Showing papers on "Liquid metal published in 2002"

Bending piezoelectrically actuated liquid metal switch

Abstract: In accordance with the invention, a piezoelectrically actuated relay that switches and latches by means of a liquid metal is disclosed. The relay operates by means of a plurality of bending mode piezoelectric elements used to cause a pressure differential in a pair of fluid chambers. The piezoelectric elements act upon a membrane which in turn acts upon a fluid which fills the chambers. The differential pressure causes the liquid metal drop to overcome the surface tension forces that would hold the bulk of the liquid metal drop in contact with the contact pad or pads near the actuating piezoelectric element. The switch latches by means of surface tension and the liquid metal wetting to the contact pads.

Micropump driven by movement of liquid drop induced by continuous electrowetting

Abstract: The present invention relates to a micropump which is driven by movement of a liquid drop based upon continuous electrowetting actuation. The continuous electrowetting means a phenomenon that the liquid drop moves as the surface tension of the liquid drop is electrically varied in succession. When a tube in which electrolyte and a liquid metal drop are inserted is applied with voltage having periodically changing polarity via metal electrodes, the surface tension of the liquid metal is varied so that the liquid metal drop reciprocates in the tube generating pressure or force, which is used as a driving force of the micropump. The micropump is operated in a low voltage and consumes a small amount of electric power.

Liquid metal thermal interface for an electronic module

Abstract: A heat dissipating system utilizes a thin layer of a high conductivity liquid metal to provide cooling for electronic sub-assemblies, such as semiconductor chips. The liquid metal preferably is gallium or its alloy which transfers heat from the chip to a heat sink or heat spreader. The system includes one or more vents that allow for filling and venting of the space occupied by the liquid. It also utilizes a flexible seal, such as an O-ring or a membrane held in place with a retainer ring, or a plug that seals the filling vent. The seal flexes to accommodate expansion and contraction of the liquid, as well as phase changes from the liquid phase to the solid phase.

Liquid-metal coolants for nuclear power

Abstract: Liquid-metal coolants for nuclear power systems are compared taking account of the general laws and individual physical-chemical properties of liquid metals, for which unique nuclear-physical and thermophysical properties, and low vapor pressure at high temperature are characteristic and the experimental data on the properties of metal melts can be generalized on the basis of thermodynamic similarity theory and the thermophysical parameters of these systems can be determined more accurately. Coolants are ranked under different thermohydraulic conditions: for the same transported power and the same Peclet number, which also fixes the Nusselt and Stanton numbers, for all melts. It is found that for heavy coolants the reactor core should be “open” with flow sections 10 times greater than for alkali metals. The lead velocity should be less than the sodium velocity by the same amount. For lithium, a core which is twice as compact is admissable, and the lithium velocity should be one-third that of sodium. The understanding of the microstructure and atomic dynamics of metal melts, physical-chemical processes occuring in such melts, and experience in handling such melts make it possible to adjust their characteristics so as to achieve prescribed performance indicators by using specific additives.

Electrostatic actuation of microscale liquid-metal droplets

Abstract: This paper reports sliding of micro liquid-metal droplets by electrostatic actuation for MEMS applications, bi-stable switching in particular. Basic theory concerning droplets on a plane solid surface is exposed followed by experimental study. Being a major parameter in the modeling of sliding droplets, the contact angle has been characterized in the case of mercury on an oxidized silicon wafer. The method used involves both traditional optical microscope and confocal laser imaging. The contact angle is found to be around 137/spl deg/ with an associated standard deviation of 8/spl deg/. The sample preparation is detailed. The droplets deposition method is based on selective condensation of mercury vapor on gold dots acting as preferred nucleation sites. This technique provides control of droplet dimensions and locations and is suitable for batch fabrication. Experimental study of electrostatic actuation coupled with finite-element method (FEM) analysis is described, leading to the determination of the sliding condition parameter, which represents a contact angle hysteresis of about 6/spl deg/. Experimental results also confirm the proportionality between minimum driving force and droplet dimension. Finally, a design optimization methodology is proposed, based on the use of finite-element model simulations.

