Showing papers on "Liquid metal published in 2012"

Characterization of Nontoxic Liquid-Metal Alloy Galinstan for Applications in Microdevices

Abstract: We have obtained interfacial properties of Galinstan, a nontoxic liquid-metal alloy, to help replace mercury in miniature devices. To prevent formation of an oxide skin that severely hinders the fluidic behavior of small Galinstan droplets and leads to inaccurate property data, we performed our experiments in a nitrogen-filled glove box. It was found that only if never exposed to oxygen levels above 1 part per million (ppm) would Galinstan droplets behave like a liquid. Two key properties were then investigated: contact angles and surface tension. Advancing and receding contact angles of Galinstan were measured from sessile droplets on various materials: for example, 146.8 and 121.5, respectively, on glass. Surface tension was measured by the pendant-drop method to be 534.6 10.7 mN/m. All the measurements were done in nitrogen at 28 with oxygen and moisture levels below 0.5 ppm. To help design droplet-based microfluidic devices, we tested the response of Galinstan to electrowetting-on-dielectric actuation.

Flexible Liquid Metal Alloy (EGaIn) Microstrip Patch Antenna

Abstract: This paper describes a flexible microstrip patch antenna that incorporates a novel multi-layer construction consisting of a liquid metal (eutectic gallium indium) encased in an elastomer. The combined properties of the fluid and the elastomeric substrate result in a flexible and durable antenna that is well suited for conformal antenna applications. Injecting the metal into microfluidic channels provides a simple way to define the shape of the liquid, which is stabilized mechanically by a thin oxide skin that forms spontaneously on its surface. This approach has proven sufficient for forming simple, single layer antenna geometries, such as dipoles. More complex fluidic antennas, particularly those featuring large, co-planar sheet-like geometries, require additional design considerations to achieve the desired shape of the metal. Here, a multi-layer patch antenna is fabricated using specially designed serpentine channels that take advantage of the unique rheological properties of the liquid metal alloy. The flexibility of the resulting antennas is demonstrated and the antenna parameters are characterized through simulation and measurement in both the relaxed and flexed states.

Direct writing of flexible electronics through room temperature liquid metal ink.

Abstract: Background Conventional approaches of making a flexible circuit are generally complex, environment unfriendly, time and energy consuming, and thus expensive. Here, we describe for the first time the method of using high-performance GaIn10-based electrical ink, a significantly neglected room temperature liquid metal, as both electrical conductors and interconnects, for directly writing flexible electronics via a rather easy going and cost effective way. Methods The new generation electric ink was made and its wettability with various materials was modified to be easily written on a group of either soft or rigid substrates such as epoxy resin board, glass, plastic, silica gel, paper, cotton, textiles, cloth and fiber etc. Conceptual experiments were performed to demonstrate and evaluate the capability of directly writing the electrical circuits via the invented metal ink. Mechanisms involved were interpreted through a series of fundamental measurements. Results The electrical resistivity of the fluid like GaIn10-based material was measured as 34.5 µΩ·cm at 297 K by four point probe method and increased with addition of the oxygen quantity, which indicates it as an excellent metal ink. The conductive line can be written with features that are approximately 10 µm thick. Several functional devices such as a light emitting diode (LED) array showing designed lighting patterns and electrical fan were made to work by directly writing the liquid metal on the specific flexible substrates. And satisfactory performances were obtained. Conclusions The present method opens the way to directly and quickly writing flexible electronics which can be as simple as signing a name or drawing a picture on the paper. The unique merit of the GaIn10-based liquid metal ink lies in its low melting temperature, well controlled wettability, high electrical conductivity and good biocompability. The new electronics writing strategy and basic principle has generalized purpose and can be extended to more industrial areas, even daily life.

Experimental evidence for a transient Tayler instability in a cylindrical liquid-metal column.

Abstract: In the current-driven, kink-type Tayler instability (TI) a sufficiently strong azimuthal magnetic field becomes unstable against nonaxisymmetric perturbations. The TI has been discussed as a possible ingredient of the solar dynamo mechanism and a source of the helical structures in cosmic jets. It is also considered as a size-limiting factor for liquid metal batteries. We report on a liquid metal TI experiment using a cylindrical column of the eutectic alloy GaInSn to which electrical currents of up to 8 kA are applied. We present results of external magnetic field measurements that indicate the transient occurrence of the TI in good agreement with numerical predictions. The interference of TI with the competing large-scale convection, resulting from Joule heating, is also discussed.

