Saturation super

Nucleation is initiated by secondary mechanisms involving the seed crystals or low super-saturation and high surface area of seed crystals eliminate or minimize nucleation seed crystals grow... 

Aeration of the hypolimnion (lower, colder layer of water in a stratified lake) without disruption of stratification has been used in deep lakes. This has the advantage of not increasing the temperature of the hypolimnion and prevents the advection of nutrient-rich water into the epilimnion (upper, warmer layer of water in a stratified lake). Oxygen injection is preferred in order to prevent the build up of nitrogen super-saturation which is toxic to fish. "... 

Helt, J.E. and Larson, M.A., 1977. Effects of temperature on the crystallization of potassium nitrate by direct measurement of super-saturation. American Institution of Chemical Engineers Journal, 23(6), 822. 

Rousseau, R.W. and Howell, T.R., 1982. Comparison of simulated crystal size distribution control systems based on nuclei density and super-saturation. Industrial and Engineering Chemistry Process Design and Development, 21, 606. 

A comparative study [10] is made for crystal-growth kinetics of Na2HP04 in SCISR and a fluidized bed crystallizer (FBC). The details of the latter cem be found in [11]. Experiments are carried out at rigorously controlled super-saturations without nucleation. The overall growth rate coefficient, K, are determined from the measured values for the initial mean diameter, t/po, masses of seed crystals before and after growth. The results show that the values for K measured in ISC are systematically greater than those in FBC by 15 to 20%, as can be seen in Table 2. On the other hand, the values for the overall active energy measured in ISC and FBC are essentially the same. 

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... 

Preparation of X-ray amorphous ZSM-5 crystallites according to procedure BT It is important that the gel formation takes place as homogeneously as possible. Because of the particular sensitivity of various silica and alumina species to the pH (63,64), the pH range between 4.5 and 8.5 was avoided. Nucleation was performed at pH 3.5-4, where a low viscous gel containing essentially monomeric silica species is rapidly formed (65).The, pH is theii raised to about 9, in order to form tetrahedral A1(0H) entities and to favour the further A1 incorporation within the zeolitic framework. NaCl was used to increase the (super)saturation of the gel, which will flocculate into a macromolecular colloid (V) and initiate the nucleation. This procedure yields 100 % crystalline zeolite after... 

Role of alkali and NH cations in the crystallization of ZSM-5 Introduced in an aqueous (alumino) silicate gel (sol), the bare alkali cations will behave in various ways firstly, they will interact with water dipoles and increase the (super) saturation of the sol. Secondly, once hydrated, they will interact with the aluminosilicate anions with, as a result, the precipitation of the so formed gel (salting-out effect). Thirdly, if sufficiently small, they also can order the structural subunits precursors to nucleation species of various zeolites (template function-fulfilled by hydrated Na+ in the case of ZSM-5 (11,48)). ... 

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. 

Mono-A-alkylation of the amides occurs under relatively mild liquiddiquid two-phase conditions (Table 5.10), using concentrated aqueous sodium or potassium hydroxide. Under soliddiquid conditions with sodium hydroxide-potassium carbonate or potassium hydroxide, or by using super-saturated aqueous potassium or sodium hydroxide, it is possible to control the reaction to obtain either the mono-or dialkylated derivatives f2-4]. Soliddiquid two-phase conditions also provide the most effective route to mono-AI-alkylalion of weakly acidic aliphatic amides, but it has been suggested that the procedure is not sufficiently selective for the monoalkylation of the more acidic amides [4],... 

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]... 

Oxygen is produced by photosynthetic organisms in the water and consumed in respiration and other oxidative processes. Often the concentration varies from super-saturation during the day to near zero at night. Because the partial pressures... 

Figure 5 shows the effect of phosphate concentration on crystallization rate Rg. Crystallization rate was obtained by weighing seeds in the reactor periodically, in which phosphate concentration drop in the bed was low enough, not to produce concentration distribution, by making the depth of the bed thin. Solubility of hydroxyapatite is so low, that the influent phosphate concentration is equal to super saturation dC. As shown in Figure 5, crystallization rate was proportional to 1.1th order of supersaturation. 

For solution on the other hand no such difficulties occur. It has already been noted that the edges of the planes are already stripped under conditions of equilibrium a small decrease in the concentration of the solution simply extends the edges further towards the centre of the plane until it is stripped entirely. The mechanism of crystal growth thus presupposes a finite degree of super-saturation, this no doubt varies with the surface energies of the crystal faces and will probably be greatest for the surfaces for which <7,1 is least,... 

Rapid Solidification and Mechanical Alloying for Preparing Super-saturated Precursors... 

Kaufman, Y. J., and D. Tanre, Effect of Variations in Super-Saturation on the Formation of Cloud Condensation Nuclei, Nature, 369, 45-48 (1994). 

At some distance close to the mineral surface, the saturation index (SI, IAP/Xsp) of pyromorphite must be greater than zero to allow local super saturation and precipitation. The question is whether this is a heterogeneous nucleation/ surface precipitation reaction or a dissolution homogeneous nucleation reaction. 

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