Showing papers on "Liquid metal published in 1996"

Thermal conductivities of molten metals: Part 1 Pure metals

Abstract: Thermal conductivity data for molten metals, published since the review of Touloukian et al. in 1970, are collated and evaluated. Where possible recommended values are given. Where availability of data permits, the Wiedemann-Franz-Lorenz equation relating electrical and thermal conductivities has been assessed. It has been found to be valid for most pure metals at their melting point.

Glass transitions and first order liquid-metal-to-semiconductor transitions in 4-5-6 covalent systems

Abstract: In this paper the glass transition phenomenology for the 4-5-6 covalent system Ge-As-Se is reviewed and then it is argued that Ge-and Si-containing liquids should exhibit much of the phenomenology of the H 2 O-based and SiO 2 -based systems which dominate the natural world. In both systems, aqueous solutions and silica-based glassformers, the wide glass-forming ranges are preceded by H 2 O-rich and SiO 2 -rich composition ranges in which there is a liquid-liquid phase separation. For both the aqueous systems and the 4–6 (and 4-5-6) systems, it is argued that the liquid-liquid transitions are driven by a structural incompatibility of low temperature open network and high temperature, denser-packed structure (the latter being metallic in the cases of Ge and Si) which lead to first order phase transitions in the supercooling liquid. The argument is supported by showing that the phenomenologies of supercooled water and supercooled liquid silicon are very similar. For the latter phenomenology, we turn to molecular dynamics computer simulations of liquid silicon using the Stillinger-Weber potential which reproduces the melting point and many qualitative features of the real material. In the supercooled liquid state, S-W silicon shows, remarkably, all the anomalies in thermodynamic and diffusive properties known for supercooled water. These culminate in a directly observable, weak first order transition to the tetrahedral network amorphous phase, (as suggested, but not established, for water) which then nucleates the crystalline polymorph in accord with the experimental finding that liquid Ge can be supercooled to, but not below, the temperature estimated for the liquid-amorphous transition in liquid Ge.

Diffusion in liquid metals

Abstract: By doing experiments in space, it was possible to avoid convection in liquid diffusion experiments for the first time. Due to the improved accuracy it was possible to check experimentally different diffusion theories. Spacelab experiments revealed a square dependence of the self-diffusion coefficient on temperature for different metals (Sn, In, Pb, Sb) and for impurity diffusion and interdiffusion in the In-Sn system. For future microgravity experiments a new shear cell was developed, and shearing was investigated during parabolic flights in model experiments. The method of hydromagnetic damping of convection for ground-based liquid metal diffusion experiments was also tested.

Measurement of contact angle in systems involving liquid metals

Abstract: A technique has been developed for measurement of the contact angle of liquid metals with solid materials. The liquid metal, when contained in a small cup (inner diameter <4 mm) forms a concave or convex mirror surface. For the present technique, an optical method was devised to measure the radius of curvature of this mirror surface, from which the contact angle can be determined. The surface of the liquid metal approaches sphericity as the diameter of its container is decreased. The optical system formed in this method is non-paraxial. An analytical formula, valid for a spherical non-paraxial mirror, for calculation of image size was deduced. The technique has been demonstrated using the mercury - graphite (15.9% total porosity) system at room temperature and the contact angle was determined to be .

Density Measurements on Levitated Liquid Metal Droplets

Abstract: Electromagnetic levitation is a useful tool for measuring thermophysical properties of high-temperature melts such as liquid metals. Due to its noncontact nature, the undercooled regime is also accessible. Density and thermal expansion of a levitated drop can be derived from volume measurements, if its mass is known. Assuming cylindrical symmetry, the volume of a drop can be determined from its cross section. Using photography, such measurements on liquid metals have been performed in the past. Here we present an improvement of this method, which replaces the photographic camera with a CCD videocamera and subsequent digital image processing. This reduces the time effect required to obtain the results and allows one to average over disturbing surface oscillations. The specific problems of digital image processing, namely resolution and edge detection, are addressed and results on nickel are presented.