Formation of Spherical and Non-Spherical Eutectic Gallium-Indium Liquid-Metal Microdroplets in Microfluidic Channels at Room Temperature

Abstract: Here, the formation of eutectic Gallium-Indium (EGaIn) liquid-metal microdroplets, both spherical and non-spherical, in microfluidic devices at room temperature is reported. Monodisperse microdroplets were created in an aqueous polyethylene glycol (PEG) solution, in oxygenated and in deoxygenated silicone oil. The volume of the droplets depends on the channel dimensions and flow rates applied, varying between 0.5 and 4 nL. Non-spherical droplets were formed in oxygenated silicone oil due to the instantaneous formation of an oxide layer. These metal "micro-rice" droplets retained their shape and did not spontaneously reflow to form shapes of the lowest interfacial energy on egress from the channel, unlike in aqueous PEG solution and in deoxygenated silicone oil. Liquid-metal droplets with such tunable morphology can potentially be used in MEMS devices for optical and electrical switches, valves and micropumps. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reconfigurable liquid metal circuits by Laplace pressure shaping

Abstract: We report reconfigurable circuits formed by liquid metal shaping with <10 pounds per square inch (psi) Laplace and vacuum pressures. Laplace pressure drives liquid metals into microreplicated trenches, and upon release of vacuum, the liquid metal dewets into droplets that are compacted to 10–100× less area than when in the channel. Experimental validation includes measurements of actuation speeds exceeding 30 cm/s, simple erasable resistive networks, and switchable 4.5 GHz antennas. Such capability may be of value for next generation of simple electronic switches, tunable antennas, adaptive reflectors, and switchable metamaterials.

A Pressure Responsive Fluidic Microstrip Open Stub Resonator Using a Liquid Metal Alloy

Abstract: This letter describes a fluidic microstrip bandstop filter with transmission properties that change in discrete states. The filter consists of a liquid metal alloy - eutectic gallium indium (EGaIn) - as the conductive component in microfluidic channels. The fluidity of EGaIn allows the open stub resonator of the filter to change its length by flowing in response to an applied pressure. A series of posts in the channel defines the length of the stub filled by the metal and dictates the pressure needed for the liquid metal to flow and thereby extend the stub length. The frequency response of the filter changes in response to the changes in the length of the resonator stub. This approach is a simple method for creating tunable filters and impedance matching sections using soft materials that change dimensions in response to pressure.

Printable tiny thermocouple by liquid metal gallium and its matching metal

Abstract: Direct printing of thermocouples by the liquid metal was proposed. The fabricated temperature sensor composed of gallium and its matching metal exhibited excellent linear dependence between thermoelectric voltage and temperature within the range from 0 to 200 °C. Further, it was disclosed that liquid metals with high purity could be used for high precision thermocouples with tiny size, which were quite convenient to be used in micro channel measurement due to their fluidity in making sensors; while liquid metals with a small amount of oxides were handy for depositing on the substrate by “hand-written” style, with thin film thickness of approximately 50 μm.

Eutectic liquid alloys for plasmonics: theory and experiment.

Abstract: We report a method based on density functional theory molecular dynamics that allows us to calculate the plasmonic properties of liquid metals and metal alloys from first principles with no a priori knowledge of the system. We show exceptional agreement between the simulated and measured optical constants of liquid Ga and the room temperature liquid In–Ga eutectic alloy (Tm = 289 K). We then use this method to analyze the plasmonic properties of various alloy concentrations in the In–Ga system. The plasmonic performance of the In–Ga system decreases with increasing In concentration. However, the benefits of a room-temperature plasmonic liquid are likely to outweigh the minor reduction in plasmonic performance when moving from pure Ga to the eutectic composition. Our results show that density functional theory molecular dynamics can be used as a predictive tool for studying the optical properties of liquid metal systems amenable to plasmonics.

Effect of pouring temperature on cooling slope casting of semi-solid Al-Si-Mg alloy

Abstract: Present trend of semi-solid processing is directed towards rheocasting route which allows manufacturing of near-net-shape cast components directly from the prepared semi-solid slurry. Generation of globular equi-axed grains during solidification of rheocast components, compared to the columnar dendritic structure of conventional casting routes, facilitates the manufacturing of components with improved mechanical properties and structural integrity. In the present investigation, a cooling slope has been designed and indigenously fabricated to produce semi solid slurry of Al-Si-Mg (A356) alloy and successively cast in a metallic mould. The scope of the present work discusses about development of a numerical model to simulate the liquid metal flow through cooling slope using Eulerian two-phase flow approach and to investigate the effect of pouring temperature on cooling slope semi-solid slurry generation process. The two phases considered in the present model are liquid metal and air. Solid fraction evolution of the solidifying melt is tracked at different locations of the cooling slope, following Schiel's equation. The continuity equation, momentum equation and energy equation are solved considering thin wall boundary condition approach. During solidification of the liquid metal, a modified temperature recovery scheme has been employed taking care of the latent heat release and change of fraction of liquid. The results obtained from simulations are compared with experimental findings and good agreement has been found.

