Defects in microstructure in palygorskite-sepiolite minerals: A transmission electron microscopy (TEM) study

Palygorskite-sepiolite minerals were investigated using transmission electron microscopy (TEM) to describe defect structures contained within individual fibers. Defects are common, and three major types were observed: omission of groups of 2:1 layer ribbon modules (polysomes) that create open channel defects (OCD), planar defects, and stacking disorder observed as 180 degrees rotations of entire polysomes. These defects may enhance crystallization rates of fibers and some defects apparently seal parts of channels within a fiber and probably block exchange of cations, H2O, and organic molecules. Open channel defects appear to be common. The defects observed in this study may explain variations in a number of properties of palygorskite-sepiolite minerals, such as exchange properties involving large organic molecules and chemical composition. Omission defects may explain the occasional occurrence of samples with anomalously high contents of H2O and the ability of some samples to absorb large organic molecules, both of which have been observed by others. (c) 2007 Published by Elsevier B.V.