Showing papers on "Liquid metal published in 2009"

Viscoelastic properties of oxide-coated liquid metals

Abstract: Many liquid metals exposed to air develop an oxide film on their outer surface. This film is sufficiently solid-like to provide mechanical stability to small liquid metal droplets, yet weak enough to allow the droplets to be malleable. These properties are useful in both micro-electronics and microfluidics; however, little is known about how to characterize them. Here we probe the elastic, yielding, and relaxation properties of oxide-coated gallium and eutectic gallium indium using a rheometer equipped with a parallel-plate geometry. By using parallel plates of different size, we show that surface stresses dominate bulk stresses. These experiments also demonstrate that the apparent elastic properties of the oxide film are highly sensitive to its strain history. Moreover, the apparent elasticity is sensitive to the stresses stored in the oxide skin. We probe these stresses and their time-dependence, with both torque and normal force measurements. We also characterize the time-dependence of the elasticity b...

High brightness X-ray metrology

Abstract: An x-ray metrology tool having only one x-ray source. The x-ray source includes a liquid metal source for heating and melting at least one metal and producing a liquid metal jet, a liquid metal collector for acquiring the liquid metal jet, a liquid metal circulation system for returning liquid metal from the liquid metal collector to the liquid metal source, and an electron beam source for directing an electron beam at the liquid metal jet anode, thereby producing an incident x-ray beam that is directable towards a sample. A detector receives emissions from the sample in response to the incident x-ray beam, and produces signals indicative of properties of the sample. A controller controls the x-ray source, acquires the signals from the detector, and determines the properties of the sample based at least in part on the signals.

Corrosion development between liquid gallium and four typical metal substrates used in chip cooling device

Abstract: The limitation of the currently available thermal management method has put an ever serious challenge for computer chip designers. A liquid metal with low melting point around room temperature was recently identified as a powerful coolant of driving heat away because of its superior thermo-physical properties and the unique ability to be driven efficiently by a completely silent electromagnetic pump. However, the adoption of gallium, one of the best candidates as metal coolant so far, may cause serious corrosion to the structure materials and subsequently affect the performance or even dangerous running of the cooling system. To address this emerging critical issue, here the compatibility of gallium with four typical metal substrates (6063 Aluminum-Alloy, T2 Copper-Alloy, Anodic Coloring 6063 Aluminum-Alloy and 1Cr18Ni9 Stainless Steel) was comprehensively investigated in order to better understand the corrosion mechanisms and help find out the most suitable structure material for making a liquid metal cooling device. To grasp in detail the dynamic corrosion behavior, an image acquisition and contrasting method was developed. Moreover, corrosion morphology analyses were performed by means of scanning electron microscope (SEM). The chemical compositions of the corroded layers were evaluated using energy dispersive spectrometry (EDS). According to the experiments, it was found that, the corrosion of the 6063 Aluminum-Alloy was rather evident and serious under the temperature range for chip cooling. The loose corrosion product will not only have no protection for the inner substrate, but also accelerate the corrosion process. Compared to the 6063 Aluminum-Alloy, T2 Copper-Alloy showed a slow and general corrosion, but part of the corrosion product can shed from the substrate, which will accelerate corrosion action and may block the flowing channel. Anodic Coloring 6063 Aluminum-Alloy and 1Cr18Ni9 Stainless Steel were found to have excellent corrosion resistance among these four specimens. No evident corrosion phenomena were found under the examination of SEM and EDS when exposed for 30 days at the temperature of 60°C, which suggests their suitability as structure materials for the flow of liquid metal. However, as for the Anodic Coloring 6063 Aluminum-Alloy, surface treatment and protection are of vital importance. The present study is of significance for making a liquid metal chip cooling device which can actually be used in the future computer industry.

Melt conditioning by advanced shear technology (MCAST) for refining solidification microstructures

Abstract: MCAST (melt conditioning by advanced shear technology) is a novel processing technology developed recently for conditioning liquid metal prior to solidification processing. The MCAST process uses a twin screw mechanism to impose a high shear rate and a high intensity of turbulence on the liquid metal, so that the conditioned liquid metal has uniform temperature, uniform chemical composition and well-dispersed and completely wetted oxide particles with a fine size and a narrow size distribution. The microstructural refinement is achieved through an enhanced heterogeneous nucleation rate and an increased nuclei survival rate during the subsequent solidification processing. In this paper we present the MCAST process and its applications for microstructural refinement in both shape casting and continuous casting of light alloys.