Electromagnetic flow measurements in liquid metals using time-of-flight Lorentz force velocimetry

Abstract: Time-of-flight Lorentz force velocimetry is a non-invasive electromagnetic measurement technique that can be used to determine both the flow rate and/or the local velocities in electrically conducting fluids like liquid metals. Using this technique, two identical so-called Lorentz force flow meters—each consisting of a permanent magnet system and an attached digital force sensor—are arranged in a row and separated by a defined distance. Each flow meter measures the Lorentz force that is generated within the melt when the electrically conducting liquid metal passes the magnetic field. This time-of-flight technique can be exploited for the flow measurement by purely cross-correlating the two force signals. Hence, the measurement becomes independent of any fluid properties and magnetic field parameters. We present results of two model experiments that demonstrate that time-of-flight Lorentz force velocimetry is feasible for non-contact measurement of both global flow rates and local surface velocity in turbulent liquid metal flow. In these experiments, we use the low-melting eutectic alloy Ga68In20Sn12 as a test melt. Moreover, to support these experimental findings, we present results of numerical simulations using the commercial codes FLUENT and MAXWELL. The numerical predictions are in good agreement with the experimental findings.

Normal Spectral Emissivity Measurement of Liquid Iron and Nickel Using Electromagnetic Levitation in Direct Current Magnetic Field

Abstract: Normal spectral emissivities of liquid iron and nickel were measured for wavelengths of 780 to 920 nm by direct measurement of normal spectral radiance using electromagnetic levitation in a direct current (DC) magnetic field A DC magnetic field suppressed surface oscillation and the transitional motion of the liquid metal droplets The normal spectral emissivities of both liquid iron and nickel show weak negative wavelength dependence and have negligible temperature dependence The normal spectral emissivities of liquid iron and nickel at 807 nm were determined respectively as 0394 ± 0012 (1600 K to 1950 K (1327 °C to 1677 °C)) and 0368 ± 0004 (1720 K to 1825 K (1447 °C to 1552 °C)) The experimental uncertainty used here is double the value of the standard deviation

Mechanism for Formation of Surface Scale during Directional Solidification of Ni-Base Superalloys

Abstract: Surface scale occurs on the external surface of directionally solidified, single-crystal turbine components. It is one of the most important casting defects because it affects the grain orientation assessment and causes incipient surface melting during heat treatment. The formation of surface scale comprises a three-stage process: (1) formation of a 0.5- to 1.5-μm Al2O3 layer around the external surface of liquid metal as a result of the mold/metal reaction between the liquid and the mold prime coat; (2) separation of the solidified metal from the mold wall during cooling, where the Al2O3 layer is stripped away from the metal surface but remains adhered to the mold; and (3) subsequent oxidation of the “bare” metal to form an oxide scale at the surface. The scale comprises a mixture of oxides. It is found that TiO2, Cr2O3, and Al2O3 form on components cast using the 1st generation alloy, SRR99; however, in the case of castings using the 3rd-generation alloy, CMSX10N it is a predominately nickel-rich oxide (likely to be NiO). On the unscaled surface, the mold and metal are in intimate contact during casting, and subsequent cooling and the Al2O3 layer around the external surface prevents subsequent oxidation of the casting surface.

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

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 280°C). 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 dispensing mode or drop on demand (DoD) mode. The continuous droplet generation mode for a nozzle with 183 μm diameter shows tear-off frequencies between 25 and 120 Hz, while droplet diameters remain constant at 210 μm 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.

Method for preparing graphene by adopting liquid catalyst aided chemical vapor deposition

Abstract: The invention discloses a method for preparing a graphene film by using a liquid metal or alloy as a catalyst and adopting chemical vapor deposition. The metal with low melting point comprises typical gallium, tin, indium and the like; and the alloy with low melting point comprises gallium-copper, gallium-nickel, indium-copper, indium-nickel, tin-copper, tin-nickel, copper-silver-tin and the like. The chemical vapor deposition is performed above the melting point of the metal or alloy catalyst, so that the continuous graphene film is formed on the surface of the catalyst and the interface of the catalyst and a substrate. Compared with the graphene grown on the surface of a solid catalyst such as copper and nickel, the invention has the advantages that the prepared graphene is controllable in layer number, low in requirement for the micro morphology of the surface of the substrate and suitable for multiple substrate materials, and the catalyst is very easy to remove. The obtained graphene positioned on the surface of the liquid has unique application value.

