An investigation of the structure of a porous substance by NMR cryodiffusometry

Cryoporosimetry and diffusometry, along with traditional techniques, are us ed to determine the characteristics of porous media. In real systems charac terized by a pore-size distribution and a complex geometry of the pore spac e, the possibilities of these methods are limited. To obtain more data on t he structure of the pore space, it was suggested that these approaches be c ombined in a unified experimental technique called cryodiffusometry. A conc ept of this technique lies in the investigation of self-diffusion in liquid -containing regions in the course of sequential stepwise melting of a subst ance precrystallized in pores. Possibilities of cryodiffusometry were demon strated by investigating of the pore structure of gypsum stone as an exampl e. An analysis of the data obtained showed that pores of the sample are sha ped like layers characterized by an equally probable alignment in space. Th e layers are longer than 40 mum and vary in thickness from 200 to more than 1000 Angstrom; in this case, regions of different thickness are randomly d istributed over the layer. The thinner the layer, the more the shape of lay er portions of different thicknesses deviates fi om spherical.