Crystalline Swelling Investigation of Montmorillonite as a Natural Nanostructured Material

Montmorillonite and other clay minerals can be considered as natural nanostructured materials. Nanostructured materials are generally artificially synthesized materials that have the constituent phases or grain structures modulated on a length scale less than 100 nm [1]. A unit layer of montmorillonite (TOT, 2:1) has two silica tetrahedral (T) sheets bonded to a central alumina octahedral (O) sheet. Montmorillonite powders are formed by the agglomeration of TOT layers whose thicknesses vary between 0.96 and 1.5 nanometer and whose widths vary between tens to hundreds of nanometers. Montmorillonite crystals carry a charge arising from isomorphous substitutions of certain atoms in their structure for other atoms of a different valence. When this is the case, a charge deficiency results and a negative potential at the surface of the crystal is created. This negative charge neutralized by cations (such as calcium, sodium or magnesium) are held at the interlayer spaces [2]. Prevalent crystal structure of montmorillonite is shown in figure (