Showing papers on "Liquid metal published in 2011"

Inherently aligned microfluidic electrodes composed of liquid metal

Abstract: This paper describes the fabrication and characterization of microelectrodes that are inherently aligned with microfluidic channels and in direct contact with the fluid in the channels. Injecting low melting point alloys, such as eutectic gallium indium (EGaIn), into microchannels at room temperature (or just above room temperature) offers a simple way to fabricate microelectrodes. The channels that define the shape and position of the microelectrodes are fabricated simultaneously with other microfluidic channels (i.e., those used to manipulate fluids) in a single step; consequently, all of the components are inherently aligned. In contrast, conventional techniques require multiple fabrication steps and registration (i.e., alignment of the electrodes with the microfluidic channels), which are technically challenging. The distinguishing characteristic of this work is that the electrodes are in direct contact with the fluid in the microfluidic channel, which is useful for a number of applications such as electrophoresis. Periodic posts between the microelectrodes and the microfluidic channel prevent the liquid metal from entering the microfluidic channel during injection. A thin oxide skin that forms rapidly and spontaneously on the surface of the metal stabilizes mechanically the otherwise low viscosity, high surface tension fluid within the channel. Moreover, the injected electrodes vertically span the sidewalls of the channel, which allows for the application of uniform electric field lines throughout the height of the channel and perpendicular to the direction of flow. The electrodes are mechanically stable over operating conditions commonly used in microfluidic applications; the mechanical stability depends on the magnitude of the applied bias, the nature of the bias (DC vs. AC), and the conductivity of the solutions in the microfluidic channel. Electrodes formed using alloys with melting points above room temperature ensure mechanical stability over all of the conditions explored. As a demonstration of their utility, the fluidic electrodes are used for electrohydrodynamic mixing, which requires extremely high electric fields (∼105 V m−1).

Liquid Metal Alloys as Self-Healing Negative Electrodes for Lithium Ion Batteries

Abstract: Improving the capacity and durability of electrode materials is one of the critical challenges lithium-ion battery technology is facing presently. Several promising anode materials, such as Si, Ge, and Sn, have theoretical capacities several times larger than that of the commercially used graphite negative electrode. However, their applications are limited because of the short cycle life due to fracture caused by diffusion-induced stresses (DISs) and the large volume change during electrochemical cycling. Here we present a strategy to achieve high capacity and improved durability of electrode materials using low-melting point metallic alloys. With gallium as an example, we show that at a temperature above the melting point of Ga, a reversible solid-liquid transition occurs upon lithiation (lithium insertion) and delithiation (lithium extraction) of Ga. As a result, cracks formed in the lithiated solid state can be “healed” once the electrode returns to liquid Ga after delithiation. This work suggests that cracking as a failure mode can be remedied by using liquid metal electrodes.

A frequency shifting liquid metal antenna with pressure responsiveness

Abstract: This letter describes the fabrication and characterization of a shape shifting antenna that changes electrical length and therefore, frequency, in a controlled and rapid response to pressure. The antenna is composed of a liquid metal alloy (eutectic gallium indium) injected into microfluidic channels that feature rows of posts that separate adjacent segments of the metal. The initial shape of the antenna is stabilized mechanically by a thin oxide skin that forms on the liquid metal. Rupturing the skin merges distinct segments of the metal, which rapidly changes the length, and therefore frequency, of the antenna. A high speed camera elucidates the mechanism of merging and simulations model accurately the spectral properties of the antennas.

Development of the lead lithium (dcll) blanket concept

Abstract: Liquid metal breeders such as Lithium or the eutectic Lead-Lithium alloy PbLi have the potential for attractive breeding blankets, especially if the liquid metal serves as breeder and coolant. However, cooling of first wall and blanket structure is a challenging task because the magnetic field degrades the heat transfer and can cause a really high pressure drop. To overcome these problems, dual coolant blankets with helium cooled FW/blanket structure and a self-cooled breeding zone had been proposed, with electrical insulation by ceramic-coatings or sandwich flow channel inserts. Such concepts are in principle simpler than helium cooled blankets, but the thermal efficiency is limited to ˜35 % as in any helium cooled blankets with steel structure. A much higher efficiency up to about 45 % became feasible when the sandwich insulator was replaced by flow channel inserts (FCI) made of a SiC composite. This FCI serves as thermal insulator too, allowing an exit temperature of ˜700° C, suitable for a BRA...

