Aluminosilicate layers

Clay mineral A layered aluminosilicate, such as kaolinite, dUte, chlorite, and montmordlonite. Most are formed by chemical weathering of rocks on land. 

Advantage has also been taken of dispersed clays to host small particles [478]. Montmorillonite clays are colloidal, layered aluminosilicates with ex-... 

Ukrainczyk, L., Chibwe, M., Pinnavaia, T.J. Boyd, S. A. (1994). ESR study of cobalt(II) tetrakis(N-methyl-4-pyridiniumyl)porphyrin and cobalt(II) tetrasulfophthalocyanine intercalated in layered aluminosilicates and a layered double hydroxide. Journal of Physical Chemistry, 98, 2668-76. 

Layered aluminosilicates catalyze chemical reactions in various ways. They stabilize high-energy intermediates, store energy in their lattice structures and catalyze redox reactions (ref. 1). They often exhibit high surface acidity (ref. 2). 

Pyrophyllite is the simplest layer aluminosilicate in which two tetrahedral Si04 layers are condensed on to the octahedral A106 layer to produce a three-sheet layer, the composition of the unit cell being [Al2(OH)2(Si205)2]2. Another ideal structure in which A1 is replaced by Mg is that of talc. In both cases the three-sheet layer is electrically neutral and the layers are stacked in the ABAB... sequence. Because of the cohesive strength of this ideal structure, neither pyrophyllite nor talc occurs in the form of the very fine particles which generally characterize clay minerals. 

BOX 1,1 Demonstration of the Nature of Inter-lamellar Bonding within Double Layer Aluminosilicates... 

Layered aluminosilicates include the micas and clay minerals they share the characteristic of having alternating layers of a gibbsite-like aluminol sheet and a silicon oxide (silanol) sheet, but differ in the stacking of these sheets, the presence of additional cations in various structural locations, and the amount of structural water and hydroxyl groups. By virtue of analogy with amorphous silica and quartz, the silanol sheets are not... 

Clay A particle less than 0.002 mm in effective diameter, (b) a soil containing a large quantity (> 40%) of clay-sized particles, (c) an inorganic particle generally as a layered aluminosilicate but may be flbrous or amorphous. 

Abstract Clays are ubiquitous constituents of the Earth s crust that serve as raw materials for traditional ceramics. Mineralogically, clays are phyllosilicates or layered aluminosilicates. Bonding is strong within layers, but weak between layers, allowing clays to break into micrometer-sized particles. When mixed with water, clays develop plasticity and can be shaped easily and reproducibly. When heated, clays undergo a series of reactions that ultimately produce crystalline mullite and a silica-rich amorphous phase. Beyond the structure and properties of clays, the science that developed to understand traditional ceramics continues to serve as the framework for the study of advanced ceramics. 

Surface area of the layer aluminosilicates available for adsorption of the reactants and the hydroxyl groups present on the surface contributing to the acidity, decide how successfully they can function as solid acids for catalysis. Consequently the study of surface acidity and its modification has attracted considerable attention. The effect of treatment of the clay with mineral and organic acids i.e., acid... 

Layered aluminosilicates are the most important secondary minerals in the clay fraction of soils. When layer silicate minerals are clay or colloidal size (<2 gm effective diameter), their large surface area greatly influences soil properties. Most of the important clay minerals have similar silicate structures. Inasmuch as clay minerals are such important clay components, and as different clay minerals can change sail properties greatly, an understanding of soil properties begins with an understanding of silicate structures. 

The wide assortment of polymer systans (polypropylene, poly(methyl methacrylate) [PMMA], polyepoxide, polystyrol, PC, etc.) is used as a polymeric matrix for nanocomposites production (Ray and Okamoto 2003). The most well-known fillers of polymeric matrix are nanoparticles (silica, metal, and other organic and inorganic particles), layered materials (graphite, layered aluminosilicates, and other layered minerals), and fibrous materials (nanofibers and nanotubes) (Thostenson et al. 2005). Nanocomposite polymer materials containing metal or metal oxide particles attract growing interest due to their specific combination of physical and electric properties (Rozenberg and Tenne 2008, Zezin et al. 2010). Nanocomposites on the base of layered materials... 

Both the nanocomposites prepared by in-situ polymerization of 2-ethnyl-pyridine (2Epy) in the presence of a layered aluminosilicate such as Ca + -... 

H. Liu, D.W. Kim, A. Blumstein, J. Kumar, and S.K. Tripathy, Nanocomposite derived fi"om intercalative spontaneous pol3fmerization of 2-eth3fnylpyridine within layered aluminosilicate montmorillonite, Chem. Mater., 13, 2756-2758 (2001). 

A new composite material was introduced in 1987 with the discovery of a nylon-6/clay hybrid (NCH) [201]. The hybrid was prepared by the in situ thermal polymerization of s-caprolactam with 8% or less montmorillonite, the clay material containing 1-nm thick exfoliated aluminosilicate layers. It exhibited a truly nanometer-sized composite of nylon-6 and layered aluminosilicate. Figure 2.14 depicts conceptually the NCH synthesis and its fine structure. The NCH exhibited high modulus, high strength, and good gas-barrier properties. The unique and superior properties led to the commercialization of NCH. It has also created a new class of nanocomposites and worldwide interest. 

Clays are colloidal layered hydrous aluminosilicates. There are relatively few examples of porphyrin intercalation into clays reported, mostly with either smectite clays or layered double hydroxides (LDH). Smectite clays consist of negatively charged layered aluminosilicate sheets. These sheets are separated by cations and water molecules. The... 

Three different types of nanomaterials, based on their dimensional characteristics, are generally used to prepare polymer nanocomposites. These include nanomaterials with only one dimension in the nanometre range (e.g. nano-clay), those with two dimensions in the nanometre scale (e.g. carbon nanotubes) and those that have all three dimensions in the nanometre scale (e.g. spherical silver nanoparticles), as stated earlier. Thus nanosize thin layered aluminosilicates or nanoclays, layer double hydroxide (LDH), a large number of nanoparticles of metals and their oxides, carbon nanotubes and cellulose nanofibres are used as nanomaterials in the preparation of vegetable oil-based polymer nanocomposites. 

Clay minerals are hydrous layered aluminosilicates. The aluminosilicate layer is composed of two types of sheets octahedral (0) and tetrahedral (T). Each sheet is composed of parallel planes of atoms, either oxygen or aluminum (silicon) in an alternating sequence. The large variability in the properties of clay minerals is related to the stacking sequence of the two basic types of sheets, T and 0, and to the uncompensated charge that develops by isomorphous substitution of unevenly charged cations. 

The state of research on MMT, which among the family of layered aluminosilicates is the most common mineral used in polymer/nanoclay hybrid materials, will be reviewed. MMT is constituted of stacks of hydrated aluminosilicate layers, whose crystal structure is composed of an octahedral alumina sheet sandwiched between two tetrahedral silica sheets (Figure 6A) The layers are separated by galleries where cations (e.g., Na+, K+) are present to balance the negative charge of the aluminosilicate sheets arising from isomorphic substitution of A1 or Si with other metals. 

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