A micromorphological study on natural and folded sepiolite

Abstract

A sepiolite from Grant County (USA) was studied with two objectives. First, from a purely methodological perspective, a comparative micromorphological study was conducted using two imaging techniques: high-resolution transmission electron microscopy (HR-TEM) and atomic-force microscopy (AFM). The second objective was to determine whether the structural change that occurred in sepiolite after heating over 500 ºC induced observable morphological changes. The fibrous morphology of epiolite was observed; furthermore, bundles and rods were observed in both the TEM and AFM imagery. However, individual laths were easily observed by TEM but could only be deduced from the irregularities of the rod surfaces by AFM. A good approximation of the lath widths (~21 nm) can be obtained from measurements using the two techniques, but AFM allows for the determination of the height of the rods (~31 nm) and shows that the mesocrystals are tabular. The folding of the structure after heating was followed by XRD and HR-TEM. The precise measurements performed by HR-TEM and AFM on the folded sepiolite show the micromorphological change in the particles, which decrease in width after folding (from ~21 nm to ~18 nm) in accord with the reduction of the unit cell.