Liquid Metal-Filled Micro Heat Pipes for Thermal Management of Solid-State Devices

Abstract: Microelectromechanical systems technology can be used to realize micro heat pipes (MHPs) for thermal management of solid-state devices in industrial applications. Similar to the uses of traditional heat pipes in the macroworld, MHPs provide a passive and efficient way of spreading heat away from a heat source. MHPs have recently been demonstrated using alcohol or water as the working fluid. Liquid metals have superior thermal properties compared to water or alcohol and have been used in macroscale heat pipes for many years. However, liquid metal working fluids have not previously been demonstrated in MHPs. By utilizing indium cold welding of micromachined silicon structures, liquid metal-filled MHPs were successfully fabricated and then evaluated. Their performance was proven to be superior to the performance of equivalent water-filled MHPs.

Liquid metal corrosion in nuclear reactor and accelerator driven systems

Abstract: Liquid metals such as Na, Li, Pb-17Li, Pb and eutectic alloy of Pb-Bi are used as the coolants in advanced nuclear energy systems. General features are presented of corrosion and mass transfer in these liquid metal systems with respect to the solubility of alloying elements of the structural materials in the coolants and the role of dissolved non-metallic impurities present in this mass transport phenomenon. The experimental results made in each liquid metal coolant system taking into account the chosen structural material are also discussed.

Natural circulation and linear stability analysis for liquid- metal reactors with the effect of fluid axial conduction

Abstract: The effect of fluid axial thermal conduction on one-dimensional liquid metal natural circulation and its linear stability was performed through nondimensional analysis, steady-state assessment, and linear perturbation evaluation. The Nyquist criterion and a root-search method were employed to find the linear stability boundary of both forward and backward circulations. The study provided a relatively complete analysis method for one-dimensional natural circulation problems with the consideration of fluid axial heat conduction. The results suggest that fluid axial heat conduction in a natural circulation loop should be considered only when the modified Peclet number is {approx}1 or less, which is significantly smaller than the practical value of a lead liquid metal-cooled reactor.

Dissolution of High Density Inclusions in Titanium Alloys

Abstract: This paper deals with the presence of High Density Inclusions (HDI) in VAR melted titanium ingots. For performance and economical reasons, the elimination of these inclusions is of utmost importance for the titanium industry. However, very few studies have considered dissolution aspects of HDIs and accurate data on their dissolution rates still lack in the literature. In the present study, we investigate the mass transport driven dissolution of some HDIs (tungsten and molybdenum) in CPTi, Ti64 and Ti17 baths. This has been done by allowing the partial dissolution of cylindrical rods in molten titanium for various controlled periods of time. Dissolution rates have been determined by measuring the dimensions of these samples before and after the experiments. In some cases, the chemical composition of the solidified bath near the sample has also been measured by Scanning Electron Microscope. It has been evidenced that the dissolution kinetics depends highly on the liquid metal agitation and temperature. The results also revealed that the dissolution of both tungsten and molybdenum is higher in pure titanium than in the investigated alloys. A numerical model describing the mass transport driven dissolution was used to determine dissolution rates numerically and to compare them to experimental results.

Factors determining the rate of the process of metal bath components evaporation

Abstract: The phenomenon of evaporation of volatile metal bath components can be observed in numerous process of both extractive metallurgy and refi ning. In some of them, this phenomenon can be considered positive, in others, however, to the contrary. In order to intensify the evaporation process or to restrain it, one must necessarily know the factors determining its rate. The most important of those factors include pressure inside the system, the gaseous atmosphere type, temperature and hydrodynamic properties of the system in which the given metallurgical process is being analysed. From a kinetic point of view, the process of volatile metal bath component evaporation can be divided into three main stages: transfer of the evaporating component from the body of the liquid phase to the interface, evaporation of the component from the interface, transfer of the evaporating component vapours from the interface to the core of the liquid phase. The mass fl ux of the evaporating component “i” transferred from the body of the liquid metal to the interface is characterised by the following relation:

