Showing papers on "Liquid metal published in 1991"

Pressure infiltration casting of metal matrix composites

Abstract: Pressure infiltration casting ∗ is a unique form of liquid infiltration which utilizes pressurized inert gas to force liquid metal into a preform of reinforcement material. The methods and equipment used for pressure infiltration casting allow for inexpensive development of composite materials, prototypes, and net-shape component production. Pressure infiltration casting's use of an enclosed die chamber with controlled pressurization makes it possible to cast in low strength molds with high infiltration pressures. The development of a number of solidification systems has enabled parts to be infiltrated and directionally solidified, producing high quality composites. The basic principles behind pressure infiltration casting and its history will be discussed in this paper. Results of research in different methods for casting composites will also be presented. These methods include: 1. (1) top fill casting-liquid metal is forced downward by a pressurized gas into a preform; 2. (2) bottom fill casting-liquid metal is forced up a fill tube into a preform by pressurized gas acting on the surface of a melt; 3. (3) top pour casting-a method developed for infiltration of high temperature alloys where the reinforcement and melt must be prevented from reacting. The methods and apparatus illustrated include sample components with aluminum and copper matrices, their microstructures, and tolerancing for net shape component production.

Nucleation and growth of Al2O3/metal composites by oxidation of aluminum alloys

Abstract: The nucleation and growth mechanisms during high temperature oxidation of liquid Al−3% Mg and Al−3% Mg−3% Si alloys were studied with the aim of enhancing our understanding of a new composite fabrication process. The typical oxidation sequence consists of an initial event of rapid but brief oxidation, followed by an incubation period of limited oxide growth after which bulk Al2O3/Al composite forms. A duplex oxide layer, MgO (upper) and MgAl2O4 (lower), forms on the alloy surface during initial oxidation and incubation. The spinel layer remains next to the liquid alloy during bulk oxide growth and is the eventual repository for most of the magnesium in the original alloy. Metal microchannels developed during incubation continuously supply alloy through the composite to the reaction interface. During the growth process, a layered structure exists at the upper extremity of the composite, consisting of MgO at the top surface, MgAl2O4 (probably discontinuous), Al alloy, and finally the bulk Al2O3 composite containing microchannels of the alloy. The bulk oxide growth mechanism appears to involve continuous formation and dissolution of the Mg-rich oxides at the surface, diffusion of oxygen through the underlying liquid metal, and epitaxial growth of Al2O3 on the existing composite body. The roles of Mg and Si in the composite growth process are discussed.

A conceptual approach for noncontact calorimetry in space

Abstract: A concept is developed and described which allows to measure the heat capacity and the effective thermal conductivity of stable and undercooled liquid metals and alloys in an electromagnetic levitation apparatus. We propose to use an ac pulse heating method which is used nowadays as a standard technique for precision measurement of low temperature heat capacities. The ideal process parameters including the drop diameter D, temperature T, and frequency of measurement ω can be optimized when the following relations hold for the external and internal relaxation time constants τ1 and τ2, respectively: ωτ1≳10 and ωτ2<0.1. Then heat capacity data can be obtained with an accuracy of better than 1% with D about 5 to 10 mm, T between 1200 and 1800 K and ω between 0.1 and 1 Hz for typical metals and alloys.

Wetting and interfacial chemistry in liquid metal-ceramic systems

Abstract: Wetting data for liquid metal-ceramic systems are reviewed, with emphasis on experimental results obtained on oxides by the sessile drop technique. Examples are given in order to illustrate the different wetting behaviours of reactive and non-reactive pure metal-ceramic pairs. The effect of oxygen on the wettability is presented both when it acts as a dissolved element and when it causes the formation of an oxide film on the liquid metal. The influnece of alloying elements is illustrated by numerous results and discussed using a thermodynamic model. Using some examples it is shown that the general behaviours holding for wettability in metal-oxide systems are also valid for the other families of ceramics.

Surface Tension Measurements of Liquid Metals by the Oscillating Drop Technique.

Abstract: An improved method for measuring the surface tension of liquid metals is proposed. Surface oscillations of an electromagnetically levitated liquid metal droplet are observed by a video camera and digital image processing is used to evaluate the spectrum of oscillations. A discussion of the theoretical background and a description of the experimental apparatus are presented. In addition, preliminary results on an FeNi sample, and an outlook for future experiments, including the measurement of viscosity, are given.

