Homogeneous nucleation is achieved in aqueous systems by creating adequately high levels of supersaturations. This process can be fully described by considering depletion of supersaturation due to simultaneous growth of the nuclei. Nielsen (1964) formulated this by integrating the growth kinetics with classical nucleation theory. This paper uses his combined nucleation-growth approach, as well as more recently developed mechanisms of adding monomers to developing nuclei (Chiang et at., 1988). The experimental data considered suggest that the systems fall into two categories: one involving the same mechanism for nucleation and growth and the other involving different mechanisms. A dimensionless parameter which evolves in the development permits the comparison of the rate of nuclei formation with that of nuclei growth. The inferences from this approach suggest further that the surface energy parameter is an indicator of the category to which a solution system belongs.
Rita Mohanty Suhas Bhandarkar Joseph EstrinDepartment of Chemical Engineering University of Rhode Island Kingston, RI 02881
IntroductionAs a basic phenomenon of phase change, homogeneous nucleation in pure vapor systems is well understood. Vaporliquid nucleation theory has been supported by the results of the superbly devised experiments which permit careful probing into the basics of the phenomenon. These include expansion cloud chamber (Schmitt, 1988), diffusion cloud chamber (Katz, 1970), and supersonic nozzle (Wegener, 1975) methods. Even for these systems, controversy exists concerning the more refined details of the theory (Lothe and Pound, 1962). Although many of the same first principles are still applicable when considering homogeneous nucleation from condensed-phase solution, the same level of understanding is not in hand. Corresponding theoretical and experimental methods are not available.The primary thrust of this paper is based on the experimental method of Nielsen (1964Nielsen ( , 1969. He employed a rapid mixing device in which two reactive solutions were introduced into each other, and the time of first visual occurrence of precipitate and the number of precipitate entities formed were measured. These were determined over a range of supersaturations which were assumed to exist momentarily after complete fluid mechanical mixing. Nielsen's modeling of the process assumes nucleation
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