Network solids concepts

Complete the concept map using the following terms covalent network solid, molecular solid, metallic solid, ionic solid, solid. 

Baekeland had to make important discoveries before he could bridge the gap between the initial concept and final products. In particular, he found that the base-catalysed condensation of phenol and formaldehyde can be carried out in two parts. If the process is carefully controlled, an intermediate product can be isolated, either as a liquid or a solid, depending on the extent of reaction. At this stage, the material consists of essentially linear molecules and is both fusible and soluble in appropriate solvents. When heated under pressure to 150 °C, this intermediate is converted to the hard, infusible solid known as bakelite . This second stage is the one at which the three-dimensional cross-linked network develops. 

Wet-weather processes have, in general, been excluded in the text, because they are based on a different concept and perform differently. Microbial and physicochemical processes are contrary to the physical processes dominating in sewers during dry-weather transport of the wastewater. When dealing with combined sewer networks in terms of pollutant loads during overflow events, dry-weather solids deposition and erosion and solids transport during high-flow events are, in addition to the rainfall/runoff hydraulic and sewer solids characteristics, the central physical in-sewer processes. Quite different process approaches are, therefore, required to describe dry-weather and wet-weather sewer performance. 

Therefore, the results of the present paper showed, that the notion of reactive medium heterogeneity connected with free volume representations, that was expected for diffusion-controlled solid phase reactions. If free volume microvoids were not connected with one another, then medium is heterogeneous, and in case of formation of overlapping percolation network of such microvoids - homogeneous. To obtain such definition is possible only within the framework of the fractal free volume conception. 

We note here that gel is a coherent solid because its structure is characterized by a polymer network, and hence, the above theoretical considerations on crystalline alloys should be applicable to gels without essential alteration. It is expected that the curious features of the first-order transition of NIPA gels will be explained within the concept of the coherent phase equilibrium if the proper calculation of the coherent energy and the elastic energy of the gel network is made. This may be one of the most interesting unsolved problems related to the phase transitions of gels. 

Different concentration limits of the filler arise from the CCA concept [22]. With increasing filler concentration first an aggregation limit O is reached. For >+, the distance of neighboring filler particles becomes sufficiently small for the onset of flocculation and clusters with solid fraction A are formed. Dependent on the concentration of filler particles, this flocculation process leads to spatially separated clusters or, for 0>0, a through going filler network that can be considered as a space-filling configuration of fractal CCA-clusters. The different cases for spherical filler particles are shown schematically in Fig. 1. 

The aim of this chapter is to discuss in general terms the use of adsorption measurements for the characterization of mesoporous solids (i.e. adsorbents having effective pore widths in the approximate range of 2-50 nm). Our approach here is mainly along classical lines and is based on the concept of capillary condensation and the application of the Kelvin equation. However it is appropriate to include a brief discussion of the relevant aspects of network percolation and density functional theory. 

As in the case of electrical failure in random conductor-insulator networks in the earlier chapter, we first discuss here the concept of stress concentration in an otherwise perfect solid, which is stressed and contains a single crack inside. Here, the stresses concentrate at the sharp edges of the crack, where it can become much larger compared to the external force. As one increases the external force, the crack starts propagating from such... 

Another way to define ionic charges consists in partitioning space into elementary volumes associated to each atom. One method has been proposed by Bader [240,241]. Bader noted that, although the concept of atoms seems to lose significance when one considers the total electron density in a molecule or in a condensed phase, chemical intuition still relies on the notion that a molecule or a solid is a collection of atoms linked by a network of bonds. Consequently, Bader proposes to define an atom in molecule as a closed system, which can be described by a Schrodinger equation, and whose volume is defined in such a way that no electron flux passes through its surface. The mathematical condition which defines the partitioning of space into atomic bassins is thus ... 

Cocrystals are becoming increasingly important as a means of controlling the properties of pharmaceutical solids by designing multiple component molecular networks that introduce the desired functionality. Because cocrystal design is based on supramolecular synthesis, it provides a powerful approach for the proactive discovery of novel pharmaceutical solid phases. Application of the fundamental concepts presented here on cocrystallization processes is essential for the pharmaceutical scientist to anticipate the formation of cocrystals during pharmaceutical processes and storage, as well as to develop reliable methods for cocrystal discovery and production. 

Once the first double-ladder-type compound had been established it was apparent that systematic study of this class of compounds should be conducted and a number of questions in context with the structures (A), (B), and (C) shown in Scheme 2.10.12 be addressed. Thus, we were and still are interested in studying the influence the identity of the spacers Z, the organic substituents R, and the electronegative substituents X and Y have on which structure is acmahy observed in solution and in the solid state, and whether these structures can be inter-converted. Furthermore, we looked at the possibility of extending the concept from double to multiple ladder-type structures and made the first attempts to assemble tetraorganodistannoxanes with double ladder-type structures to give supramolecular networks. 

In some specific cases other parameters can be considered as important in the characterisation of membrane morphology like the surface roughness, pore anisotropy and porous network connectivity [16,17]. Concepts of percolation and fractal geometry are also of interest to better describe the statistical and random structures of many porous solids [14,18,19]. 

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