# On Spontaneous Dispersion as a Cause of Microstratification of Metal Melts

## TL;DR

This paper explores how spontaneous dispersion causes microstratification in metal melts, leading to variations in particle size and atomic arrangement.

## Contribution

The study introduces a new method to assess spontaneous dispersion using three criteria and identifies particle sizes in various metal melt systems.

## Key findings

- Al–Sn melts contain colloidal-scale particles (4 nm), while Al–Si and Al–Ge melts contain atomic-scale particles (0.1 nm).
- The particle size in Cu10Ni90—Cu20Ni80 dispersion is 2 nm, and in GaInSn eutectic it is 5.6 nm.
- Long-range order violations and microlayering were observed in GaInSn, Al–Sn, and Cu–Fe melts.

## Abstract

The phenomenon of spontaneous dispersion is considered as the cause of the microstratification of metal melts. In a microstratification melt, a violation of long-range order in the arrangement of atoms (LRO) is observed, which corresponds to a dispersed particle size of more than 2 nm. Microseparation occurs due to spontaneous dispersion upon contact of liquid and solid metal or the mixing of two liquid metals. The possibility of spontaneous dispersion was assessed using three different criteria: Volmer’s cr iterion, Rehbinder’s criterion and the diffusion rate criterion. The diffusion rate criterion was obtained on the basis of the theory of rate processes, which describes how diffusing atoms overcome the interphase boundary. It has been established that Al–Sn melts contain colloidal-scale particles (4 nm), and Al–Si and Al–Ge melts contain atomic-scale particles (0.1 nm). For a system with a continuous series of Cu–Ni solid solutions in dispersion (Cu10Ni90—Cu20Ni80), the particle size is 2 nm. The particle size of the ternary eutectic GaInSn in the dispersion (Ga50In50—Ga50Sn50) is 5.6 nm, and the size of immiscible Cu–Fe melts in the dispersion (Cu80Fe20—Cu60Fe40) is 4.8 nm. Long-range order violations (LRO) and the presence of microlayering with colloidal particles larger than 20 nm were observed in the GaInSn ternary eutectic, in the Al–Sn simple eutectic with the preferential interaction of similar atoms, and in Cu–Fe melts with a monotectic phase diagram.