Thermal diffusivity of crystalline and liquid silicon and an anomaly at melting

Abstract: The thermal diffusivity of Si was measured by a laser flash method up to 1723 K. SiC and fused quartz cells were prepared for the measurement on the melt. The thermal conductivities of the crystal and the melt at the melting point were determined to be 27.3±0.3 and 56±1 W/mK, respectively. It is suggested that a new (metastable) phase exists in a narrow temperature range just above the melting point. It irreversibly transformed to ordinary liquid metal. The new phase may have very low emissivity, and/or large specific heat.

Use of water and mercury droplets to simulate Al2O3 collision/coalescence in rocket motors

Abstract: Combustion of aluminized solid propellants produces aluminum oxide droplets in a wide range of sizes. Droplets of different sizes accelerate at different rates and may collide, especially in nozzles of rocket motors. It has generally been assumed in the past that all collisions among these droplets result in coalescence. However, a model for coalescence efficiency previously developed and verified experimentally for free-falling water droplets indicates that permanent coalescence will not occur if the rotational energy of the spinning (temporarily coalesced) agglomerate exceeds the surface energy holding it together. Consequently, the extrapolation of this model to the high surface tension and impact energies of A12O3 droplets in nozzles has been studied experimentally using mercury droplets because 1) their liquidity at room temperature allows for simple and inexpensive testing, 2) they have a surface tension that is nearly that of A12O3, 3) their large diameters are easily visible, and 4) their high density generates high-impact energy at low-impact velocity. Single mercury droplets (bullets) of various diameters were rolled into a stationary mercury droplet (target) and the collision/coalescence process was recorded on videotape; bullet size, speed, and offset were obtained from a superposed grid. It was concluded that the water model accurately predicts the collision-induced coalescence of mercury and, therefore, A12O3 droplets because 1) the qualitative similarity between the collision/coalescence behavior of water droplets and liquid metal (mercury) droplets was excellent, 2) the model predicts well quantitatively whether a collision will result in coalesced mercury droplets, and 3) the model predicts well the degree of A12O3 coalescence apparently occurring in the nozzle of the Space Shuttle booster.

High-pressure, high-temperature thermophysical measurements on molybdenum

Abstract: Wire-shaped molybdenum samples were resistively pulse heated in a coaxial capacitor discharge circuit. Heating rates greater than 109 K s-1 were attained, and temperatures up to 10000 K reached. Time-correlated measurements were made with submicrosecond resolution of the current through the wire and voltage drop across it, as well as measurements of surface radiation and wire expansion. These quantities allow determination of such thermophysical properties as the heat capacity at constant pressure and the mutual dependencies between temperature, volume, specific enthalpy and electrical resistivity in superheated liquid molybdenum.

High voltage alkali metal thermal electric conversion device

Abstract: A high voltage multitube alkali metal thermal electric convertor having a plurality of closely packed tubular cells disposed in a tube sheet in a vessel and electrically connected in series, the tube sheet dividing the vessel into a high pressure high temperature portion having a wick and heater disposed therein and a low pressure low temperature portion having a wick disposed in a condenser from which heat is removed; a pump for transferring liquid metal therebetween and a tab on a wick disposed in the tubular cell to remove excess liquid metal and prevent shorting between the cells.

Passive cooling safety system for liquid metal cooled nuclear reactors

Abstract: A liquid metal cooled nuclear reactor having a passive cooling system for removing residual heat resulting from fuel decay during reactor shutdown. The passive cooling system comprises a plurality of partitions surrounding the reactor vessel in spaced apart relation forming intermediate areas for circulating heat transferring fluid which remove and carry away heat from the reactor vessel. The passive cooling system includes a closed primary fluid circuit through the partitions surrounding the reactor vessel and a partially adjoining secondary open fluid circuit for carrying transferred heat out into the atmosphere.

Properties of the liquid-vapor interface of fcc metals calculated using the embedded atom method

Abstract: The Embedded Atom Method (EAM) is used to compute density, internal energy, and structure factor for bulk liquids of the fcc metals at several temperatures above and below the melting temperature. The calculated values are found to be in generally good agreement with experiment, although the volume expansion upon melting does differ by up to 50% from the expected result for some of the elements studied. The total energy of a liquid system with surfaces is calculated, and the results are compared with the bulk liquid results to determine the enthalpy and thickness of the liquid-vapor interface. Also, the surface tension is found for Cu near the melting temperature. The EAM values for surface enthalpy and surface tension are found to be smaller than experimental values, which is consistent with results for EAM calculations of the surface energy of crystalline solids.

