Surface Tension Of Liquid Metals Research Articles

Variation of Surface Tension of Liquid Metal with Fluorides in Tungsten Inert Gas Welding

Real-time measuring and obtaining surface tension of liquid metal during the arc welding process is critical for studying the behavior of the weld pool, such as Marangoni flow and flow velocity. The dynamic variation of surface tension of weld pool during tungsten inert gas welding process with and without fluoride flux was measured by weld pool oscillation sensing system, and the effect of fluoride flux on surface tension and pool behavior was analyzed. The results show that the surface tension gradient of liquid metal can convert from a negative to a positive value in a critical arc time. The flow velocity of liquid metal and critical arc time significantly increased and decreased, respectively, with fluoride flux. The variation of surface tension, flow velocity, and critical arc time with fluoride flux was induced by arc temperature increasing.

3D printing of liquid metal circuits on fabric for stretchable heater application

Abstract Liquid metals (LMs), due to their excellent stretchability, low resistance, and high thermal conductivity, has become an ideal material for preparing stretchable circuits. 3D printing technology can produce patterns with complex structures with high precision and is suitable for low-cost large-scale production of circuits. However, the high surface tension of liquid metals limits the practical application of 3D printing of LMs. In this work, we proposed a method for preparing a mixed ink based on thermoplastic polyurethane, Cyrene solvent, and LMs, and producing stretchable LMs-based electrodes through 3D printing on a fabric substrate. The stretchable LMs-based electrode prepared by this method shows a wide range of strain response and excellent tensile recovery performance, providing theoretical guidance for the application of LMs electrodes. In addition, the LMs-based heaters showed good Joule thermal response at low voltages, as well as good tensile stability, providing a new strategy for wearable heaters.

Quantitative assessment method of thermal cycle accumulation mechanism during the pulsed laser single-channel multilayer cladding process

Pulsed laser cladding provides a periodical thermal accumulation, enabling a greater temperature gradient and cooling rate inside the substrate, which can efficiently ameliorate the microstructure of the cladding layer. It is crucial to quantitatively investigate the mechanism of the interaction for the cladding process parameters on the transient evolution of the multi-field coupling to improve the cladding quality. In this paper, a 3-D model during the single-channel multilayer pulsed laser cladding process was constructed which is grounded on the temperature-variable physical properties parameters of the material. The integrated consideration in the masking impact of the molten powder waist beam on the pulsed laser beam, the molten pool liquid metal surface tension, the influence of buoyancy on the flow, and the transient evolution of the molten pool edge morphology. The temperature, flow, and stress fields of the single-channel multilayer cladding process were computed and resolved. The mechanism in multi-field coupling impact of laser pulse frequency, laser power, and pulse duty cycle on the single-channel multilayer cladding process was emphasized. The response surface equations between each influencing factor and the cladding temperature, temperature change gradient, and thermal stress were determined according to the response surface method, and the sensitivity of each parameter was attained from the Monte Carlo method. Using SEM to observe the profile and microstructure of the cladding layer, the material hardness distribution was measured experimentally, and the effectiveness of the model was confirmed. This research supplies an essential rationale for upgrading the quality of pulsed laser cladding layers.

Recent progress in eutectic gallium indium (EGaIn): surface modification and applications

EGaIn plays an important role in flexible electronics, this paper focuses on a review of the key factors affecting the surface tension of liquid metals and surface modification methods and applications.

Thread-analogous elastic fibers with liquid metal core by drawing at room temperature for multifunctional smart textiles

Stretchable and elastic conductive fibers with liquid metal core are appealing for integration into electronic fabrics and clothing, owing to their inherent electrical conductivity even under strain. Previously, injecting liquid metal into core of hollow elastic fiber has been utilized to fabricate conductive fibers, however, hydrodynamics limits the extent to which metals can be injected, thus limiting length and cross-sectional area. Although direct printing and spinning methods using coaxial needles have been utilized to fabricate long and thin polymer-encased liquid metal fibers via single step, various parameters including extrusion rate along with viscosity and surface tension of liquid metal and polymeric shell, needs to be considered. Herein, we introduce a simple and facile method for fabricating thread analogous conductive fibers by plastically deforming liquid metal injected polymeric shell via drawing at room temperature. This simple yet effective process generates long conductive fibers with narrow cross-sectional area of the liquid metal wire continuously formed along its length. The obtained fiber can withstand deformation arising from daily activities while maintaining excellent electrical performance, thus can be used for fabricating smart textiles serving multitude of purposes.

