Showing papers on "Liquid metal published in 1993"

Structure and dynamics of expanded liquid alkali metals

Abstract: The main objective of the study of expanded liquid alkali metals like Rb and Cs is to find out how the structure, dynamics and effective interaction potential change during the expansion of the liquid metals from the melting point towards their liquid-vapour critical point. Near their critical point, the change from a liquid metal to a non-metal takes place, which implies that the interatomic forces must exhibit drastic changes when the critical point is approached. The static structure factor of expanded liquid alkali metals from the melting point up to their critical point have been measured and characteristic changes of the microscopic structure have been observed. In order to obtain additional information about dynamical properties, such as the self-diffusion coefficient, single particle and collective excitations, measurements of the dynamic structure factor of expanded liquid rubidium have been performed. In particular, these measurements provide information about the existence of collective phonon-like excitations in the expanded liquid metal and about the transition region from collective to more localized dynamical behaviour as the metal—non-metal transition is approached.

Thermophysical properties of rhenium

Abstract: Experimental investigations of the thermophysical properties of rhenium at high temperatures (above 2000 K) are scarce and quite recent. Using an isobaric expansion technique, we performed new measurements up to 7000 K under 0.12GPa argon pressure and report here enthalpy, density, temperature, and electrical resistivity data for both solid and liquid states. Agreement is good with other pulse heating results obtained on this refractory metal (T m =3453 K), except in the volume increase at melting.

Wetting and interfacial bonding in liquid metal/solid ceramic systems

Abstract: The current understanding of metal-ceramic interactions is presented based on wetting data obtained by the sessile drop technique. The nature of the bonding between metals and ceramics, with emphasis on ionocovalent oxide ceramics, is discussed using an electronic approach. Typical examples are given to illustrate the effect of oxygen on the wetting behaviour of a metal/ceramic system when it acts as a dissolved element in the liquid metal, and when it causes the formation of an oxide film on the metal surface and an oxide-like layer on the ceramic surface. The influence of alloying elements on the wetting properties is elucidated using a thermodynamic model. Following these discussions, the general behaviour of wetting and adhesion in metal/ceramic systems could thus be deduced.

Thermophysical properties of liquid platinum

Abstract: Material properties of liquid metals are inherently difficult to measure. Static measurements are difficult to make on most metals because of the typically high values of critical temperature and pressure, problems with sample-container contamination, and physical strength limits of high-pressure vessels. Data on thermophysical properties of metals are needed for a variety of applications, and measurements on most liquid metals are performed using dynamic techniques. Dynamic pulse heating experiments are typically performed on nanosecond to millisecond timescales, providing data that would not otherwise be obtainable. We use a resistive pulse heating method to reach high-temperature expanded liquid-metal states at a constant pressure. This technique can be used for a variety of metals and allows accurate data to be obtained over a wide range of temperature. Metallic wire-shaped samples (1×25 mm) are resistively heated in an inert gas atmosphere for a period of about 10−4 s by an almost-square current pulse (∼15×l03 A). Samples expand along an isobaric path, with remote diagnostics providing data on current, voltage, temperature, volume, and sound speed. These basic quantities are then used to calculate several derivative quantities. We report measurements of enthalpy, temperature, volume, electrical resistivity, and sound velocity of liquid platinum for temperatures from the melting point up to ∼5100 K.

Thermophysical properties of solid and liquid beryllium

Abstract: A submillisecond resistive heating technique under high pressure (0.12 GPa) has been used to measure selected thermophysical properties of both solid and liquid beryllium. Data have been obtained between room temperature and 2900 K. Results on enthalpy, volume expansion, electrical resistivity, and sound velocity measurements are presented.

Transition of liquid metals into vapor in the process of pulse heating by current

Abstract: The peculiarities of a liquid metal's nonequilibrium phase transition into vapor in the process of heating metallic wire samples by current impulse at the rate of 108 to 1010 K · s−1 are examined. A review of works by the article's author about a liquid metal's superheating up to the vicinity of the spinodal and explosive boiling under these conditions is given. In addition, the possibility of getting beyond the spinodal, realization of the unstable phase and its spinodal decay under the rate of heating of more than 1011 K · s−1 is analyzed.

Microsecond-resolution measurements of the thermophysical properties of liquid gold

Abstract: New experimental results obtained using an accurate technique for electrical and optical measurements on pulse-heated gold samples are given. An almost-constant current pulse is used for resistive self-heating of the sample over a time interval of 50 μs. Because of the high heating rate, the sample maintains its cylindrical shape in the liquid phase. High pressures are used to extend the investigated range of the liquid phase by suppressing boiling. The stability of the liquid sample is demonstrated by short-time photographs, obtained with a kerrcell camera. Measurements of current through the sample, voltage drop across the sample, surface radiation, and volume expansion allow the determination of the selected thermophysical properties. Specific enthalpy, electrical resistivity, temperature, density, and their mutual dependencies are obtained. In addition, the enthalpy of melting, as well as the specific heat capacity at constant pressure, is determined.