Method for electrowinning of titanium metal or alloy from titanium oxide containing compound in the liquid state

Abstract: This invention relates to a method for electrowinning of titanium metal or titanium alloys from electrically conductive titanium mixed oxide compounds in the liquid state such as molten titania slag, molten ilmenite, molten leucoxene, molten perowskite, molten titanite, molten natural or synthetic rutile or molten titanium dioxide. The method involves providing the conductive titanium oxide compound at temperatures corresponding to the liquid state, pouring the molten material into an electrochemical reactor to form a pool of electrically conductive liquid acting as cathode material, covering the cathode material with a layer of electrolyte, such as molten salts or a solid state ionic conductor, deoxidizing electrochemically the molten cathode by direct current electrolysis. Preferably, the deoxidizing step is performed at high temperature using either a consumable carbon anode or an inert dimensionally stable anode or a gas diffusion anode. During the electrochemical reduction, droplets of liquid titanium metal or titanium alloy are produced at the slag/electrolyte interface and sink by gravity settling to the bottom of the electrochemical reactor forming, after coalescence, a pool of liquid titanium metal or titanium alloy. Meanwhile carbon dioxide or oxygen gas is evolved at the anode. The liquid metal is continuously siphoned or tapped under an inert atmosphere and cast into dense and coherent titanium metal or titanium alloy ingots.

Jet break up of liquid metal in twin fluid atomisation

Abstract: For melt disintegration in spray forming and metal powder production, the liquid metal typically is atomised by means of twin fluid atomisation e.g. with inert gases. The first stage of the atomisation process is covered by the initialisation and development of surface perturbations on the liquid jet surface that subsequently grow and finally lead to the break up of the melt jet. The primary disintegration process affects all further stages of the atomisation process and hence influences the resulting spray characteristics. In this contribution, the influence of different material properties on the primary disintegration process of a metal melt in a free fall atomiser configuration is investigated. Surface instabilities of liquid metal jets up to the primary break up are analysed experimentally as well as analytically. Results of a linear instability analysis are discussed and compared to evaluations of high-speed video images. In comparison of both results the periodicity and main mechanism of the initialisation process is analysed.

Modeling of Fluid Flow and Heat Transfer in Twin-Roll Casting of Aluminum Alloys.

Abstract: A two-dimensional finite element based mathematical model of coupled turbulent fluid flow, heat transfer, and solidification in horizontal twin-roll thin strip casting was developed. Basic formulations for simulating the coupled thermal and flow fields are described in this paper. A k-e turbulence model was used to calculate the turbulent viscosity in the melt pool. A variable viscosity model was used to model the mushy region. Inlet velocity, strip/roll heat transfer coefficient, alloy composition, and melt superheat were the main process variables considered. The effect of the above process variables on the sump depth, mean strip exit temperature, roll surface temperature, and temperature gradients inside the roll, was analyzed. Twin-roll thin strip casting of aluminum alloys, is an ef- ficient way of obtaining hot-rolled strips directly from the molten metal. In this process, the molten metal is fed from a refractory feed tip into the gap between the steel rolls. The material undergoes a considerable amount of hot rolling be- fore it leaves the rolls. The heat is extracted from the melt by the water-cooled rolls. The process involves solidification of liquid metal and rolling of solidified metal before it leaves the kissing point, which is the point of least roll separation, of the two rollers. Solidification of molten metal starts at the point of first metal-roll contact and is over before the kissing point. The process has many advantages over the conventional casting technique. The primary advantages are of reduced number of steps of operation and very high cooling rates. A very high cooling rate provides microcrystalline structure with improved mechanical properties. But the process also suffers from many types of defects in the cast strip, which is pronounced at higher casting speeds and inlet temperatures. Increasing the casting speed leads to an increase in the mean exit strip temperature and thus rolling force decreases. 1) The major defects encountered are the centerline segregation, heat line formation, sticking, and surface cracks due to the induced thermo-mechanical stresses. Extent or the severity of these defects is very sensitive to the process conditions. Proper op- timization of these process conditions can lead to minimiza- tion of these defects. Hence, a detailed analysis of fluid flow and heat transfer is necessary to find the effect of these vari- ous process parameters on the extent of these defects. Various mathematical models 2-7) have been suggested in the literature to predict the fluid flow, heat transfer, and so- lidification in twin-roll casters. Most of the papers deal with fluid flow modeling in vertical twin-roll casters, but only a few papers 6, 7) deal with the fluid flow modeling in horizon- tal twin-roll casters. Miyazawa and Szekely 2) were the first