Interface regulation of diamond-doped GaInSn composites

Diamond-doped GaInSn thermal interface materials have broad application prospects in the field of electronic thermal management. However, the poor wettability of diamond and liquid metal makes the fabrication of composites through simple mechanical agitation difficult. In this study, the wettability between GaInSn and diamond was improved by reducing the surface tension of liquid metal and improving the anisotropy of the diamond surface. The diamond/liquid metal (Dia/LM) interface structure was regulated by controlling the gallium oxide content. Ga2O3 was enriched in the GaInSn and diamond contact surface, which can reduce the surface tension of the liquid metal, improve the wettability of GaInSn to diamond, produce a mechanical locking force with the diamond surface, strengthen the bonding between the liquid metal and the diamond, and reduce the thermal resistance of the liquid metal/diamond interface. The Dia/LM interface structure was controlled by using crushed diamond. Result shows that the wettability of the surface (111) of the diamond was the best. The (100) and (110) planes with poor wettability were cut by the crushed diamond cleavage step, and the area of the crystal plane with poor wettability was reduced, thus improving the wettability of the liquid metal. The improvement of the crushed diamonds' wettability was verified by molecular dynamics calculation. The composite preparation technology of diamond and the GaInSn liquid metal was optimized, and the high-performance Dia/LM thermal interface material was prepared by ultrasonic-assisted and micro-oxidation methods.

Breakup-Free and Colorful Liquid Metal Thin Films via Electrochemical Oxidation.

Thin-film metal conductors featuring high conductivity and stretchability are basic building blocks for high-performance conformable electronics. Gallium-based liquid metals are attractive candidates for thin-film conductors due to their intrinsic stretchability and ease of processing. Moreover, the phase change nature of liquid metal provides an opportunity to create conformal electronics in a substrate-free manner. However, thin liquid metal films tend to break during the solid-to-liquid transition due to the high surface tension of liquid metal. Here, we created breakup-free liquid metal thin films by the electrochemical oxidation of solid gallium films. We show that electrochemical oxidation can enhance the mechanical strength of the gallium oxide layer and its interfacial adhesion to the gallium core. When heated to the liquid state, the oxidized gallium films can maintain their structural integrity on various solid substrates, hydrogels, and even the water surface. The solid-liquid phase change-induced stiffness decrease allowed the gallium films to be conformably attached to various nonplanar surfaces upon heating or water transfer printing. Moreover, we also found that enhanced electrochemical oxidation can result in the formation of structure color due to nanoporous structures on the film surface. We also demonstrate the applications of oxidized liquid metal films in functional electronics, electrophysiological monitoring, and tattoo art.

Enhanced thermal conductivity of liquid metal composite with lower surface tension as thermal interface materials

Gallium (Ga)-based liquid metal (LM) has attracted great interest for thermal management due to its high thermal conductivity (Tc). However, the surface tension of LM is too high to wet the surface of the heat source and sink, and there are great risks of a short circuit of devices caused by LM leakage. The high surface tension also makes it difficult to well mix LM and fillers to prepare composite paste for thermal interface application. We found that the contact angle of LM on Boron nitride (BN) pill surface could decreased from 133° to 105° by doping tungsten (W) nanoparticles indicating the surface tension of LM could be decreased by doping W nanoparticles. The adding sequence of LM, W and BN were found could affect the final form of the composite, and the composite paste (LM+W-BN) can only be obtained by mixing W nanoparticles with LM first (LM + W). As contrast, other adding sequences or without W nanoparticles can only obtain composite powder. LM+W-BN paste exhibits a high Tc of 14.49 W m−1 K−1, and the stability of LM+W-BN paste under pressure, high-temperature, thermal shock and high humidity was also investigated in detail. LM+W-BN paste shows an excellent thermal management ability as a TIM by application in a light emitting diode (LED) module. This approach has also been extended to other thermal conductive fillers including carbon fiber and graphene. This work offers a simple approach to lower LM surface tension and might also enable the incorporation of other fillers, expanding the use of LM, such as integrated circuits and flexible electronics.