Casting of metal strip

Abstract: A method of casting metal wherein the molten metal is deposited on a moving planar substrate formed from an insulating refractory material. The deposited liquid metal is maintained as a liquid until the turbulence induced by the pouring of the metal onto the substrate is minimized.

Kelvin-Helmholtz instability of Couette flow between vertical walls with a free surface

Abstract: A novel type of Kelvin–Helmholtz instability model is developed from hydrodynamic theory. The classical Kelvin–Helmholtz instability involves a horizontal interface between two fluids with different parallel, uniform, horizontal velocities. If the upper fluid is a gas with a much smaller density than the lower fluid which is a liquid, then the phase velocity of the critical disturbance equals the liquid’s velocity, so that the liquid sees a standing interfacial wave. The inertial force driving the interfacial instability involves only the gas, no matter how small its density is. In a much more realistic flow model, the liquid velocity at the free surface is not uniform, but varies across the free surface. The disturbance phase velocity can only equal the liquid velocity at one point, while liquid on either side of this point moves faster or slower than the wave. The inertial forces in the liquid then dominate and the gas plays a negligible role. The concept is developed from a Couette flow hydrodynamic model where the fluid flows between two parallel vertical walls with a free surface. The importance of a nonuniform liquid velocity is demonstrated. This modified theory will be applied in future work to study the ejection instability at the interface of the liquid metal and inert cover gas in sliding electrical contacts.

Measurements of thermophysical properties of nickel with a new highly sensitive pyrometer

Abstract: A new, sensitive, and fast (response time, 100 ns) pyrometer used for the measurement of temperature in pulse heating experiments is described. The monochromatic instrument may use two detectors, namely, a Si diode and an InGaAs diode. Since monochromatic pyrometers usually are “self-calibrated” with the plateau of the melting transition of the investigated metal, a high sensitivity is desirable. The pyrometer is sensitive down to 1000 K and may be used at the melting plateau of copper, a reference point on the International Temperature Scale of 1990. A wide temperature range in a single measurement is possible with the use of a fast operational amplifier with linear and logarithmic outputs. Electrical resistivity, heat capacity, and enthalpy of nickel were measured in the temperature range 1500 to 2200 K using a fast pulse heating technique.

Quantitative evaluation of contact thermal conductance in a vacuum as a result of simulating the effect of cooling

Abstract: Contact thermal conductance is much lower in a vacuum than normal pressure conditions. When we cool SR beamline optics, such as mirror components, a water cooled copper plate which is attached to the optics is used. In order to increase the effect on cooling an indium sheet or liquid metal, such as Ga, In-Ga, is inserted between the optics and the plate. We experimentally obtained contact thermal conductance in a vacuum, which was essential to computing the thermal distribution of optics. And we simulated our cooling system using a beamline mirror component.

Near-field photon tunneling devices using liquid metal

Abstract: A near-field photon tunneling device consisting of a plurality of optical waveguides, such as optical fibers, arranged in juxtaposition with a variable tunnel gap through which photons from at least one of said optical fibers can be caused to tunnel, and wherein the tunnel gap is filled with a metal that is liquid at room temperature or at moderately elevated temperature. The width of the tunnel gap and the corresponding thickness of the liquid metal layer is remotely controllable. The control mechanisms for the width of the gap include optical means, piezo-electric elements and temperature sensitive means. The devices include optical couplers of the head-on and side-on types, optical modulators and switches, as well as display units.

Liquid metal MHD and heat transfer in a tokamak blanket slotted coolant channel

Abstract: A liquid metal MHD (magnetohydrodynamic)/heat transfer test was conducted at the ALEX (Argonne Liquid Metal Experiment) facility of ANL (Argonne National Laboratory), jointly between ANL and NIIEFA (Efremov Institute). The test section was a rectangular slotted channel geometry (meaning the channel has a high aspect ratio, in this case 10:1, and the long side is parallel to the applied magnetic field). Isothermal and heat transfer data were collected. A heat flux of /spl sim/9 W/cm/sup 2/ was applied to the top horizontal surface (the long side) of the test section. Hartmann numbers to 1050 (2 Tesla), interaction parameters to 9/spl times/10/sup 3/, Peclet numbers of 10-200, based on the half-width of the small dimension (7 mm), and velocities of 1-75 cm/sec. were achieved. The working fluid was NaK (sodium potassium eutectic). All four interior walls were bare, 300-series stainless steel, conducting walls.