A 12–18 GHz electrostatically tunable liquid metal RF MEMS resonator with quality factor of 1400–1840

Abstract: In this paper we present a novel tunable RF MEMS resonator that is based upon electrostatic control over the morphology of a liquid metal droplet (LMD). We demonstrate a LMD evanescent-mode cavity resonator that simultaneously achieves wide analog tuning from 12 to 18 GHz with a measured quality factor of 1400–1840. A droplet of 250-µm diameter is utilized and the applied bias is limited to 100 V. This device operates on a principle called Electro-Wetting On Dielectric (EWOD). The liquid metal employed is a non-toxic eutectic alloy of Gallium, Indium and Tin known as Galinstan. This device also exploits interfacial surface energy and viscous body forces that dominate at nanoliter scale.

Rheology of liquid metals and alloys

Abstract: The flow behavior and viscosity of liquid Zn, Sn, Cd, Bi-42 wt%Sn, Zn-7 wt%Al, and Sn-3 wt%Ag-0.5 wt%Cu were characterized and quantified with rotational rheometry experiments. Evidences from this study shows these liquid systems uniquely exhibit a shear thinning and time-independent (non-thixotropic) flow behavior in all the evaluated shear rate regimes. We have attempted to offer a physical explanation from prior-art for the observed unique flow behavior of the liquid metal systems. The strong short range atomic order in these metals significantly contribute to their flow behavior and at any shear rate the viscosity obeys the standard Arrhenius energy equation for temperature dependence.

A wireless passive RCS-based temperature sensor using liquid metal and microfluidics technologies

Abstract: A novel wireless and passive temperature sensor that utilizes microfluidic and liquid metal technologies for the temperature-dependent modification of the sensor's radar echo is introduced. Liquid metal is used to dynamically alter the number of antenna elements activated along a linear array configuration with respect to temperature. In this way, the sensed temperature value can be accurately quantified by the change in radar cross section (RCS) of the device. Simulation and measurements of the backscattered power of the temperature-reconfigurable array were performed to verify the concept and benchmark the sensitivity and temperature range of the sensor. This study is based on the number of elements activated by the short-circuiting of their gap through the temperature-expansion of liquid metal inside a bridging microfluidic channel. For the first time the remote measurement of temperature based on the RCS variability of a microfluidics-realized sensor is presented. It features an RCS range of 9 dBsm at 29.5 GHz corresponding to a tunable temperature range of at least 20°K and a resolution of 1.8 dBsm per element activated resulting in a temperature resolution around 4°K. It has to be noted that numerous major challenges encountered in the feeding and encapsulation of liquid metal inside microfluidic channels were addressed and preliminary guidelines for a novel generation of wireless sensors based on liquid metal and microfluidic technologies have been established for the first time.

