Salt hydrates stability

PGME APA Ampidllin 70 Enzyme preparations stabilized by inorganic salt hydrates. 84... 

Figure 7.35 Mallik 2002 geothermal gradient and hydrate stability curve for pure water and water containing 40 ppt salt. Note the depths of the thermal stimulation test and the six pressure stimulation (MCT) tests. (From Wright, J.F., et al., in Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada, Geological Survey of Canada Bulletin 585, including CD (2005). With permission.)...

Stability studies on the API include the evaluation of various forms of the active moiety, (e.g., different salts, hydrates, solvates, and polymorphs). After the API has been defined, stability studies are carried out as the... 

Fig. 7. Schematic representation of AMDH solution structures. The active structures have two parts a catalytically active core, conceivably similar to that in non-halophilic MDH, and protruding loops, required for stabilization in KCl, NaCl, and MgCl2 solvents. In potassium phosphate the protein dimer is stabilized by the hy-drophobicity of the core and the protruding loops are disordered. In KCl (or NaCl) the protein is stabilized by the interaction of the loops in a specific protein—water-salt hydration network. In MgCl2 a similar structure exists with the same amount of water molecules coordinated by fewer salt ions. In low salt concentration, the protein is unfolded and its hydration is like that of nonhalophilic proteins. From Zaccai el al. (1989), with permission.

Salts and Stabilizers Effects. Electrolytes, specifically mineral salts, have a definite effect on coacervates since they carry a charge and are therefore capable of changing the charge of the coacervate. If an added salt has a greater affinity for water than the coacervate, it dehydrates the coacervate drop, and thus breaks it down and converts it to a precipitate. The more hydrated the coacervate, the harder it is for it to hold water and the less salt is required for its precipitation. 

These internal salts are stabilized by hydration. Removal of the water of crystallization causes polymerization. The nucleophilic phenolic anion attacks the a carbon of the sulphonium ion, generating a linear chain... 

Forbes, R.T. York, P. Fawcett, V. Shields, L. Physicochemical properties of salts of p-aminosalicylic acid. I. correlation of crystal structure and hydrate stability. Pharm. Res. 1992, 9 (11), 1428-1435. 

The evaporation of saturated solutions and the stability of salt hydrates can be treated by the phase rule. According to the rule,... 

FIGURE 10 Seismic reflection profile across a salt diapir beneath the continental slope off North Carolina in the southeastern United States. GHSZ indicates gas hydrate stability zone within the sediments. The BSR, denoting the base of the gas hydrate stability zone, rises markedly over the diapir because of the thermal and chemical effects created by the diapir. This doming of the base of gas hydrate stability forms a trap for gas. Compare this to the middle diagram of Figure 9. 

Thus, summing up this section, we can say the anion affects poly-hydrate stability within one structure, the number of the hydrates forming in the system, their structures. In some cases it depends on the anion, whether clathrate formation occurs or not. This occurs in the case with tetraamylammonium and methyl- and ethyltributylammonium salts (see section 4), which do not form hydrates, if the anion is bromide, but which do, if the anion is fluoride, hydroxide or chloride. 

Silica gels are dispersions of colloidal silica obtained by a sol-gel process. The process consists in precipitating colloidal silica from an aqueous solution of sodium silicate by adding hydrochloric or sulfuric acid. The colloidal precipitate or gel consists mainly of hydrated silica (SiOj.nHjO). After filtration the precipitated silica is washed in order to remove residual salts and stabilized by adding ammonia or sodium hydroxide. The stabihzed gel is then dried and later calcined to obtain an activated material, usually in the form of small beads. Major producers are E.I. DuPont de Nemours, Akzo, and Nalco Chemicals Co. 

Mohammadi, A.H., Martinez-Lopez, J.F., Richon, D., 2007. Determination of hydrate stability zone using electrical conductivity data of salt aqueous solution. Fluid Phase Equilibria 253,36-41. 

The definition of solubility permits the occurrence of a single solid phase which may be a pure anhydrous compound, a salt hydrate, a non-stoichiometric compound, or a solid mixture (or solid solution, or "mixed crystals"), and may be stable or metastable. As well, any number of solid phases consistent with the requirements of the phase rule may be present. Metastable solid phases are of widespread occurrence, and may appear as polymorphic (or allotropic) forms or crystal solvates whose rate of transition to more stable forms is very slow. Surface heterogeneity may also give rise to metastability, either when one solid precipitates on the surface of auiother, or if the size of the solid particles is sufficiently small that surface effects become important. In either case, the solid is not in stable equilibrium with the solution. See (21) for the modern formulation of the effect of particle size on solubility. The stability of a solid may also be affected by the atmosphere in which the system is equilibrated. 

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