A Molecular Dynamics Simulation Study of the Cavitation Pressure in Liquid Al

Abstract: To understand the formation mechanism of hot tearing defects generated during casting, a knowledge of the pressure at which cavities form spontaneously in the liquid metal is required. In this work, molecular dynamics (MD) simulations were used to compute the cavitation pressure P c in liquid Al, where atomic interactions were described by an embedded atom method potential. The cavitation pressure was computed for various initial conditions and system sizes, and using classic nucleation theory, P c was extrapolated from MD length and time scales to those appropriate for casting. A value of P c ≈ −670 MPa was obtained, which is several orders of magnitude less than that predicted from hot tearing models. To investigate the possible role of heterogeneous nucleation sites, the P c simulations were repeated on solid–liquid systems that were simultaneously solidifying. In addition, the influence of a trace impurity Mg on the cavitation pressure was also investigated. Neither the impure Mg atoms nor the solid–liquid interfaces act as heterogeneous sites.

Liquid metal electrodes for rechargeable batteries

Abstract: An electrode for a lithium ion battery includes a liquid metal having a melting point that is below the operating temperature of the battery, which transforms from a liquid to a solid during lithiation, and wherein the liquid metal transforms from a solid to a liquid during delithiation.

Electronic device with cooling by a liquid metal spreader

Abstract: An electronic device with cooling of a heat dissipation source, by a liquid metals spreader, the device including at least one heat dissipation source, at least one spreader through which at least one liquid metal circulation channel passes forming a loop routed below a heat dissipation source, at least one heat sink, and at least one electromagnetic pump moving the liquid metal in the at least one channel such that the liquid metal absorbs heat dissipated by a heat dissipation source and transports the absorbed heat to be evacuated by the heat sink. Each spreader includes at least two plates made of an electrical insulating material located on each side of at least one bar made of deformable material.

A numerical study on the use of liquid metals (gallium and mercury) as agents to enhance heat transfer from hot water in a co-flow mini-channel system

Abstract: Enhancement in the heat removal from hot water co-flowing in a mini-channel in a direct contact manner with two liquid metals, gallium and mercury, is investigated numerically. Results show that the liquid metals lead to superior heat removal from hot water co-flowing in the channel as compared to the case when only water flows in the channel. Moreover, it is found that gallium yields higher heat removal from water than mercury by about 15 %. This percentage, representing the superiority of gallium over mercury increases to about 20 % under conditions when the mass flow rate of both the liquid metal and the co-flowing water are doubled. The results reported showed numerical mesh independence. However, the results show much dependence on the spatial discretization scheme adopted where it is found that first order upwind scheme yields somewhat over predicted heat exchange rates in the channel, as compared with the case when a second order scheme is used. It is found further that the channel efficiency in removing heat from the water is remarkable in the first half of the overall channel length where in general the heat removed in the first 10 mm of the channel length is found to be about 70 % of the total heat removed. This percentage is a bit less than that when only water flows in the channel.

Electron contribution to energy of alkali metals in the scheme of an embedded atom model

Abstract: The behavior of the energy of molecular dynamics models of alkali metals constructed using the embedded atom potential at high temperatures is discussed. Pair potentials and embedding potentials for lithium, sodium, potassium, rubidium, and cesium are presented as uniform analytical expressions. If the parameters of the potential of the embedded atom model (EAM) are selected based on the known dependence of the density of liquid metal on temperature, then, as temperature approaches the critical one, the actual energy increases faster than the energy of the models in all cases. The thermal contribution of electron gas to the energy of metal is considered as the cause of the discrepancy. It is shown that it is possible to eliminate the discrepancy between energies of models and the actual metal at high temperatures, if the energy of thermal excitation of electrons is taken into consideration. The difference between the actual energy of metal and the energies of EAM for liquid Li, K, and Cs is almost equal to the contribution of the thermal energy of electrons. The thermal energy of electrons is taken into account in analysis of data obtained using shock compression.

Atomic transport and surface properties of some simple liquid metal using one component plasma system

Abstract: In the present paper, we have calculated diffusion coefficient, viscosity coefficient, and surface tension of liquid metals near melting point (Li, Na, K, Rb, Cs, Mg, Al, Pb, and Bi). We have applied our newly constructed model potential to describe electron ion interaction with one component plasma reference system. We have also investigated the effect of different correction functions such as those of Hartree, Hubbard and Sham, Vashista and Singwi, Taylor, Ichimaru and Utsumi, Farid et al., and Sarkar et al. on the above-said properties. It is observed that the present results are found to be in good agreement with those of experimental data as well as with other theoretical results.