Showing papers on "Liquid metal published in 2005"

Oxidation Mechanism of Steels in Liquid–Lead Alloys

Abstract: The oxidation mechanism of steels in liquid–lead alloys (lead or lead–bismuth) was studied. Parametric dependencies of oxidation, including oxygen-concentration effects, oxidation-rate constant and corrosion-rate effects, are analyzed. An oxidation model is developed based on the assumptions that the chemical reactions are at equilibrium locally, and scale removal is due to mass-transfer corrosion. The model shows that outward-iron diffusion in the solid phase (oxide layer) controls the oxide growth and mass-transfer rate in the flowing-boundary layer determines the corrosion-product transport in the liquid phase (liquid–lead alloy). The oxide thickness depends on both the parabolic oxide-growth-rate constant and the mass-transfer-corrosion rate. For long-term operation, the outer layer of a duplex-oxide layer can be completely removed by flowing lead alloys and it is expected that a pure-chromium-oxide layer forms underneath the Fe–Cr spinel if iron is heavily depleted. The oxide thickness and steel weight change are very different from those of the pure parabolic law and they are classified into distinct and universal categories. The model is validated partially by application to interpreting the measured oxide behavior of several steels in a lead-bismuth eutectic-test loop.

Thermally conductive compositions and methods of making thereof

Abstract: A composition comprising at least one liquid metal having a melting point less than 35°C; at least one electrically insulating solid filler comprising thermally conducting materials; at least one resin is provided. The composition is both thermally conducting and electrically insulating and has utility in the preparation of electronic devices comprising heat generating and heat dissipating structures. In one instance a composition is provided which comprises a liquid metal selected from the group consisting of gallium, gallium alloys, and mixtures thereof, a boron nitride particulate filler, and a silicone resin, wherein said liquid metal and particulate filler are present in a volume ratio of about 1:0.4 to about 1: 10. A method of making and using such a composition is also provided.

High temperature ultrasonic transducers for imaging and measurements in a liquid Pb/Bi eutectic alloy

Abstract: In some nuclear reactors or accelerator-driven systems (ADS) the core is intended to be cooled by means of a heavy liquid metal, for example, lead-bismuth (Pb/Bi) eutectic alloy. For safety and licensing reasons, an imaging method of the interior of ADS, based on application of ultrasonic waves, has thus to be developed. This paper is devoted to the description of developed various ultrasonic transducers suitable for long term imaging and measurements in the liquid Pb/Bi alloy. The results of comparative experimental investigations of the developed transducers of different designs in a liquid Pb/Bi alloy up to 450/spl deg/C are presented. Prototypes with different high temperature piezoelectric materials were investigated: PZT, bismuth titanate (Bi/sub 4/Ti/sub 3/O/sub 12/), lithium niobate (LiNbO/sub 3/), gallium orthophosphate (GaPO/sub 4/) and aluminum nitride (AlN). For acoustic coupling with the metal alloy, it was proposed to coat the active surface of the transducers by diamond-like carbon (DLC). The radiation robustness was assessed by exposing the transducers to high gamma dose rates in one of the irradiation facilities at SCK/spl middot/CEN. The experimental results proved that the developed transducers are suitable for long-term operation in harsh conditions.

Heterogeneous thermal interface for cooling

Abstract: The present invention is a thermal interface for coupling a heat source to a heat sink. One embodiment of the invention comprises a mesh and a liquid, e.g., a thermally conductive liquid, disposed in the mesh. The mesh and the thermally conductive liquid are adapted to contact both the heat source and the heat sink when disposed therebetween. In one embodiment, the mesh may comprise a metal or organic material compatible with the liquid. In one embodiment, the liquid may comprise liquid metal. For example, the liquid may comprise a gallium indium tin alloy. A gasket may optionally be used to seal the mesh and the liquid between the heat source and the heat sink. In one embodiment, the heat source is an integrated circuit chip.

