Clays structural properties

As a function of their structural properties, clays interact differently with organic and inorganic contaminants. Two major groups of clay minerals are selected for discussion here (a) kaolinite, with a 1 1 layered structured aluminosilicate and a surface area ranging from 6 to 39 m g" (Schofield and Samson 1954) and (b) smectites with a 2 1 silicate layer and a total surface area of about 800m g" (Borchardt 1989). 

The nature of the interfacial structure and dynamics between inorganic solids and liquids is of particular interest because of the influence it exerts on the stabilisation properties of industrially important mineral based systems. One of the most common minerals to have been exploited by the paper and ceramics industry is the clay structure of kaolinite. The behaviour of water-kaolinite systems is important since interlayer water acts as a solvent for intercalated species. Henceforth, an understanding of the factors at the atomic level that control the orientation, translation and rotation of water molecules at the mineral surface has implications for processes such as the preparation of pigment dispersions used in paper coatings. 

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... 

A pottery glaze is a mixture of chemical compounds. When the glaze is heated, chemical changes take place. As a potter works with clay, the clay properties (its elasticity, its color, its texture) change as chemical changes take place within the clay structure. 

The above results are related to the structural properties of the clay minerals. In the case of kaolinite, the tetrahedral layers of adjacent clay sheets are held tightly by hydrogen bonds. Therefore, only readily available planar external surface sites exist for exchange. With smectite, the inner peripheral space is not held together by hydrogen bonds, but instead it is able to swell with adequate hydration and thus allow for rapid passage of ions into the interlayer. 

Provided in this chapter is an overview on the fundamentals of polymer nanocomposites, including structure, properties, and surface treatment of the nanoadditives, design of the modifiers, modification of the nanoadditives and structure of modified nanoadditives, synthesis and struc-ture/morphology of the polymer nanocomposites, and the effect of nanoadditives on thermal and fire performance of the matrix polymers and mechanism. Trends for the study of polymer nanocomposites are also provided. This covers all kinds of inorganic nanoadditives, but the primary focus is on clays (particularly on the silicate clays and the layered double hydroxides) and carbon nanotubes. The reader who needs to have more detailed information and/or a better picture about nanoadditives and their influence on the matrix polymers, particularly on the thermal and fire performance, may peruse some key reviews, books, and papers in this area, which are listed at the end of the chapter. 

In this chapter, an overview of the fundamentals of PNs is described, according to the author s understanding and experience as well as support from numerous references and review articles. The content of this chapter covers all kinds of inorganic nanoadditives, but, because the most widely investigated and thus understood nanoadditives used to enhance the thermal and fire resistance of the polymers are clays (natural or synthetic) followed by the CNTs and colloidal particles, the focus of the chapter is primarily on clays, particularly on the silicate clays and LDHs, as well as the CNTs. This includes structure, properties, and surface treatment of the nanoadditives, design of the modifiers, synthesis, characterization of the structure/morphology, and thermal and fire... 

R.K. Bharadwaj, A.R. Mehrabi, C. Hamilton, C. Trujillo, M. Murgs, R. Fan, A. Chavira, and A.K. Thomson, Structure-properties relationships in crosslinked polyester-clay nanocomposites, Polymer, 2002, 43 3699-3705. 

Note the relative concentrations of H+ ion and other cations as percents of the soil CEC values in Table 10.5. Important ions adsorbed on soils, but rarely measured, may include NH, and on waterlogged soils may also include Fe + and Mn. The data in Table 10.5 show that below about pH 5, protons occupy a large fraction of clay surface sites. Below pH 3 to 4, protons occupy all the sites and tend to destroy clay structures. This, of course, makes it difficult to study the surface and sorptive properties of clays in acid solutions. The proton competes effectively with other cations for exchange sites, even when its concentration is 10 to 100 times less than that of the cations. 

Significant replacement of monovalent metal cations on layer silicate clay surfaces by protons can occur if the electrolyte concentration is very low. The long-term result, beyond hydrolytic exchange, is acidic decomposition of the clay structure in part, and release of structural AP or Mg + to solution. These multivalent cations may then readsorb onto exchange sites, influencing the rheological properties of clays in very dilute salts. Some of the anomalous behavior of Na -smectites suspended in... 

Intercalated composites in an intercalated composite the insertion of polymer into the clay structure occurs in a crystallographically regular fashion, regardless of the clay to polymer ratio. An intercalated nanocomposite is normally interlayered by only a few molecular layers of polymer and properties of the composite typically resemble those of ceramic materials. 

We have studied activation of montmorillonite with mineral acid H2SO4. The effect of acid activation on structural properties of clay is interpreted in terms of XRD patterns, surface area and acidity measurement while the catalytic property is evaluated from the aniline alkylation reaction. 

Before delving into NMR measurements on clay systems, it is worthwhile to review clay structure very briefly and point out some of the reference material on this subject. An excellent review was published in 1988 that focuses mainly on the catalytic properties and structure of pillared clays [1]. 

Smectite clays consist of 1 nm thick aluminosilicate layers separated by sodium and calcium counterions. As little as 1 to 5 wt% of these layered clays can significantly improve the mechanical properties of nylon, polyolefins, and other polymers (78). Delaminating the clay structure by replacement of the sodium or calcium ions with a polymer-compatible surfactant, a quaternary ammonium ion surfactant, for example, is essential to generate a large polymer-clay interfacial area, as shown in Figure 11.21 (79). Ammonium ion head groups of the dispersant bind to the surface of the clay by Coulombic forces, and the hydrophobic alkyl tails bind to the polymer by van der Waals forces. 

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