Showing papers on "Liquid metal published in 2014"

Emerging Applications of Liquid Metals Featuring Surface Oxides

Abstract: Gallium and several of its alloys are liquid metals at or near room temperature. Gallium has low toxicity, essentially no vapor pressure, and a low viscosity. Despite these desirable properties, applications calling for liquid metal often use toxic mercury because gallium forms a thin oxide layer on its surface. The oxide interferes with electrochemical measurements, alters the physicochemical properties of the surface, and changes the fluid dynamic behavior of the metal in a way that has, until recently, been considered a nuisance. Here, we show that this solid oxide “skin” enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects.

Liquid metal enabled pump

Abstract: Small-scale pumps will be the heartbeat of many future micro/nanoscale platforms. However, the integration of small-scale pumps is presently hampered by limited flow rate with respect to the input power, and their rather complicated fabrication processes. These issues arise as many conventional pumping effects require intricate moving elements. Here, we demonstrate a system that we call the liquid metal enabled pump, for driving a range of liquids without mechanical moving parts, upon the application of modest electric field. This pump incorporates a droplet of liquid metal, which induces liquid flow at high flow rates, yet with exceptionally low power consumption by electrowetting/deelectrowetting at the metal surface. We present theory explaining this pumping mechanism and show that the operation is fundamentally different from other existing pumps. The presented liquid metal enabled pump is both efficient and simple, and thus has the potential to fundamentally advance the field of microfluidics.

Diverse transformations of liquid metals between different morphologies.

Abstract: Transformation from a film into a sphere, rapid merging of separate objects, controlled self-rotation, and planar locomotion are the very unusual phenomena observed in liquid metals under application of an electric field to a liquid metal immersed in or sprayed with water. A mechanism for these effects is suggested and potential applications - for example the recovery of liquid metal previously injected into the body for therapeutic purposes - are outlined.

Liquid Metal Actuator for Inducing Chaotic Advection

Abstract: Chaotic advection plays an important role in microplatforms for a variety of applications. Currently used mechanisms for inducing chaotic advection in small scale, however, are limited by their complicated fabrication processes and relatively high power consumption. Here, a soft actuator is reported which utilizes a droplet of Galinstan liquid metal to induce harmonic Marangoni fl ow at the surface of liquid metal when activated by a sinusoidal signal. This liquid metal actuator has no rigid parts and employs continuous electrowetting effect to induce chaotic advection with exceptionally low power consumption. The theory behind the operation of this actuator is developed and validated via a series of experiments. The presented actuator can be readily integrated into other microfl uidic components for a wide range of applications.

Influence of Water on the Interfacial Behavior of Gallium Liquid Metal Alloys

Abstract: Eutectic gallium indium (EGaIn) is a promising liquid metal for a variety of electrical and optical applications that take advantage of its soft and fluid properties. The presence of a rapidly forming oxide skin on the surface of the metal causes it to stick to many surfaces, which limits the ability to easily reconfigure its shape on demand. This paper shows that water can provide an interfacial slip layer between EGaIn and other surfaces, which allows the metal to flow smoothly through capillaries and across surfaces without sticking. Rheological and surface characterization shows that the presence of water also changes the chemical composition of the oxide skin and weakens its mechanical strength, although not enough to allow the metal to flow freely in microchannels without the slip layer. The slip layer provides new opportunities to control and actuate liquid metal plugs in microchannels—including the use of continuous electrowetting—enabling new possibilities for shape reconfigurable electronics, se...

Effect of Microtextured Surface Topography on the Wetting Behavior of Eutectic Gallium–Indium Alloys

Abstract: Liquid-embedded elastomer electronics have recently attracted much attention as key elements of highly deformable and "soft" electromechanical systems. Many of these fluid-elastomer composites utilize liquid metal alloys because of their high conductivities and inherent compliance. Understanding how these alloys interface with surfaces of various composition and texture is critical to the development of parallel processing technology, which is needed to create more complex and low-cost systems. In this work, we explore the wetting behaviors between droplets of gallium-indium alloys and thin metal films, with an emphasis on tin and indium substrates. We find that metallic droplets reactively wet thin metal foils, but the wettability of the foils may be tuned by the surface texture (produced by sputtering). The effects of both composition and texture of the substrate on wetting dynamics are quantified by measuring contact angle and droplet contact diameter as a function of time. Finally, we apply the Cassie-Baxter model to the sputtered and native substrates to gain insight into the behavior of liquid metals and the role of the oxide formation during interfacial processes.