Oxygen tensioactivity on liquid-metal drops

Abstract: The influence of oxygen on the surface tension of liquid metals is a topic of undoubted interest as the formation of oxide films, or even oxygen contamination of the metal interface, represents the main source of error indetermining the surface tension. The evaluation of gas-atmosphere mass exchanges under stationary conditions allows the evaluation of an effective oxygen pressure at which the oxidation of metal becomes evident. This effective oxygen pressure can be considered as a property of the system and, according to experimental evidence, can be many orders of magnitude greater than the equilibrium pressure. The measurement of the surface tension is a good way of studying interface properties, their temporal change and their connections to transport and reaction rates. This paper represents a review of a work undertaken with the aim of understanding oxygen mass transport at the liquid metal surface in relation to the study of capillary phenomena at high temperature.

The heat transfer during filling of a high-pressure die-casting shot sleeve

Abstract: Microstructures in high-pressure die-cast products (HPDC) are important for the mechanical properties. During filling of the shot sleeve, the liquid metal dissipates superheat and solidification starts. The solidification may result in externally solidified crystals (ESCs) or cold flakes in the product [H.I. Laukli, L. Arnberg, O. Lohne, Int. J. Cast Metals Res. 18 (2005) 65–72]. The temperature of the melt in the shot sleeve is influenced by several parameters, such as liquid metal superheat, the heat transfer coefficient (HTC), surface properties of the shot sleeve and alloy composition. In order to get a better quantitative understanding of the heat loss during filling, investigations of the temperature history in both liquid metal and the shot sleeve wall have been carried out. A replica of an industrial shot sleeve was made and filling experiments were carried out. Thermocouples at different locations and depths in the melt and steel cylinder were used to measure the temperatures. The thermal field in the shot sleeve was also modelled using the simulation software MAGMASOFT ® . The results from the casting experiments and casting simulations were compared to estimate the heat transfer coefficient.

Measuring and tailoring capillary forces during liquid metal infiltration

Abstract: A new technique is proposed for the direct measurement of capillary forces in systems of relevance to the infiltration processing of metal matrix composites Capable of handling melt temperatures up to 1500 K and infiltration pressures up to 20 MPa, the technique is essentially a high-temperature analogue of mercury porosimetry Its accuracy is demonstrated by comparison with other techniques and its use is illustrated with the infiltration of diamond particle preforms by Al and Al-Si alloys at 973 K (c) 2006 Elsevier Ltd All rights reserved

On the dynamic response of externally wetted ionic liquid ion sources

Abstract: The electrostatic extraction of nearly monochromatic solvated ions from externally wetted emitters is possible in the case of some ionic liquids or room temperature molten salts. These compact devices are similar to liquid metal ion sources but positive or negative ion beams can be obtained simply by selecting the appropriate polarity for the power supply. dc operation on a single polarity over relatively long periods of time induces electrochemical degradation of the liquid–metal system making voltage alternation at frequencies of the order of 1 Hz necessary to sustain chemical neutrality. This periodic interruption forces a non-steady state behaviour. In particular, the ion current onset is delayed from a square-shaped voltage input signal by a few milliseconds for tungsten metal emitters wetted with the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate, setting the upper bound for the alternation frequency at about 75 Hz. The dependences of these delays on absolute applied voltages are experimentally explored for this compound, suggesting that viscous drag is the main factor determining the dynamic response.

