Showing papers on "Liquid metal published in 1997"

Layering of a liquid metal in contact with a hard wall

Abstract: When a liquid makes contact with a solid wall, theoretical studies1,2,3,4 indicate that the atoms or molecules will become layered adjacent to the wall, giving rise to an oscillatory density profile. This expectation has not, however, been directly verified, although an oscillatory force curve is seen for liquids compressed between solid surfaces5. Here we present the results of an X-ray scattering study of liquid gallium metal in contact with a (111) diamond surface. We see pronounced layering in the liquid density profile which decays exponentially with increasing distance from the wall. The layer spacing is about 3.8 a, which is equal to the repeat distance of (001) planes of upright gallium dimers in solid α-gallium. Thus it appears that the liquid near thewall assumes a solid-like structure similar to the α-phase, which is nucleated on freezing at lower temperatures. This kind of ordering should significantly influence flow, capillary osmosis, lubrication and wetting properties5,6, and is likely to trigger heterogeneous nucleation of the solid.

X-ray reflectivity studies of liquid metal and alloy surfaces

Abstract: Surface-induced atomic layering at the liquid/vapor interface in liquid metals has been observed using x-ray reflectivity on sputtered clean surfaces under ultrahigh vacuum conditions. A well-defined quasi-Bragg peak is obtained for surfaces of elemental Ga and a Ga-In alloy at large wave vectors qz;2.3‐2.5 A 21 . These results are an unambiguous indication of atomic layering with an interlayer spacing d;2p/qz52.5‐2.7 A. For liquid Ga, the amplitude of the electron-density oscillations, which is significantly underestimated by existing theory and molecular simulation, decays with a characteristic length of 6 A, which is twice that of Hg. Results on the alloy show a clear enrichment of indium at the topmost surface layer, consistent with the Gibbs adsorption rule. The enrichment consists of a single monolayer, with subsequent layers at the bulk eutectic composition. In order to suppress mechanically excited surface waves, the measurements were performed on thin liquid metal films (,0.5 mm deep!, which leads to a macroscopically curved surface due to the large surface tensions in liquid metals. The experimental challenges posed by measurements on curved surfaces and the techniques that were developed are discussed in detail. @S0163-1829~97!01324-6#

High performance PbLi blanket

Abstract: A novel blanket concept is described. The proposed design Is a dual coolant concept based on ferritic steel as structural material using helium to cool the first wall. The temperature of the entire steel structure is maintained below the 550/spl deg/C limit. The breeding zone is cooled by circulating the liquid metal breeder to external heat exchangers. Flow channel inserts are employed in the poloidal liquid breeder ducts, serving both as electrical and thermal insulator between the flowing liquid metal and the steel structure. In this way, a liquid metal exit temperature of about 700/spl deg/C is achievable, allowing either an advanced Rankine steam cycle or closed-cycle helium gas turbine (Brayton cycle) as the power conversion system. A gross thermal efficiency of about 45% can be achieved with either system.

Thermal contact resistance across a copper-silicon interface

Abstract: An experimental setup to measure the thermal contact conductance across a silicon-copper (Si-Cu) interface is described, and the results obtained are presented. The resulting thermal contact resistance data are used in estimating the thermo-mechanical and optical performance of optical substrates cooled by interfaced copper cooling blocks. Several factors influence the heat transfer across solid interfaces. These include the material properties, interface pressure, flatness and roughness of the contacting surfaces, temperature, and interstitial material, if any. Results presented show the variation of thermal contact conductance as a function of applied interface pressure for a Cu-Si interface. Various interstitial materials investigated include iridium foil, silver foil and a liquid eutectic (Ga-In-Sn). As expected, thermal contact resistance decreases as interface pressure increases, except in the case of the eutectic, in which it was nearly constant. The softer the interstitial material, the lower the thermal contact resistance, Liquid metal provides the lowest thermal contact resistance across the Cu-Si interface, followed by the iridium foil, and then the silver foil.

Predeposited transient phase electronic interconnect media

Abstract: A method of attaching an electronic component to a substrate comprising the steps of depositing a spray metal coating atop a substrate. An electronic component is placed atop a coating. A liquid metal is dispensed on or near the component. The liquid metal wets the component and the coating. The metal is reacted with the coating to form an electrically conductive bond with the substrate and adheres the component to the substrate. The reactive metal may be heated to a temperature which makes it liquid and facilitates wetting the coating and component. Suitable materials for the spray metal coating include copper, nickel, tin, bismuth, lead and silver and mixtures thereof. Suitable liquid metals generally include low melting temperature metals such as gallium and indium and mixtures thereof.

