3D quantification of pore scale geometrical changes using synchrotron computed microtomography

Synchrotron microtomography is a non-destructive 3D-characterisation technique providing a three-dimensional mapping of mu, the linear X-ray absorption coefficient of the material under investigation. At each voxel (volume element in 3D images, by analogy to pixel, picture element in 2D) the value of mu is the average of the absorption coefficients of the different solids andfluids contained into it at the moment of acquisition. When the considered sample is composed of several materials having dissimilar mu values, it is possible, by segmentation, to transform the p mapping into a 3D image of the different constitutive materials. Furthermore, microtomography being non-destructive, it is possible to modify the sample between two acquisitions and to follow the induced evolutions in 3D with an unrivalled precision. Synchrotron microtomography has been used to characterise the 3D-microstructure evolutions of two samples submitted to two different processes. in the first case a lithium borate powder sample isfollowed during natural sintering. Morphological changes are shown as well as a solid-solid phase change that is quantified in 3D. In the second case, the modifications induced by reactive percolation of CO2 saturated water within a natural limestone sample are characterized. The process permitting to proceedfrom the data acquired on the tomography beam line to a series of 3D images of the same sample at the different stages of its evolution is presented. The obtained results illustrate the possibilities offered by this quantitative 3D imaging technique to improve the understanding of multi-scale coupled reactive transport processes in porous materials.