Electrokinetics at liquid/liquid interfaces

Abstract: Electrokinetic effects at liquid/liquid interfaces have received considerably less attention than at solid/liquid interfaces. Because liquid/liquid interfaces are generally mobile, one might expect electrokinetic effects over a liquid/liquid interface to be faster than over an equivalent solid surface. The earliest predictions for the electrophoretic mobility of charged mercury drops – distinct approaches by Frumkin, along with Levich, and Booth – differed by , where is the radius of the drop and is the Debye length. Seeking to reconcile this rather striking discrepancy, Levine & O’Brien showed double-layer polarization to be the key ingredient. Without a physical mechanism by which electrokinetic effects are enhanced, however, it is difficult to know how general the enhancement is – whether it holds only for liquid metal surfaces, or more generally, for all liquid/liquid surfaces. By considering a series of systems in which a planar metal strip is coated with either a liquid metal or liquid dielectric, we show that the central physical mechanism behind the enhancement predicted by Frumkin is the presence of an unmatched electrical stress upon the electrolyte/liquid interface, which establishes a Marangoni stress on the droplet surface and drives it into motion. The source of the unbalanced electrokinetic stress on a liquid metal surface is clear – metals represent equipotential surfaces, so no field exists to drive an equal and opposite force on the surface charge. This might suggest that liquid metals represent a unique system, since dielectric liquids can support finite electric fields, which might be expected to exert an electrical stress on the surface charge that balances the electric stress. We demonstrate, however, that electrical and osmotic stresses on relaxed double layers internal to dielectric liquids precisely cancel, so that internal electrokinetic stresses generally vanish in closed, ideally polarizable liquids. The enhancement predicted by Frumkin for liquid mercury drops can thus be expected quite generally over ideally polarizable liquid drops. We then reconsider the electrophoretic mobility of spherical drops, and reconcile the approaches of Frumkin and Booth: Booth’s neglect of double-layer polarization leads to a standard electro-osmotic flow, without the enhancement, and Frumkin’s neglect of the detailed double-layer dynamics leads to the enhanced electrocapillary motion, but does not capture the (sub-dominant) electrophoretic motion. Finally, we show that, while the electrokinetic flow over electrodes coated with thin liquid films is faster than over solid/liquid interfaces, the Dukhin number, , which reflects the importance of surface conduction to bulk conduction, generally increases by a smaller amount [ ], where is the thickness of film and is the length of the electrode. This suggests that liquid/liquid interfaces may be utilized to enhance electrokinetic velocities in microfluidic devices, while delaying the onset of high- electrokinetic suppression.

Harvesting low grade heat to generate electricity with thermosyphon effect of room temperature liquid metal

Abstract: Based on thermosyphon effect of room temperature liquid metal, a technical strategy of harvesting low grade heat to generate electricity was proposed. A conceptual system was constructed and an open circuit voltage of 2.62 V with an electrical output power of 110 mW was yielded when the heating power was 45.6 W. This method resolves the difficulty of installing an electric generator in confined space and significantly enlarges the area for converting heat to electricity. Due to its simplicity, avoidance of moving parts, wide working temperature range, and self powering feature, this electric generation system is extremely reliable, completely silent, and flexible.

X-ray investigation of melt flow behavior under magnetic stirring regime in laser beam welding of aluminum

Abstract: The use of magnetic fields to influence weld bead shape and dilution in laser welding of aluminum alloys was recently suggested. It was already demonstrated for the case of laser welding of hot-cracking sensitive aluminum alloys with silicon-containing filler wire that applying alternating magnetic fields has an impact on the dilution of silicon in the melt pool, yielding a sufficient silicon content throughout the weld and allowing to suppress hot-cracking. However, the interaction mechanisms between the aluminum melt and the magnetic field are still subject of current investigations and are not fully revealed yet. The behavior of the melt flow under influence of an external magnetic field can be visualized by microfocused high-speed x-ray transmission imaging. To do so, high density tracer materials such as tin (Sn) and tungsten (W) particles that follow the melt flow are introduced into the base material. It can be seen that the additionally induced forces of the magnetic field cause higher velocities in the melt pool. Moreover, the flow of molten liquid perpendicular to the magnetic field is modified. The experimental results are discussed in light of general theoretical assumptions concerning a liquid metal flow under the influence of an external magnetic field. It is established that the effect of the alternating magnetic field can be explained as an anisotropic pulsating electromagnetic force brake that causes a specific deflection of the liquid metal flow.