On the nature of the armature-rail interface: liquid metal effects

Abstract: This is an experimental study of the nature of the armature-rail interface during hypervelocity launch in a railgun. It is part of a multidisciplinary modeling and experimental effort to improve the understanding of contact physics. Conditions that occurred at the interface are inferred from studies of the surfaces of recovered copper rails. Melt lubrication is observed at the armature-rail interface. Liquid aluminum metal from the contact faces of the solid aluminum armature forms at the armature-rail interface as a result of frictional and joule heating. The liquid aluminum is quenched by the relatively cool copper rail, and a quenched metal deposit is formed. Characterization of the deposit has shown a rapidly quenched microstructure. The mean grain size measured by transmission electron microscopy is 200 nm-the finest grain size reported for a melt quenched aluminum alloy film. The deposit thickness is less than 25 /spl mu/m and is rough with an oxidized surface. The thicker films crack, curl, and detach easily from the rail surface. The experiments were performed in a 25-mm square-bore railgun, with a ratio of interface current to armature contact width of 20-35 kA/mm. The liquid production rate by armature melting at the interface is found to be about 1 mg/C, We conclude that in solid armature railguns with sufficiently thick, liquid aluminum melt lubrication, the rail does not erode. Instead a deposit forms on the rail surface. Depending upon the film thickness and the quench stresses, the film detaches easily.

An experimental study of silver and palladium partitioning between solid and liquid metal, with applications to iron meteorites

Abstract: — Solid metal/liquid metal partition coefficients for Ag and Pd were determined experimentally as a function of the S concentration of the metallic liquid. Silver is incompatible in solid metal and strongly sensitive to the S content of the metallic liquid; partition coefficients for Ag decrease more than an order of magnitude with increasing S content of the metallic liquid and can be expressed as: where k(Ag) is the molar solid metal/liquid metal partition coefficient and XS is the molar S content of the metallic liquid. The partition coefficient of Pd is less variable but changes from modestly incompatible to modestly compatible in solid metal with increasing S content of the metallic liquid: With these new partition coefficients for Pd and a fractional crystallization model, Pd abundance trends recorded in iron meteorite groups are modeled successfully. Measured Ag distribution between troilite-rich nodules and adjacent metal in iron meteorites also agree well with experimental solid metal/liquid metal equilibrium values. However, observed Pd metal/nodule distributions do not agree with experimentally determined partition coefficients, which suggests a more complex history than simple solid metal/liquid metal equilibrium.

Bubble and liquid flow characteristics in a wood's metal bath stirred by bottom helium gas injection

Abstract: A model study was carried out to elucidate bubble and liquid flow characteristics in the reactor of metals refining processes stirred by gas injection. Wood’s metal with a melting temperature of 70 °C was used as the model of molten metal. Helium gas was injected into the bath through a centered single-hole bottom nozzle to form a vertical bubbling jet along the centerline of the bath. The bubble characteristics specified by gas holdup, bubble frequency, and so on were measured using a two-needle electroresistivity probe, and the liquid flow characteristics, such as the axial and radial mean velocity components, were measured with a magnet probe. In the axial region far from the nozzle exit, where the disintegration of rising bubbles takes place and the radial distribution of gas holdup follows a Gaussian distribution, the axial mean velocity and turbulence components of liquid flow in the vertical direction are predicted approximately by empirical correlations derived originally for a water-air system, although the physical properties of the two systems are significantly different from each other. Under these same conditions, those turbulent parameters in high-temperature metals refining processes should thus be accurately predicted by the same empirical correlations.

Numerical study on the solidification of liquid metal droplets impacting onto a substrate

Abstract: The problem of normal incidence impact with solidification of a spherical liquid metal droplet onto a rigid planar substrate is studied. The Navier-Stokes equations are solved using a finite volume formulation with a fixed grid. The free surface of the droplet is tracked by the volume-of-fluid method. The surface tension on the droplet surface is evaluated by a continuum surface force model. The energy equation is modeled by using an enthalpy-based formulation. The method developed provides a comprehensive model of the dynamic and thermal aspects of the impact process. The effects of several parameters on the spread of the droplet on the substrate are determined. A correlation for the maximum spread factor is obtained and is in agreement with the experimental data available in the literature.

