Interface-Controlled Phase Separation of Liquid Metal-Based Eutectic Ternary Alloys

Abstract

Liquid metals (LMs) are immiscible in many common electrolytic solutions and, when immersed in them, establish phase boundaries that display intriguing interfacial characteristics. The application of a cathodic potential to such interfaces may trigger phase separation of solute elements out of the LMs. Here, we investigate this possibility in two of the most researched and industrially used eutectic ternary LMs of Galinstan (Ga-In-Sn) and Field’s metal (FM, In–Bi–Sn). We observe that upon surface perturbation by an applied electric potential, solute elements compete to segregate out of the LM alloys according to their energy levels. The nature of the electrolytic solutions plays a key role in the separation process as they dictate whether solute metals are expelled selectively in their pure form or as binary compounds. For example, in a phosphate-based aqueous electrolyte, nano-sized Sn-based entities are selectively expelled from Galinstan, while only Bi-based structures leave the surface of FM. In contrast, in a non-aqueous electrolyte, nano-sized binary compounds of Sn–In and Bi–Sn are separated from the surfaces of Galinstan and FM, respectively. We show that selectivity in the surface separation process, achieved by the alteration of the electrolytic solutions, is due to the interplay between the electrodynamic interactions and the electrocapillary effect. This study presents two key findings: (a) it is essential to carefully consider the possibility of component separation in electrochemical systems based on LMs and (b) it demonstrates interfacial metallurgical pathways to process alloys for refining metals into specific purities, component ratios, and dimensions.

Gallium-based liquid metals as reaction media for nanomaterials synthesis

“…5e–g). 8 Moreover, the interfacial crystal formation within metallic liquid–solid coexisting systems leads to unique growth dynamics, crystal structures and arrangements that are distinct from traditional solvent precipitation (Fig. 5h).…”

“…6,7 Consequently, various metal elements can dissolve, precipitate, diffuse mutually and form intermetallic compounds within the LM matrix, making them ideal reaction media for materials synthesis. [8][9][10][11] Significantly, Ga features a low standard reduction potential (E 0 [Ga 3+ /Ga 0 ] = −0.529 V vs. the standard hydrogen electrode (SHE)), endowing it with a highly active surface for catalytic or reduction interface reactions. 12,13 More interestingly, LMs spontaneously form an ultra-thin oxide layer when exposed to air.…”

High‐Throughput Ammonia Production from Nitrate Using Liquid Metal Synthesized Bismuth Nano‐Catalyst

“…Introducing an excess of Bi into liquid Ga metals can create a peculiar dynamic equilibrium, resulting in intriguing phenomena such as nucleation and local ordering of Bi elements. [9] Following the Bi─Ga phase diagram, our primary strategy involves alloying Bi and Ga at 350 °C (Bi: 2.5% and Ga: 97.5% weight percentage). [31] Accordingly, Bi at the chosen concentration is a dissolved element in liquid Ga, forming a homogeneous alloy at 350 °C.…”

“…[8] In contrast, when segregation occurs via the application of an external electric field while the alloy is still liquid, it is possible to directly and completely expel nanoscale solute metals from the alloy, a process known as "metal expulsion." [9] Our recent research has demonstrated that electrochemistry can induce direct metal expulsion from liquid alloys using interfacial perturbations. [10] When liquid alloys are submerged in electrolytes, a liquid-liquid interface with distinct physical and chemical characteristics is formed.…”

“…[ 7 ] However in general, it is challenging to passively separate metallic nanoclusters from the core of the liquid metal alloys due to their high surface tension and surface oxidation. [ 8 ] In contrast, when segregation occurs via the application of an external electric field while the alloy is still liquid, it is possible to directly and completely expel nanoscale solute metals from the alloy, a process known as “metal expulsion.” [ 9 ]…”