High-Temperature Properties of Liquid Boron from Contactless Techniques

Abstract: The density, surface tension, and spectral and total hemispherical emissivities of liquid boron obtained with contactless diagnostics are reported for temperatures between 2360 and 3100 K. It is shown that, contrary to previous expectations, liquid boron is denser than the solid at its melting point. It is also shown that the high total emissivity of 0.36 is not consistent with that of a liquid metal as recently claimed. Finally, good agreement is found with previously reported surface tensions and spectral emissivities of liquid boron.

X-ray source provided with a liquid metal target

Abstract: The invention relates to an X-ray source which is provided with a liquid metal target (3) which flows through a system of ducts (6) and is conducted through a duct section (8) whose flow cross-section is reduced relative to that of the system of ducts. The X-ray source is characterized notably in that there is provided a pressure source (12, 13; 14; 16) for acting on the liquid metal target (3) in such a manner that in the operating condition of the X-ray source the pressure in the liquid metal target (3) at the area of the reduced flow cross-section equals essentially a selectable reference value (Ps) or remains essentially in a pressure range between selectable limit values (Ps1, Ps2) of the pressure. A comparatively small thickness of a window which is transparent to an electron beam can thus be realized in conjunction with a comparatively high flow speed, that is, without having to accept the risk of cavitations. The invention also relates to an X-ray apparatus provided with an X-ray source of this kind.

Natural convection in a liquid metal heated from above and influenced by a magnetic field

Abstract: Natural convection in a liquid metal heated locally at its upper surface and affected by a vertical magnetic field is investigated both experimentally and numerically. The experiments are conducted in a cylindrical test cell of large aspect ratio which is typical for application. The cell is filled with the liquid alloy GaInSn in eutectic composition. Temperature and velocity are measured using thermocouples and an electric potential probe, respectively. In the absence of the magnetic field the experimental results indicate a dependence of the Nusselt number on the Rayleigh number according to the law Nu∝Ra0.191. The particular value of the scaling exponent is in excellent agreement with the prediction of a scaling analysis for laminar, boundary layer-type flow in a low-Prandtl number fluid. Furthermore the experiments demonstrate that the Nusselt number and therefore the convective heat losses can be decreased by about 20% when a magnetic field of moderate strength (B=0.1 T) is present. The numerical simulations solve the Boussinesq equations in an axisymmetric geometry using a finite element method. The results of the simulations are both quantitatively and qualitatively in good agreement with the experimental observations. Deviations are attributed to the three-dimensional characteristics of the flow.

High temperature interaction behavior at liquid metal-ceramic interfaces

Abstract: Liquid metal/ceramic interaction experiments were undertaken at elevated temperatures with the purpose of developing reusable crucibles for melting reactive metals. The metals used in this work included zirconium (Zr), Zr-8 wt.% stainless steel, and stainless steel containing 15 wt.% Zr. The ceramic substrates include yttria, Zr carbide, and hafnium (Hf) carbide. The metal-ceramic samples were placed on top of a tungsten (W) dish. These experiments were conducted with the temperature increasing at a controlled rate until reaching set points above 2000 °C; the systems were held at the peak temperature for about five min and then cooled. The atmosphere in the furnace was argon (Ar). An outside video recording system was used to monitor the changes on heating up and cooling down. All samples underwent a post-test metallurgical examination. Pure Zr was found to react with yttria, resulting in oxygen (O) evolution at the liquid metal-ceramic interface. In addition, dissolved O was observed in the as-cooled Zr metal. Yttrium (Y) was also present in the Zr metal, but it had segregated to the grain boundaries on cooling. Despite the normal expectations for reactive wetting, no transition interface was developed, but the Zr metal was tightly bound to yttria ceramic. Similar reactions occurred between the yttria and the Zr-stainless steel alloys. Two other ceramic samples were Zr carbide and Hf carbide; both carbide substrates were wetted readily by the molten Zr, which flowed easily to the sides of the substrates. The molten Zr caused a very limited dissolution of the Zr carbide, and it reacted more strongly with the Hf carbide. These reactive wetting results are relevant to the design of interfaces and the development of reactive filler metals for the fabrication of high temperature components through metal-ceramic joining. Parameters that have a marked impact on this interface reaction include the thermodynamic stability of the substrate, the properties of the modified interface, the temperature-dependent solubility limits of the liquids and solid phases, and the high-temperature stoichiometry of the ceramic.