Acoustic metal jet fabrication using an inert gas

Abstract: A method for manufacturing metal structures in which minute drops of a liquid metal are emitted from an acoustic device through an inert gas. The presence of the inert gas at the surface of the liquid metal prevent the formation of an oxide skin which would absorb acoustic energy and hinder droplet formation and emission. The droplets are then emitted towards a substrate, which may form as a carrier, where they may be used to form solder bumps, circuit traces, or accreted to form a three dimensional device.

An analytical model for optimal directional solidification using liquid metal cooling

Abstract: In what follows, a model is developed that describes the optimal processing parameters for directional solidification using liquid metal cooling (LMC). The model considers a sample with a flat geometry and, as a first approximation, can be used to treat the flat sections of a turbine blade. The model predicts (1) the optimal withdrawal rate of the casting from the hot zone, (2) the temperature gradient in the liquid at the solidification interface, and (3) the temperature profile along the length of the casting. The model is then used to perform a sensitivity analysis of the LMC process. Cooling bath temperature, baffle thickness, shell thickness, and shell thermal conductivity are shown to have a strong influence on system performance.

Wetting in nonreactive liquid metal-oxide systems

Abstract: Pure metal/oxide interfacial energies are characterized by weak Van der Waals and electronic interactions. The intrinsic contact angles in these systems are larger than 90°. The roughness of the ceramic increases the apparent contact angle and may lead to the formation of composite surfaces that are not fully penetrated by the metal. Oxygen dissolved in the metal adsorbs at the liquid metal/vapor and the liquid metal/ceramic interfaces, leading to improved wetting with contact angles as low as 70°. Statistical thermodynamic models of the interfaces are in good agreement with the experimental adsorption isotherms. The combination of a metallic ternary addition and dissolved oxygen offers the potential for increased wetting, but the identification of suitable additions remains elusive. Increases in temperature lead to modest decreases in contact angle, and do not appear to be a practical route to improved wetting in nonreactive systems.

Rotating sealing device

Abstract: A rotating sealing device for sealing between a wall separating two mediums under substantially different pressure and a rotatable shaft utilizes a combination of a liquid metal seal comprising at least one liquid metal ring and a shield means which prevents contamination of the metal ring by gases coming into contact with the liquid metal. Magnetic fluid seal, a ring of an oil material, or inert gas may be used as a shield to protect the liquid metal.

Field-emission processes from a liquid–metal surface

Abstract: This work presents the generalization of experimental and theoretical investigations of different field-emission phenomena from liquid metal. The dynamics, emission ability, and stability of the processes are described for specific regimes of electric field. A description of the stability is possible if one considers the character of the conducting-fluid surface instabilities that always precede every type of field emission from liquid in a strong electric field. We investigated the electrohydrodynamic effects in liquid–metal emitters operating in the field–ion, field–electron, and explosive–emission modes in direct-current, nanosecond-pulse, and microsecond-pulse regimes.

Non-contact Generation of Compression Waves in a Liquid Metal by Imposing a High Frequency Electromagnetic Field

Abstract: In order to confirm the fact that compression waves can be generated in an electrically conductive liquid by using an electromagnetic field. Pressure oscillations in a liquid gallium were directly measured under the imposition of a high frequency magnetic field and a mathematical model based on the electromagnetic field theory and the compressible fluid dynamics has been developed. The pressure oscillation with the double frequency of the imposed magnetic field was not only isotropic but also in proportion to the square of the intensity of the magnetic field. These observations coincide with the prediction derived from the mathematical model. Furthermore, the measured distribution of the pressure oscillation in a liquid gallium agrees well with the result of the mathematical model.

