Crystallization in small droplets: Competition between homogeneous and heterogeneous nucleation

Crystals are formed via nucleation and subsequent growth. In many cases, it is not easy to decide if nucleation occurs in the volume (homogeneous nucleation) or on a foreign surface, structure defects etc. (heterogeneous nucleation). This work is focused on crystal nucleation in a small supercooled liquid droplet when nuclei are formed in the volume or on the droplet surface simultaneously. The kinetic equations of homogeneous and heterogeneous nucleation are solved numerically to determine the size distribution of crystal nuclei and nucleation rate of both processes in Ni liquid droplet. The decrease of the number of atoms within the droplet volume in consequence of homogeneous and heterogeneous nucleation is taken into account. The number of nucleation sites on droplet surface decreases as new heterogeneous nuclei are formed. It is shown how both nucleation processes occur simultaneously.