Supersaturation relative

T — T (4) the ratio of the solute concentration and the equiUbrium concentration, c A, which is known as relative saturation or (5) the ratio of the difference between the solute concentration and the equiUbrium concentration to the equiUbrium concentration, s — [c — c which is known as relative supersaturation. This term has often been represented by O s is used here because of the frequent use of O for iaterfacial energy or surface tension and for variance ia distribution functions. 

It ean be seen from these definitions of driving foree that sparingly soluble substanees ean easily exhibit high levels of relative supersaturation. Henee, the erystallization proeess ean be very fast and the preeipitation diffieult to eontrol, espeeially on the large seale (see Sohnel and Garside, 1992). 

Supersaturation can be expressed as the concentration driving force Ac, the supersaturation ratio, S, or the relative supersaturation, a ... 

Some of the reports are as follows. Mizukoshi et al. [31] reported ultrasound assisted reduction processes of Pt(IV) ions in the presence of anionic, cationic and non-ionic surfactant. They found that radicals formed from the reaction of the surfactants with primary radicals sonolysis of water and direct thermal decomposition of surfactants during collapsing of cavities contribute to reduction of metal ions. Fujimoto et al. [32] reported metal and alloy nanoparticles of Au, Pd and ft, and Mn02 prepared by reduction method in presence of surfactant and sonication environment. They found that surfactant shows stabilization of metal particles and has impact on narrow particle size distribution during sonication process. Abbas et al. [33] carried out the effects of different operational parameters in sodium chloride sonocrystallisation, namely temperature, ultrasonic power and concentration sodium. They found that the sonocrystallization is effective method for preparation of small NaCl crystals for pharmaceutical aerosol preparation. The crystal growth then occurs in supersaturated solution. Mersmann et al. (2001) [21] and Guo et al. [34] reported that the relative supersaturation in reactive crystallization is decisive for the crystal size and depends on the following factors. 

When a reagent is added to an analyte solution forming a sparingly soluble compound, the solubility product for that compound is immediately exceeded and the solution is said to be supersaturated. The relative supersaturation Rs is given by... 

Nucleation and particle growth rates related to relative supersaturation. 

Despite the importance of the precipitation of calcium phosphates, there is still considerable uncertainty as to the nature of the phases formed in the early stages of the precipitation reactions under differing conditions of supersaturation, pH, and temperature. Although thermodynamic considerations yield the driving force for the precipitation, the course of the reaction is frequently mediated by kinetic factors. Whether dicalcium phosphate dihydrate (CaHPO HoO, DCPD), octacalcium phosphate (Ca HfPO, 2.5 H20, OCP), hydroxyapatite (Cag (PO fOH), HAP), amorphous calcium phosphate (ACP), or a defect apatite form from aqueous solution depends both upon the driving force for the precipitation and upon the initiating surface phase. Thermodynamically, the relative supersaturation, o, is given by... 

RELATIVE SUPERSATURATION. The free energy that drives nucleation and crystal growth is directly related to a substance s relative supersaturation (RS), and the latter is a unitless parameter equal to [X]instantaneous/... 

The higher the relative supersaturation, the more likely nucleation becomes, and the faster crystal growth proceeds. Molecules or ions will remain dissolved provided that the conditions are energetically favorable. However, all molecules above a certain threshold solution activity will remain in, or become part of, the solid phase. Molecules are in equilibrium between the solid state and the dissolved state. The extent to which the equilibrium balance favors the dissolved phase indicates the degree of solubility. 

Figure 4. Phase diagram for crystallization as a function of relative supersaturation.

NUCLEATION. Nucleation creates a new phase that is organizationally more related to the crystal lattice than to the monomeric species that undergoes crystallization. This process permits solutions that are of high relative supersaturation to crystallize and thereby reach equilibrium between liquid and sohd phases . Nucleation occurs when the local concentration of components that will comprise the solid phase exceeds a threshold level as a result of short-range concentration fluctuations in the bulk solution. In this respect, the kinetics of nucle-... 

RELATIVE SUPERSATURATION SCALAR COUPLING RELAXATION Scatchard equation,... 

As may be seen Figures 4, 5 and 6, the crystallization rate increased with relative supersaturated pressure, and the power number of the correlative lines between these two variables were cdmost as shown 1 Equaticxi 2. 

Figure 4. Correlation between relative supersaturated pressure and crystallization rate (unseeded, 283 K)...

Light precipitates indicates that the relative supersaturation between sample and reagent is too high. Prepare new tests with a decreased RNA and/or precipitant concentration or dilute the droplet by vapour diffusion by adding water into the reservoir. 

In both sexes, CCM-OJ provided an alkali load that significantly increased urinary pH compared to basal levels and versus milk consumption, and also increased urinary citrate excretion versus basal levels. An elevated urine pH and citrate level are generally considered to reduce Ca oxalate supersaturation and crystallization potential (Odvina, 2006). However, in this study the relative supersaturation measurement for Ca oxalate was not different between the CCM-OJ and milk treatment groups, or between either treatment and the basal levels. Although the alkalizing effect of milk was less than that of CCM-OJ, it also induced a higher urinary pH compared to basal levels (p <. 01 and p <. 05 in women and men, respectively). 

Why is high relative supersaturation undesirable in a gravimetric precipitation ... 

What measures can be taken to decrease the relative supersaturation during a precipitation ... 

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