Kinetic critical radius in nucleation and growth processes - Trapping effect

The critical nucleus size - above which nuclei grow but below which they dissolve - during diffusion-controlled nucleation in a binary solid-solid phase transformation process is calculated using the kinetic Monte Carlo technique. If atomic jumps are slower in an A-rich nucleus than in the embedding B-rich matrix, the nucleus traps the A atoms approaching its surface. It does not have enough time to eject A atoms before new ones arrive, even if this were favourable thermodynamically. In this case, the critical nucleus size can be as much as an order of magnitude smaller than expected from equilibrium thermodynamics or without trapping.