Investigation of Microstructures in Naturally and Experimentally Deformed Reference Clay Rocks Using Innovative Methods in Scanning Electron Microscopy

Abstract

The application of ion-beam milling techniques to clays allows investigation of the porosity at nm resolution using scanning electron microscopy (SEM). Imaging of pores by SEM of surfaces prepared by broad ion beam (BIB) gives both qualitative and quantitative insights into the porosity and mineral fabrics in 2D representative cross-sections. The combination of cryogenic techniques with ion-beam milling preparation (BIB and FIB, focused ion beam) allows the study of pore fluids in preserved clay-rich samples. Characterization of the pore network is achieved, first, using X-ray computed tomography to provide insights into the largest pore bodies only, which are generally not connected at the resolution achieved. Secondly, access to 3D pore connectivity is achieved by FIB-SEM tomography and the results are compared with 2D porosity analysis (BIB-SEM) and correlated with bulk porosity measurements (e.g. mercury injection porosimetry, MIP). Effective pore connectivity was investigated with an analog of MIP based on Wood's metal (WM), which is solid at room temperature and allows microstructural investigation of WM-filled pores with BIB-SEM after injection. Combination of these microstructural investigations at scales of ,1 mm with conventional stressstrain data, and strain localization characterized by strain-fields measurement (DICdigital image correlation) on the same sample offers a unique opportunity to answer the fundamental questions: (1) when, (2) where, and (3) how the sample was deformed in the laboratory. All the methods above were combined to study the microstructures in naturally and experimentally deformed argillites. Preliminary results are promising and leading toward better understanding of the deformation behavior displayed by argillites in the transition between rocks and soils.#

Quantitative characterization of three-dimensional pore structure in hardened cement paste using X-ray microtomography combined with centrifuge driven metal alloy intrusion

“…Therefore the classification of threshold value is subjective [13] . In order to reduce subjectivity, contrast agents have been applied in porosity characterization of porous material, such as Wood's metal [14][15][16][17][18] , polymethylmethacrylate (PPMA) [19] and mercury [20] . Pore structure [14][15][16] was analyzed only on 2D using Wood's metal combined with high pressure.…”

“…Pore structure [14][15][16] was analyzed only on 2D using Wood's metal combined with high pressure. Wood's metal was also used in clay rock [17] to obtain 3D structure of materials combined with focused ion beam (FIB). PPMA [19] and mercury [20] were applied to research pore structure in crystalline rock with ordinary CT imaging.…”

Imaging connected porosity of crystalline rock by contrast agent‐aided X‐ray microtomography and scanning electron microscopy

“…SEM-EDS imaging can be enhanced using contrast agents to highlight features. Wood's metal is an alloy of different metals that has a low melting point (70°C), which is an often used contrast agent to highlight pore space in variety of materials (Abell et al, 1999;Hildenbrand & Urai, 2003;Kaufmann, 2009;Desbois et al, 2016). Wood's metal also has good X-ray attenuation coefficient which is why it has also been used as a contrast agent in X-ray tomography (Pyrak-Nolte et al, 1995;1997).…”

“…Wood's metal also has good X-ray attenuation coefficient which is why it has also been used as a contrast agent in X-ray tomography (Pyrak-Nolte et al, 1995;1997). Wood's metal has been reported to intrude at least 10 nm size pores (Klaver et al, 2015) and 4.1 nm pore sizes have been reported as well (Desbois et al, 2016). This however can still leave notable amount of pore space unfilled, if there are mineral phases with very small pore sizes.…”

“…, ; Hildenbrand & Urai, ; Kaufmann, ; Desbois et al. , ). Wood's metal also has good X‐ray attenuation coefficient which is why it has also been used as a contrast agent in X‐ray tomography (Pyrak‐Nolte et al.…”