Liquid Metal/Metal Oxide Frameworks

Abstract: A new platform described as the liquid metal/metal oxide (LM/MO) framework is introduced. The constituent spherical structures of these frameworks are made of micro- to nanosized liquid metal spheres and nanosized metal oxides, combining the advantages of both materials. It is shown that the diameters of the spheres and the stoichiometry of the structures can be actively controlled. Additionally, the liquid suspension of these spheres demonstrates tuneable plasmon resonances. These spherical structures are assembled to form LM/MO frameworks which are capable of demonstrating high sensitivity towards low concentrations of heavy metal ions, and enhanced solar light driven photocalalytic activities. These demonstrations imply that the LM/MO frameworks are a suitable candidate for the development of future high performance electronic and optical devices.

Liquid phase 3D printing for quickly manufacturing conductive metal objects with low melting point alloy ink

Abstract: Conventional 3D metal printings are generally time-consuming as well as lacking of high performance printable inks. From an alternative way, here we proposed the method of liquid phase 3D printing for quickly making conductive metal objects. Through introducing metal alloys whose melting point is slightly above room temperature as printing inks, several representative structures spanning from one, two and three dimension to more complex patterns were demonstrated to be quickly fabricated. Compared with the air-cooling in a conventional 3D printing, the liquid-phase-manufacturing offers a much higher cooling rate and thus significantly improves the speed in fabricating the target metal objects. This unique strategy also efficiently prevents the liquid metal inks from air oxidation, which is hard to avoid otherwise in an ordinary 3D printing. The key physical factors (such as properties of the cooling fluid, air pressure within the syringe barrel and needle diameter, types and properties of the printing ink) and several interesting intermediate fluids interaction phenomena between liquid metal and conventional cooling fluids such as water or ethanol, which evidently affecting the printing quality, were disclosed. In addition, a basic route to make future liquid phase 3D printer incorporated with both syringe pump and needle arrays was also suggested. The liquid phase 3D printing, which owns potential values not available in a conventional method, opens an efficient way for quickly making conductive metal objects in the coming time.

Atomized spraying of liquid metal droplets on desired substrate surfaces as a generalized way for ubiquitous printed electronics

Abstract: A direct electronics printing technique through atomized spraying for patterning room-temperature liquid metal droplets on desired substrate surfaces is proposed and experimentally demonstrated for the first time. This method is highly flexible and capable of fabricating electronic components on various target objects, with either flat or rough surfaces, made of different materials, or having different orientations from 2D to 3D geometrical configurations. With a pre-designed mask, the liquid metal ink can be directly deposited on the substrate to form various specific patterns which lead to the rapid prototyping of electronic devices. Further, extended printing strategies were also suggested to illustrate the adaptability of the method. For example, it can be used for making transparent conductive film with an optical transmittance of 47 % and a sheet resistance of 5.167Ω/□ due to natural porous structure. Different from the former direct writing technology where large surface tension and poor adhesion between the liquid metal and the substrate often impede the flexible printing process, the liquid metal here no longer needs to be pre-oxidized to guarantee its applicability on target substrates. One critical mechanism was that the atomized liquid metal microdroplets can be quickly oxidized in the air due to its large specific surface area, resulting in a significant increase of the adhesion capacity and thus firm deposition of the ink to the substrate. This study paved a generalized way for pervasively and directly printing electronics on various substrates which are expected to be significant in a wide spectrum of electrical engineering areas.

Liquid Metal: An Innovative Solution to Uniform Graphene Films

Abstract: The self-limited chemical vapor deposition of uniform single-layer graphene on Cu foils generated significant interest when it was initially discovered. Soon after, the fabrication of real uniform graphene was found to need extremely precise control of the growth conditions. Slight deviations terminate the self-limiting homogeneous growth, inevitably leading to multilayer graphene formation. Here we propose an innovative way to utilize liquid metals to resolve this thorny problem. In stark contrast to the low carbon solubility found in solid metals (e.g., Cu), catalytically decomposed carbon atoms are embedded in liquid metals. During cooling, the homogeneous solidified surface forms from the quasi-atomic smooth liquid surface, and carbon precipitation is blocked by the frozen metal lattices, which are insoluble to carbon. The underlying liquid bulk acts as a container to buffer the excess carbon supply, which normally would lead to the formation of multilayer graphene in the conventional CVD process. As ...

