Silicates Phyllo

In addition to the inorganic hydroxyl groups which are exposed on many mineral surfaces (metal oxides, phyllo-silicates and amorphous silicate minerals) we need to consider the particular features relating to charge on the silica surfaces of layer silicates. 

In conclusion, exfoliated sheets of Mg-phyllo(organo)silicates containing pendant amino groups have been used to stabilize Au, Ag, Pd and Pt nanopartides. The nanoparticle-decorated day sheets can be easily dispersed in water. These metal nanopartides... 

Clay minerals are hydrous layer silicates of colloidal dimensions, with most if not all of the individual platy particles in the colloidal range of c. 1 nm-1 pm (van Olphen, 1976 Van Damme et al., 1985). The term phyllosilicate (phyllo = leaf like) is applied to the broad group of hydrous silicates with layer structures. The essentia] components of the phyllosilicate structure are two-dimensional tetrahedra and octahedra of oxygen atoms (or ions). The coordinating atoms (or cations) in the centre of the tetrahedra are for the most part Si, but Al3 or Fe3+ may also be present. The coordinating cations in the octahedra are usually Al3, Mg2+, Fe3 or Fe2. Some clay structures (e.g. hectorite) can be synthesized in a reproducible and relatively homogeneous form. 

Mineralogica1 structural types may have an effect on silica release rates as has been mentioned earlier. That is, isolated silica tetrahedra and small units (neso-, soro-silicates) release silica more quickly than single or double chains (ino-silicates) which in turn are more reactive than three dimensionally linked tetrahedra (tec to-silicates) or tetrahedra arranged in sheets (phyllo-silicates). But such structures are not the only cause for variations in silica release rates. 

Other lines of textural evidence, however, stiU provide support for asteroidal alteration of the Cl chondrites. These include (i) crosscutting phyllo-silicate-rich veins (Tomeoka, 1990) and (ii) the presence of carbonates that appear to represent fragments of an earlier generation of carbonate veins or resemble vein fillings (Richardson, 1978 Endress and Bischolf, 1996). 

The octahedral occupancy distinguishes these verdine facies or odinite minerals from other sedimentary and in fact all metamorphic phyllo-silicate minerals. These relations are clearly demonstrated by Hornibrook and Longstaffe (1996). 

A, which is relative to twice the gallery expansion by two layers of polymer. Figure 16.21 shows structural arrangement of PEO intercalated into phyllo-silicate (montmorillonite). Other organic components such as crown ethers can also be used. This is an example that ionic structures can be regularly located within the structure of the composite. These ionic structures can be useful in ion selective sen-... 

Fig. 3. Correlation of the 5 CS tensor components of Si nuclei in silicate compounds with the bond lengths of the Si -O bonds directed along the axially symmetric tensors. Only compounds with nearly or fully axially symmetric chemical shift tensors are included. The values of Grimmer are supplemented with additional data from Heidemarm [1 Calcio-Chondrit (100 ppm, 1.62 A) 2 a-Di-Calcium-Silicate-Hydrate (14 ppm, 1.69 A) 3 Phyllo-Silic-Acid (115 ppm, 1.59 A) 4 Dellait (54 ppm, 1.694 A)].

The molecular structure of liquid water is not yet a precise quantitative concept despite the many studies carried out using the methods indicated in Fig. 2.1. What has emerged from these studies over the past dozen years is a firm qualitative—or perhaps semiquantitative—picture of the I, V, and D structures that is reasonably self-consistent and sufficiently detailed to serve as a basis for interpreting data on aqueous solutions and phyllo-silicate suspensions. 

FIGURE 19 SEM image of intact (A) and broken (B) hollow spheroids of synthetic Mg-phyllo(hexadecyl)silicate prepared by microemulsion methods. Scale bar represents 20 microns. (From Ref. 228.)... 

The stratified structure results by the unlimited association of the bands. In these structures the tetrahedra are united through three common comers, the 0 Si ratio being equal to 2.5. The stmctural types of phyllo-silicates can be subdivided after the symmetry of the lattice s closures for the resulted planes and after the number of the layers that are framed by the cations which ensure the cohesion between the layers by ionic bonds. 

FIGURE 4.47 (a) Tetragonal and (b) hexagonal types of stratified phyllo-silicates structures after The Chemistry of Silicates (2003). 

FIGURE 4.48 The structure of (a) kaolinite (b) talcum phyllo-silicates after (Bunn 1954 Evans 1964 Knox and Gold, 1964 Ramachandran, 1964). 

Langasite is a kind of materials with framework structure without inversion symmetry i. quartz and BeO are also framework structure which is formed mainly by a covalent bond such as Si04, AIO4, Zn04. Especially, silicates including lanj ite make many framework structures by connection of Si04 tetrahedra as cydo-, ino-, phyllo-, and tecto-silicates. These framework structures are noticed recently for appHcations on many kinds of properties such as zeolite for optical properties by absorption of special compwimds. 

Subclasses also exist and the most useful ones are probably the neso-, soro-, cyclo-, ino-, phyllo-, and tecto-silicates which give some indication of the state of polymerization of SiOt tetrahedra into rings, chains, bands, sheets, networks, and so forth. 

Gutscher et al. (1989) Gutscher, D. Miihlethaler, B Portmann, A. Reller, A. Conversion of azurite into tenorite Studies in Conservation 34 (1989) 117-122 GCven (1988) Giiven, N. Smectites In Hydrous Phyllo-silicates. Reviews inMineralogy, Mineralogical Society of America (1988) 497-552... 

The turbostratic arrangement (X-ray line diagrams) confirms that the examined phyllo-silicate belongs to the group of smectites. In effect, no other phyllosilicates with turbostratic structure are known. 

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