Oxide transformation and break-up of liquid metal in boiling solutions

Abstract

The non-toxic gallium-based liquid metals (LMs) are promising for various newly emerging areas due to having excellent fluidity, high electrical and heat conductivity. However, the oxide layers often affect their applications. In this paper, we disclosed a straightforward boiling strategy to efficiently remove the oxide of LM in deionized water. Meanwhile such method was also demonstrated to be capable of quickly breaking up LM into droplets (mean 0.51 mm, SD 0.20 mm) in NaCl solution, which has important value for manufacture purpose. According to the force analysis, surface tension of LM dominates the interaction between solution bubbles and LM under the same heating conditions. Then we characterized the surface morphology and compositions of LM droplets boiled (LMDB) using scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and tested the dynamic force between a rod and LMDB. It was shown that after being boiled in water, most of Ga2O3 was transformed to scattered α-GaOOH nanorods which has less restriction to the deformation of LM and large resistance force (0.8 mN) was tested; otherwise, after boiled in NaCl solution, more Ga2O3 with contact patch structure reduces the surface resistance of LM (0.2 mN) and makes it to be broken up by bubbles. The different surface products are determined by the inhibition of hydrolysis of Ga3+ by NaCl solution. This study paved a simple way for oxide removal in neutral solution and mass production of LMD. It also suggests an efficient approach for exploring mechanisms of interactions between LM and bubbles, which is difficult to study otherwise in sonication.