On the Design of Microfluidic Implant Coil for Flexible Telemetry System

Abstract: This paper describes the realization of a soft, flexible, coil fabricated by means of a liquid metal alloy encased in a biocompatible elastomeric substrate for operation in a telemetry system, primarily for application to biomedical implantable devices. Fluidic conductors are in fact well suited for applications that require significant flexibility as well as conformable and stretchable devices, such as implantable coils for wireless telemetry. A coil with high conductivity, and therefore low losses and high unloaded Q factor, is required to realize an efficient wireless telemetry system. Unfortunately, the conductivity of the liquid metal alloy considered-eutectic gallium indium (EGaIn)-is approximately one order of magnitude lower than gold or copper. The goal of this paper is to demonstrate that despite the lower conductivity of liquid metal alloys, such as EGaIn, compared with materials, such as copper or gold, it is still possible to realize an efficient biomedical telemetry system employing liquid metal coils on the implant side. A wireless telemetry system for an artificial retina to restore partial vision to the blind is used as a testbed for the proposed liquid metal coils. Simulated and measured results show that power transfer efficiency of 43% and 21% are obtained at operating distances between coils of 5 and 12 mm, respectively. Further, liquid metal based coil retains more than 72% of its performance (voltage gain, resonance bandwidth, and power transfer efficiency) when physically deformed over a curved surface, such as the surface of the human eye. This paper demonstrates that liquid metal-based coils for biomedical implant provide an alternative to stiff and uncomfortable traditional coils used in biomedical implants.

Channelless Fabrication for Large‐Scale Preparation of Room Temperature Liquid Metal Droplets

Abstract: The room-temperature liquid metal (RTLM), which is far from being fully exploited, is emerging as an ideal material for fabricating micro-droplets owing to its strong surface tension and easy phase control property. In order to find out a low-cost and technically simple way for quickly preparing metal particles in large-scale, here a channelless fabrication method based on stream jetting and self breaking up mechanisms of the RTLM when injected into and interact with the matching solution was proposed. Various typical factors on influencing the droplets generation behavior were experimentally investigated and clarified, such as the effects of the aperture size of the injection needle, the density, viscosity of the liquids and surfactants etc. Further, as an illustration of the flexibility of the present method, the direct construction of a three-dimensional porous metal block with foam-structures inside was also demonstrated. This study opened an extremely simple way for large scale fabrication of liquid metal micro-droplets and particles which has rather important practical values. It also suggests a highly efficient approach for visualizing and investigating the fundamental mechanisms of fluids interactions between RTLM and general solution.

Mixing in a liquid metal electrode

Abstract: Fluid mixing has first-order importance for many engineering problems in mass transport, including design and optimization of liquid-phase energy storage devices. Liquid metal batteries are currently being commercialized as a promising and economically viable technology for large-scale energy storage on worldwide electrical grids. But because these batteries are entirely liquid, fluid flow and instabilities may affect battery robustness and performance. Here we present estimates of flow magnitude and ultrasound measurements of the flow in a realistic liquid metal electrode. We find that flow does substantially affect mass transport by altering the electrode mixing time. Above a critical electrical current density, the convective flow organizes and gains speed, which promotes transport and would yield improved battery efficiency.

Weight and volume changing device with liquid metal transfer

Abstract: This paper presents a weight-changing device based on the transfer of mass. We chose liquid metal (Ga-In-Tin eutectic) and a bi-directional pump to control the mass that is injected into or removed from a target object. The liquid metal has a density of 6.44g/cm3, which is about six times heavier than water, and is thus suitable for effective mass transfer. We also combine the device with a dynamic volume-changing function to achieve programmable mass and volume at the same time. We explore three potential applications enabled by weight-changing devices: density simulation of different materials, miniature representation of planets with scaled size and mass, and motion control by changing gravity force. This technique opens up a new design space in human-computer interactions.

Liquid metal actuation-based reversible frequency tunable monopole antenna

Abstract: We report the fabrication and characterization of a reversible resonant frequency tunable antenna based on liquid metal actuation. The antenna is composed of a coplanar waveguide fed monopole stub printed on a copper-clad substrate, and a tunnel-shaped microfluidic channel linked to the printed metal. The gallium-based liquid metal can be injected and withdrawn from the channel in response to an applied air pressure. The gallium-based liquid metal is treated with hydrochloric acid to eliminate the oxide layer, and associated wetting/sticking problems, that arise from exposure to an ambient air environment. Elimination of the oxide layer allows for reliable actuation and repeatable and reversible tuning. By controlling the liquid metal slug on-demand with air pressure, the liquid metal can be readily controllable to connect/disconnect to the monopole antenna so that the physical length of the antenna reversibly tunes. The corresponding reversible resonant frequency changes from 4.9 GHz to 1.1 GHz. The antenna properties based on the liquid metal actuation were characterized by measuring the reflection coefficient and agreed well with simulation results. Additionally, the corresponding time-lapse images of controlling liquid metal in the channel were studied.