Numerical Simulation of Turbulent Flow and Heat Transfer in the Wedge-Shaped Liquid Metal Pool of a Twin-Roll Caster

Abstract: Controlled flow and heat transfer are important for the quality of a strip in a twin-roll continuous casting process. A numerical study was carried out to investigate the two-dimensional turbulent flow and heat transfer in the liquid stainless-steet-filted wedge-shaped cavity formed by the two counterrotating roils in a twin-roll continuous casting system. The turbulent characteristics of the flow were modeled using a low-Reynolds-number k-e turbulence model due to Launder and Sharma. The arbitrary nature of the computational domain was accounted for through the use of a nonorthogonal boundary-fitted coordinate system on a staggered grid. A control-volume-based finite difference scheme was used to solve the transformed transport equations. This study is primarily focused on elucidating the inlet superheat dissipation in the melt pool with the rolls being maintained at a constant liquidus temperature of the steel. A parametric study was carried out to ascertain the effect of the inlet superheat, t...

Single channel double-duct liquid metal electrical generator using a magnetohydrodynamic device

Abstract: A single channel double-duct liquid metal electrical generator using a magnetohydrodynamic (MHD) device. The single channel device provides useful output AC electric energy. The generator includes a two-cylinder linear-piston engine which drives liquid metal in a single channel looped around one side of the MHD device to form a double-duct contra-flowing liquid metal MHD generator. A flow conduit network and drive mechanism are provided for moving liquid metal with an oscillating flow through a static magnetic field to produce useful AC electric energy at practical voltages and currents. Variable stroke is obtained by controlling the quantity of liquid metal in the channel. High efficiency is obtained over a wide range of frequency and power output.

Apparatus for de-gassing molten metal

Abstract: Argon injection nozzles are provided in a close-spaced series lengthwise along a treatment trough, in which liquid aluminum is conveyed. The gas is blown in at high Reynolds No, whereby the jets break up into small bubbles. A high average bubble population density is achieved over the whole volume of liquid metal in the treatment trough. De-gassing is achieved in a metal residence time of 15 to 60 seconds, whereby the trough in which treatment takes place can be small.

Performance of Liquid Metal Heat Pipes During a Space Shuttle Flight

Abstract: This study investigated liquid metal heat pipe performance in a microgravity environment. Three stainless-steel/potassium heat pipes were flown on Space Shuttle mission STS-77 in May 1996. The objectives of the experiment were to characterize the frozen startup and restart transients, to compare the flight and ground test data to establish a performance baseline for analytical model validation, and to assess the three different heat pipe designs. Microgravity operation did not adversely impact the startup or restart behavior of the heat pipes. The heat pipes operated within the predicted performance envelopes. The three designs had distinct startup characteristics, yet were similar in steady-state performance. These results will serve as a benchmark for further liquid metal heat pipe studies and space system applications.

Mass transport phenomena at the liquid metal/substrate (metal, carbide) interface

Abstract: We have developed a model that describes surface mass transport in dissimilar materials such as liquid metal/substrate (metal, structural ceramic) and verified the model with experimental data taken from the literature and generated in our research on liquid aluminum and silicon carbide at 933 and 1253 K. Knowing the size of contact angles of drops on substrates as a function of time and temperature in a controlled atmosphere allows the calculation of apparent surface diffusion coefficients that are characteristic of the systems under consideration. Apparent surface diffusion appear to be two components related to adhesional wetting (physical effect), Ds, and reactive wetting (chemical effect), Dr, and can be expressed by the following equation: Ds +Dr = (γLV/ η) cos πeλLT= constant, where γLV and η are the surface tension and viscosity of the liquid, respectively; λ is a geometrical roughness of the solid surface; and πe is a contact angle at equilibrium.

Compatibility of structural materials with liquid lead-bismuth and mercury

Abstract: Both liquid Hg and Pb-Bi eutectic have been proposed as possible target materials for spallation neutron sources. During the 1950s and 1960s, a substantial program existed at BNL as part of the Liquid Metal Fuel Reactor program on compatibility of Bi, Pb, and their alloys with structural materials. Subsequently, compatibility studies of Hg with structural materials were performed in support of development of Rankine-cycle Hg turbines for nuclear applications. This paper reviews our understanding of the corrosion/mass-transfer reactions of structural materials with these liquid-metal coolants. Topics discussed include the basic solubility relations of Fe, Cr, Ni, and refractory metals in these liquid metals, results of inhibition studies, role of oxygen on corrosion, and specialized topics such as cavitation corrosion and liquid-metal embrittlement. Emphasis is on utilizing the understanding gained in this earlier work on the development of heavy-liquid-metal targets in spallation neutron sources.