Method and apparatus for applying a compound of a metal and a gas onto a surface

Abstract: A method of applying a compound of a metal and a reactive gas onto a surface by depositing a metal from a liquid metal cluster ion source onto said surface in the presence of a gas on the surface to combine with the deposited metal while isolating the gas from the source of the metal cluster ions.

Thin film magnetic recording medium with controlled grain morphology and topology

Abstract: A magnetic storage medium is composed of a non-wettable substrate upon which a transient liquid metal layer is deposited and maintained as a distribution of discontinuous liquid features. A magnetic film layer is deposited on the transient liquid metal layer resulting in a reaction of the liquid metal with the magnetic film. The topology of the magnetic film is controllable by adjusting the thickness of the transient liquid metal layer.

Kinetics of gas-to-liquid transfer of particles in metal matrix composites

Abstract: The distribution of reinforcing particles in metal matrix composites produced by casting techniques depends on the interaction between various solid and liquid phases during transfer of particles from gas to liquid, transfer of particles from liquid to solid and during particle-particle interaction in the liquid. Only the first issue will be addressed in this paper. In order to predict particle behavior during gas-to-liquid transfer thermodynamic and kinetic models have been proposed. The total free energy change involved in the transfer of a particle from gas to liquid must be negative for this transfer to occur spontaneously. A new model based on the force balance on the particle has been developed. The governing equation includes a surface energy component which can be calculated from sessile drop experiments assuming equilibrium surface thermodynamics. The critical acceleration, acr required for particle incorporation may then be evaluated. Nevertheless it must be emphasized that sessile drop data are for vacuum, not for atmospheric environment. In the latter case, oxide films forming on the melt will influence the transfer and alter the value of the required force. In order to try to include the influence of oxide films forming on the surface of the liquid metal in the calculation of the critical acceleration, an approach involving experimental work with a two-bucket centrifugal apparatus was used. From these experiments a critical angular speed for which incorporation occurs can be determined. Thus another critical acceleration for incorporation (ωcr2R) can be calculated. If ωcr2R is equal to the previous acceleration acr the role of oxide films is negligible. If, on the contrary, there are differences they can be attributed to the presence of oxide films on the surface of the metal. Validation of the model has been carried out using data collected from sessile drop experiments and from experiments consisting of centrifuging spheroidal ceramic particles in aluminum melts. During the experiments alumia, zirconia, SiC-coated zirconia, and graphite-coated zirconia particles have been used. The basic criterion for selection of these materials was ϱP >ϱL. Calculation of the incorporation acceleration requires knowledge of wetting angles. Accordingly, sessile drop experiments were also performed to determine the wetting angles for some various metal-ceramic systems that were not available in the literature.

Analysis of Liquid Metal MHD Fluid Flow and Heat Transfer Using the KAT Code

Abstract: A new computer code has been developed with the capability to model laminar liquid metal fluid flow and heat transfer in relatively complex geometries at parameter values greater than previously po...

MHD Heat Transfer in Elongated Rectangular Ducts for Liquid Metal Blankets

Abstract: Laminar heat transfer in self-cooled liquid metal blankets can be enhanced by increasing the aspect ratio of the ducts. To determine the potential benefits of elongated rectangular ducts, numerical...

Liquid metal cooled nuclear reactor plant system

Abstract: A liquid metal cooled nuclear reactor having a passive cooling system for removing residual heat resulting for fuel decay during reactor shutdown, or heat produced during a mishap. The reactor system is enhanced with sealing means for excluding external air from contact with the liquid metal coolant leaking from the reactor vessel during an accident. The invention also includes a silo structure which resists attack by leaking liquid metal coolant, and an added unique cooling means.