Electro-hydrodynamic shooting phenomenon of liquid metal stream

Abstract: We reported an electro-hydrodynamic shooting phenomenon of liquid metal stream. A small voltage direct current electric field would induce ejection of liquid metal inside capillary tube and then shooting into sodium hydroxide solution to form discrete droplets. The shooting velocity has positive relationship with the applied voltage, while the droplet size is dominated by the aperture diameter of the capillary nozzle. Further, the motion of the liquid metal droplets can be flexibly manipulated by the electrodes. This effect suggests an easy going way to generate metal droplets in large quantity, which is important from both fundamental and practical aspects.

First results of flowing liquid lithium limiter in HT-7

Abstract: Two different types of flowing liquid lithium limiters were firstly installed and successfully tested in HT-7 tokamaks in 2012 and some encouraging results were obtained. Two limiters of the first type, called FLiLi limiters, used a thin lithium layer flowing under gravity. The other type had lithium-metal infused trenches (LIMIT) for thermoelectric magnetohydrodynamic drive of the liquid metal flow. The surface of one of the FLiLi limiters was coated by evaporated lithium before liquid lithium was injected by Ar pressure into a special distributor of the limiter. Then the liquid lithium could slowly move along the plasma facing guide surface of the limiter due to gravity. For LIMIT, it was found that liquid lithium could flow along the trenches as expected with a velocity of about 3.7 ± 0.5 cm s−1 driven by the electromagnetic force, which came from the interaction between the thermoelectric current and magnetic field. Use of flowing liquid lithium limiters in HT-7 resulted in reduction of particle recycling, suppression of impurity emission and improvement of the confinement.

Electric current induced flow of liquid metals: Mechanism and substrate-surface effects

Abstract: Long range, continuous flow of liquid metals occurs upon application of an electric current. Here, we report experimental results elucidating the mechanism of current-induced liquid metal flow, and its dependence on substrate surface condition. It is shown that the observed flow is diffusion-controlled, with the flow-rate depending linearly on applied current density, indicating that it is driven by electromigration. The effective charge number for liquid electromigration, Z*, of several pure metals, such as Al, Bi, Ga, Sn, and Pb, were deduced from the experimental results and were found to be close to the elemental valency. With the exception of liquid Pb, Z* for all liquid metals tested in this study were positive, indicating that: (i) electron wind contributes much less to Z* in liquid metals than in solids, and (ii) with a few exceptions, liquid metals generally flow in the direction of the electric current. On smooth substrates which are wetted well by the liquid metal, flow occurs in a thin, continuous stream. On rough surfaces which are poorly wetted, on the other hand, discrete beads of liquid form, with mass transport between adjacent beads occurring by surface diffusion on the substrate. A rationale for the role of substrate roughness in fostering this observed transition in flow mechanism is presented.

Design, Fabrication, and Characterization of Liquid Metal Microheaters

Abstract: This paper reports design, fabrication, and characterization of liquid metal-based microheaters. Liquid metal microheaters designed via finite element simulation were fabricated by simply injecting eutectic gallium indium into polydimethylsiloxane (PDMS) microfluidic chips bonded to either silicon or PDMS substrates. Considering the net positive volume change of the microheater upon heating, both nonpressurized and pressurized contacts between the power supply and the liquid metal wires were investigated. The pressurized contact was found to provide more reliable electrical connection, thus more stable long-term operation than the nonpressurized contact. Due to higher thermal conductivity, liquid metal microheaters with silicon substrate exhibit better temperature uniformity than ones with PDMS substrate. However, liquid metal microheaters with PDMS substrate are flexible and deformable, thus more suitable than ones with silicon substrate when microheaters should be applied to nonflat objects.

