Crystallisation, dissolution and diffusion in a Solid-Metal in Liquid-Metal colloidal system

The presence of solvated metallic elements with high mobility enables many applications of liquid metals (LMs) such as in catalysis, phase change materials, welding, soldering, and additive manufacturing. While the processes of crystallisation and dissolution in LM resemble those of traditional solvents, they have not been studied in great detail. Furthermore, crucial observations of solute mass transport speeds (flux) in LM have not been evaluated yet, despite being discovered within catalytic environments. Thereby for processes like phase change materials and additive manufacturing, the fundamental chemistry is underexplored. We hypothesise that a deeper understanding of these fundamental properties is obtained by studying the phase-change behaviour of solid metal in liquid metal colloidal systems. We have employed transmission electron microscopy (TEM) to examine the dissolution and crystallisation processes of a Ga-Cu colloidal system. This approach involves in-situ heating and cooling TEM analysis with a specialised TEM holder. TEM analysis shows that upon heating, the Ga₂Cu crystal begins to dissolve from its outermost layers, progressing until complete dissolution occurs. Recrystallisation then occurs in a supercooled environment, where the solute rapidly crystallises. This crystallisation process involves substantial mass transport within the LM, allowing for the estimation of the directional atom flux of Cu (valued -0.02 mol/m²s at 178 °C).