Investigation of the tripoli porous structure by small-angle neutron scattering

The characteristics of the tripoli porous structure have been investigated by small-angle neutron scattering (SANS). Tripoli is a finely porous sedimentary rock formed by small spherical opal particles. Its main component is aqueous silica SiO2 · nH2O (80–90%). Tripoli is widely used in practice as a working medium for sorption filters and in some other commercial and construction technologies. The shape of the experimental SANS curves indicates the presence of small and large pores in tripoli. The small-pore size was estimated to be ∼100 Å. The size of large pores turned out to be beyond the range of neutron wave vector transfers Q that are available for the instrument used; however, their size was indirectly estimated to be ∼(2000–2500) Å. The pores of both groups behave as surfacetype fractal scatterers with the fractal dimension D ∼ 2.2‐2.6. The densities of pores of these two groups differ by approximately three orders of magnitude (∼1016 and ∼1013 cm−3 for small and large pores, respectively); the fraction of large pores amounts to 70–80% of the total pore volume. The found pore characteristics (their densities, sizes, and relative volumes) are in satisfactory agreement (when a comparison is possible) with the absorption data.