Particle growth precipitation Nucleation

In a particular system, the nature of the precipitated particles will be determined by the relative rates of nucleation and particle growth. Where nucleation predominates, small particles are produced and a colloid may... 

Precipitates form by nucleation and by particle growth. If nucleation predominates, a large number of very fine particles results if particle growth predominates, a smaller number of larger particles is obtained. 

By carefully controlling the precipitation reaction we can significantly increase a precipitate s average particle size. Precipitation consists of two distinct events nu-cleation, or the initial formation of smaller stable particles of precipitate, and the subsequent growth of these particles. Larger particles form when the rate of particle growth exceeds the rate of nucleation. 

An increase in the time required to form a visible precipitate under conditions of low RSS is a consequence of both a slow rate of nucleation and a steady decrease in RSS as the precipitate forms. One solution to the latter problem is to chemically generate the precipitant in solution as the product of a slow chemical reaction. This maintains the RSS at an effectively constant level. The precipitate initially forms under conditions of low RSS, leading to the nucleation of a limited number of particles. As additional precipitant is created, nucleation is eventually superseded by particle growth. This process is called homogeneous precipitation. ... 

In an effort to separate particle nucleation from that of particle growth, and thus obtain a narrow size distribution without any further postpreparative separation treatment (such as selective precipitation), single-source molecular inorganic clusters have been employed. The clusters used have discrete units with... 

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. 

The prediction of the evolution of the PSD in Interval II is simpler than that in the ether intervals and it was for this reason that it was discussed first. Even the qualitative features of particle formation in Interval I are in doubt and the relative importance of homogeneous (ije., oligomeric precipitation) versus heterogeneous (i.e., micellar) nucleation mechanisms are not fully understood. For tbis reason, detailed solutions to Eq. (S) in this Interval, when c is nonzero, appear to be premature. Moreover, in many emulsion polymerizations, the precise details of events occurring in Interval I are masked by the subsequent particle growth in Intervals II and III. 

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