Stretchable Electrodes Based on Over-Layered Liquid Metal Networks.

Liquid metals are attractive materials for stretchable electronics owing to their high electrical conductivity and near-zero Young's modulus. However, the high surface tension of liquid metals makes it difficult to form films. A novel stretchable film is proposed based on an over-layered liquid-metal network. An intentionally oxidized interfacial layer helps to construct uninterrupted indium and gallium nanoclusters and produces additional electrical pathways between the two metal networks under mechanical deformation. The films exhibit gigantic negative piezoresistivity (G-NPR), which decreased the resistance up to 85% during the first 50% stretching. This G-NPR property is due to the rupture of the metal oxides, which allows the formation of liquid eutectic gallium-indium (EGaIn) and the connection of the over-layered networks to build new electrical paths. The electrodes exhibiting G-NPR are complementarily combined with conventional electrodes to amplify their performance or achieve some unique operations.

Interlocking-interface-enabled thermally deformable liquid metal/polymer membrane with high bonding strength

HypothesisThe high surface tension of liquid metal (LM) causes interface incompatibility and poor bonding strength with many substrates. Fine adjustment towards the properties of the surface area is sufficient to introduce strong bonding. Hence, we hypothesize that the interlocking structure using hydrophilic polyvinyl alcohol (PVA) as a “bridge” should be helpful for tight interfacial bonding of LM with polymeric substrates, thus achieving high-performance LM/polymer membranes, which have wide applications in the field of soft sensors and robotics. ExperimentsThe bulk EGaIn was fabricated into LM nanoparticles (LMNPs@PVA) solution. Then, PVA molecules were “doped” into the surface crosslink of the plasma treated polymer substrate by an interfacial penetrating method. Afterward, the solution was evenly dropped on the surface of the treated substrate to obtain the LMNP/polymer membrane after the water evaporated. Photothermal actuators were fabricated based on the membranes. FindingsDuring the interlocking structure, PVA macromolecules could be doped and trapped onto the top surfaces of various polymer substrates as binding “bridges” between the LMNPs and the matrix materials. The achieved LMNP membrane exhibites satisfactory bonding strength, durability and water-assisted erase-reprint, which can be used as soft photothermal actuators with remote laser control.

Machine learning-based model of surface tension of liquid metals: a step in designing multicomponent alloys for additive manufacturing

The surface tension (ST) of metallic alloys is a key property in many processing techniques. Notably, the ST value of liquid metals is crucial in additive manufacturing processes as it has a direct effect on the stability of the melt pool. Although several theoretical models have been proposed to describe the ST, mainly in binary systems, both experimental studies and existing theoretical models focus on simple systems. This study presents a machine learning model based on Gaussian process regression to predict the surface tension of multi-component metallic systems. The model is built and tested on available experimental data from the literature. It is shown that the model accurately predicts the ST value of binaries and ternaries with high precision, and that identifying certain trends in the ST values as a function of alloy composition is possible. The ability of the model to extrapolate to higher-order systems, especially novel concentrated alloys (high entropy alloys, HEA), is discussed.

Effect of Atomic Size on the Isothermal Bulk Modulus and Surface Tension of Liquid Metals

The isothermal bulk modulus \(K_{{T_{m}}}\) and surface tension γm of liquid metals at the melting point increase with decreasing atomic size a, and these dependences are similar to one another. It is shown that transition metals with a hexagonal closed-packed and body-centered cubic structure are concentrated above the γm−\(K_{{T_{m}}}\) regression line, and face-centered cubic metals are below this line. In alkali, alkaline earth, rare earth metals, the surface tension γm with a change in the isothermal bulk modulus \(K_{{T_{m}}}\) increases several times more intensively than in transition metals. The reduced quantities of isothermal bulk modulus and surface tension have been introduced. The reduced surface tension demonstrates high coincidence with atomic size parameter a−2, and the reduced isothermal bulk modulus with atomic size parameter a−3. The ratio of the surface tension to the product of the atomic size and the isothermal bulk modulus γm×(a \(K_{{T_{m}}}\))−1 compares the energy of atoms on the surface and in the bulk.

