Effect of oxidation on the Mechanical Properties of Liquid Gallium and Eutectic Gallium-Indium

TL;DR

This study investigates how oxidation affects the mechanical properties of liquid gallium and eutectic gallium-indium, revealing that oxide skin influences yield stress, surface tension, and wettability, with properties transitioning at a critical acid concentration.

Contribution

It introduces a scaling technique to accurately measure intrinsic viscosity and models the oxide skin’s impact on surface stress and yield stress in liquid metals.

Findings

Oxide skin causes a yield stress that affects liquid metal behavior.

Intrinsic viscosity can be precisely measured using a scaling technique.

Surface stress from the oxide skin mimics surface tension and influences wettability.

Abstract

Liquid metals exhibit remarkable mechanical properties, in particular large surface tension and low viscosity. However, these properties are greatly affected by oxidation when exposed to air. We measure the viscosity, surface tension, and contact angle of gallium (Ga) and a eutectic gallium-indium alloy (eGaIn) while controlling such oxidation by surrounding the metal with an acid bath of variable concentration. Rheometry measurements reveal a yield stress directly attributable to an oxide skin that obscures the intrinsic behavior of the liquid metals. We demonstrate how the intrinsic viscosity can be obtained with precision through a scaling technique that collapses low- and high-Reynolds number data. Measuring surface tension with a pendant drop method, we show that the oxide skin generates a surface stress that mimics surface tension and develop a simple model to relate this to the yield stress obtained from rheometry. We find that yield stress, surface tension, and contact angle all transition from solid-like to liquid behavior at the same critical acid concentration, thereby quantitatively confirming that the wettability of these liquid metals is due to the oxide skin.