Nanoscale uniformity of pore architecture in diatomaceous silica: A combined small and wide angle X-ray scattering study

Combined small and wide angle IZ-ray scattering (SAXS and WAXS) analysis was applied to purified biogenic silica of cultured diatom frustules and of natural populations sampled on marine tidal flats. The overall WAXS patterns did not reveal crystalline phases (WAXS domain between 0.07 to 0.5 nm) in this biogenic silica, which is in line with previous reports on the amorphous character of the SiO2 matrix of diatom frustules, One exception was the silica of the pennate species Cylindrotheca fusiformis Reimann et Lewin, which revealed wide peaks in the WAXS spectra, These peaks either indicate the presence of a yet unknown crystalline phase with a repetitive distance (d-value approximate to 0.06 mn) or are caused by the ordering of the fibrous silica fragments; numerous girdle bands. The SAXS spectra revealed the size range of pores (diameter d between 3.0 and 65 nm), the presence of distinct pores (slope transitions), and structure factors (oscillation of the spectra). All slopes varied in the range of -4.0 to -2.5, with two clear common regions among species: d <10 nm (slopes 4, denoted as region I and also called the Pored region), and 10.0 <d