Apparatus and method for liquid metals treatment

Abstract: This invention relates to an apparatus (high shear device) and method for treating liquid metals by intensive melt shearing. The apparatus comprises a stator and a rotor with a small gap between them to provide intensive melt shearing for dispersing efficiently and distributing uniformly gas, liquid and solid phases in liquid metals without severe turbulence at the melt surface. The device can be extended to a multistage high shear pump by arranging individual rotor/stator assemblies either concentrically (one in another) or vertically. The device and high shear pump can be readily integrated into existing casting processes. The device is suitable for use in casting processes including high pressure die casting, low pressure die casting, gravity die casting, sand casting, investment casting, direct chill casting, twin roll casting, and any other casting process which requires liquid metal as a feedstock. In addition, the device is particularly suitable for providing conditioned liquid metal for both shape casting and continuous (or semi-continuous) casting of metallic materials, preparing high quality semi-solid slurries, solidification processing of particulate reinforced metal matrix composites, mixing immiscible metallic liquids and degassing of liquid metals prior to any casting processes.

Density and surface tension of heavy liquid-metal coolants: Gallium and indium

Abstract: The density and surface tension of liquid high-purity gallium and indium as a function of temperature were studied. The sessile drop method was used to obtain these parameters. Experiments were carried out from the melting points to ∼1300 K in a high vacuum. The confidence error of the experiments was 0.5 and 1% for density and surface tension, respectively. The results of this research are compared with recommended reference data in the literature.

Self-Driven Electronic Cooling Based on Thermosyphon Effect of Room Temperature Liquid Metal

Abstract: Thermal management has been a critical issue for the safe running of an electronic device. Driving liquid metal with low melting point to extract heat from the thermal source is highly efficient because of its superior thermophysical properties over conventional coolant such as water or the like. In this paper, utilizing thermosyphon effect to drive room temperature liquid metal for electronic cooling was proposed for the first time with its technical feasibility demonstrated. This may lead to a self supported cooling which just utilizes the waste heat produced by the hot chip to drive the flow of liquid metal. And the device thus fabricated will be the one without any external pump and moving elements inside. A series of conceptual experiments under different operational conditions were performed to evaluate the cooling performance of the new method. Meanwhile, the results were also compared with that of water cooling by ways of thermal infrared graph and temperatures acquired by thermocouples. According to the measurements, it was found that the cooling performance of liquid metal was much stronger than that of water, and this will become even better with the increase of heat load, and height difference between the cooler and heater. A theoretical thermal resistance model was established and convective heat transfer coefficient was calculated to interpret the phenomenon with uncertainty analyzed. With further improvement of the present system and liquid metal coolant, this method is expected to be flexibly useful for heat dissipation of light-emitting diode (LED) street lamp, desk computer and radio remote unit (RRU), where confined space, efficient cooling, low energy consumption, dust-proof and water-proof are critically requested. [DOI: 10.1115/1.4005297]

Pneumatic dispensing of nano- to picoliter droplets of liquid metal with the StarJet method for rapid prototyping of metal

Abstract: This study presents a new, simple and robust, pneumatically actuated method for the generation of liquid metal micro droplets in the nano- to picoliter range. The so-called StarJet dispenser utilizes a star-shaped nozzle geometry that stabilizes liquid plugs in its center by means of capillary forces. Single droplets of the liquid metal can be pneumatically generated by the interaction of the sheathing gas flow in the outer grooves of the nozzle and the liquid metal. For experimental validation, a print head was build consisting of silicon chips with a star-shaped nozzle geometry and a heated actuator (up to 280C). The silicon chips are fabricated by Deep Reactive Ion Etching (DRIE). Chip designs with different star-shaped geometries were able to generate droplets with diameters in the range of the corresponding nozzle diameters. The StarJet can be operated in two modes: Either continuous droplet dis- pensing mode or drop on demand (DoD) mode. The continuous droplet generation mode for a nozzle with 183 lm diameter shows tear-off frequencies between 25 and 120 Hz, while droplet diameters remain constant at 210 lm for each pressure level. Metal columns were printed with a thickness of 0.5-1.0 mm and 30 mm height (aspect ratio (30), to demonstrate the directional stability of droplet ejection and its potential as a suitable tool for direct prototyping of the metal microstructures.

