  The influence of the interlayer cations, sonication and grinding on surface
area of the vermiculite from Santa Olalla has been studied. For untreated
samples the surface area increases with the size of the exchanged cation and
only the samples with the largest cations (NH+ and K+) show some microporosity.
Sonication produces an increase of the surface area but the amount of
micropores remains almost unchanged. Grinding leads to a significant increase
of the surface area and of the microporosity. In the ground samples the
percentage of micropores contributing to the surface area is influenced by the
interlayer cation and the extent of N2 penetration by the water kept in the
sample at a given degassing temperature. From transmission electron microscopy,
thermogravimetry and XRD (d00l diffraction peaks) it can be concluded that
grinding produces imperfections in crystal ordering, some alteration in the
crystal edges, and a significant release of loosely bound water at temperatures
up to 450 8C. These effects are responsible for the high surface area and
microporosity measured by the N2 adsorption.
