Super solubility

To ensure that all the overall crystal-growth rate coefficients are measured under the conditions without nucleation, the metastable region of the solution has to be determined first and therefore the solubility and super solubility need to be measured. 

Essentially, the key process in the preparation of ultrafine powders by reaction-precipitation is crystallization from a solution. As mentioned in the previous chapter, crystallization from a solution includes two steps nucleation and crystal-growth. Both can occur only in a supersaturated solution and spontaneous nucleation can occur only when the concentration of the solute in the solution is over the super solubility of the substance involved. The rate equation for nucleation derived from the principles of thermodynamics is represented by [ 182]... 

With the usual addition of a precipitant to a solution, as schematically represented in Fig. 9, the local concentration rises temporarily above that of the super-solubility curve, which causes rapid nucleation of the precipitate. When after homogenizing the liquid, the final concentration is lower than that of the supersolubility curve, nucleation has already proceeded and the crystallites precipitated are stable. Consequently, the concentration has to be maintained continuously... 

Traditionally, the objective of precipitation is to obtain a well-dispersed metal hydroxide (or carbonate) phase on a support through its precipitation from an aqueous metal solution onto a support powder by adding a base. The support powder is suspended in the metal salt solution. Upon addition of, say, NaOH, the pH increases strongly and metal hydroxide species are generated. When their concentration exceeds the (super)solubility limit, metal hydroxide particles can... 

The studies of Barret et al. [7] (closed system) allowed to estabhshthe curves of super-solubility, oversaturation of solution in relation to the C-S-H, as well as the curves of metastable equilibriums, corresponding to the supersaturated solutions. These curves were plotted in the Ca0-Si02-H20 system at the temperature 21 °C (Fig. 3.4). It is worthwhile to remind also the classic Flint and Wells curve (Fig. 3. 4). The two branches of this curve can be distinguished. The CD (Fig. 3.4) corresponds... 

Functional derivatives of polyethylene, particularly poly(vinyl alcohol) and poly(acryLic acid) and derivatives, have received attention because of their water-solubility and disposal iato the aqueous environment. Poly(vinyl alcohol) is used ia a wide variety of appHcations, including textiles, paper, plastic films, etc, and poly(acryLic acid) is widely used ia detergents as a builder, a super-absorbent for diapers and feminine hygiene products, for water treatment, ia thickeners, as pigment dispersant, etc (see Vinyl polymers, vinyl alcohol polymers). 

Samples were analyzed by gas chromatography (GC). Water solubility was determined by equilibration of analytical grade material with water at constant temperature. Equilibrium was approached from both under and super saturation conditions and samples were analyzed by GC. Vapor pressures were determined by the Knudsen effusion method. 

The important consequence of eq. (6.60) is that the solubility of the solid increases with decreasing radius of crystal. Although the effect is small this illustrates the need for super-saturation on homogeneous nucleation in a liquid. Super-saturation is necessary in order to obtain nucleation since the solubility of the nuclei is higher... 

A batch cooling crystallization is one of the most commonly used crystallization method. In this process super saturation of a liquid is achieved by means of a cooling process. The solubility of the solute (in the solvent) decreases with a decrease in temperature this leads to precipitation of the solute. 

Water Solubility and Super-Hydrophobic Properties of CNTs... 

In this model there is no stomach compartment but possible dissolution in the stomach can be partly accounted for by defining the boundary conditions (C and r ) in the beginning of the intestine. If fast dissolution is expected in the stomach, the boundary conditions for C can be set to 1, that is, the luminal concentration when entering the intestine equals the saturation solubility in the intestine. If no dissolution is expected in the stomach, the starting value for C will be 0. C can then have all values between 0 and 1 as the boundary condition and this results in the restriction that super-saturation in the intestine due to fast dissolution and high solubility in the stomach can not be accounted for. Assuming that the difference between the mass into and out of the intestine is equal to the mass absorbed at steady state, the Tabs can be calculated from Eq. 17 [40]... 

Chen, C.R., Lin, Y.H., Cho, S.L., Yen, S.Y., and Wu, H.L., Investigation of the dissolution differenee between acidic and neutral media of acetaminophen tablets containing super disin-tegrant and a soluble excipient, Chem. Pharm. Bull., 45 509-512 (1997). 

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