Particle nucleation

The Penniman-Zoph process involves the preparation of seeds or nucleating particles by the alkaU precipitation of ferrous sulfate. The reaction is carried out at alow temperature using an excess of ferrous ions. The hydroxide is then oxidized to the seeds of hydrated ferric oxide ... 

This equation ceases to be applicable when t, > c/2kG since nuclei generated at t = 0 will then have penetrated the reactant particle. It is, therefore, necessary to make a subtraction from this equation to allow for interface removal resulting from the consumption of first-nucleated particles. At time 2 (>c/2kG) (fe = 2kG/kNc) [28]... 

This critical molecular weight increases with the solubility of the polymer and is low enough so that all the oligomers are captured or nucleate particles before their radicals are terminated. As a result, nearly all polymerization takes place in the particles and the polymer concentration in the diluent phase is low. 

The final one is to nucleate particles heterogeneously only on the support surfaces, not homogeneously independently from the surfaces, as shown in Figure 4. 

The reaction is sustained by addition of iron metal which reacts with the sulfuric acid formed, regenerating Fe(n) in solution. To ensure that the desired crystal form precipitates, a seed of a-FeO(OH) is added. However, with appropriate choice of conditions, for example of pH and temperature and by ensuring the presence of appropriate nucleating particles, the precipitation process may be adapted to prepare either the orange-brown y-FeO(OH), the red a-Fe203 or the black Fe304. 

Intrinsic nucleators particles of solid PCM. They have to be kept separately from the PCM as they would otherwise melt with the PCM and thereby become inactive. 

In the general case, nxoift.x) consists of two types of polymer particles contribution from newly generated (nucleated) particles which assumed property plt.t) and contribution from newly introduced particles which grew to property p(t,x). 

First, for the case in which only solute concentration measurements are available, pseudo-experimental data are simulated and used in the parameter estimation scheme. Even with noise-free data, the recovered parameters differ greatly from the true parameters and the uncertainties of the nucleation parameters are large. This indicates that there exists a large set of quite different b and ki, pairs that would lead to very similar solute concentration profiles. The insensitivity of the objective function to the nucleation parameters can be attributed to the fact that the mass of a nucleated particle is almost negligible and the change in the solute concentration is primarily due to seed growth. 

In discussing the mechanisms of the formation of monodispersed colloids by precipitation in homogeneous solutions, it is necessary to consider both the chemical and physical aspects of the processes involved. The former require information on the composition of all species in solution, and especially of those that directly lead to the solid phase formation, while the latter deal with the nucleation, particle growth, and/or aggregation stages of the systems under investigation. In both instances, the kinetics of these processes play an essential role in defining the properties of the final products. 

In the nucleation step, there must be sites upon which the crystals can form. This is similar to seeding the clouds to cause water to precipitate (rain). There are two sources for these nucleating particles homogeneous and heterogeneous agents. 

In later experiments, Izumi et al. (47, 48) examined aerosol formation during photooxidation of a variety of hydrocarbons in an evacuable smog chamber. No seed particles were used in these experiments, but good estimates of the yield of aerosol from photochemical oxidation of the hydrocarbon precursors were obtained by using EAA data. In some cases, the volumetric yield was found to decrease with decreasing precursor concentration (Figure 4), so the finite vapor pressure of the reaction products limited nucleation, particle growth, or both. 

Keywords Emulsion polymerization Kinetics Particle nucleation Particle growth Molecular weight distribution Nonlinear polymers... 

The distinguishing feature of droplet nucleation as opposed to micellar or homogeneous nucleation is the nature of the particle at birth . Droplets, which are nucleated into particles, begin as nearly 100% monomer. Micellar or homogeneous nucleated particles start out with much lower monomer concentrations and eventually swell to around 60% (for MMA) in the presence of monomer droplets. This fundamental difference may lead to large differences between miniemulsion and macroemulsion polymerizations in radical desorption and/or intraparticle termination during Intervals I and II. 

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