Hectorite structural formulas

Chemical analyses and structural formulas of stevcnsite and hectorite samples... 

Figure 1. The hectorite structure, an idealized, unit cell formula being Na0.tr [Lit., Mg,.st](Sig. )0,c(0H,F)t. Key O, oxygen , OH and occasionally fluoride. The tetrahedral sites are occupied mainly by silicon magnesium and lithium occupy the octahedral sites.

Hectorite is the trioctahedral equivalent of montmorillonite and owes its charge to octahedral replacements of Mg by Li. The structural formula is... 

Mostly focused on cationic clays, and particularly on montmorillonite and hectorite, smectite-type layered silicates and clay-based nanofillers have recently been extended to the family of LDH. Hydrotalcite-like LDH materials are described according to the ideal formula, [M1/ xM"l(OH)2]frl(lra [A H20]inter, where Mn and Mm are metallic cations, A the anions, and intra and inter denote the intralayer and interlayer domain, respectively. The structure consists of brucite-like layers constituted of edge-sharing octahedra. The presence of trivalent cations induces positive charges in the layers that are counterbalanced by interlamellar anions (Scheme 15.16). 

Montmorillonite, hectorite, and saponite are the most widely investigated clays. Their structure and formula are shown in Figure 9.1 and Table 9.1, respectively. Montmorillonite is a very popular choice for nanocomposites because of its small particle size (<2 pm) and hence the easy diffusion of polymer into the clay particles. They also have high aspect ratios (10-2000) and high swelling capacity, which are essential for efficient intercalation of the polymer. The physical mixture of a polymer and a clay may not form a nanocomposite. This situation is analogous to that in a polymer blend, and separation into discrete phases takes place in most cases. Pristine clay usually contains hydrated Na+ or K+ ions. Obviously,... 

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