Properties of Clays

Copolymer of anionic and cationic monomers Acrylic acid, methacrylic acid, 2-acrylamido-2-methyl-propane sulfonic acid  

Water-soluble polymers with sulfosuccinate derivative-based [42,46] 

The unit layers stack together face-to-face and are held in place by weak attractive forces. The distance between corresponding planes in adjacent unit layers is called the c-spacing. A clay crystal structure with a unit layer consisting of three sheets typically has a c-spacing of about 9.5 X 10 mm. 

In clay mineral crystals, atoms having different valences commonly will be positioned within the sheets of the structure to create a negative potential at the crystal surface. In that case, a cation is adsorbed on the surface. These adsorbed cations are called exchangeable cations because they may chemically trade places with other cations when the clay crystal is suspended in water. In addition, ions may also be adsorbed on the clay crystal edges and exchange with other ions in the water. 

Two types of swelling may occur. Surface hydration is one type of swelling in which water molecules are adsorbed on crystal surfaces. Hydrogen bonding holds a layer of water molecules to the oxygen atoms exposed on the crystal surfaces. Subsequent layers of water molecules align to form a quasi-crystalline structure between unit layers which results in an increased c-spacing. All types of clays swell in this manner. 

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The multitude of variation in clay minerals is caused by substitution in the octahedral and tetrahedral layers resulting in charge deficits. The manner in which the charge deficit is balanced leads to many of the useful and unique properties of clay minerals. 

Clay particles are so finely divided that clay properties are often controlled by the surface properties of the minerals rather than by bulk chemical composition. Particle size, size distribution, and shape the nature and amount of both mineral and organic impurities soluble materials, nature, and amount of exchangeable ions and degree of crystal perfection are all known to affect the properties of clays profoundly. 

Rosenqvist, I. T. (1962). The influence of physicochemical factors upon the mechanical properties of clays. Proc. 9th Nat. Conf. on Clays and Clay Minerals, pp. 12-27. 

Theng, B.K.G. 1979. Formation and properties of clay-polymer complexes. Amsterdam. 

Theng, BKG, Eormation and Properties of Clay-Polymer Complexes, Elsevier, New York, 1979. 

Colloid and Surface Properties of Clays and Related Minerals, Rossman F. Giese... 

As for the drying properties of clay-water mixtures when wet clay dries at ambient temperature, the water of plasticity that surrounds the particles... 

Common ancient ceramic materials often found in archaeological excavations, such as fired brick and pottery, were made mostly from a mixture of a secondary clay and fillers. The nature, composition, and properties of clay have been already discussed the nature of the fillers, the changes undergone by the clay as well as by the fillers during their conversion to ceramics, and the unique properties of ceramic materials, are reviewed in the following pages. Attention is drawn also to studies that provide information on the composition and characteristics of ancient ceramic materials. 

A combination of SIPS with the stabilising and synthesis-favouring properties of clay minerals was studied by Rode et al. (1999) in experiments involving dry/wet cycles. The simultaneous use of both SIPS and clay minerals as catalytically active surfaces led to peptides up to and including the hexamer (Gly)6. The question as to whether this technique fulfils prebiotic conditions can (within certain limitations) be answered positively, since periodic evaporation phases in limited areas (lagoons, ponds) are conceivable. The container material could have consisted of clay minerals. Further progress in the area of peptide synthesis under conditions which could have been present on the primeval Earth can be expected. 

The discovery of the working properties of clays must have resulted in one of humankind s first expressions of representational art, roughly contemporaneous with the discovery of the colouring properties of natural pigments and their use in cave art. The additional discovery that the result of the manipulation of this art form could be rendered permanent by the use of fire must indeed have been a source of wonder. The earliest fired ceramic so far known is a small moulded figurine from Dolni Vestonice in what was Czechoslovakia, dated to approximately 26000 years BP (Vandiver et al., 1989). By approximately 10000 years ago, simple utilitarian vessels were being produced in the Near and Far East. 

A method [62] has been described for the determination of down to 2.5pg kg-1 alkylmercury compounds and inorganic mercury in river sediments. This method uses steam distillation to separate methylmercury in the distillate and inorganic mercury in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet digestion with nitric acid and potassium permanganate [63]. The well known adsorptive properties of clays for alkylmercury compounds does not cause a problem in the above method. The presence of humic acid in the sediment did not depress the recovery of alkylmercury compounds by more than 20%. In the presence of metallic sulphides in the sediment sample the recovery of alkylmercury compounds decreased when more than lmg of sulphur was present in the distillate. The addition of 4M hydrochloric acid, instead of 2M hydrochloric acid before distillation completely, eliminated this effect giving a recovery of 90-100%. 

Simple Models. The surface chemical properties of clay minerals may often be interpreted in terms of the surface chemistry of the structural components, that is, sheets of tetrahedral silica, octahedral aluminum oxide (gibbsite) or magnesium hydroxide (brucite). In the discrete site model, the cation exchange framework, held together by lattice or interlayer attraction forces, exposes fixed charges as anionic sites. 

Theng, B.K.G. Formation and Properties of Clay-Polymer Complexes" Developments in Soil Science, Vol. 9) Elsevier, Amsterdam, 1979 ch. 12, pp. 283-326. 

Catalytic properties of clay-particle-incorporated a- 704 Fe203 were investigated in the photodecomposition of saturated carboxylic acids... 

From a morphological point of view, there are four fundamental parameters that can be adjusted to maximize the barrier properties of clay nanocomposites. 

That clay is an extremely important raw material will be clear from the fact that chapter 8 is entirely devoted to it. This chapter explains how clay is formed in nature, which composition it has, the structure of important clay minerals and the properties of clay. One property is highlighted here and that is the very varied composition of clay and the relatively large number of substances - apart from the clay minerals - which are present in clay. For most products made of clay the complex composition of this clay poses no problems in the production process nor for the final product properties. In this respect, these... 

In Chapter 4 we learned how silicates give clay its plastic properties. In this chapter we will see how carbon atoms bond in chain arrangements to produce organic compounds that can have the plastic properties of clay. We will study sculpture and describe molecular forms as sculptures. Finally, we will see how organic molecules, microscopic sculptures, have the same properties as macroscopic sculptures, which are visible to the naked eye. 

Clay Minerals and Clay Colloids. The literature on clays and clay colloids is expansive, but there remains a degree of uncertainty in many areas of their study due to their inherent heterogeneity. Descriptions of the structures and properties of clay minerals can be found in Grim (1968), Brindley and Brown (1980), Newman and Brown (1987), Sposito et al. (1999), and Giese and van Oss (2002). 

Giese R. F., and van Oss, C. J. (2002). Colloid and Surface Properties of Clays and Related Minerals, Marcel Dekker, New York. 

Harrington, J.F. and Horseman, S.T. (1999) Gas transport properties of clays and mudrocks. In Geological Society, Special Publications, London, pp. 107-124... 

Brown, K.W. Shrinking and Swelling of Clay, Clay Strength, and Other Properties of Clay Soils and Clays in Minerals in Soil Environments, Dixon, J.B. Weed, S.B., Eds., Soil Sd. Soc. Amer. Madison, 1977, pp. 689-707. 

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