Nucleation pathway of core-shell composite nucleus in size and composition space and in component space

TL;DR

This paper investigates the nucleation process of core-shell composite nuclei using kinetic theory, analyzing the pathway in size, composition, and component spaces, and deriving formulas for critical and post-critical nuclei.

Contribution

It introduces a comprehensive kinetic framework for core-shell nucleation in multiple spaces and derives formulas for critical and post-critical nuclei considering free-energy landscapes.

Findings

Kinetics at the saddle point are best described in size and composition space.

Post-critical nucleus kinetics are better characterized in component space.

Free-energy landscape details are irrelevant for post-critical nucleus kinetics.

Abstract

The kinetics of nucleation of a core-shell composite nucleus that consists of a core of stable final phase surrounded by a wetting layer of intermediate metastable phase is studied using the kinetic theory of binary nucleation not only in the size and composition space but also in the component space. The steady-state solution of the Fokker-Planck equation is considered. Various formulas for the critical nucleus at the saddle point as well as for the post-critical nucleus are derived. The kinetics of nucleation at the saddle point is more appropriately characterized in the size and composition space, while the kinetics of the post-critical nucleus is more appropriately described in the component space. Although both the free-energy landscape and the reaction rates play decisive role to determine the kinetics of nucleation at the saddle point, the details of the free energy landscape are irrelevant to the kinetics of the post critical nucleus.