Citation: Shentu, J.; Pan, J.; Chen, H.; He, C.; Wang, Y.; Dodbiba, G.; Fujita, T. Characteristics for Gallium-Based Liquid Alloys of Low Melting Temperature. Metals 2023, 13, 615. https://doi.org/10.3390/ met13030615 Academic Editors: Gunter Gerbeth and Roberto Montanari Received: 16 February 2023 Revised: 13 March 2023 Accepted: 16 March 2023 Published: 19 March 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metals Article Characteristics for Gallium-Based Liquid Alloys of Low Melting Temperature Jianfei Shentu 1 , Jiatong Pan 1 , Hao Chen 1 , Chunlin He 1 , Youbin Wang 1 , Gjergj Dodbiba 2 and Toyohisa Fujita 1, * 1 College of Resources, Environment and Materials, Guangxi University, Nanning 530004, China 2 Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan * Correspondence: fujitatoyohisa@gxu.edu.cn; Tel.: +86-1479-5734-1009 Abstract: Gallium alloys are ideal base carriers for temperature-sensitive ferrofluids, which can be used for energy convection, soft robotics, microchannels, magnetorheological devices, etc. In this study, gallium was mixed with different substances (In, Sn, Zn, Ge, and Al) to obtain a low melting point, reduce the wetness and adhesion of its alloys, and realize low viscosity. The melting point, contact angle on certain solid plates, viscosity, and viscoelasticity of the gallium alloys were measured, and some useful gallium alloys were obtained. The experimental results showed that Ga 80 In 10 Sn 10 had lower wettability at a larger contact angle of 148.6 ◦ on the Teflon plate. Here, (Ga 80 In 10 Sn 10 ) 97 Zn 3 with a melting point of 8.2 ◦ C, lower than the melting point of Galinstan, was developed. It had a viscosity about three times that of water at room temperature and an elastic response from 0.1 to 100 Hz at a 1% strain amplitude for the viscoelasticity. It was expected that a kind of temperature-sensitive magnetic fluid with a gallium-based liquid alloy as the base carrier liquid would be prepared in the future with Teflon as the container to achieve energy conversion under the drive of the magnetic field. Keywords: Ga alloy; melting point; viscoelasticity; wetness; eutectic; Galinstan; contact angle; magnetic fluid 1. Introduction Gallium alloy has been studied for making lead-free solders [1]. However, here, the low melting temperature of the gallium alloy was studied for processing, chemistry, and func- tion [2]. More specifically, gallium alloys are ideal base carriers for temperature-sensitive ferrofluid (magnetic fluid) and energy convection. They can also be used in various fields such as “soft robotics [3], microchannel [4], magnetorheological fluid [5], 3D printing [6], catalysis, energy storage [7], chemical sensors [8], etc.” Our group studied gallium-based ferrofluid [9]. Temperature-sensitive ferrofluid is very suitable as a medium for energy transportation and energy conversion and has important application prospects in the heat dissipation components of electronic products such as computers and cell phones [10,11], and can also be applied to ferrofluid temperature difference power generation, ferrofluid temperature difference drives, magnetic refrigeration, magnetic heating, magnetic thermal medicine, and other fields [12]. Currently, most temperature-sensing ferrofluids are based on oil or water. However, problems exist, such as high viscosity, low thermal conductivity, and small magnetic variation with temperature changes [13]. The liquid metal gallium and its liquid alloy are ideal for thermosensitive ferrofluid carrier liquids [14]. Gallium (density 5.91 g/cm 3 , thermal conductivity 40.6 W·m -1 k -1 ) has a melting point of 29.8 ◦ C. Therefore, it has the advantage of remaining liquid when used at room temperature. It has been reported that when silicon nanoparticles are dispersed in metal gallium with a melting point of 30 ◦ C, they remain liquid even at 0 ◦ C due to the super-cooling effect [15]. Some gallium alloys can remain liquid at room temperature, with good electrical and Metals 2023, 13, 615. https://doi.org/10.3390/met13030615 https://www.mdpi.com/journal/metals