Variability of the morphology of the pore space in Boom Clay from BIB-SEM, FIB and MIP investigations on representative samples. 2nd project report

The direct characterization of pore morphologies at nm-scale in very fine-grained samples is difficult due to sample preparation. In this study, the effect of various drying techniques on the observed porosities was first studied. The combination of Broad-Ion-Beam (BIB) cross-sectioning and SEM-imaging was then used to produce high quality, polished cross-sections and image pores down to a few nm in size. In order to study porosities, the porosity segmentation method (manually and automatically) was further developed. All samples show homogeneous intra-phase porosities and pore morphologies, but differences between samples investigated occur at the interfaces between different mineral phases. Characteristic pore morphologies and total visible porosities were found for different mineral phases, present in the investigated samples. Pore-size distributions from manual and automatic segmentations of porosity are nearly identical within a pore-size range between 50-600 nm (ER), but deviations occur above and below this range. In addition to the BIB-SEM, some first serial FIB-SEM experiments on Boom Clay were performed. These yield a 3-dimensional insight to the pore space, suggesting for possible interconnections between different pores in the clay-matrix of the sample to be larger than 15 nm in diameter.