X-ray source having a liquid metal target

Abstract: A liquid metal (9) is arranged as an x-ray target such that it flows past an electron impact zone (8). A pressure medium (11) is provided in a pressure region (10) that is separate from the liquid metal region (7), and exerts a pressure on the liquid metal (9) in the fluid metal region to drive it past the electron impact zone (8). The pressure region includes a rechargeable pressure accumulator (R3) for applying the pressure. Independent claims are also included for an x-ray emitter, and an x-ray apparatus.

Numerical modeling and experimental verification of mold filling and evolved gas pressure in lost foam casting process

Abstract: A simple mathematical model is developed to describe a lost foam casting process. Different aspects of the process, such as liquid metal flow, transient heat transfer, foam degradation and gas elimination were incorporated into this numerical model. Fluid velocity, temperature distribution within molten metal and pressure building-up in the mold cavity are predicted as a function of filling time and filling height. The model was verified by comparison of the predicted velocity profiles, temperature fields and back-pressures with the experimental data conducted in this work. Both coated and uncoated foam patterns were used in experimental part of this study. A good agreement between the predictions and the experimental data was found.

Solution for sealing porous metal substrates and process of applying the solution

Abstract: An aqueous inorganic solution for sealing the porosity of metal components made of sintered compacted powered metal and castings formed from liquid metal, and a process for applying the solution onto the components. The solution consists primarily of a blend of inorganic metallic salt silicates with the metal ions being taken from Group 1A elements.

Investigation of ultrasonic properties of a liquid metal used as a coolant in accelerator driven reactors

Abstract: In this paper the techniques developed for investigation of liquid Pb/Bi alloy acoustic properties and experimental results are presented. Measurements of ultrasound velocity were performed using pulse echo technique and a correlation processing in a temperature range 160/spl divide/460/spl deg/C. For transmission and reception of ultrasonic signals bismuth titanate Pz46 5 MHz ultrasonic transducers with a stainless steel waveguide were developed. Various acoustic coupling methods between the waveguide and liquid metal alloy were investigated. The ultrasound velocity dependency upon temperature is presented. The investigation carried out confirms the feasibility of the ultrasonic technique for imaging of the interior of the MYRRHA [1] type nuclear system.

Controlling the adhesion force for electrostatic actuation of microscale mercury drop by physical surface modification

Abstract: Under electrostatic actuation, mercury droplet can act as a contact and moving part in a microswitch system. In order to reduce the actuation voltage while keeping the electrical advantages of liquid-solid contact, the contact properties of mercury droplet on structured surfaces are investigated in this paper. Forces to actuate a mercury droplet on different structured surfaces are theoretically analyzed and experimentally tested. Both results confirm our claim that the adhesion forces of liquid metal droplets on a solid surface can be designed by physical modification of the surface. The criteria for detaching a mercury droplet from solid surface was predicted and verified by experimental results.

