Clay properties Kaolinite, Montmorillonite

The typical clay minerals—kaolinite, montmorillonite, etc.—have microscopic plate-Uke structures which are believed to be chiefly responsible for their plasticity (formabihty) when wetted with water. Other important properties (1) hardening when dried and permanency when fired (2) shrink-... 

Of special significance with respect to their properties as sorbents are the clay minerals (e.g. kaolinite, montmorillonite, vermiculite, illite, chlorite), mainly due to their high exchange capacity. 

Clay minerals are aluminium silicates of either the two-layered kaolinite type or threelayered montmorillonite type. Only three clay minerals are commonly used in the polymer industries, kaolinite, montmorillonite and chlorite, and these will be discussed below. Chlorite, because it usually occurs with talc and has essentially the same properties, is discussed with that mineral. Talc (magnesium silicate) is widespread but is commonly found with other magnesium minerals such as magnesite. 

Application of the model to clay-solution aggregates showed that the radiofrequency dispersions of these systems at 10-50 MHz are fairly well described by the model. These dispersions were found to depend on the clay type (kaolinite, illite, montmorillonite), degree of consolidation, and soil fabric these properties are reflected in the values of the geometrical parameters and of the dielectric constant of the solid which fit the dispersion curves best. 

Montmorillonite clays absorb water readily, swell greatly and confer highly plastic properties to a soil. Thus soil stress (Section 14.8) occurs most frequently in these soils and less commonly in predominantly kaolinitic types. Similarly, a soil high in bentonite will show more aggressive corrosion than a soil with a comparable percentage of kaolinite. A chalky soil usually shows low corrosion rates. Clay mineralogy and the relation of clays to corrosion deserves attention from corrosion engineers. Many important relationships are not fully understood and there is need for extensive research in this area. 

Numerous forms of laminations in clay-based ceramic products as - opposed to oxide and non-oxide ceramics - are influenced by the specific properties of the clay minerals. Such clay minerals as kaolinite, halloysite, montmorillonite or illite are finely dispersed, from approx. 5 to 1000 nm, and consequently have a large specific surface of approx. 5 to 100 vo g, and are furthermore of an anisometric morphology, having the geometric shape of lamella, little rods, strips, etc. 

Layer-type silicates with base exchange or intercalation properties are represented by well-known clay minerals such as kaolinite, Al2Si205(0H)4, and montmorillonite, Al, ( 7Mgo 338140,0 (OH)2-Nao.33 (Figure 5.55). 

Clay deposits are composed principally of fine quartz and clay minerals. The three major clay minerals are kaolinite, illite and montmorillonite. Both kaolinite and illite have non-expansive lattices, whereas that of montmorillonite is expansive. In other words, montmorillonite is characterized by its ability to swell and by its notable cation exchange properties. 

---