Surface tensions of Undercooled liquids Aluminum, Tantalum, Tungsten and Niobium

ABSTRACT Measurement of the surface tension of refractory liquid metals up to date is a difficult task. Values of the surface tension of liquid metals, in general, in the undercooled region are lacking. Here we have calculated the surface tensions of undercooled liquids Aluminium (Al) and the three refractory metals Tantalum (Ta), Tungsten (W) and Niobium (Nb) using our previously reported statistical thermodynamic equation. The calculations have been carried out below and above the melting temperature (Tm) of the metal thus covering the undercooled region by about 300 K below Tm. For Al, there was a notable jump at the melting point upon cooling where the surface excess entropy changed by 30%. This stems from the increased ordering at the surface upon cooling. The observed abrupt change indicates a first order surface phase transition at Tm from a pure liquid surface to a solid like surface structure upon cooling. For the other metals studied, the change was less pronounced. From the calculated value of the fraction of surface broken bond, it is concluded that the surface structure of the studied metals resemble that of simple metals. The calculated surface tensions above the melting point of the metals show good agreement with measured ones. Below the melting point of the metals, measurements are lacking that emphasise the importance of our calculations.

Numerical investigation on the performance of gas-lift pump with large density ratio of liquid to gas

Heavy liquid metals such as sodium and liquid lead-bismuth eutectic (LBE) have excellent heat transfer capability and receive increasing attention as the primary coolant in fast reactors and accelerator driven systems (ADS). In ADS system, coolant system is designed as natural circulation, to simplify the primary system, improve the compactness of reactors and most important of all is to increase the inherent safety of reactor. Because the electromagnetic pump that drives the flow of liquid metal is eliminated in the coolant natural circulation system. In such situation, gas-lift technique named gas-lift pump could be adopted to enhance the coolant natural circulation capacity. The open research on the performance of gas-lift liquid metal pump is much less than that of air- lift water pump. The physical properties of large density ratio of liquid to gas, small kinematic viscosity and high surface tension of liquid metal is believed to have effects on the performance of gas-lift liquid metal pump. The present paper carries out some preliminary numerical simulation work on the two-phase flow characteristics of argon-liquid LBE in the up-riser tube and the performance of gas-lift liquid metal pump. Eulerian-Eulerian two-fluid model is used to describe the two-phase flow. Some interphase momentum transfer models from literature are used to account for the interfacial momentum transfer between liquid and gas phases. SST k-ω model with mixture treatment is used to compute the turbulence parameters of the homogeneous mixing phase in the present study. The influence of such parameters as argon injection superficial velocity, submergence ratio and diameter of up-riser tube on the discharged LBE mass flow rate and pressure drop of gas-lift pump are checked. The results could be helpful for the design of the gas-lift liquid metal pump.

Liquid metal enabled continuous flow reactor: A proof-of-concept

Liquid metal enabled continuous flow reactor: A proof-of-concept

A combined numerical and experimental study to elucidate primary breakup dynamics in liquid metal droplet-on-demand printing

Droplet-on-demand liquid metal jetting is emerging as a powerful technology for the additive manufacturing of metallic parts. The success of this method hinges on overcoming several technological challenges. The principal one among these challenges is the controlled repeatable ejection of single uniform droplets. Due to the high density and surface tension of liquid metals, the droplet ejection process occurs near the minimal extremes of the printability phase diagram, defined by acceptable ranges for the Weber (We) and Ohnesorge (Oh) numbers. In this work, we experimentally demonstrate the satellite-free ejection of pneumatically actuated molten tin droplets in this extreme corner of printability and use a combination of high-speed video analysis and volume-of-fluid modeling to elucidate the droplet dynamics. While the simulations at low Oh and We can correctly describe several aspects of the breakup process, such as an increasing tail and pinch-point near the nozzle, no single parameter set can completely capture the droplet shape at breakup. Instead, the experimental droplet dynamics appear to include features from both high and low Oh breakup. This disagreement is ascribed to the incomplete description of the droplet ejection process including wetting and exit effects near the nozzle opening and surface effects such as transient cooling and oxide formation.

