orientation in the growing subchondral bone and in the adjacent mineralized growth cartilage are obtained. Orientation maps of HA crystallites over a large field of view (~ 3 × 3 × 3 mm3) close to the ossification (bone-growth) front are compared with high-resolution X-ray propagation phase-contrast computed tomography images. The HA crystallites are found to predominantly orient with their crystallite c-axis directed towards the ossification front. Distinct patterns of HA preferred orientation are found in the vicinity of cartilage canals protruding from the subchondral bone. The demonstrated ability of retrieving 3D orientation maps of bone-cartilage structures is expected to give a better understanding of the physiological properties of bones, including their propensity for bone-cartilage diseases