Application of the embedded atom model to liquid metals: Liquid sodium

Abstract: The procedure for the calculation of the embedded atom model (EAM) potential for liquid metal, which involves the use of diffraction data on the structure of material in the vicinity of the melting point, is applied to lithium. In fitting the parameters of EAM potential, use is made of data on the structure of lithium at 463, 523, and 868 K, as well as on the thermodynamic properties of lithium at temperatures up to 3400 K. The use of the method of molecular dynamics (MD) and of the EAM potential enables one to obtain good agreement with experiment as regards the structure, density, and potential energy of liquid metal at temperatures up to 3000 K, as well as along the shock adiabat up to pressures of ∼260 GPa. The predicted value of bulk modulus at 463 K is close to the actual value. The self-diffusion coefficients under isobaric heating increase with temperature by the power law with exponent of 1.7182. The obtained potential is inadequate for describing crystalline lithium. The predicted melting temperature of lithium with EAM potential is 428 ± 2 K and is close to real temperature.

Electric current induced liquid metal flow: Application to coating of micropatterned structures

Abstract: Although electric fields have been widely used to induce flow of electrolytes, electrically induced long-range flow of metallic liquids has never been reported. Here we show that liquid pure metals can be made to flow in a continuous stream by applying an electric current to an underlying conductive film. This flow occurs in the direction of applied current and is thought to be driven by liquid electromigration. The phenomenon is expected to engender many applications where controlled delivery of a continuous liquid metal stream is desired, such as microfluidics, nanolithography, and patterned conformal coatings. The last application is demonstrated here.

Method for preparing metal liquid mixed with granule having high heat-transfer performance

Abstract: The invention relates to a method for preparing a metal liquid mixed with particles which has high heat transferring performance The method comprises the following steps: a particles as a solute and liquid metal as a solvent are mixed to form the liquid metal mixed with the particles; the ratio of mass portions of the particles to the liquid metal is between 1 to 01 and 1 to 99; and b the liquid metal mixed with the particles is subjected to mechanical stirring and ultrasonic dispersion in order that the particles in the liquid metal are evenly dispersed, thereby obtaining the metal liquid mixed with the particles Through the method, the prepared metal liquid mixed with the particles has high thermal conductivity

Supply of a liquid-metal target in x-ray generation

Abstract: Closed-loop circulation for providing liquid metal to an interaction region at which an electron beam is to impact upon the liquid metal to produce X-rays is presented. In a method according to the invention, the pressure of the liquid metal is raised to at least 10 bar using a high-pressure pump (312). The pressurized liquid metal is then conducted to a nozzle (332) and ejected into a vacuum chamber (330) in the form of a spatially continuous jet. After passage through the vacuum chamber, the liquid metal is collected in a collection reservoir (334), and the pressure of the liquid metal is raised to an inlet pressure, e.g. using a primer pump (322), suitable for the inlet of the high-pressure pump. The invention also relates to a corresponding circulation system and an X-ray source provided with such circulation system.

