Clays general structure

The clay fraction, which has long been considered as a very important and chemically active component of most solid surfaces (i.e., soil, sediment, and suspended matter) has both textural and mineral definitions [22]. In its textural definition, clay generally is the mineral fraction of the solids which is smaller than about 0.002 mm in diameter. The small size of clay particles imparts a large surface area for a given mass of material. This large surface area of the clay textural fraction in the solids defines its importance in processes involving interfacial phenomena such as sorption/desorption or surface catalysis [ 17,23]. In its mineral definition, clay is composed of secondary minerals such as layered silicates with various oxides. Layer silicates are perhaps the most important component of the clay mineral fraction. Figure 2 shows structural examples of the common clay solid phase minerals. 

The maximum amount of Fe2+ the octahedral sheets of the 2 1 dioctahedral clays generally contain is 12% (Fig.26). This is equivalent to approximately 0.25—0.30 octahedral positions. Due to the relatively large size of the Fe2 + ion, the structure can apparently adjust to only about half as much Fe2+ as Mg. 

Figure 1. Generalized structure of a 2 1 phyllosilicate (e.g., smectite clay). There are two different octahedral sites corresponding to cis-M04(0H)2 and trans-MO OH. (Modified from Grimm, R.E. "Clay Mineralogy" McGraw-Hill, 1968).

Forming techniques used for clay-based ceramics require control of water content in the batch. Water content, in turn, affects the response of the clay during forming [27], As the water content of the batch increases, the yield point of the clay-water mixture, and thus the force required to form the desired shape, generally decreases [26], However, the relationship is complex and depends on the composition of the clay, its structure, additives to the batch, and other factors [14], One method for quantifying the behavior of clay-water pastes is to measure the plastic yield point as a function of water content [14], The water contents and maximum yield points in torsion are compared for several clays in Table 9. Kaolins and plastic fire clays require the least amount of water to develop their maximum plasticity, ball clays require an intermediate amount, and bentonite requires the most. 

Hitherto the most successful pillaring has been carried out on smectite type clays. The original research on pillaring included several series of unsuccessful experiments on mica, vermiculite and the sheet silicic acid minerals magadiite, silhydrite and kenyaite. Recently renewed attention has focused on these and other alternative sheet structures. They include rectorite, zirconium phosphates, tetrasilicic micas, hydrotalcites and silicic acids, the general structural features of which are shown in Figure 4. 

A number of factors can influence the amount of exchangeable ammonium in soils. Soil porosity, clay mineral structure, presence of other cations, and organic matter content are a few examples. The cation concentration of freshwater wetlands is generally lower than that of coastal wetlands and would result in higher partition coefficients in freshwater wetlands relative to coastal wetlands. 

General structure of smectite clays and their properties... 

Figure 8.1 Generalized structures of Montmorillonite clay in polymeric composites...

As an adjective applied to metals base represents the opposite of noble, i.e. a base metal would be attacked by mineral acids, base exchange An old term used to describe the capacity of soils, zeolites, clays, etc. to exchange their cations (Na, K, Ca ) for an equivalent of other cations without undergoing structural change. An example of the general process of ion exchange. ... 

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