Flow of molten slag and iron at 1500 °C to 1600 °C through packed coke beds

Abstract: The blast furnace dripping zone is of great importance to the mass transfer of elements such as sulfur, carbon, and silicon, to and from the liquid metal phase. To understand mass transfer in the dripping zone, not only mass-transfer reactions and kinetics should be known, but the flow phenomena and process dynamics should be understood as well. The flow of hot metal and slag in the dripping zone was studied in experiments, in which liquid slag and metal trickled through a packed coke bed at 1500 °C to 1600 °C. The results indicate that slag and iron flow concurrently in a funicular type of flow. The iron flows through the core of the voids in the bed and is enveloped by slag, which flows filmwise in between the coke and the iron. This mode of flow allows for a large contact area between slag and iron, through which mass can be transferred. While flowing, the liquid can only pass and access a void, if and when the fluid capillary pressure at the void neck can be overcome. As a result, liquid droplets collect into rivulets. These rivulets flow down, along the accessible voids, using only a part of the available volume. The residence times of the fluids in the bed depend partly on the length of the pathway and are a function of the bed structure, the void neck distribution, and the stochastics of the flow. During flow, slag may react with coke, thus changing the distribution of the slag composition, and its sulfur capacity. In addition, the residence time distribution of the slag and the liquid holdup change as a result of these reactions. Holdup and residence time distribution of the liquids as measured in the experimental setup could not be modeled quantitatively, most likely due to the doubly distributed nature (in space and in time) of the model parameters, induced by reactions between slag, coke, and liquid metal.

Application of high frame-rate neutron radiography to liquid-metal two-phase flow research

Abstract: Liquid metal two-phase flows in metallic vessels were studied by using high frame-rate neutron radiography. Both a bubble column and a gas-lift loop arrangement have been considered. Liquid velocity field of two-phase flow in a flat bubble column with rectangular cross-section was measured precisely by the particle tracking velocimetry. In a gas-lift loop, simultaneous measurements of void fraction by using high frame-rate neutron radiography and four-sensor probe were also performed to observe the bubble-probe interaction. Asymmetric Abel inversion was applied to compare the radial void fraction profiles. Measured radial void fraction profiles obtained by neutron radiography and electrical conductivity probe agreed well with each other. From these measurements, the measurement error and basic characteristics of gas–liquid metal two-phase flow were clarified.

Co-continuous Metal-Ceramic Nanocomposites

Abstract: A room temperature technique was developed to produce continuous metal nanowires embedded in random nanoporous ceramic skeletons. The synthesis involves preparation of uniform, nanoporous ceramic preforms, and subsequent electrochemical metal infiltration at room temperature, so to avoid materials incompatibilities frequently encountered in traditional high temperature liquid metal infiltration. Structure and preliminary evaluations of mechanical and electronic properties of copper/alumina nanocomposites are reported.

A modified steady state apparatus for thermal conductivity measurements of liquid metals and semiconductors

Abstract: An experimental arrangement based on the steady-state concentric cylinder method has been developed for the measurement of the thermal conductivity of liquid metal and semiconductor alloys over a wide temperature range (up to 1700 K) under ambient pressures of argon gas (up to 1 MPa). Particular attention has been paid to minimization of heat leakage and convection heat flows. The various experimental errors are analysed. Thermal conductivity data for molten Pb, Sn and the semiconducting alloy TlAsTe2 are reported.

About liquid metal/ceramic interface interaction mechanism and mode of a new intermediate compound formation

Abstract: In a number of non-equilibrium liquid metal/solid contact systems, when chemical boundary reaction occurs and intermediate compound is formed, a high degree of wettability takes place. So wettability is commonly related to the chemical phase formed at the phase boundary. The microscopic studies which reveal interface layer of a new phase confirm this point of view. In an investigation of interface boundary at high-temperatures by new neutron spectroscopic techniques, intermediate compound layer has not been detected when a metal alloy, containing adhesion-active element (titanium), was in a liquid aggregate state. This is an important fact for high-temperature capillarity science. In the present paper, this question is discussed, and proof (experimental data and theoretical consideration) is given to support the contention that compound layer of necessary thickness (usually, very small) to promote good wettability is formed when metal alloy is in liquid state.

