Solid in water

As a liquid, chlorine is amber colored and is 1.44 times heavier than water. In solid form, it exists as rhombic crystals. Various properties of chlorine are given in Table 2. 

Mass is balanced at the beginning and the end of process. The evaporated water in solid-state fermentation may not be required for energy balance. 

X-ray powder diffractometry offers a unique advantage in the quantitative analyses of mixtures consisting of the anhydrous and hydrated forms of a compound. In order to appreciate this, it is necessary to understand the interaction of water with solids. There are four possible states of water in solids [48] (1) adsorbed on the solid surface, (2) absorbed or dissolved in the solid, (3) associated... 

The papers of Mallon and Ray [98, 123] can be regarded as the state of the art in understanding and modelling solid-state polycondensation. They assumed that chain ends, catalysts and by-products exist solely in the amorphous phase of the polymer. Because of the very low mobility of functional groups in the crystalline phase, the chemical reactions are modelled as occurring only in the amorphous phase. Additionally, the diffusion of by-products is hindered by the presence of crystallites. The diffusivity of small molecules was assumed to be proportional to the amorphous fraction. Figure 2.32 shows the diffusion coefficients for the diffusion of EG and water in solid PET. 

Figure 2.32 Diffusion coefficients for EG and water in solid PET at different temperatures, according to Mallon and Ray [98], Kang [122], Gao et al. [155] and Ravindranath and Mashelkar [121]...

The non-destructive character of vibrational spectroscopy techniques, such as NIR, makes them novel tools for in-line quality assurance (100). NIR has been widely used for the measurement of water in various applications (101). NIR can be applied for both quantitative analysis of water and for determining the state of water in solid material. This gives a tool for understanding the physicochemical phenomena during manufacture of pharmaceutical granulation. 

Konty MJ. Distrubution of water in solid pharmaceutical systems. Drug Dev Ind Pharm 1988 14(14) 1991-2027. 

Blinc and Hadzi [64]. In contrast, however the following linear relationship has been reported [65] for water in solid hydrates ... 

The results obtained suggest that the positive role of crystallized water in solid phase synthesis of zircon from a mechanically activated mixture of hydrated oxides consists only in a reduction of the mechanical hardness of the oxides. If one of the two oxides is hydrated, the degree of its amorphization is higher. If both oxides are hydrated, then mechanochemical processes occur, simultaneously with increasing extent of amorphization, to give oxygen-saturated polyhedra of zirconium, which cannot interact with Asi and Bsi polyhedra to form zircon in the course of thermal treatment. 

In liquid hydrazine, hydrogen bonding occurs between the hydrazine molecules similar to the hydrogen bonding in liquid water. In solid hydrazine, the hydrogen bonds have NH-N distances between 319 and 367 pm. In hydrazine hydrate, each hydrazine molecule is linked via six hydrogen bonds to surrounding water molecules so that the hydrazine molecules are separated from each other by water molecules. Some physical properties of hydrazine and hydrazine hydrate are shown in Table 16. 

This study presents new data supporting that the mechanism of water adsorption on the microporosity is governed by physical adsorption. According to the results presented in this paper, the use of water adsorption seems to be a very interesting tool for the characterisation of CMS. Water adsorption allows to complete the characterisation of microporosity, because it is adsorbed in the range of ultramicroporosity, which is not accessible to CO2. Pore volumes obtained from water adsorption data using the density of water in solid phase (0.92 g/cc) are quite similar to the corresponding micropore volumes obtained from CO2 adsorption data. 

Pore volumes have been obtained from water adsorption considering two different water densities. The density of water in solid phase (0.92 g/cc) has been used to estimate the micropore volume from the amount of water adsorbed until relative pressure around 0.6. In the other hand, the liquid water density has been used to calculate the water volume adsorbed on the relative pressure range around 0.6-0.95. The pore volumes obtained from water adsorption data are quite similar to the corresponding micropore and mesojxrre volumes obtained by nitrogen adsorption, which seems to corroborate that water adsorbs in the microporosity as solid ice, while it adsorbs in the mesoporosity as liquid. 

TABLE 3-XIII Relative Frequency Shifts and Band Widths of Polymers of Water in Solid Nitrogen ... 

FIGURE 3-25 Total integrated absorption relative to monomeric water in solid nitrogen (2097). S, = total absorption of stretching m( es Zb = total absorption of bending mode. 

In Figure 2 is shown the spectrum obtained by photolysis of water in solid argon at wavelengths longer than 1450 A. This spectrum consists of two doublets, one having a value of A hl5% greater than, and the other a value of A 0.46% smaller than, the free atom values. The corresponding deviations in g are... 

The most useful spectral methods for the characterization of water in solids are Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and powder X-ray diffraction (XRD). A thorough treatment of these methods is not given here instead the example of ampicillin presented by Brittan, et sdP is summarized. 

Solid-state NMR is a method that promises to increase the understanding of the state of water in solids and its specific influence on the chemicals of interest. In Fig. 18, for example, it is clear that the solid-state NMR spectra of ampicillin trihydrate is a very different form than that for the anhydrous form. Although three carbonyl resonances present in the anhydrous form (169.7, 172.7, and 174.6 ppm), it is interesting that only two (170.4 and 172.6 ppm) are fully resolved in the hydrate form. Thus, in the latter, two of the three carbonyls are equivalent. Evidence also exists for differences in carbons in the aromatic ring based on the presence of water of hydration. 

Real progress has been made in the last 10 years, providing pharmaceutical scientists with a solid basis for understanding the interaction of water with solids of pharmaceutical interest. Much of this progress has been the consequence of a paradigm shift the model of the solid as an inert substrate is almost never valid. Further characterization of the state of water in solid-water systems may ultimately provide a basis for the design of stable formulations and permit the establishment of performance-based specifications for pharmaceutical excipients. 

Finally, one can use the suspension approach [65] to determine water in solid samples that would otherwise act as adsorption systems. The sample is suspended in a water-miscible dry polar solvent such as ethylene glycol monomethyl ester (EGME). The second solvent displaces water from the solid sample and dissolves it if the water concentration in EGME is low enough (less than 5% v/v), then the peak area is linearly related to the concentration. 

The activity of water in a mixture or solid is defined as the ratio of the vapor pressure of water in the mixture to that of a reference, usually the vapor pressure of pure water. In solids drying or drying of solutions, the vapor pressure (or water activity) is lower than that for pure water. Therefore, the water activity value equals 1 for pure water and < 1 when binding is occurring. This is caused by thermodynamic interactions between the water and the drying material. In many standard drying references, this is called bound water. 

Several highly selective methods have been developed for the determination of water in solid and liquid samples. One of these, the Karl Fischer method, is described in Section 20C-5. Several others are described in the monographs by Mitchell and Smith. 

Ratio of vapor pressure exerted by water in solid to that of pure water at the same temperature. 

Consider the heat of solution of a process in which an ionic compound is the solute and water is the solvent. For example, what happens when solid NaCl dissolves in water In solid NaCl, the Na and CP ions are held together by strong positive-negative (electrostatic) forces, but when a small crystal of NaCl dissolves in water, the three-dimensional network of ions breaks into its individual units. (The structure of solid NaCl is shown in Figure 2.12.) The separated Na+ and CP ions are stabilized in solution by their interaction with water molecules (see Figure 4.2). These ions are said to be hydrated. In this case water plays a role similar to that of a good electrical insulator. Water molecules shield the ions (Na+ and CP) from each other and effectively... 

Incidentally, we note that fi is a more fundamental quantity than T and that the constant kB does not possess any universal character but depends essentially on specific properties of water in solid, liquid, and gas states. 

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