Retrieving the spatially resolved preferred orientation of embedded anisotropic particles by small-angle X-ray scattering tomography

Abstract

Experimental nondestructive methods for probing the spatially varying arrangement and orientation of ultrastructures in hierarchical materials are in high demand. While conventional computed tomography (CT) is the method of choice for nondestructively imaging the interior of objects in three dimensions, it retrieves only scalar density fields. In addition to the traditional absorption contrast, other contrast mechanisms for image formation based on scattering and refraction are increasingly used in combination with CT methods, improving both the spatial resolution and the ability to distinguish materials of similar density. Being able to obtain vectorial information, like local growth directions and crystallite orientations, in addition to scalar density fields, is a longstanding scientific desire. In this work, it is demonstrated that, under certain conditions, the spatially varying preferred orientation of anisotropic particles embedded in a homogeneous matrix can be retrieved using CT with small-angle X-ray scattering as the contrast mechanism. Specifically, orientation maps of filler talc particles in injection-moulded isotactic polypropylene are obtained nondestructively under the key assumptions that the preferred orientation varies slowly in space and that the orientation of the flake-shaped talc particles is confined to a plane. It is expected that the method will find application in in situ studies of the mechanical deformation of composites and other materials with hierarchical structures over a range of length scales.

Small-angle X-ray scattering tensor tomography: model of the three-dimensional reciprocal-space map, reconstruction algorithm and angular sampling requirements

“…with no preferred orientation of the nanostructure or for unidirectional orientation of the nanostructure parallel to the rotation axis (Schroer et al, 2006;Feldkamp et al, 2009;Jensen et al, 2011). Skjønsfjell et al (2016) have shown that, with strict assumptions on the sample, the orientation distribution can be retrieved from measurements using a single rotation axis by fitting a model of the X-ray scattering to the experimental SAXS pattern. For more general anisotropically oriented scatterers, SAXS acquisition using two rotation axes is needed (see Fig.…”

Validation study of small-angle X-ray scattering tensor tomography

“…Recent developments have enabled the tomographic reconstruction of the orientation for anisotropically scattering samples (Skjønsfjell et al, 2016;Schaff et al, 2015;Liebi et al, 2015Liebi et al, , 2018Gao et al, 2019). Under strict assumptions on the sample, such as known dimensions of the scattering particles and slowly varying orientation confined in one plane, the orientation distribution can be obtained from a single rotation axis (Skjønsfjell et al, 2016). For general anisotropically oriented scatterers, two rotation axes are used to retrieve the 3D reciprocal space (Schaff et al, 2015;Liebi et al, 2015).…”

Improving grazing-incidence small-angle X-ray scattering–computed tomography images by total variation minimization

“…In the GISAXS-CT method, CT images are ISSN 1600-5767 reconstructed from sinograms obtained by scanning GISAXS measurements along the direction (Y) perpendicular to the X-ray beam at each rotation angle (). This technique has been applied to transmission smallangle X-ray scattering (SAXS)-CT as well as GISAXS-CT methods (Schroer et al, 2006;Schaff et al, 2015;Skjønsfjell et al, 2016;Liebi et al, 2018). Since CT images are reconstructed from the sinograms of the scattering intensities, one can obtain the spatial distributions of structural information corresponding to the scattering intensities.…”

“…Since CT images are reconstructed from the sinograms of the scattering intensities, one can obtain the spatial distributions of structural information corresponding to the scattering intensities. This technique has been applied to transmission smallangle X-ray scattering (SAXS)-CT as well as GISAXS-CT methods (Schroer et al, 2006;Schaff et al, 2015;Skjønsfjell et al, 2016;Liebi et al, 2018). In these methods, CT images are reconstructed from the sinograms using filtered back-projection (FBP).…”