Formation of Crystal Nuclei in Liquid Metals

TLDR

Nucleation in liquid metals is governed by critical size and interfacial energy, and in large masses it is typically catalyzed by extraneous interfaces. The authors calculated interfacial energies between crystal nuclei and liquids from nucleation frequencies of small droplets using homogeneous nucleation theory, and derived one‑atom‑thick interface energies σg from those σ values. In very small droplets, reproducible minimum nucleation frequencies are observed; the ratio of one‑atom‑thick interface energy σg to the heat of fusion ΔHf is about 0.45 for most metals but ~0.32 for H₂O, Bi, Sb, and Ge, indicating that crystal‑structure complexity influences supercooling through its effect on ΔHf.

Abstract

The known facts about nucleation phenomena in liquid metals are interpreted satisfactorily on the basis of the critical size and interfacial energy concepts. In large continuous masses nucleation is almost always catalyzed by extraneous interfaces. However, in very small droplets the probability that a catalytic inclusion is present is so much less that their minimum nucleation frequencies are reproducible and form a consistent set of values. Interfacial energies, σ, between crystal nuclei and the corresponding liquids have been calculated from nucleation frequencies of small droplets on the basis of the theory of homogeneous nucleation. Energies of interfaces, σg, one atom thick and containing N atoms were calculated from the σ's. The ratio of σg to the gram atomic heat of fusion, ΔHf, was approximately 0.45 for most metals but ∼0.32 for H2O, Bi, Sb, and Ge. The effect of relative complexity of crystal structure upon the supercooling behavior of pure metals apparently is a reflection of its effect upon ΔHf.