Eutectic Alloy Of Gallium Research Articles

Scalable Microwires through Thermal Drawing of Co-Extruded Liquid Metal and Thermoplastic Elastomer.

This article demonstrates scalable production of liquid metal (LM)-based microwires through the thermal drawing of extrudates. These extrudates were first co-extruded using a eutectic alloy of gallium and indium (EGaIn) as a core element and a thermoplastic elastomer, styrene-ethylene/butylene-styrene (SEBS), as a shell material. By varying the feed speed of the co-extruded materials and the drawing speed of the extrudate, it was possible to control the dimensions of the microwires, such as core diameter and shell thickness. How the extrusion temperature affects the dimensions of the microwire was also analyzed. The smallest microwire (core diameter: 52 ± 14 μm and shell thickness: 46 ± 10 μm) was produced from a drawing speed of 300.1 mm s-1 (the maximum attainable speed of the apparatus used), SEBS extrusion speed of 1.50 mm3 s-1, and LM injection rate of 5 × 105 μL s-1 at 190 °C extrusion temperature. The same extrusion condition without thermal drawing generated significantly large extrudates with a core diameter of 278 ± 26 μm and shell thickness of 430 ± 51 μm. The electrical properties of the microwires were also characterized under different degrees of stretching and wire kinking deformation which proved that these LM-based microwires change electrical resistance as they are deformed and fully self-heal once the load is removed. Finally, the sewability of these microwires was qualitatively tested by using a manual sewing machine to pattern microwires on a traditional cotton fabric.

Long-Term Corrosion of Eutectic Gallium, Indium, and Tin (EGaInSn) Interfacing with Diamond.

Thermal transport is of grave importance in many high-value applications. Heat dissipation can be improved by utilizing liquid metals as thermal interface materials. Yet, liquid metals exhibit corrosivity towards many metals used for heat sinks, such as aluminum, and other electrical devices (i.e., copper). The compatibility of the liquid metal with the heat sink or device material as well as its long-term stability are important performance variables for thermal management systems. Herein, the compatibility of the liquid metal Galinstan, a eutectic alloy of gallium, indium, and tin, with diamond coatings and the stability of the liquid metal in this environment are scrutinized. The liquid metal did not penetrate the diamond coating nor corrode it. However, the liquid metal solidified with the progression of time, starting from the second year. After 4 years of aging, the liquid metal on all samples solidified, which cannot be explained by the dissolution of aluminum from the titanium alloy. In contrast, the solidification arose from oxidation by oxygen, followed by hydrolysis to GaOOH due to the humidity in the air. The hydrolysis led to dealloying, where In and Sn remained an alloy while Ga separated as GaOOH. This hydrolysis has implications for many devices based on gallium alloys and should be considered during the design phase of liquid metal-enabled products.

The Thermal Conductivity of Near-Eutectic Galinstan (Ga68.4In21.5Sn10) Molten Alloy

The need for new heat transfer agent for many applications, namely in the consumer electronics industry, requires materials, liquids at room temperature, with high thermal conductivity. From the different possibilities, Galinstan, a eutectic alloy of Gallium, Indium, and Tin with a melting point (Tm = 283.4 K) has been proposed for many applications, namely for replacing the toxic mercury element, used for many years. It is the purpose of this paper to report thermal conductivity measurements of Galinstan, product name Gallium/Indium/Tin Eutectic (NL-011), Ga68.4In21.5Sn10. The method used was the transient hot strip (THS), using a platinum metal-film sensor, produced by PVD in ceramic substrates, and electrically insulated with a heat-shrinkable coating. The details of the data acquisition system and measuring procedure are reported. Measurements were performed between 28 °C and 103 °C (301 K to 376 K), at atmospheric pressure, with an estimated uncertainty of 6%, and compared with available literature. Data were correlated for linear interpolation. This type of sensor is applied to molten metals for the first time, proofing to concept to future applications in molten metals and molten salts at higher temperatures.Graphical

Conjugate heat transfer of a turbulent tube flow of water and GaInSn with azimuthally inhomogeneous heat flux