Microstructural Changes in Brazing Sheet due to Solid-Liquid Interaction

Abstract: Aluminium brazing sheet is the material of choice to produce automotive heat exchangers. Although in Dutch the official translation of aluminium brazing sheet is “aluminium hardsoldeerplaat” the English name is used in the industry. Aluminium brazing sheet is basically a sandwich material and consists of an aluminium core alloy, typically an AA3XXX alloy (containing Mn) or an AA6XXX alloy (containing Mg and Si) with a clad alloy of the AA4XXX (containing Si) series. The core alloy gives the final product the desired properties after brazing. The core alloys are designed in such a way that after the brazing cycle, the condition is reached where the core has its optimum properties. Properties like strength and corrosion resistance are the main engineering parameters. Typically the core alloy is single side or both side clad and the thickness of the clad alloy ranges between 5 and 20% of the total thickness. The AA4XXX alloy used for aluminium brazing sheet has a melting range between 570°C and 610°C while the melting range of a typical AA3XXX core alloy lies above 610°C. This difference in temperature between the two alloys is used to join complex shaped products in “one shot”. At the brazing temperature, typically around 600°C, the AA4XXX clad alloy is completely molten. Due to capillary forces and surface tension differences, the molten clad alloy will flow to connect adjacent pieces. The process by which joining is taking place is called the brazing process. During this brazing process liquid metal from the clad alloy is in close contact with the solid core alloy. At this stage an interaction between the two phases can take place. Several types of interaction between the two phases can take place but the interaction that is referred to as Liquid Film Migration is the topic of study in this thesis. Liquid Film Migration is, however, not the only name given in literature to what seems to be the same interaction. Liquid Film Migration is causing a significant change in microstructure and element distribution of the core alloy. These changes are detrimental to the corrosion resistance of the final product. Although the name Liquid Film Migration was given to the process responsible for the observed changes no conclusive evidence has been presented to confirm the existence of a liquid film in aluminium brazing sheet. The literature available on Liquid Film Migration in aluminium brazing sheet has given some information on the conditions favourable for Liquid Film Migration to occur. These conditions are residual strain in the core alloy present at the peak brazing temperature and a small grain size of the core alloy. This thesis focussed on the occurrence of LFM in brazing sheet and the possible mechanism and driving forces behind it. Two different core alloys with the same clad alloy were processed and studied for their susceptibility to Liquid Film Migration. Conditions were created that according to literature should result in different degrees of Liquid Film Migration. Brazing took place in a standard brazing furnace or in a salt bath. The salt bath would enable a kinetic study since time and temperature are well controlled. The study of the samples after brazing indeed showed a different response to the applied processing. The main observation was that the onset of recrystallization of the core alloy plays a major role in the occurrence of Liquid Film Migration. A detailed study of the liquid film showed the accumulation of constituents and dispersoids which were originally present in the core alloy. The measured diffusion profiles of silicon in front of the liquid film coincide with theoretical diffusion profiles as if they originated from a moving boundary. From the diffusion profiles of silicon, the kinetics of the moving liquid film was extracted resulting in an inverse square root dependence of the velocity with time. An estimation of the energies available in the system showed that the coherency strain energy could not be the driving force for Liquid Film Migration in aluminium brazing sheet. Most likely the energy is supplied by the reduction of the (sub)grain size. This is supported by the fact that strained samples that do not recrystallize during brazing are the ones showing the highest degree of Liquid Film Migration. Based on these findings, the residual strain present in the form of sub-grains or dislocations is considered to provide the energy for the movement of the liquid film. A qualitative assessment of the residual strain present in samples after brazing supported the hypothesis that indeed this residual strain is the energy source needed for the movement of the liquid film. The mechanism behind liquid film migration has been found to be similar to the recrystallization process caused by Strain Induced Boundary Migration. It was presented that lowering the surface energy between grains by a liquid film would allow the boundary to move at lower dislocation densities compared to a non liquid infiltrated grain boundary. Recrystallization would reduce the dislocation density taking away the driving force to spport liquid film migration. Liquid film migration and strain induced boundary migration are both in competition for the same energy. Strain induced boundary migration can take place during the whole brazing cycle while liquid film migration only can occur in the presence of a liquid. This means that the clad alloy has to be at least partly molten to allow wetting of the grain boundaries. When recrystallization by strain induced boundary migration takes place no liquid film migration will occur. A theoretical approach to determine the velocity of the liquid film was in reasonable agreement with the observations. The main obstacle to completely quantify liquid film migration is the uncertainty of the development of the film thickness in time. As demonstrated, recrystallization plays a critical role in the onset of liquid film migration. A through Process Model was used to determine if such model could be used to predict recrystallization based on thermal mechanical process input parameters and alloy chemistry. Unfortunately the model lacks sensitivity to predict the onset of recrystallization in this study. However the model contains all necessary modules to ensure that after fine tuning for this application, more predictive power can be expected.

Liquid Metal Based Mini/Micro Channel Cooling Device

Abstract: Effective heat dissipation is of great importance in many engineering fields. In this paper, we investigated a newly emerging method to significantly improve the cooling capability of micro channel devices, through implementing liquid metal with low melting point as the powerful coolant. A series of experiments with different working fluids and volume flow were performed, and the different cooling effects between liquid metal and water were compared. In order to better evaluate the cooling capability of liquid metal based micro channel cooling device, the hydrodynamic and heat transfer theory involved was discussed. The results indicated that, when the system operated in a relatively high velocity, micro channel cooling devices with liquid metal as coolant could produce higher convective heat transfer coefficient compared to those with traditional cooling fluids. And under the same pump power, not only the thermal resistance of liquid metal based micro channel could be much smaller, but also the coolant volume flow could be decreased. What is more, the liquid metal can be driven by a highly efficient electromagnetic pump without any noise. Therefore, more compact and energy-saving micro channel cooling devices with better cooling capability may come into reality. This new method is rather practical, and is expected to be important for realizing an extremely high heat dissipation rate.Copyright © 2009 by ASME

Experimental model of the interfacial instability in aluminium reduction cells

Abstract: A solution has been found to the long-standing problem of experimental modelling of the interfacial instability in aluminium reduction cells. The idea is to replace the electrolyte overlaying molten aluminium with a mesh of thin rods supplying current down directly into the liquid metal layer. This eliminates electrolysis altogether and all the problems associated with it, such as high temperature, chemical aggressiveness of media, products of electrolysis, the necessity for electrolyte renewal, high power demands, etc. The result is a room temperature, versatile laboratory model which simulates Sele-type, rolling pad interfacial instability. Our new, safe laboratory model enables detailed experimental investigations to test the existing theoretical models for the first time.

