Nucleation, growth

A very different nucleation scheme by Grieser and co-workers employs ultrasonic irradiation of salt solutions to create H- and OH- radicals in solution [73]. These radicals proceed to nucleate growth of quantum-sized (Q-state) particles of cadmium sqlfide. Similar initiation has been used for polymer latices [74]. 

The nucleation, growth, and morphology of crystals are influenced by both temperature and stress. 

The boiling mechanism can conveniently be divided into macroscopic and microscopic mechanisms. The macroscopic mechanism is associated with the heat transfer affected by the bulk movement of the vapor and Hquid. The microscopic mechanism is that involved in the nucleation, growth, and departure of gas bubbles from the vaporization site. Both of these mechanistic steps are affected by mass transfer. 

The size-dependent agglomeration kernels suggested by both Smoluchowski and Thompson fit the experimental data very well. For the case of a size-independent agglomeration kernel and the estimation without disruption (only nucleation, growth and agglomeration), the least square fits substantially deviate from the experimental data (not shown). For this reason, further investigations are carried out with the theoretically based size-dependent kernel suggested by Smoluchowski, which fitted the data best ... 

The relative nucleation growth kinetics for this system are given by the relation (adapted from Garside and Jancic, 1979)... 

The model is able to predict the influence of mixing on particle properties and kinetic rates on different scales for a continuously operated reactor and a semibatch reactor with different types of impellers and under a wide range of operational conditions. From laboratory-scale experiments, the precipitation kinetics for nucleation, growth, agglomeration and disruption have to be determined (Zauner and Jones, 2000a). The fluid dynamic parameters, i.e. the local specific energy dissipation around the feed point, can be obtained either from CFD or from FDA measurements. In the compartmental SFM, the population balance is solved and the particle properties of the final product are predicted. As the model contains only physical and no phenomenological parameters, it can be used for scale-up. 

Hounslow, M.J., 1990b. Nucleation, growth and aggregation rates from steady-state experimental data. American Institution of Chemical Engineers Journal, 36, 1748-1753. 

Sohnel, O., Mullin, J.W. and Jones, A.G., 1988. Nucleation, growth and agglomeration during the batch precipitation of strontium molybdate. Industrial and Engineering Chemistry Research, 27, 1721-1728. 

Zauner, R. and Jones, A.G., 2000a. DeteiTnination of nucleation, growth, agglomeration and disruption kinetics from experimental precipitation data The calcium oxalate system. Chemical Engineering Science, 55, 4219-4232. 

The condition p2 a] < 1 has to be satisfied to assure nucleation growth, and if y is larger, the steady-state solution can be obtained ... 

MT-associated proteins (MAPs) are attached to MTs in vivo and play a role in their nucleation, growth, shrinkage, stabilization and motion. Of the MAPs, the tau family proteins have received special attention as they are involved in the pathophysiology of Alzheimer s disease. 

Decomposition of a single solid J- Nucleation - Growth Interface phenomena. Geometric control... 

In addition, it is of interest to note that investigations of the microscopic processes leading to nucleation, growth, oriented growth by the surfactant monolayer, and growth inhibition of nanoparticles in reversed micelles and of confinement and adsorption effects on such phenomena represent an intriguing and quite unexplored research field [218]. 

By electrodeposition of CuInSe2 thin films on glassy carbon disk substrates in acidic (pH 2) baths of cupric ions and sodium citrate, under potentiostatic conditions [176], it was established that the formation of tetragonal chalcopyrite CIS is entirely prevalent in the deposition potential interval -0.7 to -0.9 V vs. SCE. Through analysis of potentiostatic current transients, it was concluded that electrocrystallization of the compound proceeds according to a 3D progressive nucleation-growth model with diffusion control. 

In Nature, however, we always have a contiiinous distribution of particles. This means that we have all sizes, even those of fractional parentage, i.e.-18.56n, 18.57p, 18.58 p, etc. (supposing that we can measure 0.01 p differences). The reason for this is that the mecheuiisms for particle formation, i.e.- precipitation, embryo and nucleation growth, Ostwald ripening, and sintering, are random processes. Thus, while we may speak of the "statistical variation of diameters", and while we use whole numbers for the particle diameters, the actuality is that the diameters are fractional in nature. Very few particle-size" specialists seem to recognize this fact. Since the processes are random in nature, we can use statistics to describe the... 

Turkevich who established the first reproducible standard procedure for the preparation of metal colloids [44] also proposed a mechanism for the stepwise formation of nanoclusters based on nucleation, growth, and agglomeration [45,46]. This model, refined by data from modern analydical techniques and results from thermodynamic and kinetic studies, is in essence stiU valid today (Figure 2) [82]. 

Pioneering studies by Gardea-Torresdey et al. [28,29] reported for the first time the formation of gold and silver nanoparticles by living plants. Their study demonstrated that alfalfa plants can form gold and silver nanoparticles. Furthermore, these researchers reported that nucleation/ growth of the metallic nanoparticles took place inside the plants. This study opened new and exciting ways to synthesize metallic nanoparticles [30,31]. 

Layadi et al. have shown, using in. situ spectroscopic ellipsometry, that both surface and subsurface processes are involved in the formation of /xc-Si [502, 503]. In addition, it was shown that the crystallites nucleate in the highly porous layer below the film surface [502, 504], as a result of energy released by chemical reactions [505, 506] (chemical annealing). In this process four phases can be distinguished incubation, nucleation, growth, and steady state [507]. In the incubation phase, the void fraction increases gradually while the amorphous fraction decreases. Crystallites start to appear when the void fraction reaches a maximum... 

Wunderlich, B. "Macromolecular Physics Crystal Nucleation, Growth, and Annealing," Vol. 2, Academic Press, New York, 1976. 

Analytical solutions of the self-preserving distribution do exist for some coalescence kernels, and such behavior is sometimes seen in practice (see Fig. 40). For most practical applications, numerical solutions to the population balance are necessary. Several numerical solution techniques have been proposed. It is usual to break the size range into discrete intervals and then solve the series of ordinary differential equations that result. A geometric discretization reduces the number of size intervals (and equations) that are required. Litster, Smit and Hounslow (1995) give a general discretized population balance for nucleation, growth and coalescence. Figure 41 illustrates the evolution of the size distribution for coalescence alone, based on the kernel of Ennis Adetayo (1994). 

Wada, N., Yamashita, K. and Umegaki, T. (1995) Effects of divalent cations upon nucleation, growth and transformation of calcium carbonate polymorphs under conditions of double diffusion. Journal of Crystal Growth, 148, 297-304. 

We now turn to the question of developing a CFD model for fine-particle production that includes nucleation, growth, aggregation, and breakage. Applying QMOM to Eq. (114) leads to a closed set of moment equations as follows ... 

Solvent, in general, can affect crystallization during any of three stages - nucleation, growth and transformation. Here, we are concerned only with the first of these stages. 

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