Laser diode package with enhanced cooling

Abstract: A laser diode package assembly includes a reservoir filled with a fusible metal in close proximity to a laser diode. The fusible metal absorbs heat from the laser diode and undergoes a phase change from solid to liquid during the operation of the laser. The metal absorbs heat during the phase transition. Once the laser diode is turned off, the liquid metal cools off and resolidifies. The reservoir is designed such that that the liquid metal does not leave the reservoir even when in liquid state. The laser diode assembly further includes a lid with one or more fin structures that extend into the reservoir and are in contact with the metal in the reservoir.

Arrangement and method for storing electric energy in electrochemical cells with a large diameter and high storage capacity

Abstract: An electrochemical cell assembly has electrochemical cells of large diameter and high storage capacity, making it particularly useful for stabilization of electric supply systems. The assembly includes at least one electrochemical cell composed of a layer of: a liquid metal or liquid metal alloy forming the cathode, a liquid electrolyte layer, and a layer of a liquid metal or liquid metalloid forming the anode. An electrically insulating inner tube is provided along the vertical axis of the assembly, the presence of which prevents the occurrence of the Tayler instability or other instabilities caused in the liquids by the current flow, and thus prevents the intermixing of the liquids. Another very efficient option for increasing the maximum current of the cell is that of conducting a current having a suitable direction and intensity through the interior of the inner tube.

Experimental evidence of Alfven wave propagation in a Gallium alloy

Abstract: Experiments with a liquid metal alloy, Galinstan, are reported and show clear evidence of Alfven wave propagation as well as resonance of Alfven modes. Galinstan is liquid at room temperature and, although its electrical conductivity is not as large as that of liquid sodium or NaK, it has still been possible to study Alfven waves, thanks to the use of intense magnetic fields up to 13 T. The maximal values of Lundquist number, around 60, are similar to that of the reference experimental study by Jameson [J. Fluid Mech. 19, 513 (1964)]. The generation mechanism for Alfven waves and their reflection is studied carefully. Numerical simulations have been performed and have been able to reproduce the experimental results, despite the fact that the simulated magnetic Prandtl number was much larger than that of Galinstan. An originality of the present study is that a poloidal disturbance (magnetic and velocity fields) is generated, allowing us to track its propagation from outside the conducting domain, hence without interfering.

Some Thermophysical Properties of Liquid Cr‐Mn‐Ni‐Steels

Abstract: In the last years new Cr-Mn-Ni-TRIP/TWIP steels have been developed at the Institute of Iron and Steel Technology, Freiberg University of Mining and Technology. Within the Collaborative Research Center SFB 799, the ZrO2-ceramic-TRIP-steel composite materials are produced using the infiltration of open foam ceramics with liquid steel and using powder metallurgy with small additions of ceramic powder before sintering. The thermophysical properties of liquid steel play an important role in both production routes. They affect the infiltration efficiency in one process and the produced powder size in the other, and therefore finally determine the composite properties. In this work some of these properties were estimated, as they are not available in literature. The investigated steels contain approximately 16% chrome, 7% manganese and 3% to 9% nickel. The surface tension was estimated using two methods: the drop weight method and the maximum bubble pressure method. In the drop weight method similar conditions at the gas/metal interface exist as during the atomization or the infiltration process, where liquid metal is exposed to high volume of inert gas. In all these cases the evaporation of manganese affects the surface tension. For comparison of results and for estimation of the liquid steel density the maximum bubble pressure method was used where the evaporation of manganese is limited. The wettability on partially MgO-stabilized ZrO2 ceramic substrates and its change with contact time was determined using the sessile drop method.

Theoretical Calculations of the Surface Tension of Liquid Transition Metals

Abstract: The surface tension of pure liquid mercury in the temperature range 273 K to 523 K (0 °C to 250 C°) was calculated using our previously reported equation. The results were compared with the experimental data and showed a good agreement. The surface tension of mercury decreases linearly with temperature, confirming a negative slope, and therefore shows the usual linear temperature dependence. The calculated surface excess entropy (0.21) is in excellent consistence with the experimental value (0.22). The surface tension also was calculated for many d-block metals (Ti, Zr, Fe, Co, Ni, Cu, Zn, Cd, Ag, Au, Pd, and Pt) at their melting points. The calculated values were compared with the existing experimental data.