An experimental study of the conjugate heat transfer in a turbulent tube flow with azimuthally homogeneous and inhomogeneous heat flux distribution, where the tube is heated with a constant heat flux only over the half circumference, is presented. Using two fluids with clearly different Prandtl numbers (water and a liquid metal alloy), thermohydraulic effects that occur when fluids with very low Prandtl number are used in contrast to ordinary fluids (e.g. water with Pr≈1) are discussed. The test section is validated with water (Pr=5−7.4) for a Reynolds number in the range of 5·103<Re<4.2·104. The experimental data agree excellently with literature data. The maximum nondimensional temperature at the inner surface of the tube is expressed using a simple relationship based on the efficiency of a fin with an adiabatic tip. A near eutectic alloy of gallium, indium and tin (GaInSn, Pr=0.03) is used for the liquid metal experiments. The Péclet number is varied within the range of 240<Pe<3·103. Based on the experimental data of this work, an adapted correlation for the Nusselt number in a turbulent liquid metal tube flow with azimuthally homogeneous heat flux is provided:Nu=4.364+0.0276·Pe0.803The experimental data underlines, that the azimuthally averaged Nusselt number for an azimuthally inhomogeneous heat flux distribution can also be calculated with this correlation with an acceptable level of accuracy. Remarkably, the ratio of the local convective heat transfer coefficient to the azimuthally averaged value for GaInSn reaches a value up to 0.6 at the location of the maximum wall temperature. This is in strong contrast to water, where this ratio is close to unity.

Turbulent heat transfer in a liquid metal tube flow with azimuthally inhomogeneous heat flux

An experimental study of the convective heat transfer in a turbulent liquid metal tube flow with azimuthally inhomogeneous heat flux is presented. Prior to the liquid metal experiments, the validation of the test section was realized using water. These results showed a very good agreement with literature data. For the liquid metal experiments, an eutectic alloy of gallium, indium and tin (GaInSn) was used. The Péclet number was varied between 1400 and 3600, thus in a regime of forced convection. Experiments with homogeneous heating over the full circumference of the tube and inhomogeneous heating over half of the circumference with the other half being insulated, were performed. The azimuthally averaged Nusselt number and the temperature distribution in the tube wall were investigated. The results suggest that the azimuthally averaged Nusselt number for water and liquid metal tube flows with inhomogeneous heating over the circumference can be calculated sufficiently well with literature correlations for uniform heat flux. For an inhomogeneous heat flux the azimuthal temperature gradient in the tube wall increases for higher Reynolds number and is more pronounced for GaInSn than for water. Furthermore, impurities like oxide particles significantly decrease the liquid metal convective heat transfer coefficient.

Design and calibration of permanent magnet probes for the local measurement of velocity and temperature in a liquid metal backward facing step flow

The simultaneous and local measurement of velocity and the temperature of a non-isothermal liquid metal flow has been an ongoing research topic over decades. The motivation is to obtain a detailed panorama of a liquid metal flow for the validation of turbulent heat flux models. So-called permanent magnet probes were used in the past for the local measurement of velocity and temperature profiles in liquid sodium in rather canonical flow configurations. The next step is to measure velocity and temperature profiles in a more complex flow geometry, namely a vertical confined backward facing step. For this, the permanent magnet probe must be adapted regarding its design, calibration procedure and temperature correction method. Particularly, considering that for this experiment the eutectic alloy of gallium, indium and tin was used as a working fluid, instead of liquid sodium, as in the mentioned past experiments. The main design aspects for a permanent magnet probe found in the literature are summarized and applied to the present probe. A calibration strategy for the probe was developed and implemented for the measurement of mean velocity profiles. A wetting procedure for the probe is proposed. The measured probe sensitivity for all six used probes agrees well with the theoretical estimations. The highest uncertainty contribution to measured sensitivity is related to the typical wetting issues of gallium–indium–tin. Future implementation of permanent magnet probes in general gallium–indium–tin experiments can make use of the developed know-how shared in this work.Graphic abstract

Liquid Metal-Triggered Assembly of Phenolic Nanocoatings with Antioxidant and Antibacterial Properties

Liquid metal (LM) catalysts have been demonstrated to accelerate chemical reactions, providing an intriguing route to fine chemical synthesis with immense technological implications. Herein, we explore gallium-based LMs as catalysts to promote the oxidative self-polymerization of natural polyphenols, an emerging class of natural building blocks for surface functionalization with diverse biochemical properties. The oxidative polymerization of polyphenols, triggered by eutectic alloy of gallium and indium, results in nanocoatings with remarkably high reaction kinetics. The oxidative polymerization occurs in a wide pH range including an acidic environment—a condition previously unexplored for the deposition of phenolic coatings. The LM triggers the generation of highly active radical species from the oxidant causing the rapid oxidation of the polyphenols and their subsequent deposition on a range of different substrates. We further show that the LM-based catalytic system addresses several other limitations of existing coating methods including a narrow pH range, substrate specificity (precursor–dependent), and low coating uniformity. Finally, we demonstrate that the phenolic nanocoatings obtained from the acidic pH environment have excellent antioxidant and antibacterial properties without requiring any post-functionalization step. This process for creating phenolic nanocoatings may find applications in a wide range of industries, food science, and biomedicine.