Interfacial phenomena between fluxes for continuous casting and liquid stainless steel

Abstract: Casting powders melt on the surface of the liquid metal forming a liquid slag layer. Samples taken during casting revealed convective flows in the flux layer and mass exchange with the liquid metal. It is demonstrated that concentrations of certain elements are considerably higher at the phase boundary than in the bulk of the metal and slag phase. Disturbances of interfacial tension produced by mass and charge transfer evidently cause strong shearing forces which act in parallel with the phase boundary. These forces induce convective movements in the flow boundary layer. Convective flows next to the interface between two liquids have been studied in laboratory experiments using various liquids. The results show that the movement velocity of volume elements next to the interface (due to disturbances of interfacial tension) are dependent on liquid layer thickness and on liquid properties. A new dimensionless number describing this manner of convective flow and suitable for evaluation of experimenta...

Monodisperse spherical metal particles and manufacturing method therefor

Abstract: It is an object of the present invention to provide spherical metal particles having excellent monodispersity. The present invention relates to a method of manufacturing monodisperse spherical metal particles characterized by passing liquid metal through a porous membrane so as to disperse the resulting liquid metal particles in a continuous liquid phase.

Material flow in metal foams studied by neutron radioscopy

Abstract: Two kinds of experiments are presented in this paper: In the first lead alloy foams were generated in a furnace by expanding a foamable precursor material containing metal and a blowing agent. Vertical columns of liquid metal foam were scanned with a beam of neutrons while recording the time-dependent local neutron transmission. The resulting transmission profiles reflect the kinetics of material redistribution in liquid metallic foams under the influence of gravity (drainage). In the second experiment pre-fabricated solid lead foams were re-melted in a furnace. Neutron transmission profiles were also obtained in these experiments. Results of each type of experiment are presented and compared with theoretical predictions for the density profile of aqueous foams.

Crystallization dynamics of a liquid metal drop impinging onto a multilayered substrate

Abstract: Thermal and hydrodynamic processes that occur during impingement of a liquid metal drop onto a multilayered substrate are numerically studied. The mathematical model is based on the Navier–Stokes equations for an incompressible liquid and on substrate and drop heat‐transfer equations that take into account the surface‐tension forces and metal solidification. The effect of the impact velocity, initial drop diameter, metal overheating, and temperature and thermophysical characteristics of the substrate on the morphology of the solid drop, its height, contact‐spot diameter, and total solidification time was examined numerically. The simulation results are found to be in satisfactory agreement with experimental data.

Gel of elemental material or alloy and liquid metal and salt

Abstract: A method of producing a non-metal element or a metal or an alloy thereof from a halide or mixtures thereof. The halide or mixtures thereof are contacted with a stream of liquid alkali metal or alkaline earth metal or mixtures thereof in sufficient quantity to convert the halide to the non-metal or the metal or alloy and to maintain the temperature of the reactants at a temperature lower than the lesser of the boiling point of the alkali or alkaline earth metal at atmospheric pressure or the sintering temperature of the produced non-metal or metal or alloy. A continuous method is disclosed, particularly applicable to titanium.

Temperature effect on the local order of liquid Ni, Ag, and Pb: A molecular dynamics study

Abstract: In this work we calculate structural properties as a function of temperature for liquid Ni, Ag, and Pb using constant-energy molecular dynamics. The metallic interaction is mimicked by a tight-binding n-body potential, based on the second-moment approximation of the density of states. The inherent structures of the liquid state are analyzed through a common-neighbor analysis to extract the microstructural order as a function of temperature. For each liquid metal, our simulations show that the icosahedral order has a significant presence, on the order of 65%, and that the crystalline order is about 25% in the range of temperatures studied here. The icosahedral order remains constant with temperature for the three liquid metals, but changes in the type of crystalline order occur for Ag and Pb at 1500 and 900 K, respectively.

Physical arc appearance and electrode phenomena of vacuum arcs in axial magnetic fields [vacuum interrupters]

Abstract: An experimental study of high current vacuum interrupters with axial magnetic field contact geometries is presented. Arc visualisation shows a progressive constriction of the arc, the temperature of the contacts is very homogeneous and in excess of the melting temperature, and shadowgraphy shows the presence of an agitated liquid. From this, the authors deduce that it is by the flow of liquid contact material that the heat of the arc is distributed across the contact surface. This knowledge stimulates the conception of a new type of liquid metal flow (LMF) vacuum interrupter with a 30% improvement in interrupting capability.