Solid-state materials salt-like

Another type of gel expands and contracts as its structure changes in response to electrical signals and is being investigated for use in artificial limbs that would respond and feel like real ones. One material being studied for use in artificial muscle contains a mixture of polymers, silicone oil (a polymer with a (O—Si—O—Si—) — backbone and hydrocarbon side chains), and salts. When exposed to an electric field, the molecules of the soft gel rearrange themselves so that the material contracts and stiffens. If struck, the stiffened material can break but, on softening, the gel is reformed. The transition between gel and solid state is therefore reversible. 

Solid state reactions are also very common in producing oxide materials and are based on thermal treatment of solid oxides, hydroxides and metal salts (carbonates, oxalates, nitrates, sulphates, acetates, etc.) which decompose and react forming target products and evolving gaseous products. Solid-state chemistry states that, like in the case of precipitation, powder characteristics depend on the speed of the nucleation of particles and their growth however, these processes in solids are much slower than in liquids. 

A, while that between the pairs is 3.383(6) A. The 7r-stacked arrays of cations are linked by centrosymmetric pairs of Se(2)—N(l ) contacts, thereby generating ribbons running along the y-direction. These four-center Se—N supramolecular synthons, which are common in diselenadiazolylium salts and diselenadiazolyl radicals, are likely to dominate the solid-state structures of reduced diselenazolyl materials. 

Figure 1.5 illustrates this point with the example of salt and water. To the teacher, the salient points to note about these images are likely to be clear water is a pure substance because it consists only of one type of entity (water molecules, part (c)) sodium chloride is a pure substance as there is a constant composition (the alternation of Na+ and Cl in part (a)) throughout the material. The solution (part (b)) shows the sodium and chloride ions mixed up with molecules of water. To the student, the distinction between pure substance and mixture may be less clear the order in NaCl is not present in water (because it is in the liquid state, not the solid state) and - unlike water - sodium chloride does not comprise one type of entity at this submicroscopic scale. 

As part of the salt screening process, the potential formation of polymorphic forms and solvates should be evaluated to determine which salt form is most appropriate for development based on target attributes (see also Chapter 2). Each potential salt and/or polymorphic form should be evaluated to ascertain its stability at accelerated conditions (temperature and humidity). The water sorption of each should be evaluated to determine if the material will likely be incompatible with excipients that contain moisture. Following the synthesis of different salt forms each must be evaluated by a battery of chemical and physical tests. Given the importance of this work, an entire chapter in this text is devoted to solid-state characterization and the reader is encouraged to peruse them for further details. 

Table 14. Properties of narrow-pore zeolites and zeolite-like materials used in solid-state ion exchange with noble metal salts...

Cadmium is found naturally deep in the subsurface in zinc, lead, and copper ores, in coal, shales, and other fossil fuels it also is released during volcanic activity. These deposits can serve as sources to ground and surface waters, especially when in contact with soft, acidic waters. Chloride, nitrate, and sulfate salts of cadmium are soluble, and sorption to soils is pH-dependent (increasing with alkalinity). Cadmium found in association with carbonate minerals, precipitated as stable solid compounds, or coprecipitated with hydrous iron oxides is less likely to be mobilized by resuspension of sediments or biological activity. Cadmium absorbed to mineral surfaces (e.g., clay) or organic materials is more easily bioaccumulated or released in a dissolved state when sediments are disturbed, such as during flooding. 

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