Relationship of phase diagrams and surfaces of new phase nucleation rates

Abstract

Experimental and theoretical investigations of vapor nucleation began about 100 years ago. Until the 1980s, experiments generally measured only critical supersaturation values. Since then, measurement procedures have substantially improved and nucleation rates can now be measured as a function of temperature, vapor activities, and pressure with high accuracy. Nucleation theory has made obvious progress, but the understanding of nucleation phenomenon is far from complete. New approaches to conceptualizing nucleation are necessary in order to identify possible new directions for further improvement of nucleation theory. One such approach is the analysis of the topology of nucleation rate surfaces. The creation of a nucleation rate surface is based on knowledge of phase equilibrium diagrams, limited experimental nucleation results, and a few plausible assumptions. In this article, the surfaces of the nucleation rates as a function of pressure or activity for single and binary systems for nucleation from metastable vapor, liquid, and crystalline states are constructed. By using surface topology analysis, some problems in nucleation theory are more clearly formulated and future directions for improvement can be found. Currently, it is not possible to create a universal nucleation theory based only on first principles. Partial theoretical success can be obtained only in the case of systems with well-known molecular interaction potentials. By scaling the experimental nucleation rate surfaces for portions of the phase diagrams that are identical to one another, a semiempirical nucleation rate surface for an unknown system can be created from its phase diagram. Scaling should give quantitative nucleation rates. Phase diagrams must be more fully incorporated into the interpretation of experimental nucleation results and nucleation theory development.