Structure studies layered clay minerals

The best formed plate textures are found in crystals with a layer lattice, and generally in all crystals having the form of thin plates. Diffraction pattern (Fig.7) indicates a texture of this type, and was obtained from crystals in the shape of thin hexagonal plates. The specific role of the oblique-texture type electron diffraction patterns have in the study of clay minerals having layer structures (B.B.Zviagin, 1964, 1967). 

Incorporation of nanofrllers into polymer matrix has been proved to be a powerful tool in order to increase the polymer properties (Lin et al. 201 la, b). It is widely accepted that addition of nanofrller into bio-based matrixes in order to fabricate nano-biocomposite materials could be a powerful solution to improve these properties (Alexandre and Dubois 2000 Bordes et al. 2009 Sinha Ray and Okamoto 2003). Studies on mbular silica-based naturally occurring nanoparticles as reinforcing material is still new (Ismail et al. 2008 Prashantha et al. 2011). Halloysite particles are readily obtainable and are much cheaper than other nanoparticles such as CNTs. More importantly, the unique crystal structure of HNTs resembles that of CNTs, and therefore halloysite particles may have the potential to provide cheap alternatives to expensive CNTs because of their mbular stmcture in nanoscale. Moreover, due to its similarity to other layered clay minerals such as MMT, halloysite has the potential to be further intercalated or exfoliated chemically or physically (Tang et al. 2011). 

Many studies have been made of the rates of water evolution from layer-type silicate minerals which contain structural hydroxyl groups (clays and micas). Variations in composition of mineral specimens from different sources hinders comparison of the results of different workers. Furthermore, the small crystallite sizes and poor crystallinity that are features of clays limit and sometimes prevent the collection of ancillary observations (e.g. microscopic examination and diffraction measurements). 

Based on the study of expanding clay minerals, two models of water adsorbed on silicate surfaces have been proposed. One states that only a few layers (<5) of water are perturbed by the silicate surface, the other concludes that many layers (perhaps 10 times that number) are involved. The complexity of the interactions which occur between water molecules, surface adsorbed ions, and the atoms of the silicate mineral make it very difficult to unequivocally determine which is the correct view. Both models agree that the first few water layers are most perturbed, yet neither has presented a clear picture of the structure of the adsorbed water, nor is much known about the bonding of the water molecules to the silicate surface and to each other. 

Our approach has been to study a very simple clay-water system in which the majority of the water present is adsorbed on the clay surfaces. By appropriate chemical treatment, the clay mineral kao-linite will expand and incorporate water molecules between the layers, yielding an effective surface area of approximately 1000 m2 g . Synthetic kaolinite hydrates have several advantages compared to the expanding clays, the smectites and vermiculites they have very few impurity ions in their structure, few, if any, interlayer cations, the structure of the surfaces is reasonably well known, and the majority of the water present is directly adsorbed on the kaolinite surfaces. 

In conclusion thermal degradation studies on Nautilus pompilius indicate that mineralizing matrix and aragonite shell represent a true structural entity. By the sharing of oxygens in protein and mineral lattices we will generate phase boundaries of the type that are present, for instance, in the common clay mineral kaolinite. Here, aluminum octahedra and silica tetrahedra incorporate the same oxygens and hydroxyls, and layers composed of octahedra and tetrahedra arise (Fig. 13). 

Teppen et al. [89] have used a flexible model for clay minerals that allows full movement of the M-O-M bonds in the clay structure, where M represents Si, Al, or other cations in the octahedral sheet. This model was used in MD simulations of interactions of hydrated clay minerals with trichloroethene [90, 91]. The simulations suggest that at least three distinct mechanisms coexist for trichloroethene sorption on clay minerals [90], The most stable interactions of trichloroethene with clay surfaces are by full molecular contact, coplanar with the basal surface. The second type more reversible, less stable is adsorption through single-atom contact between one chlorine atom and the surface. In a third mechanism, trichloroethene interacts with the first water layer and does not interact with clay surface directly. Using MC and MD simulation the structure and dynamics of methane in hydrated Na-smectite were studied [92], Methane particles are solvated by approximately 12-13 water molecules, with six oxygen atoms from the clay surface completing the coordination shell. 

The montmorillonite (Chapter 1, Table 1.2) clay mineral can be used as a model substance in the study of the interfacial processes of rocks and soils. It is a layer silicate, a member of the smectite group. Its structure is appropriate for modeling the most important interfacial processes in geological formations. Besides, it is a fairly widespread mineral in rocks and soils, and plays an important role in the nutrient cycle of soils. In addition, it has many agricultural, industrial, and environmental applications. 

Illite as a non-swelling clay mineral of layer structure plays a very important role in our studies. This special role is due to the fact that both sides of the surface of the silicate lamellae are made up of Si04-tetrahedron planar lattices, and this structure - even when hydrophobized - is identical with the surface structure of montmorillonite and vermiculite, both of which are of the swelling type. 

Tsipursky SI, Drits VA (1984) The distribution of octahedral cations in the 2 1 layers of dioctahedral smectites studied by oblique-texture electron diffraction. Clay Minerals 19 177-193 Tsipursky SI, Kameneva MYu, Drits VA (1985) Structural transformations of Fe -containing 2 1 dioctahedral phyllosihcates in the course of dehydroxylation. 5th Meet Eur Clay Groups, Prague, p 569-577... 

Trioctahedral Chlorite. This is encountered in virtually all fine-grained fractions of the sections studied. There are no swelling layers in the structure of this mineral which exhibits a high degree of crystallinity. The d(o6o) reflex at 1.532 A indicates that the chlorite is trioctahedral. There are no mixed-layer clays of the chlorite-montmorUlo-nite type, nor swelhng chlorites nor, in view of the lack of any other structure, any minerals containing hydrate-sheets between their layers. 

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