Separation of Metal Droplets from Slag

Abstract: The motion of liquid metal droplets in molten slags was studied using low temperature physical modeling and X-ray observations at high temperatures. Experiments were done to assess settling times of metal droplets in slags. Experimental work included oil and water modeling and high temperature experiments utilizing a furnace equipped with an X-ray fluoroscopy apparatus. Results show that settling times of metal droplets in stagnant slags and water droplets in a variety of oils can be accurately predicted utilizing Stokes' equation modified for the appropriate experimental conditions. It was also found that gas stirring in slags, whether by chemical reaction or gas injection, and slag foaming increases droplet settling times. Stable foams resulting from the reaction of FeO in the slag and carbon in the metal as well as gas injection in the metal phase caused rafts to form which could permanently hold droplets up to about 5 mm in diameter at the top of the slas. For better separation, slags with low viscosities are recommended and foaming should be avoided.

Energy spread in liquid metal ion sources at low currents

Abstract: In previous work, attempts to lower the energy spread in liquid metal ion sources (LMIS) by resorting to low current operation have rarely been successful. We have found the energy spread of gallium LMIS to be ≊4.5 eV full width at half‐maximum for emission currents from 0.45 μA down to 13 nA. Our experimental results suggest that this occurs because emission <0.45 μA is formed by pulses of height 0.45 μA and an appropriate duty cycle. Several observations support this hypothesis: (1) For sources that had a minimum current, below which they could not be made to operate, the minimum current was always 0.45 μA at room temperature, regardless of apex radius or surface roughness. (2) Emission ≤0.45 μA from blunt sources at room temperature always showed pulses of height 0.45 μA, and a clear transition to dc at 0.45 μA. The pulse height and transition current rose with source temperature. (3) Emission ≤0.45 μA from sharp sources always showed pulsing from the lowest currents up to the current at which the ampl...

Analysis of Velocity and Temperature Fields of Molten Metal in DC Electric Arc Furnace

Abstract: Recently some small scale industries have started using DC electric arc furnace to recycle scrap materials, however modelling and simulation data are very limited in the literature. Therefore, it appears that a numerical simulation could provide many important components for predicting suitable operating conditions, better design and efficient control of the process. With this objective, a numerical simulation model is developed under certain simplifying assumptions. A SIMPLER algorithm is used to solve the model equations.Computed results show that the circulating patterns and the patterns of increasing the temperature of the melt are significantly affected by the change in bottom electrode diameter and these calculated results present very important information. For example, a furnace can be designed in such a way that the melt temperature can be increased uniformly throughout the bath which is very important for making homogeneous alloys. It is also found that the effect of natural convection on melt circulation is negligible, that is, circulation is totally controlled by the electromagnetic force field. In addition to the flow field data, data obtained from the electromagnetic field computations are also presented.

Modeling and Experimental Study of Gaseous Oxidation of Liquid Iron Alloys

Abstract: On the basis of the experimental results and thermodynamic and kinetic theories, a system reaction model was developed for liquid iron reacting with O2/CO2/CO/N2 gases. For verification of the model, laboratory-scale experiments using a levitation melting technique were carried out on the kinetics of simultaneous oxidation of carbon, silicon, and manganese in a liquid metal droplet by oxygen and/or carbon dioxide in nitrogen gas. Both reaction model predictions and experiments show that for medium- or high-carbon (1.64 and 3.38 pct carbon, respectively) liquid iron, oxidation of silicon and manganese occurs at 1873 K only after cessation of the vigorous decarburization reaction, but that they proceed from the beginning in a low-carbon (0.4 pct carbon) run. The oxidation of silicon was accompanied by oxidation of manganese because of the reduction of the activity of manganese oxide once an oxide formed on the surface of the metal droplet. In a low-temperature run (< 1633 K), the metal surface was covered by a solid or very viscous oxide layer and the reaction proceeds far more slowly. The reaction model does not interpret reaction behavior at lower temperature because diffusion in the oxide layer may be the rate-controlling step, and this mechanism has not been included in the model.