Voltage-induced penetration effect in liquid metals at room temperature.

Room-temperature liquid metal is discovered to be capable of penetrating through macro- and microporous materials by applying a voltage. The liquid metal penetration effects are demonstrated in various porous materials such as tissue paper, thick and fine sponges, fabrics, and meshes. The underlying mechanism is that the high surface tension of liquid metal can be significantly reduced to near-zero due to the voltage-induced oxidation of the liquid metal surface in a solution. It is the extremely low surface tension and gravity that cause the liquid metal to superwet the solid surface, leading to the penetration phenomena. These findings offer new opportunities for novel microfluidic applications and could promote further discovery of more exotic fluid states of liquid metals.

Temperature and oxygen adsorption coupling effects upon the surface tension of liquid metals

An accurate knowledge of the surface tension of liquid metals is critical for many theoretical and practical applications, especially in the current context of emerging growth of nanotechnology. The surface tension and its temperature dependence are drastically influenced by the level of impurities in the metal such as oxygen, sulphur or carbon. For this reason, experimental surface tension data of metals reported in literature are scattered. Strictly speaking, when referring to the surface tension of liquid metals, both variables temperature and oxygen content must be specified. There exists no clear formalism describing the coupling effect temperature and the oxygen content upon the surface tension of liquid metals. The aim of this work is to fill this gap. A thermodynamically self-consistent formulation for the surface tension of liquid metals and semiconductors as a function of temperature and oxygen content is established. According to the proposed formalism, a reliable expression for the surface tension of pure and oxygen saturated metals is then derived. The proposed model is found to be in good agreement with available experimental data, showing a good predictive capability. Aluminium is chosen and thoroughly evaluated as a case study, due to its very high sensitivity to oxygen level. Its surface tension is explicitly formulated as a function of temperature and oxygen content.

High-throughput production of uniformly sized liquid metal microdroplets using submerged electrodispersion

Microdroplets of gallium-based liquid metal alloys have enabled various applications in the fields of biomedicine, electronics, and chemistry. However, due to the high surface tension of liquid metal, high-throughput production of uniformly sized liquid metal microdroplets is challenging using conventional acoustic or microfluidic methods. Here, adapting the submerged electrodispersion technique that has conventionally been used for generating water-based microdroplets, we develop a simple and straightforward platform for the high-throughput production of near-monodisperse (coefficient of variation less than 5%) liquid metal microdroplets in oil without using microfluidic devices. We demonstrate the capabilities of this method for producing liquid metal microdroplets (diameters ranging from tens to hundreds of micrometers) and introduce a spinning disk to induce a flow of oil phase for preventing the coalescence of the microdroplets. The simplicity and remarkable abilities demonstrated for this method may pave the path for the development of future innovative applications based on liquid metal microdroplets.

Experimental modulation and theoretical simulation of zonal oscillation for electrostatically levitated metallic droplets at high temperatures

The second- and third-order zonal oscillations of metallic droplets at high temperatures beyond 2000 K were experimentally achieved by electrostatic levitation. To quantitatively describe the suspension stability of different metallic droplets, a stability factor model was proposed as a function of the surface tension and density. The influences of droplet size and temperature on the oscillation pattern, oscillation frequency, and oscillation amplitude were analyzed. As a supplement to experiment, a feasible mathematical model of droplet deformation and oscillation, coupling the effects of electrostatic and flow fields, was established to study the underlying mechanism of droplet dynamics at high temperatures. The simulation not only reproduced the experimental observations, but also predicted the evolution characteristics of higher-order oscillations. The inherent relationships between the oscillation frequency and the droplet size, density, and surface tension of liquid metals were systematically investigated by simulation. Moreover, the suspension stabilities of nine typical metallic droplets were derived and compared with the simulation results.