REGULARITIES OF HYDROLYSIS OF ALUMINUM ACTIVATED BY Ga-In-Sn EUTECTIC ALLOY AND ZINC

Aluminum is a promising metal for creating energy-storing substances (ESS) on its basis for hydrogen evolution from water as a result of its of activating aluminum and providing it with the ability to react with water, special attention is paid to methods of alloying it with additions of low-melting metals and alloys, in particular, the eutectic alloy of gallium, indium and tin is perspective alloy for alloying aluminum and obtaining ESS, capable of releasing hydrogen from water without additional heating. The temperature at which stable interaction of aluminum activated by low-melting metals and alloys with water begins to be determined by the temperature at which alloying metals on the surface of aluminum crystallites become liquid. The melting point of the four-component Ga61In25Sn13Zn1 eutectic is about 3 °C, what is about 8 °C lower than the melting point of the Ga-In-Sn eutectic. Therefore, in this work, aluminum was activated by the eutectic alloy of gallium, indium and tin, as well as zinc, and the regularities of the hydrolysis of the obtained EAPs were investigated.&#x0D; Comparative volumetric determinations of hydrogen, which was released during the hydrolysis of 95 wt.% Al + 5 wt.% Ga-In-Sn eutectic and 92 wt.% Al + 5 wt.% Ga-In-Sn eutectic + 3 wt.% Zn alloys, showed that the introduction of zinc into activated aluminum led to a significant acceleration of hydrogen evolution from water at low temperatures (25 and 40 °C). The effective rate constants of hydrolysis of the zinc-doped alloy, calculated using the modified Prout-Tompkins equation, were 1.33, 1.75, 2.19, and 2.58 min-1 at temperatures of 25, 40, 55, and 70 °C, respectively. The effective activation energy of the process, calculated from the temperature dependence of the effective rate constant, was 12.6 kJ·mol-1, which indicates diffuse control of the hydrolysis rate. An analysis of the X-ray diffraction pattern of the products of the hydrolysis of 92 wt.% Al + 5 wt.% Ga-In-Sn eutectic + 3 wt.% Zn alloy at the temperature of 55 °C showed that they contain boehmite, baerite and small amounts of alloying metals.

Tuning the Rectification Ratio by Changing the Electronic Nature (Open-Shell and Closed-Shell) in Donor-Acceptor Self-Assembled Monolayers.

This Communication describes the mechanism of charge transport across self-assembled monolayers (SAMs) of two donor-acceptor systems consisting of a polychlorotriphenylmethyl (PTM) electron-acceptor moiety linked to an electron-donor ferrocene (Fc) unit supported by ultraflat template-stripped Au and contacted by a eutectic alloy of gallium and indium top contacts. The electronic and supramolecular structures of these SAMs were well characterized. The PTM unit can be switched between the nonradical and radical forms, which influences the rectification behavior of the junction. Junctions with nonradical units rectify currents via the highest occupied molecular orbital (HOMO) with a rectification ratio R = 99, but junctions with radical units have a new accessible state, a single-unoccupied molecular orbital (SUMO), which turns rectification off and drops R to 6.