Parametric investigation of current pulses in a liquid metal ion emitter

Abstract: The presence of current pulses superimposed on the dc level of the ion current in liquid metal ion sources has been known for a long time. This work investigates the behaviour of the pulses for varying temperature and working liquid metal. Attempts are made to explain the differences observed in the threshold current for the appearance of the pulses and also in their terminal, or saturation, frequency. Differences are also found between sources using the same working metal, although the pulse appearance threshold current is the same for a given metal. The experimental results indicate that a low source operating temperature is desirable if droplet emission is to be minimized.

Free surface Nvier-Stokes flows with simultaneous heat transfer and solidification/melting

Abstract: A mathematical model to analyse some key aspects of the metal cast process is described involving the filling of the mould by liquid metal and simultaneously, undergoing both cooling and solidification (re-melting) phase change. A computational solution procedure based upon a finite volume discretisation approach, on both structured and unstructured meshes, is described. The overall flow solution procedure is based on the pressure correction algorithm SIMPLE suitably adapted to: (a) solve for the free surface with minimal smearing by the SEA algorithm, and (b) solve for the solidification/melting phase change using an enthalpy conservation algorithm developed by Voller, but with its root in the work of Crank many years ago.

Thermal bonding of light water reactor fuel using nonalkaline liquid-metal alloy

Abstract: Light water reactor (LWR) fuel performance is limited by thermal and mechanical constraints associated with the design, fabrication, and operation of fuel in a nuclear reactor. These limits define ...

Ultrasonic connecting method and connecting structure

Abstract: PROBLEM TO BE SOLVED: To obtain a high strength connection without impairing large damage to a substrate under the conditions of low load and small amplitude by disposing a third metal of a melting point of a specific temperature or lower between both connecting members, and ultrasonic connecting Al or Al alloy to other metal with a low connecting load in a wide surface. SOLUTION: A Cu lead 4 having an Sn film 5 having a low melting point (300 deg.C or lower) and formed at a connecting surface side by partial plating on an Si device 3 formed with an Al-Si connecting film 1 is disposed on an Si substrate 2. A load is applied to the lead 4 by a W bonding tool 6 from above, heat from a heater 8 is transferred to the lead 4 via the tool to heat it, and an ultrasonic vibration 7 is also applied to the lead 4. In the connecting step, simultaneously upon collapsing of an Al oxide film, the surface is covered with liquid metal, and hence Al clean surface is easily protected even in the case of a low load. Thus, the Al or Al alloy can be metallurgically connected to other metal in a wide surface. Therefore, it can be connected without developing an excess stress at a member.

Work of adhesion in ceramic oxide/liquid metal systems

Abstract: On the basis of experimental data given in the literature, a model for the determination of the work of adhesion was successfully applied in non-reactive oxide Al2O3 ZrO2 UO2/liquid metal systems. According to this model, the non-transition metals interact with oxides via dispersion forces, whilst the transition metals additionally establish chemical-type equilibrium bonds with the oxide surface. The assumptions of the model for both system categories are discussed and they are in good agreement with other theoretical and experimental findings.

Solid/liquid interface detection in casting processes by gamma-ray attenuation

Abstract: A liquid metal/solid metal interface detecting device comprises in general a radiation source for generating gamma radiation, which is directed to pass through a strand extruded from a continuous casting mold. A detector detects the gamma radiation passing through the partially solidified strand to determine a spatial profile for a liquid metal/solid metal interface by relying on the different gamma radiation attenuation characteristics of the solid metal and the liquid metal. Preferably, the gamma radiation is at energies of greater than one million electron volts. In some embodiments, a movable support carries the radiation source and the detector and moves the radiation source and detector along and around the ingot enabling generation of a three-dimensional profile of the liquid metal/solid metal interface by utilizing tomographic imaging techniques. Alternatively, solidification at a single region is determined and this information is used to control the formation of the strand in process controller implementations. Surface temperature detectors can also be used to provide more information about the solidification.

