Abstract: The porous structure of expanded graphite and expanded vermiculite has been studied in situ under uniaxial stress. The properties of a porous material being related to the matrix and to the porosity, the in situ evolution under of the crystalline structure (of the matrix) under high pressure have been first investigated using diamond anvil cell. The equation of state of expanded vermiculite has been established. This first part of this work allowed giving a particular insight to the study of the unsolved high pressure phase of graphite. Combining Raman scattering data and calculations, a new structure, called Z-Carbon, has been proposed. Thanks to the specific technical developments of this work, the porosities of expanded graphite and expanded vermiculite based systems have been studied in situ under uniaxial stress. The used of fractal model in data analysis allowed following the evolution of the fractal dimension and of the apparent specific surface The studied samples were made of compressed forms of expanded graphite and expanded vermiculite in which the basal plane of the crystallites have a preferential orientation. The uniaxial stress was taken perpendicular and parallel to this preferential direction. The porous structure of the expanded graphite sample was found to undergo an irreversible collapse of the pores or a cracks and creation and propagation. Additional electrical and porosity measurements supported the proposed models. In the expanded vermiculite based systems, the crack apparition was observed under uniaxial stress.