Dynamic surface tension measurements on a molten metal-oxygen system: The behaviour of the temperature coefficient of the surface tension of molten tin

Abstract: In order to point out the interactions of oxygen with a liquid metal and to study the influence of the actual operating conditions, dynamic surface tension measurements of a liquid test metal (tin), were performed under vacuum conditions by using the large drop method. This classical method has been improved by applying a new experimental procedure which allowed to obtain reliable surface tension measurements at high temperature as a function of time and varying the oxygen content. Further, complementary information on molten metal-oxygen interactions can be obtained. In particular, in this work, the trend of the surface tension temperature coefficient has been analysed as a function of different operative parameters, highlighting some crucial points such as the dependence of the temperature coefficient on the accuracy of the surface tension experimental data and the influence of the dissolved oxygen. It was demonstrated that the surface tension and its temperature coefficient do not depend on the quantity of dissolved oxygen when this is inside a certain range of values.

High heat flux accelerator targets cooling with liquid-metal jet impingement

Abstract: 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 heattransfer 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. � 2006 Elsevier Ltd. All rights reserved.

Analysis of Literature Models on Viscosity of Binary Liquid Metallic Alloys on the Example of the Cu-Ag System

Abstract: The aim of this paper is to review all the existing literature models on the concentration dependence of the viscosity of binary liquid alloys and to check them against the measured viscosity values in the binary liquid Cu-Ag system at 1373K.

Method and apparatus for vacuum deposition by vaporizing metals and metal alloys

Abstract: The invention relates to a method and device for vacuum deposition by thermal evaporation of metals and alloys. The offered device (figure 1) contains a melting crucible (1) with molten material (liquid metal) (2), one or several crucibles (3) of evaporation device (4) in a vacuum chamber (5), a heated liquid-metal pipe (6), connecting the said melting crucible to the said evaporation crucibles through a magnetohydrodynamic (MHD) circuit (7) of static melt pressure. The circuit (7) is provided with an MHD pump (8) and incorporates the liquid-metal pipe (6) sectors, which are adjacent to the MHD pump, heated liquid-metal pipes (9, 10) and (11), a heated reservoir (13), connected to the liquid-metal pipe (6) sector before the MHD pipe through the liquid-metal pipe (11) and to an expander (12), installed in the said pipe (9), through the liquid-metal pipe (10). Spaces above the melt in the expander and reservoir are interlinked with a pipe (14), connected to a vacuum pumping system (not shown). Two electrical sensors (15) of the melt level L are installed in the expander. The melt level L in the expander and in the evaporator is delta h high relative the melt level L0 in the MHD circuit reservoir, i.e. the MHD pump should provide pressure delta h. The present technical solution allows increasing the stability of metals and alloys evaporation in long-run processes and thus increasing the productivity. The solution may be used for the deposition of various functional coatings in electronics, metallurgy, mechanical engineering. It is possible to evaporate zinc, magnesium, cadmium, lithium, zinc - magnesium alloy with this method.

Oxygen transport phenomena at the liquid metal-vapour interface

Abstract: A system made of an atmosphere, a liquid metal and an oxide phase at a given temperature and total pressure is zero-variant and allows only a particular set of partial pressures, compatible with thermodynamic equilibrium. For any different gas composition the system will show a tendency to evolution. Therefore, classical thermodynamics cannot give the answers to a number of problems of major interest, such as those concerning the conditions for interface saturation and oxide formation. Strictly speaking these are kinetic problems, but they can still be treated as pseudo-thermodynamic questions. The key to the problem is in considering the characteristic times of evolution, which suggest stationary state approximation for the condensed phases. In many instances, the evaluation of gas-atmosphere mass exchanges under stationary conditions makes it possible to determine the effective oxygen pressure at which the oxidation of the metal becomes evident. Surface tension measurements allow this condition to be detected with a good accuracy. According to experimental evidence, the effective oxygen pressure can be many orders of magnitude greater than the equilibrium value. The problem needs different theoretical approaches according to the molecular mechanisms involved. Moreover, from the experimental point of view, there are particularly delicate questions regarding the accuracy and the significance of the oxygen control and measurement.