Shape and stability computations of electromagnetically confined liquid metal boundaries

Abstract: High-frequency electromagnetic shaping of liquid metal boundaries involves a coupling between the molten metal interface and the magnetic fields. Modeling a stable molten metal and air interface requires a self-consistent solution. Previous work by the authors describes a two-part iterative free boundary solution procedure applied to liquid metal column cross sections. This article describes the extension of this methodology to axisymmetric systems and, in addition, shows that the method predicts Rayleigh-Taylor type instabilities. Thus, the equilibrium free boundaries calculated using this method are statically stable equilibria.

Measurement of velocity in high-temperature liquid metals

Abstract: There is a paucity of methods available for the measurement of velocity in high-temperature liquid metals. This is due to the hostile environmental conditions which characterize liquid metals. This article proposes and appraises a new velocity measurement technique for liquid metal flows at high temperatures. The melting rates of metallic spheres in metal baths of the same chemical composition as the spheres are studied under isothermal conditions. It is dem-onstrated that the metallic sphere can be used as a probe for measuring the average velocity in a metal flow system over a distance equivalent to the diameter of the sphere. The system that was chosen for study is the commercial purity aluminum bath. The experimental calibration setup examined three different elements: (a) it introduced a stationary sphere in a metallic bath of a given temperature and compared its melting rate with that of a moving sphere with known external velocity along the periphery of a circle in a metallic bath of the same temperature; (b) three different sphere diameters were used; and (c) a range of bath temperatures was investi-gated. By studying the effect of these three elements concurrently, it was possible to determine the interplay of these elements. Results showed that the sphere melting time was related linearly to the flow velocity for the range of velocities of 0 to 40 cm/s and for bath superheat up to 100 °C. In order to verify the accuracy of the results obtained by the proposed technique, a comparison was undertaken between mathematical predictions and experimental results of a fluid flow field obtained in an AC induction furnace with molten aluminum. These predictions were made by solving numerically the relevant differential equations under the appropriate boundary conditions. The experimental results attained using the proposed technique were in close agreement with those from the mathematical predictions.

The study of thermal processes in an electrode submitted to an electric arc

Abstract: This article investigates the thermal phenomena that are occurring in an electrode submitted to an electric arc in air at atmospheric pressure. Our purpose is to get a better understanding of the electrode erosion phenomena concerning vaporization or liquid droplets ejection. For that we propose an original experimental device allowing the measurement of the liquid and vapor quantities created under the arc root. The principle of this device is based on the ejection of the liquid metal through centrifugal movement of the electrodes during the arc. Some results are given relatively to Ag, Cu and AgSnO 2 cathodes and anodes. Then we present a numerical modelling of the thermal phenomena induced in the electrode by the heat transferred from the arc root. We propose a method to solve the difficulties related to this kind of free boundary problems induced by the fact that the elecatrode material may undergo various phase changes. Finally we show how to use this numerical computation and the experimental results in order to estimate the power density input at a copper anode

Electrolysis cell and method for metal production

Abstract: An electrolytic reduction cell for the production of metal is provided, in which liquid metal is deposited at or adjacent an upper surface of a cathode. The electrolytic reduction cell includes an anode structure and a cathode located beneath the anode structure, wherein an upper portion of the cathode comprises an aggregate of particles sized and shaped such that in operation of the cell liquid metal is present in at least an upper part of the aggregate and a slurry of liquid metal and particles is established, the slurry comprising a substantially uniform dispersion of the particles in a continuous liquid phase of the liquid metal, the slurry having a viscosity sufficiently high such that under operating conditions of the cell the slurry is relatively immobile. Methods for the production of a metal by electrolysis in the electrolytic cell are also provided.

Irradiation performance of nitride fuels

Abstract: The properties and advantages of nitride fuels are well documented in the literature. Basically the high thermal conductivity and uranium density of nitride fuels permit high power density, good breeding ratios, low reactivity swings, and large diameter pins compared to oxides. Nitrides are compatible with cladding alloys and liquid metal coolants, thereby reducing fuel/cladding chemical interactions and permitting the use of sodium-bonded pins and the operation of breached pins. Recent analyses done under similar operating conditions show that - compared to metal - fuels mixed nitrides operate at lower temperatures, produce less cladding strain, have greater margins to failure, result in lower transient temperatures, and have lower sodium void reactivity. Uranium nitride fuel pellet fabrication processes were demonstrated during the SP-100 program, and irradiated nitride fuels can be reprocessed by the PUREX process. Irradiation performance data suggest that nitrides have low fission gas release and swelling rates thereby permitting favorable pin designs and long lifetime. The objective of this report is to summarize the available nitride irradiation performance data base and to recommend optimum nitride characteristics for use in advanced liquid metal reactors.