Metallic nanoemulsion with galinstan for high heat-flux thermal management

Galinstan is a eutectic alloy of gallium, indium, and tin, of which thermal conductivity is ∼27 times higher than that of water, while the dynamic viscosity is only twice. Thus, heat transfer coefficient can be remarkably enhanced with a small penalty of pumping power. However, the direct use of galinstan can suffer from practical issues such as oxidation and low specific heat. Therefore, galinstan is mixed with a coolant as an additive to form a colloidal fluid; i.e., dispersion of nanoscale galinstan droplets in a coolant to enhance the thermal conductivity. It is expected that this “metallic nanoemulsion” can contribute to substantial improvement in heat transfer capability. Also, the common issues with colloidal fluids such as rapid sedimentation, erosion, and clogging, can be minimized by the “fluidity” of the liquid metal.It was shown that ultrasonic emulsification can yield nanodroplets with a few hundreds of nanometer or smaller. However, the long exposure of galinstan to oxygen in water inevitably results in severe oxidation of the droplets. Theoretical analysis was also conducted to examine the feasibility of the metallic nanoemulsion as a microchannel heat-sink working fluid. Effective medium theory was used to evaluate the thermal conductivity of the mixture. The viscosity change was also predicted considering both the viscosity of dispersed phase and interaction between the droplets. Under one-dimensional laminar flow assumption, mass, momentum, and energy conservation equations were analytically solved. The effect of high thermal conductivity of galinstan was evident; the convection heat transfer capability was greatly enhanced, while the high viscosity due to the nanoscale blending and the low specific heat of galinstan reduce the flow rate and thus increase the caloric thermal resistance.

Molecular series-tunneling junctions.

Charge transport through junctions consisting of insulating molecular units is a quantum phenomenon that cannot be described adequately by classical circuit laws. This paper explores tunneling current densities in self-assembled monolayer (SAM)-based junctions with the structure Ag(TS)/O2C-R1-R2-H//Ga2O3/EGaIn, where Ag(TS) is template-stripped silver and EGaIn is the eutectic alloy of gallium and indium; R1 and R2 refer to two classes of insulating molecular units-(CH2)n and (C6H4)m-that are connected in series and have different tunneling decay constants in the Simmons equation. These junctions can be analyzed as a form of series-tunneling junctions based on the observation that permuting the order of R1 and R2 in the junction does not alter the overall rate of charge transport. By using the Ag/O2C interface, this system decouples the highest occupied molecular orbital (HOMO, which is localized on the carboxylate group) from strong interactions with the R1 and R2 units. The differences in rates of tunneling are thus determined by the electronic structure of the groups R1 and R2; these differences are not influenced by the order of R1 and R2 in the SAM. In an electrical potential model that rationalizes this observation, R1 and R2 contribute independently to the height of the barrier. This model explicitly assumes that contributions to rates of tunneling from the Ag(TS)/O2C and H//Ga2O3 interfaces are constant across the series examined. The current density of these series-tunneling junctions can be described by J(V) = J0(V) exp(-β1d1 - β2d2), where J(V) is the current density (A/cm(2)) at applied voltage V and βi and di are the parameters describing the attenuation of the tunneling current through a rectangular tunneling barrier, with width d and a height related to the attenuation factor β.

Replacing AgTSSCH2-R with AgTSO2C-R in EGaIn-Based Tunneling Junctions Does Not Significantly Change Rates of Charge Transport

This paper compares rates of charge transport by tunneling across junctions with the structures Ag(TS) X(CH2 )2n CH3 //Ga2 O3 /EGaIn (n=1-8 and X= SCH2  and O2 C); here Ag(TS) is template-stripped silver, and EGaIn is the eutectic alloy of gallium and indium. Its objective was to compare the tunneling decay coefficient (β, Å(-1) ) and the injection current (J0 , A cm(-2) ) of the junctions comprising SAMs of n-alkanethiolates and n-alkanoates. Replacing Ag(TS) SCH2 -R with Ag(TS) O2 C-R (R=alkyl chains) had no significant influence on J0 (ca. 3×10(3) A cm(-2) ) or β (0.75-0.79 Å(-1) )-an indication that such changes (both structural and electronic) in the Ag(TS) XR interface do not influence the rate of charge transport. A comparison of junctions comprising oligo(phenylene)carboxylates and n-alkanoates showed, as expected, that β for aliphatic (0.79 Å(-1) ) and aromatic (0.60 Å(-1) ) SAMs differed significantly.

Replacing AgTSSCH2‐R with AgTSO2C‐R in EGaIn‐Based Tunneling Junctions Does Not Significantly Change Rates of Charge Transport

AbstractThis paper compares rates of charge transport by tunneling across junctions with the structures AgTSX(CH2)2nCH3 //Ga2O3 /EGaIn (n=1–8 and X= SCH2 and O2C); here AgTS is template‐stripped silver, and EGaIn is the eutectic alloy of gallium and indium. Its objective was to compare the tunneling decay coefficient (β, Å−1) and the injection current (J0, A cm−2) of the junctions comprising SAMs of n‐alkanethiolates and n‐alkanoates. Replacing AgTSSCH2‐R with AgTSO2C‐R (R=alkyl chains) had no significant influence on J0 (ca. 3×103 A cm−2) or β (0.75–0.79 Å−1)—an indication that such changes (both structural and electronic) in the AgTSXR interface do not influence the rate of charge transport. A comparison of junctions comprising oligo(phenylene)carboxylates and n‐alkanoates showed, as expected, that β for aliphatic (0.79 Å−1) and aromatic (0.60 Å−1) SAMs differed significantly.

