1:1 clay structures, description

The hydration properties of clay minerals can be understood from the perspective of various types of acid-base interactions that may occur between several structurally defined sites in the clay matrix and surrounding water molecules. To facilitate discussion, a short description of clay structure is needed. 

Sams and Andrea (2001) describe the effect of clay in sandstone on elastic properties and present various model calculations. They start with some statements The shape and location of clay within sandstones have a large impact on the P-wave and S-wave velocities of the rock. They also have large effect on reservoir properties and the interpretation of those properties from seismic data and well logs. Numerical models of different distributions of clay - structural, laminar, and dispersed clay - can lead to an understanding of these effects . The description of clay effects and the derivation of models are difficult as a result of the following features (Sams and Andrea, 2001) ... 

Time-dependent fluids are those for which structural rearrangements occur during deformation at a rate too slow to maintain equilibrium configurations. As a result, shear stress changes with duration of shear. Thixotropic fluids, such as mayonnaise, clay suspensions used as drilling muds, and some paints and inks, show decreasing shear stress with time at constant shear rate. A detailed description of thixotropic behavior and a list of thixotropic systems is found in Bauer and Colhns (ibid.). 

Read descriptions of the four types of solid bonding structures and select one type to model in clay. 

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). 

The theoretical results described here give only a zeroth-order description of the electronic structures of iron bearing clay minerals. These results correlate well, however, with the experimentally determined optical spectra and photochemical reactivities of these minerals. Still, we would like to go beyond the simple approach presented here and perform molecular orbital calculations (using the Xo-Scattered wave or Discrete Variational method) which address the electronic structures of much larger clusters. Clusters which accomodate several unit cells of the crystal would be of great interest since the results would be a very close approximation to the full band structure of the crystal. The results of such calculations may allow us to address several major problems ... 

The two-dimensional structures are extended networks formed by the linking of the metal-oxygen polyhedra and the phosphate tetrahedra. These are sheet structures and often resemble those of naturally occurring clay minerals. The sheets are usually anionic and the protonated (cationic) amine molecules, located between the two sheets, render the framework neutral. The two-dimensional structures are intermediates between the one-dimensional chains and the three-dimensional structures, and the literature on phosphate networks contains descriptions of several layered materials, owing to the wide compositional diversity exhibited by them [22-24]. The layered materials are of interest because they act as precursors for the three-dimensional structures. 

The solid-state structure of the photosynthetic reaction centre complexes has inspired several studies of light-induced electron transfer in solid media. A particularly useful medium is provided by porous glass which facilitates rapid electron-transfer reactions without the involvement of polar solvents. Solid matrices suitable for light-induced electron-transfer processes are also provided by silica, zeolites, and clays. A theoretical description has been reported for dealing with the distribution of separation distances between donor and acceptor that is often found in the solid state. ... 

This section reviews several of the methods that are used to categorize clays. First, the structure of clay minerals will be discussed. Next, the mechanism of formation for kaolinite will be reviewed followed by a description of the types of deposits in which clays are found. The section will end with a description of the types of clays used in the ceramics industry. 

The limitations imposed on DDL theory as a molecular model by these four basic assumptions have been discussed frequently and remain the subject of current research.In Secs. 1.4 and 3.4 it is shown that DDL theory provides a useful framework in which to interpret negative adsorption and electrokinetic experiments on soil clay particles. This fact suggests that the several differences between DDL theory and an exact statistical mechanical description of the behavior of ion swarms near soil particle surfaces must compensate one another in some way, at least in certain applications. Evidence supporting this conclusion is considered at the end of the present section, whose principal objective is to trace out the broad implications of Eq. 5.1 as a theory of the interfacial region. The approach taken serves to develop an appreciation of the limitations of DDL theory that emerge from the mathematical structure of the Poisson-Boltzmann equation and from the requirement that its solutions be self-consistent in their physical interpretation. TTie limitations of DDL theory presented in this way lead naturally to the concept of surface complexation. 

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