Numerical simulation of solidification of molten aluminum alloys in cylindrical molds

Abstract: A finite element model for the solidification of molten metals and alloys in cylindrical molds is developed using the energy equation in terms of temperature and enthalpy. TheNewton-Raphson technique was used to solve the resulting nonlinear algebraic equations. A computer program is developed to calculate the enthalpy, temperature, and fraction solid per the classical Lever rule, Scheile equation, and Brody-Flemings models. Cooling curves are calculated for pure metal (aluminum), two eutectic alloys (Al-33.2 pct Cu and Al-12.6 pct Si), and three hypoeutectic alloys (Al-2.2 pct Cu, Al-4.5 pct Cu and Al-7 pct Si) and are compared with the experimental curves.

Method for atomizing liquid metal utilizing liquid flow rate sensor

Abstract: A method and apparatus for atomizing liquid metal are disclosed. A vessel supplies liquid metal through a pouring channel to an atomizing nozzle. A flow sensor provides at least one gas flow into the liquid metal, and determines a pressure difference from the gas flow. A processor determines the liquid metal flow rate through the nozzle from the pressure difference. A control adjusts the liquid metal flow rate in response to the determined liquid metal flow rate, and the liquid metal is atomized.

Capillary Instability of a Jet of Liquid Metal

Abstract: A system based on ink-jet technology has been used to demonstrate the controlled generation of monodispersed 100 μm diameter molten solder droplets. Oxide formation on the surface of the molten solder jet was shown to have a drastic effect on the droplet formation process. If the oxygen is not removed from the environment, no jet break up occurs. The growth rate of a radial disturbance on a capillary jet of molten solder is similar in magnitude to that predicted by Rayleigh and Weber theory, but the agreement is not good enough to say that these theories are valid for the liquid metal jet

On hydrogen transport and edge plasma modeling of liquid-metal divertors

Abstract: The steady-state operational conditions for large tokamaks impose high performance requirements that cast suspicion on the employment of conventional solid surface divertors. Flowing liquid-metal divertors are thus being considered as an alternative. A preliminary evaluation is made of some aspects of this concept. To understand the hydrogen (i.e., deuterons and tritons) recycling behavior in liquid metals, the transport and chemistry aspects of the hydrogen/liquid-metal interaction are investigated, including hydrogen gettering, tritium inventory, and blistering caused by hydrogen bubble eruptions. It is shown that when operating in the high-recycling model (i.e., as the liquid metal is filled with deuterons and tritons, one implanting ion will immediately cause the emission of one neutral particle), lithium would have a large tritium inventory. Gallium, on the other hand, does not have the same problem because of its negligible hydrogen solubility and the decomposition of its hydrides in the temperature range of interest. However, to avoid blistering, the flow speed of a gallium neutralizer has to be high. An edge plasma simulation model is briefly introduced, and its outcome for the high-recycling liquid-metal (lithium and gallium) divertors is presented. This model gives more realistic predictions of plasma temperature than some of the existing simulation models.more » Results of this model show that denser and cooler edge plasmas can be achieved by liquid-metal divertors than by conventional stationary surface divertors. Evaporation and sputtering of liquid-metal divertors are shown not to be as serious a problem as might be suspected at first glance. 22 refs., 2 figs., 1 tab.« less

The structural and dynamical liquid-glass transition for metallic sodium

Abstract: The authors perform a molecular-dynamics simulation for the liquid metal sodium to study the glass transition temperature. Using the same set of liquid to glass structure factors, this is done (a) structurally by calculating the Wendt-Abraham parameter and (b) dynamically by solving the non-linear integral equation embodied in the mode-coupling theory. The glass transition temperature obtained from the former is distinctly lower than that from the latter. In an attempt to explain such a difference in the glass transition temperature, the authors draw attention to some works on shear viscosity coefficients and analyse the latter results in light of the basic hypothesis of the mode-coupling formulation. It appears that the glass transition point obtained in the context of mode-coupling theory for metallic sodium is reasonably predicted, and that the Wendt-Abraham glass transition point, determined directly from the structure data, seems numerically closer to the calorimetric glass transition temperature. Also, the authors compare the metallic non-ergodicity form factor obtained from the molecular-dynamics simulation with the corresponding asymptotic formula proposed in the mode-coupling theory, and they agree reasonably well with each other. The effect of the pair potential on the non-ergodicity form factor is also discussed briefly for both the hard-sphere and the metallic systems.

