Kinetics of nucleation from aqueous solution

Abstract

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

Reaction crystallization kinetics of benzoic acid

“…In Figure 4, the classic representation of total crystal number concentration and induction time vs. initial supersaturation ratio is shown. The curves are nonlinear, which indicates that different mechanisms dominate in different regions (Nielsen, 1969;Mohanty et al, 1990). Both curves exhibit a decreasing slope at decreasing supersaturation.…”

“…Nielsen's expression linking the nucleation rate to the total number concentration was extended by Mohanty et al (1990) to account for growth controlled by surface integration: Crystal growth is usually described as a two-step process in which solute molecules are first transported to the crystal surface by diffusion through the boundary layer and are then incorporated into the crystal lattice by surface integration. The fundamental driving force for growth (as well as for nucleation) is the difference in chemical potential between the crystallizing substance in the solution and in the crystal.…”

A New Population Balance Model for Crystal Size Distributions: Reversible, Size-Dependent Growth and Dissolution

“…If the smaller clusters dissolve totally, the number of clusters is reduced, as observed in ripening (1). Homogeneous nucleation can be represented as growth by activated clustering of solute molecules, which approximate ions in stoichiometric proportion (11). The free energy of formation, expressed in terms of the supersaturation S = m/m ∞ and a geometric factor ε, reaches a maximum…”

Fundamental study of the dissolution of calcium phosphonates from porous media

“…Some of the more pronounced phosphonate applications are found in such places as cooling water towers, boiler water systems, paper mills, and petroleum production systems (Monsanto, 1986a,b). Phosphonates are advantageous in scale-prevention treatments because they have the ability to slow or prevent scale-nucleation/crystal-growth processes and are stable over a wide range of conditions such as temperatures and pressures (Kan et al, 1994;Mohanty et al, 1990;Estrin, 1990;Nancollas, 1979;Walton, 1967;Hach, 1980). In addition to scale inhibition, phosphonates are effectively utilized in many industrial processes as dispersants, bleaching agents, or corrosion inhibitors (Monsanto, 1986a,b).…”