A Direct Procedure for Determining the number of Plates in Tactoids of Smectites: The Na/Ca-Montmorillonite Case

Abstract

Abstract--The dispersion of clays is of great importance in determining various soil properties such as hydraulic conductivity. A procedure which involves fixing followed by embedding of clay particles in an epoxy resin is described. This procedure enables the observation of cross sections of clay tactoids under a transmittance electron microscope, and the determination of the number of plates per tactoid. The use of the procedure for the determination of the relation between the exchangeable sodium percentage (ESP) and tactoid size in suspensions of a Na/Ca bentonite system is presented. It was demonstrated that even at ESP 5 significant dispersion already occurs, the average number of plates per tactoid being 6.6 as compared to 16.1 at ESP 0.

The Microstructure of Three Na+ Smectites: The Importance of Particle Geometry on Dehydration and Rehydration

“…This confirms the overestimation of the thicknesses measured at the lower magnification. The formation of these panicles is not believed to be an artifact of the method since a similar technique was capable of isolating monolayers in colloidal suspensions (Shomer and Mingelgrin, 1978) and for a synthetic Na + laponite at suction pressures similar to this study (Tessier and Grimaldi, 1993). Desiccation increased the number of layers in each particle by bringing smaller panicles together.…”

Adsorption of Dimethylanilines on Montmorillonite in High-Pressure Liquid Chromatography

“…Microscopic observations and photographs were made on a Cambridge Stereoscan 180 scanning electron microscope (SEM) and on a Philips-300 transmission electron microscope (TEM). The samples for TEM were prepared by the procedure of Shomer and Mingelgrin (1978). Ultrasections were prepared with an ultratome LKB-3.…”

Particle Association in Smectite Sols by Transmission Electron Microscopy

“…This procedure has been routinely used in the biological sciences for encapsulating cell pellets (Ryter and Kellenberger, 1958) and isolated cells (De Haller et al, 1961). It previously had been applied to clay suspensions (Shomer and Mingelgrin, 1978).…”

“…Models describing various types of particle association have been proposed, and the experimental data have been used to discriminate between models (Swartzen- AUen and Matijevic, 1974;van Olphen, 1977). Although this approach has been useful in understanding clay suspensions, direct observations confirming such proposed types of particle association have been reported only once (Shomer and Mingelgrin, 1978).…”