The Process of Nucleation

Once nuclei form in a supersaturated solution, they begin to grow by accretion and, as a result, the concentration of the remaining material drops. There is thus a competition for material between the processes of nucleation and of crystal growth. The more rapid the nucleation, the larger the number of nuclei formed before relief of the supersaturation occurs and the smaller the final crystal size. This, qualitatively, is the basis of what is known as von Weimam s law [86] ... 

In this case, it is not necessary to overcome an energy barrier for nucleation to occur. Decomposition into two phases occurs without involving the process of nucleation. Separation into two phases in this type of system is called spinodal decomposition, and is seen among silicate minerals such as the pyroxene and feldspar groups. Generally, the boundaries between the two phases are wavy rather than flat, but the two phases are in a specific crystallographic relation. 

The potentiostatic transient can be divided into three time intervals. At the beginning, the first time interval, the current decays during the process of nucleation and growth. This is the double-layer charging current, iAX. In the second... 

The addition of surfactants, which can either adsorb on the surface of a nucleus or act as a center for inducing nu-cleation, can be used to control the process of nucleation and the stability of the resulting nuclei. This is due to their effect on the specific surface energy, on the one hand, and their ability to incorporate the material in the micelles, on the other. 

The processes of nucleation and growth in aqueous systems are conceptually similar to those observed in their higher-temperature counterparts. Typically, the metal perchlorate salt is dissolved in water, and the thiol stabilizer is added (commonly, 1-thioglycerol). After the pH is adjusted to > 11 (or from 5-6 if ligand is a mercaptoamine ) and the solution is deaerated, the chalcogenide is added as the hydrogen... 

Several factors must be considered when deciding whether a given precipitation reaction is a feasible basis for an analytical method solubility certainly is one, another relates to physical properties, and still another to chemical purity and stability. The physical properties of a precipitate are influenced by the mode of its formation as well as by the specific compound involved. Broadly speaking, precipitates and their properties depend on the processes of nucleation, crystal growth, and aging. This chapter deals with these topics and also the properties of colloidal precipitates. 

Then, viscosity, supercooling, and cooling rate evidently determine the process of nucleation (i.e., ti). However, their effect on the free energy for TAG nucleation has not been evaluated. In the same way, the interaction among such... 

Generally, the process of nucleation in electrodeposition of metals can be considered as occuring on ideal or real substrates. Ideal substrates are considered free of ciystal imperfections and are characterized by an atomically smooth, homogeneous surface which does not exhibit preferred nucleation sites. On such substrates the number of nucleation sites, Zo, is equal to the number of adsorption sites Ns (cf. Section 8.3). 

The apparent cause for such eflFective removal of the finely divided salt particles dp = 0.01 to 1.0/u.m) and the residual ash particles is the process of nucleation that occurs when excess water in the gas condenses on the solids during the cooling operation. This process allows the soluble particles to be dissolved in the scrubbing liquid and the insoluble ones to be enlarged for easier capture. Theoretically, the ash particles could serve as condensation nuclei for the salt particles the ash particles then could be wetted by dissolution of the adhering salts and could cause eflFective size growth in the insoluble solids with concurrent ease of removal. 

The process of nucleation apparently is dominant in removal of the entrained solid salts, whereby most of the residual ash also is removed by scrubbing liquid with low contact time. Whatever the reason, the process is eflFective at low pressure loss. 

The geometric models of solid state reactions are based upon the processes of nucleation and growth of product nuclei by interface advance. These processes are discussed individually in the next section, followed by a description of the ways in which these contributions are combined to give rate equations for the overall progress of reaction. 

In order to achieve a monodisperse suspension or polydisperse system with particular particle size contribution, it is necessary to control the process of nucleation and particle growth. With most disperse systems, where the particles have some finite solubility, the smaller particles will have higher solubilities than their larger counterparts. With time, molecular diffusion occurs from the smaller to the larger particles, and this results in a shift in the particle size distribution to larger values this process is referred to as Ostwald ripening. 

In the first place, passage from the molecular state to a particle involves passing through the intermediate size range of 1—10 nm in the process of nucleation. We can see rather generally what this involves in the following way a more rigorous alternative treatment will be mentioned in Chapter 11. 

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