Mica types

Weiss A (1963) Mica-type layer silicates with alkylammonium ions. Clays Clay Miner 10 191-224... 

PDMS nanocomposites with layered mica-type silicates were also reported.374 A two-step sol-gel process of the in situ precipitation of silica led to the development of siloxane-based nanocomposites with particularly high transparencies.3 5 Some unusual nanocomposites prepared by threading polymer chains through zeolites, mesoporous silica, or silica nanotubes were reviewed.3 6 Poly(4-vinylpyridine) nanocross-linked by octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane was reported.377... 

If mica-type sites are truly indicative of mica surfaces, and so on for montmoril Ionite etc., then of the clays examined, only the mica could be regarded as pure. The Montana vermiculite contained much montmoril Ionite, the Fithian illite contained mica and montmoril Ionite, the Wyoming bentonite contained some mica,... 

A. Weiss, Organic derivatives of mica-types layer silicates, Angew. Chem. Internat. Edit, vol. 2, pp. 134-143,1963. 

If we now consider the bulk compositions of the mixed-layered minerals which contain both expandable and non-expandable layers, two series are apparent, one between theoretical beidellite and illite and one between theoretical montmorillonite and illite (Figure 25). The intersection of the lines joining muscovite-montmorillonite and beidellite-celadonite (i.e., expandable mineral to mica), is a point which delimits, roughly, the apparent compositional fields of the two montmorillonite-illite compositional trends for the natural mixed layered minerals (Figure 26). That is, the natural minerals appear to show a compositional distribution due to solid solutions between each one of the two montmorillonite types and the two mica types—muscovite and celadonite. There is no apparent solid solution between the two highly expandable (80% montmorillonite) beidellitic and montmorillonitic end members. The point of intersection of the theoretical substitutional series beidellite = celadonite and muscovite-montmorillonite is located at about 30-40% expandable layers— 70-60% illite. This interlayering is similar to the "mineral" allevardite as defined previously. It appears that as the expandability of the mixed... 

Vaia, R. A., Vasudevan, S., Krawiec, W., Scanlon, L. G., and Giannelis, E. P. New polymer electrolyte nanocomposites Melt intercalation of poly(ethylene oxide) in mica-type silicates, Adv. Mater. (1995), 7, 154-156. 

In the case of mica-type layered silicates it has been recently demonstrated that nanocomposites (both intercalated and delaminated) can be synthesized by direct melt intercalation even with high molecular weight polymers [7-18]. This synthetic method is quite general and is broadly applicable to a range of commodity polymers from essentially non-polar polystyrene, to weakly polar polyethylene terephthalate), to strongly polar nylon. Nanocomposites can, therefore, be processed using currently available techniques such as extrusion, thus lowering the barrier towards commercialization. 

Table 1. Structure and chemistry of Mica-type layered silicates...

Intercalation of electroactive polymers such as polyaniline and polypyrrole in mica-type layered silicates leads to metal-insulator nanocomposites. The conductivity of these nanocomposites in the form of films is highly anisotropic, with the in-plane conductivity 10 to 10 times higher than the conductivity in the direction perpendicular to the film. Conductive polymer/oxide bronze nanocomposites have been prepared by intercalating polythiophene in V2O5 layered phase, which is analogous to clays. °° Studies of these composites are expected not only to provide a fundamental understanding of the conduction mechanism in the polymers, but also to lead to diverse electrical and optical properties. 

Swelling mica-type clay minerals composed of octahedral and tetrahedral sheets are widely utilized in preparing two-dimensional heterostructural nanohybrids, most likely because of their natural ubiquity, high stability, swelling property, and wide applications. In fact, smectite and vermiculite groups have been the preferred layer components to be hybridized with a variety of inorganic and organic components. 

The immobilization of metal complex catalysts on polymers and inorganic oxides has received considerable attention as a means of combining the best advantages of homogeneous and hetereo-geneous catalysis (1-6). The swelling layer lattice silicates known as smectite clay minerals have added an important new dimension to metal complex Immobilization. These compounds have mica-type structures in which two-dimensional silicate sheets are separated by monolayers of alkali metal or alkaline earth cations (7). The structure of a typical smectite, hectorite, is illustrated in Figure 1. 

Barshad, I., 1950. The effect of interlayer cations on the expansion of the mica type of crystal lattice. Am. Mineral., 35 225—238. 

An organically modified mica-type silicate (OMTS) was prepared by an ion-exchange reaction from MMT and bis(2 hydroxy ethyl) methyl tallow - alkyl am-... 

Figure 68 Schematic representation of the modifioation of mica-type siiicate minerai to aiiow the intercaiation of a Ziegler-Natta oiefin poiymerization cataiyst preoursor.

Clays with mica-type lattices, especially vermiculite and illite, can also react with many organic compounds to form complexes in which the organic substance is held in the clay lattice. The rate of reaction with vermiculite is fairly rapid but very slow with illite and mica. Differences in behavior of these minerals has been attributed to surface area and to the density of charge on the surface. 

The crystal structure of a natural sample of a 2M2 lepidolite (a mica-type mineral) from the island of Elba (Italy) has been determined by singlecrystal X-ray diffraction techniques and compared with that of a second 2M2 lepidolite from Rozna (Czechoslovakia) and other related structures. The two sets of unit-cell parameters are collated in Table 38. The most interesting features which emerge from the comparison are the constant presence of remarkable octahedral ordering and the almost identical composition of the tetrahedral sheets (Elba Si3 3oAlo.64 Rozna Sis soAlo.ei)... 

V. Mehrotra and E.P. Giannelis, Metal-insulator molecular multilayers of electroactive polymers intercalation of polyaniline in mica-type layered silicates. Solid State Commun., 11, 155-158 (1991). 

During the ablation experiment, temperature within the char layer exceeds 1000°C and approach 2000-2500°C at the surface. At these temperatures, any carbonaceous residue from the pol3oner will contain graphite. Additionally, mica-type layered silicates, such as montmorillonite, irreversibly transform into other aluminosilicate phases. Between 600 and 1000 C, montmorillonite dehydroxylates and has been observed to initially transform into spinel, cristobolite, mullite and/or pyroxenes (enstatite) (24). At temperatures greater than 1300 C, mullite, cristobolite and cordierite form and subsequently melt at temperatures in excess of 1500 C (mullite 1850 C, pure cristobolite 1728°C and cordierite --ISSO C) (25). The presence of an inorganic that transforms into a high viscosity melt on the surface of the char will improve ablation resistance by flowing to self-heal surface flaws. This is known to occur in silica-filled ablatives (26). 

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