Liquid metal movement during plasma arc cutting

Abstract: The forces acting on the melt (aerodynamic drag, gravity, viscosity and surface tension) during plasma arc cutting are analyzed. The main forces acting on the melt are believed to be the aerodynamic drag force and surface tension. Estimations show that gravity is significant only for thick metal plates. The equation of motion of the liquid metal is derived. This equation allows the velocity and thickness of the liquid metal inside the cut to be calculated (if the gas flow rate is known). In order to determine the gas flow rate, the heat transfer through the liquid layer should be considered. (The plasma jet heats and melts the solid metal through this layer.) As was shown by Shamblin and Amstead, a thick liquid layer can constitute significant thermal resistance for heat transfer. In order to use the power of the plasma jet efficiently, the liquid layer thickness should not exceed a certain limit. Since the layer thickness decreases as the plasma gas velocity increases, this implies a lower limit to the gas flow rate. It is found that the actual gas flow rates are close to but do not exceed this limit.

Gallium alloy interconnects for flip-chip assembly applications

Abstract: For miniature interconnection applications, innovative material systems based on gallium alloys offer potentially attractive alternatives over commonly used bonding materials, such as solders and conductive adhesives, without the reliability and environmental drawbacks. Gallium alloys are mechanically alloyed mixtures of a liquid metal and metallic powders, formed at room temperature which cure to form solid intermetallic interconnects. Through the course of this work, gallium alloys have been investigated for flip-chip interconnect applications. Specifically, this paper presents the results of a preliminary feasibility study demonstrating the applicability of gallium alloys as flip-chip on laminate interconnect materials. The topics covered include the test vehicle assembly process, reliability screening results, preliminary failure mode analysis, and interconnect microstructure analysis. To demonstrate preliminary feasibility and application, gallium alloyed with copper and nickel was used as micro-miniature interconnects between bare silicon chips and printed circuit boards. This initial study shows feasibility of such interconnects and the reliability tests demonstrate sufficient cyclic fatigue reliability in the presence of underfill material. Moreover, through the course of this work a new micro-dispensing technology for gallium alloys was developed which leverages existing industry infrastructure. This initial study represents a significant advancement in microelectronic interconnect materials unveiling the potential for an innovative lead-free interconnect alternative.

Performance Analysis of a Liquid Metal Heat Pipe Space Shuttle Experiment.

Abstract: : Future spacecraft technologies require advanced high-temperature thermal control systems. Liquid metal heat pipes are considered ideally suited for such applications. However, their behavior during microgravity operation is not yet understood. This study investigated liquid metal heat pipe performance in such an environment. Three stainless steel/potassium heat pipes were flown on space shuttle mission STS-77 in May 1996. The objectives of the experiment were characterization of the frozen startup and restart transients, comparison of flight and ground test data to establish a performance baseline for analytical model validation, and assessment of three different heat pipe designs. Heat pipe performance was characterized prior to the flight experiment. Predicted performance envelopes for each heat pipe were determined from theoretical calculations. Performance baselines were established from ground thermal vacuum test results. These pre-flight results were compared with those from the flight experiment. Thermal resistances were calculated for comparison of each heat pipe design.

Numerical analysis of fluid flow with free surface and phase change under electromagnetic force

Abstract: In this study, fluid flow of liquid metal with free surface and melting of metal under electromagnetic force was investigated numerically. The computational code was developed by the authors based upon a finite difference method to simulate the free surface flow and the eddy current simultaneously. The VOF method was introduced to treat the free surface, and magnetic vector potential was used for eddy current analysis. The free surface shape predicted by the code agreed with that obtained experimentally. Furthermore, the code was improved to calculate the phase change (melting) of solid metal by Joule heating due to eddy current. Numerical results of melting of metal were also demonstrated.