Numerical Study on Metal/Slag Drainage Rate Deviation during Blast Furnace Tapping

Abstract: Remarkable deviation of metal fraction in the liquid drained out of blast furnace tap hole has been occasionally observed between the operated tap holes and/or tapping time stages. Introducing the concept of low permeability zone whose wall, due to the difference in two liquid phases' viscosity and/or wettabilitiy to coke particle, allows for metal to permeate freely but for slag not to permeate, the liquid drainage behaviors are examined by furnace hearth mathematical model simulations.The deviation of metal fraction between two operated tap holes is materialized under the hypothesis that furnace heath is divided into two sections by planar vertical low permeability wall (VLPW). While, the variation of time series change in liquid metal fraction during tapping operation is reproduced by hypothesizing the formation of cylindrical low permeability wall (CLPW) which concentrically parts the furnace hearth into center and peripheral area.Since the results of calculation for VLPW or CLPW formation indicate the notable raise of liquid level in furnace which could influence on abrupt increase of blowing pressure, the effectiveness of several operational optimization is assessed, resulting in suggestive conclusion that increasing the initial tap hole diameter is the most effective.

StarJet: Pneumatic Dispensing of Nano- to Picoliter Droplets of Liquid Metal

Abstract: In this work we present a novel, simple and robust, pneumatically actuated dispenser for nano- to picoliter sized droplets of liquid metals. The so called StarJet dispenser utilizes a star-shaped nozzle geometry that stabilizes plugs of liquid in the centre of the nozzle by capillary force. This minimizes the wall contact of the liquid plug and reduces contact line friction. Individual droplets of liquid metal can be pneumatically generated by interplay of the sheathing gas flow in the outer grooves of the nozzle and the liquid metal. The working principle was first discovered and studied by Computational Fluid Dynamic (CFD) simulations. For experimental validation silicon chips with the star-shaped geometry were fabricated by Deep Reactive Ion Etching (DRIE) and assembled into a printhead. With different nozzle chips volumes between 120 pl and 3.6 nl could be generated at natural frequencies of 90 Hz and 400 Hz. The StarJet can either be operated as drop on demand or as continuous droplet dispenser. We printed columns of metal with 0,5 to 1,0 mm width and 40 mm height (aspect ratio ≫40) to demonstrate the directional stability of the ejection.

A silicon-based galinstan magnetohydrodynamic pump

Abstract: This paper presents the design, fabrication and characterization of a novel Magnetohydrodynamic (MHD) pump engineered to actuate Galinstan; a non-toxic liquid metal alloy of gallium, indium and tin. The MHD micro-pump is fabricated using Silicon MEMS fabrication technology. MHD µ-pump design and fabrication has been demonstrated before. While previous research has focused on actuating ionic solutions only, the research presented in this paper demonstrates for the first time micro-actuation of Galinstan. Such an actuation scheme has wide ranging applications from micro-cooling to reconfigurable liquid metal RF-MEMS.

Measurements of time-dependent liquid-metal magnetohydrodynamic flows in a flat rectangular duct

Abstract: In the helium-cooled lead lithium (HCLL) blanket, which has been chosen as a reference concept for a liquid-metal breeding blanket to be tested in ITER, the heat is removed by helium cooled plates aligned with the strong toroidal magnetic field that confines the fusion plasma. The liquid breeder lead lithium circulates through gaps of rectangular cross-section between the cooling plates to transport the generated tritium towards external extraction facilities. Under the action of the strong magnetic field, liquid metal flows in conducting rectangular ducts exhibit jet-like velocity profiles in the thin boundary layers near the side walls, which are parallel to the magnetic field like the cooling plates in HCLL blankets. The velocity in these side layers may exceed several times the mean velocity in the duct and it is known that these layers become unstable for sufficiently high Reynolds numbers. The present paper summarizes experimental results for such unstable time-dependent flows in strong magnetic fields, which have been obtained in the MEKKA liquid metal laboratory of the Forschungszentrum Karlsruhe. In particular, spatial and temporal scales of perturbation patterns are identified. The results suggest that the flow between cooling plates in a HCLL blanket is laminar and stable. The observed time-dependent flow behavior appears at larger velocities so that the present results are more relevant for applications in dual coolant concepts where high-velocity jets have been predicted along side walls.

Experimental study of mhd flows in a prototypic inlet manifold section of the dcll test blanket module

Abstract: This paper presents preliminary results on a magnetohydrodynamic (MHD) flow in a prototypic distribution and collection manifold relevant to the Dual Coolant Lead Lithium (DCLL) blanket concept. A series of experiments has been carried out in order to understand the mechanisms that determine the division of flow from a single supply channel to three parallel channels stacked in the direction the magnetic field lines. First flow rate data show that for a relatively high interaction parameter ( N> 90), a uniform flow distribution is achieved with less than 5% flow unbalance. For lower values of N , the ratio between the outer to the central channels flow rates is found to follow a N m type scaling law, with m =1 /4 for 60