Kinetics of Nucleation: The Steady State

Abstract

The kinetics of steady-state nucleation are treated using a generalized Becker–Döring formulation. The concepts of critical nucleus, dynamic equilibrium, and steady-state nucleation are examined in detail. Two classes of nucleation are defined: (1) rapidly increasing stability nucleation in which the decay probability decreases very rapidly with increasing cluster size in the size region of the critical nucleus and (2) slowly increasing stability nucleation in which the decay probability decreases very slowly with increasing cluster size in the size region of the critical nucleus. It is shown that in the steady state the critical nuclei may be considered to be in dynamic equilibrium with the smaller nuclei only for the first class of nucleation. In addition, the equation for the rate of nucleation, generally accepted as being the rate at which critical nuclei grow to the next larger size, is shown to be valid only for the first class of nucleation in the steady state. The rapidly (slowly) increasing stability nucleation is shown to be characteristic of small (large) cluster nucleation at low (high) temperatures.