Liquid metal flow measurement by neutron radiography

Abstract: Visualization of a liquid metal flow and image processing methods to measure the vector field are carried out by real-time neutron radiography The JRR-3M real-time thermal neutron radiography facility in the Japan Atomic Energy Research Institute was used Lead—bismuth eutectic was used as a working fluid Particles made from a gold—cadmium intermetallic compound (AuCd 3 ) were used as the tracer for the visualization The flow vector field was obtained by image processing methods It was shown that the liquid metal flow vector field was obtainable by real-time neutron radiography when the attenuation of neutron rays due to the liquid metal was less than 1/e and the particle size of the tracer was larger than one image element size digitized for the image processing

Experiments on expanded liquid metals at high temperatures

Abstract: The electrical resistivity of liquid tungsten was measured using electric pulse heating of the wires inside capillary tubes. Under “fast” heating (10 µs) or “slow” heating (50 µs), the wire expands and fills the inner cavity of the capillary. On the oscillogram traces of the voltage drop across the wire, one can see the phases solid, liquid, fast expansion, and then the moment when the cavity is filled with the metal. Using the voltage drop, current, and volume of the capillary cavity, one can calculate the electrical resistivity,ρ, of the expanded metal. Tungsten densities from 7.5 to 1 g · cm−3(3 x 1022 to 0.5 x 1022 atoms · cm−3) were investigated at temperatures from 10 x 103 to 14 x 103 K. For these densities, the electrical resistivity increased from 0.5 to 5mΩ·cm.

Solid/liquid interface detection in continuous casting processes by gamma -ray attenuation

Abstract: A liquid metal/solid metal interface detecting device comprises in general a radiation source for generating gamma radiation, which is directed to pass through a strand extruded from a continuous casting mold A detector detects the gamma radiation passing through the partially solidified strand to determine a spatial profile for a liquid metal/solid metal interface by relying on the different gamma radiation attenuation characteristics of the solid metal and the liquid metal Preferably, the gamma radiation is at energies of greater than one million electron volts In some embodiments, a movable support carries the radiation source and the detector and moves the radiation source and detector along and around the ingot enabling generation of a three-dimensional profile of the liquid metal/solid metal interface by utilizing tomographic imaging techniques Alternatively, solidification at a single region is determined and this information is used to control the formation of the strand in process controller implementations

Bearing e.g. for rotary anodes of X=ray tubes

Abstract: The bearing includes an opening filled with liquid metal. Two or more parts of the bearing have sealing surfaces bordering the liquid metal. The sealing surfaces are adjacent each other to form a sealing joint. A material is provided between the sealing surfaces to form a mixing phase with the liquid metal. The material is plastically deformable and is in the form of a sealing ring. The liquid metal includes a gallium alloy, and the material may be a nickel compound. The bearing is e.g. a spiral groove bearing for positioning a rotary anode in the vacuum housing of an X-ray tube.

Radioactive scrap metal decontamination technology assessment report

Abstract: Within the DOE complex there exists a tremendous quantity of radioactive scrap metal. As an example, it is estimated that within the gaseous diffusion plants there exists in excess of 700,000 tons of contaminated stainless steel. At present, valuable material is being disposed of when it could be converted into a high quality product. Liquid metal processing represents a true recycling opportunity for this material. By applying the primary production processes towards the material`s decontamination and re-use, the value of the strategic resource is maintained while drastically reducing the volume of material in need of burial. Potential processes for the liquid metal decontamination of radioactively contaminated metal are discussed and contrasted. Opportunities and technology development issues are identified and discussed. The processes compared are: surface decontamination; size reduction, packaging and burial; melting technologies; electric arc melting; plasma arc centrifugal treatment; air induction melting; vacuum induction melting; and vacuum induction melting and electroslag remelting.