Replacing −CH2CH2– with −CONH– Does Not Significantly Change Rates of Charge Transport through AgTS-SAM//Ga2O3/EGaIn Junctions

This paper describes physical-organic studies of charge transport by tunneling through self-assembled monolayers (SAMs), based on systematic variations of the structure of the molecules constituting the SAM. Replacing a -CH(2)CH(2)- group with a -CONH- group changes the dipole moment and polarizability of a portion of the molecule and has, in principle, the potential to change the rate of charge transport through the SAM. In practice, this substitution produces no significant change in the rate of charge transport across junctions of the structure Ag(TS)-S(CH(2))(m)X(CH(2))(n)H//Ga(2)O(3)/EGaIn (TS = template stripped, X = -CH(2)CH(2)- or -CONH-, and EGaIn = eutectic alloy of gallium and indium). Incorporation of the amide group does, however, increase the yields of working (non-shorting) junctions (when compared to n-alkanethiolates of the same length). These results suggest that synthetic schemes that combine a thiol group on one end of a molecule with a group, R, to be tested, on the other (e.g., HS~CONH~R) using an amide-based coupling provide practical routes to molecules useful in studies of molecular electronics.

Molecular Rectification in Metal−SAM−Metal Oxide−Metal Junctions

This Article compares the ability of self-assembled monolayers (SAMs) of alkanethiolates with ferrocene (Fc) head groups (SC(11)Fc), and SAMs of alkanethiolates lacking the Fc moiety (SC(10)CH(3) and SC(14)CH(3)), to conduct charge. Ultraflat surfaces of template-stripped silver (Ag(TS)) supported these SAMs, and a eutectic alloy of gallium and indium (EGaIn), covered with a skin of gallium oxide (presumably Ga(2)O(3)), formed electrical top-contacts with them. EGaIn is a liquid at room temperature, but its spontaneously formed surface oxide skin gives it apparent non-Newtonian properties and allows it to be molded into conically shaped tips; these tips formed soft electrical contacts with SAMs and formed stable SAM-based tunneling junctions in high (70-90%) yields. Measurements of current density, J, versus applied voltage, V, showed that tunneling junctions composed of SAMs of SC(11)Fc rectify current with a rectification ratio R approximately 1.0 x 10(2) (R = |J(-V)|/|J(V)| at +/-1 V and with a log-standard deviation of 3.0). In contrast, junctions lacking the Fc moiety, that is, junctions composed of SAMs of SC(n-1)CH(3) (with n = 11 or 15 and presenting terminal CH(3) groups), showed only slight rectification (R = 1.5 (1.4) and 2.1 (2.5), respectively). A statistical analysis of large numbers (N = 300-1000) of data gave detailed information about the spread in values and the statistical significance of the rectification ratios and demonstrated the ability of the experimental techniques described here to generate SAM-based junctions in high yield useful in physical-organic studies.

High heat-flux accelerator targets: Cooling with liquid metal jet impingement

In order to evaluate the performance of jet impingement for high heat-flux cooling, experimental cooling loops based on water and liquid metal jet impingement were designed and constructed. The current liquid metal system, based on an eutectic alloy of gallium and indium (GaIn) with a melting point of 15.7 °C, employs an annular inductive electromagnetic pump. The experiments showed that it is capable of accommodating a heat flux of about 20 MW/m 2 over an area of 10 −4 m 2. The jet velocity is less than 4 m/s and the required differential pressure from the pump is less than 10 5 Pa. In the present work the experimental section is supplemented by a theoretical one in which the cooling capability of impinging jets of liquid metal is modeled. In particular, turbulent flow in a dead end associated with the rear surface of a high-temperature target, and the corresponding heat-transfer process, are considered. The developed novel analytical model embodies the main peculiarities of the heat-transfer process and agrees fairly well with the experimental data. In addition, a detailed direct numerical simulation was done with the STAR-CD code. The gross underprediction of the turbulent heat transfer rate by the STAR-CD code is attributed to overprediction of the eddy viscosity in liquid metal flows.