Modeling of Electromagnetic Field and Liquid Metal Pool Shape in an Electroslag Remelting Process with Two Series-Connected Electrodes

Abstract: A three-dimensional finite-element model has been developed to understand the electromagnetic field and liquid metal pool shape in an electroslag remelting (ESR) process with two series-connected electrodes. The magnetic vector potential is introduced into the Maxwell’s equations, and the nodal-based method is used to solve a three-dimensional harmonic electromagnetic field. The heat transfer of the solidifying processes of ingot is modeled by a source-based enthalpy method, and the Joule heating is included in an inner source. The results show the main part of the current flows through the slag cap and a little enters into ingot in a two-series-connected electrode ESR system. As the interaction of self-induced and mutual-induced of two electrodes occurs, the skin effect is significantly suppressed by the neighbor effect. A symmetrical pattern of magnetic flux density in a two-series-connected electrode ESR system is displayed. The magnetic flux density between two electrodes is reinforced and reduced at the outside of two electrodes. The maximum Joule heat power density is located at the interface of slag and electrodes, and it decreases with an increase of the electrode immersion depth. The averaged Joule heat power density increases when slag cap thickness is reduced. With the increase of ingot height, the liquid metal pool shape changes from arc shaped to “V” shaped. When the ingot height is more than the diameter in the ESR processes, the liquid metal pool shape is constant.

Actively convected liquid metal divertor

Abstract: The use of actively convected liquid metals with j???B force is proposed to facilitate heat handling by the divertor, a challenging issue associated with magnetic fusion experiments such as ITER. This issue will be aggravated even more for DEMO and power reactors because the divertor heat load will be significantly higher and yet the use of copper would not be allowed as the heat sink material. Instead, reduced activation ferritic/martensitic steel alloys with heat conductivities substantially lower than that of copper, will be used as the structural materials. The present proposal is to fill the lower part of the vacuum vessel with liquid metals with relatively low melting points and low chemical activities including Ga and Sn. The divertor modules, equipped with electrodes and cooling tubes, are immersed in the liquid metal. The electrode, placed in the middle of the liquid metal, can be biased positively or negatively with respect to the module. The j???B force due to the current between the electrode and the module provides a rotating motion for the liquid metal around the electrodes. The rise in liquid temperature at the separatrix hit point can be maintained at acceptable levels from the operation point of view. As the rotation speed increases, the current in the liquid metal is expected to decrease due to the v???B electromotive force. This rotating motion in the poloidal plane will reduce the divertor heat load significantly. Another important benefit of the convected liquid metal divertor is the fast recovery from unmitigated disruptions. Also, the liquid metal divertor concept eliminates the erosion problem.

Liquid metal embrittlement of the T91 steel in lead bismuth eutectic: The role of loading rate and of the oxygen content in the liquid metal

Abstract: The mechanical behavior of the T91 martensitic steel tempered at 750 °C has been studied in liquid lead–bismuth eutectic (LBE) and in inert atmosphere. Several conditions were considered to point out the most sensitive embrittling factor. The Small Punch Test technique has been employed by using smooth specimens in air, in Ar–3.5%H 2 gas, in low oxygen content LBE and in oxygen saturated LBE at different temperatures and different loading rates. The T91 steel exhibited in general a high degree of ductility. However, even with oxygen saturated LBE, it has been possible to observe LME at low strain rate. Furthermore, low oxygen content in LBE and an increase in temperature promoted the LME. It turns out that the strain rate appeared as the critical parameter for the occurrence of LME of the T91 steel in LBE.

The Effect of Processing Conditions on Heat Transfer During Directional Solidification via the Bridgman and Liquid Metal Cooling Processes

Abstract: Finite-element-based solidification modeling was used to investigate the thermal characteristics of the Bridgman and liquid metal cooling (LMC) directional solidification (DS) processes. Physically representative boundary conditions were implemented within a finite-element model to test its applicability to a broad range of processing conditions. The dominant heat-transfer step for each case was identified. Relationships between the thermal gradient and the solid–liquid interface position relative to the transition region of the furnace were developed. The solidification rate, the local velocity of the solid–liquid interface, and the cooling rate as a function of withdrawal rate were analyzed. The curvature of the solid–liquid interface varies with the processing conditions and influences the local thermal condition and, therefore, the morphological development of dendritic structure during solidification. An extensive sensitivity analysis of process conditions was conducted for both the Bridgman and LMC techniques. The relative importance of process parameters on the resulting thermal conditions during solidification was identified. A protocol for determination of preferred process conditions was defined. The maximum axial thermal gradient at the surface of the casting occurs when the solid–liquid interface is just above the baffle for both the Bridgman and LMC DS processes, independent of casting geometry or mold-heater temperature.