X-ray studies on the nano- and microscale anisotropy in compacted clays: Comparison of bentonite and purified calcium montmorillonite

Abstract

Exceptional water retention properties make compacted clays and clayrocks attractive materials in waste management applications, e.g. as buffer materials and barrier formations for radionuclide release in geological disposal of spent nuclear fuel elements. Consisting of particles with a very high aspect ratio, clay materials exhibit significant structural anisotropy with potential implications on their performance. In this work, the micron-scale and nanometer-scale anisotropy in compacted calcium montmorillonite and MX-80 bentonite were investigated and quantified under varying humidity conditions; the utilized novel experimental method combines X-ray microtomography (XMT) and small-angle X-ray diffraction to near-simultaneously characterize both the micronscale 3D morphology and mineralogical properties such as clay platelet spacing in platelet stacks (tactoids) and tactoid orientation. Sedimentation during the purification process and lack of accessory minerals were found to induce much stronger orientation in purified Ca-montmorillonite as compared to the MX-80. In highly anisotropic samples, the orientation of microcracks visualized with XMT under low humidity conditions was found to correlate with the local orientation of clay tactoids measured with X-ray diffraction. The proposed experimental method can be applied to a wide range of similar materials, such as shales or samples from clayrock formations.

Spatially-localized bench-top X-ray scattering reveals tissue-specific microfibril orientation in Moso bamboo

“…Set-up 1 consists of two separate, independently operable, X-ray devices, which are described in detail in [1, 19, 25]. The two functionalities are connected by a shared sample manipulator stage, which allows the spatial alignment of the sample to be calibrated into XMT coordinates for the scattering modality.…”

“…The same set-up is also used here to present an X-ray diffraction tomography (XDT) measurement on Moso bamboo with different diffraction-dependent contrasts. The localized X-ray scattering (LXS) set-up used in this article has previously been presented with an application to micrometeorites [1, 18] and to compacted clays [19]. …”

Investigation of Coupled Processes and Impact of High Temperature Limits in Argillite Rock: FY17 Progress. Predecisional Draft

“…The ability of in situ heating also provides the unique opportunity to see directly the modification of the sample during the loss of moisture. XR-μCT can also be coupled with other XR scattering-based techniques when a precise correlation with the hydration state of the clay structure (wideangle X-ray powder diffraction) or the size of the clay tactoids (small-angle X-ray scattering) needs to be directly correlated with the development of desiccation cracks (e.g., Suuronen et al 2014).…”

Fabric Investigation of Natural Sensitive Clay from 3D Nano- and Microtomography Data

“…Methods from materials science, such as scanning and transmission electron microscopy (SEM/TEM), mercury intrusion porosimetry (MIP), and wide or small angle X-ray or neutron scattering (W/SAXS, SANS) (e.g., Glatter and Kratky 1982;Toer and Reimer 1998;Giesche 2006) have been introduced in geomechanics to further probe clays at microscale despite their inherent limitations for use in fine-grained materials (Yao and Liu 2012;Deirieh et al 2018). The ultimate aim is to link the micro and macro response (e.g., Pusch 1970;Delage and Lefebvre 1984;Djéran-Maigre et al 1998;Hicher et al 2000;Ringdal et al 2010;Delage 2010;Hattab and Fleureau 2011;Hattab et al 2013;Suuronen et al 2014;Wensrich et al 2018;Birmpilis et al 2019;Cotecchia et al 2019;Delage and Tessier 2021;Abed and Sołowski 2020;Schuck et al 2020;Dor et al 2020;Zhao et al 2020). Regardless of the experimental method, either a bulk response of the complete sample volume (MIP, W/SAXS, SANS), a twodimensional (2D) map of the integrated response along the transmitted X-ray/electron beam (scanning W/SAXS and TEM), or a 2D surface profile (with a certain depth of view) is obtained (SEM).…”