Observations on the Role of Interfacial Phenomena in Materials Processing

Abstract: Examples of the role interfacial phenomena can play in materials processing are highlighted in the description of a number of recent research studies conducted at Imperial College. Interfacial phenomena play critical roles in increasing or retarding the rates of chemical reaction and in promoting or hindering wetting and dispersion of phases in each other.The reduction of ilmentite to iron and titanium carbide or titanium oxycarbide has been studied with the ultimate aim of achieving separation of the titanium and its subsequent conversion to pigment grade titanium dioxide. The need to achieve good separation of iron from other reaction products is then a prime concern. The effects of reducing conditions on the wetting of titanium carbides and oxycarbides by iron alloys has therefore been studied. It seems that associative adsorption of titanium and carbon may be responsible for the observed effects of dissolved titanium and carbon on the wetting of TiC by liquid iron alloys.As a result of this work a further project has been generated involving the identification of conditions for achieving good dispersions of refractory carbides including titanium carbide in iron alloys. The major motivation behind this work was the desire to develop a cheap casting based process for the production of iron based metal matrix composites capable of producing near net shape products. As a result of this work a novel rapid testing technique for the assessment of the wettability and compatibility of potential filler materials with liquid metal matrices has been developed. The technique employs levitation and quenching of liquid metal drops containing added filler materials to permit assessment of alloy composition, filler coatings and temperature on matrix/filler interactions. The levitation technique has been further utilised in a study of the conditions required for dispersion or non dispersion of second phase particles in liquid superalloys. In this case the cleanliness of the superalloys achieved during recycling procedures is determined by the ease with wich inclusions can be removed. Some observations with ternary oxides also indicate the importance of the associative adsorption phenomenon.The importance of interfacial considerations has also been highlighted by our studies on the production of aluminium-titanium-boron grain refining master alloys from fluoride fluxes. Entrapment of the products can result from emulsification occurring during the reduction reactions. A detailed study of this phenomenon has been conducted using a modified sessile drop technique. The results obtained indicate the critical role that interfacial tension plays in determining the ease of metal-flux separations and in determining whether products are dispersed in the metal or slag.The kinetics of metal-salt reactions were also found to be of importance. Fast transfer of Ti and B to the metal results in the build up to TiAl3. TiB2 or AlB12 at the interface. These compounds when present at the interface can be wet by the flux and result in emulsion formation. Inhibition of emulsification can be achieved by the presence of surface active elements such as magnesium and calcium.The role of interfacial phenomena in influencing the kinetics of the reduction of slags has been studied in an investigation of the kinetics of alkali metal oxide release from silicate melts. The kinetics of K2O and Na2O release during heating in graphite crucibles has been studied from binary alkali oxide-silicon dioxide melts and from a wide range of CaO-Al2O3-SiO2 slags. The contribution of the wetting of the graphite by the slag towards influencing reaction kinetics represents a notable feature of the study.

Microscopic Approach of Adhesion and Wetting of Liquid Metal on Solid Ionocovalent Oxide Surface

Abstract: The adhesion and wetting of non-reactive liquid metals with solid ionocovalent oxides are studied on thebasis of the experimental work of adhesion W data obtained with the sessile drop method.An analysis of theexperimental W values of different liquid metals on various solid oxides is first performed to evidence the de-pendence of the work of adhesion of a metal/oxide system on the electron density of the metal and on thethermodynamic stability of the oxide.An electronic model is then proposed to describe the microscopic mech-anism of metal-oxide interactions.Based on the model,the contact angle and the work of adhesion of differentliquid metals on various solid oxides can be interpreted and estimated,and their correlations to the variousphysical quantities of the oxides can be easily deduced.The basic consideration of the model is that the adhe-sion between a metal and an oxide is assured by the electron transfer from the metal into the oxide valenceband which is not completely filled of electrons at high temperatures,and is enhanced when this electron trans-fer at the metal/oxide interface is intensified.The influence of interface defects on the wetting and adhesion issuggested and discussed.

Process for treating a molten metal during a casting operation using a filter and filter used therefor

Abstract: The filter for molten metal comprises a series of at least two plates (2, 2a, 2b) made from refractory mineral material which together define one or more cavities (4, 5), these plates each including a series of holes (3, 3a, 3b) permitting the passage and the filtration of the liquid metal. At least one of the cavities (4, 5) contains a material (12) for treating the said metal, particularly a material having inoculant properties with respect to the liquid metal. Use, in particular, for simultaneously filtering and treating molten metals and improving the quality of the metals.