Abstract
Synchrotron radiation X-ray tomographic microscopy (SRXTM) was used to characterize the three-dimensional microstructure, geometry and distribution of different phases in two shale samples obtained from the North Sea (sample N1) and the Upper Barnett Formation in Texas (sample B1). Shale is a challenging material because of its multiphase composition, small grain size, low but significant amount of porosity, as well as strong shape- and lattice-preferred orientation. The goals of this round-robin project were to (i) characterize microstructures and porosity on the micrometer scale, (ii) compare results measured at three synchrotron facilities, and (iii) identify optimal experimental conditions of high-resolution SRXTM for fine-grained materials. SRXTM data of these shales were acquired under similar conditions at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory, USA, the Advanced Photon Source (APS) of Argonne National Laboratory, USA, and the Swiss Light Source (SLS) of the Paul Scherrer Institut, Switzerland. The data reconstruction of all datasets was handled under the same procedures in order to compare the data quality and determine phase proportions and microstructures. With a 10× objective lens the spatial resolution is approximately 2 µm. The sharpness of phase boundaries in the reconstructed data collected from the APS and SLS was comparable and slightly more refined than in the data obtained from the ALS. Important internal features, such as pyrite (high-absorbing), and low-density features, including pores, fractures and organic matter or kerogen (low-absorbing), were adequately segmented on the same basis. The average volume fractions of low-density features for sample N1 and B1 were estimated at 6.3 (6)% and 4.5 (4)%, while those of pyrite were calculated to be 5.6 (6)% and 2.0 (3)%, respectively. The discrepancy of data quality and volume fractions were mainly due to different types of optical instruments and varying technical set-ups at the ALS, APS and SLS.
Highlights
X-ray absorption tomographic microscopy is a non-destructive, high-resolution and three-dimensional (3D) imaging method, which is based on different linear attenuation coefficients of constituent phases (Beer–Lambert’s law)
Raw projection images of sample N1 collected at each facility internal microstructure (Figs. 6 and 7) and to calculate volume are quite distinctive, those from the Advanced Light Source (ALS) and the fractions (Table 2) and aspect ratio
The resolution of the Swiss Light Source (SLS) [Figs. 2(a) and 2(c)] which contain several bright horizontal streaks. These stripe patterns are caused by X-ray beam inhomogeneities owing to reflections on the multilayer system is of the order of two pixels; any feature smaller than 3 mm3 [i.e. (1.44 mm)3 = 2.99 mm3] was excluded from calculations composition of a monochromator mirror (Table 1)
Summary
X-ray absorption tomographic microscopy is a non-destructive, high-resolution and three-dimensional (3D) imaging method, which is based on different linear attenuation coefficients of constituent phases (Beer–Lambert’s law). The technique has long been used to characterize microstructures of a wide variety of materials such as biomedical specimens. Agatston et al, 1990), engineering materials Beckmann et al, 2007; Meirer et al, 2011), concretes Monteiro et al, 2009), fossils Gai et al, 2011) and food products Tomography has been performed with synchrotron X-ray sources, which provide a brilliant and intense X-ray beam. The high X-ray brilliance allows us to carry out experiments with ad hoc tuned monochromatic radiation, resulting in low-noise data with optimal contrast.
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