Direct imaging of coal pore space accessible to liquid metal

Abstract: The pore space in coals which is accessible to a liquid metal such as mercury has been directly imaged for a rank suite ranging from a lignite up to an anthracite The experimental protocol used was designed to simulate mercury infiltration porosimetry (MIP) A quenchable liquid metal, Wood's alloy (melting point approximately 70 o C), was used in place of mercury Analysis of each of the samples was performed by scanning electron microscopy The results indicate that the metal-accessible pores in the lowest rank coal in this report are roughly cylindrical The spatial distribution of such pores, however, indicate that they constitute a highly rough, topologically complex particle surface, and not an interconnected cylindrical pore network

Inclusion decanting process for nickel-based superalloys and other metallic materials

Abstract: In a method of remelting metallic materials, particularly nickel-based superalloys, in which the melting operation is carried out in a cooled copper crucible under clean vacuum conditions by means of electromagnetic inductors, the magnetic field applied to the mass of molten metal has a frequency between 50 Hz and 5×10 6 Hz, preferably between 5×10 3 Hz and 5×10 5 Hz, so as to effect simultaneously electromagnetic stirring of the liquid metal and a surface concentration at the cold walls of the mass to be recast of all the non-conductive particles, especially ceramic inclusions, thereby achieving an inclusion decanting.

Thin film magnetic medium with controlled grain morphology and topology for improved performance

Abstract: A magnetic storage medium is composed of a non-wettable substrate upon which a transient liquid metal layer is deposited and maintained as a distribution of discontinuous liquid features. A magnetic film layer is deposited on the transient liquid metal layer resulting in a reaction of the liquid metal with the magnetic film. The topology of the magnetic film is controllable by adjusting the thickness of the transient liquid metal layer.

MHD pressure drop of liquid metal flow in circular duct under variable transverse magnetic field

Abstract: (1991). MHD Pressure Drop of Liquid Metal Flow in Circular Duct under Variable Transverse Magnetic Field. Journal of Nuclear Science and Technology: Vol. 28, No. 2, pp. 159-161.

Laminar natural convection heat transfer from a horizontal circular cylinder to liquid metals

Abstract: The objective of the present study is to clarify the heat transfer characteristics of natural convection around a horizontal circular cylinder immersed in liquid metals. Experimental work concerning liquid metals sometimes involves such a degree of error that it is impossible to understand the observed characteristics in a measurement. Numerical analysis is a powerful means to overcome this experimental disadvantage. In the present paper we first show that the Boussinesq approximation is more applicable to liquid metals than to ordinary fluids and that the present analysis gives accurate heat transfer rates, even for a cylinder with a relatively large temperature difference (>100 K) between the heat transfer surface and fluid. It is found from a comparison of the present results with previous work that the correlation equations that have already been proposed predict values lower than the present ones.

High-production rotary furnace steelmaking

Abstract: The invention is a process for steelmaking in a rotary furnace from a solid metallic charge adapted to realize greatly increased heat transfer and melting rates and thereby greater steel production. A hot liquid metal bath is maintained over the length of an oxy-fuel fired rotary furnace. Solid metallic scrap is continually introduced by way of a charge end opening into a melting zone, wherein the bath melting point temperature is depressed on the order of 300 degrees celsius at the furnace charge end, by means of coincident additions of supplementary carbon into the melt. The effect is a multifold increase in temperature differential between the flame temperature and the temperatures of the furnace walls and charge, with a proportionate increase in the quantity of heat transferred. In order to maintain this depressed temperature, a corresponding increased quantity of cold solid scrap is required to be charged into the melt and advanced along the furnace, according a dramatic production rate increase in relation to the prior art. The preferred embodiment provides an intermediate annular dam which substantially confines unmelted solid charge to the melting zone, over which melted metal overflows into an all-liquid refining and temperature-adjustment zone preceding discharge, with overall firing and furnace interior gas flow countercurrent to the general charge movement, thus allowing the steel discharge temperature to be controlled independently of the heating rate. Other benefits include increased refractory life, less oxidation of charge and refractory consitituents, and substantially less particulates and pollutants discharged in the process off-gas.

Advancing liquid metal reactor technology with nitride fuels

Abstract: A review of the use of nitride fuels in liquid metal fast reactors is presented. Past studies indicate that both uranium nitride and uranium/plutonium nitride possess characteristics that may offer enhanced performance, particularly in the area of passive safety. To further quantify these effects, the analysis of a mixed-nitride fuel system utilizing the geometry and power level of the US Advanced Liquid Metal Reactor as a reference is described. 18 refs., 2 figs., 2 tabs.

A New Critical Heat Flux Correlation for Boiling Liquid Metals

Abstract: This paper reports on correlations for the dryout heat flux for sodium in tube and grid bundles that have been developed based on experimental results and analytical considerations. The main feature of these correlations is that they are derived from thermal, hydrodynamic, and geometrical parameters. These parameters are the subcooling, the inlet and outlet vapor quality, the mass flow rate, the latent heat of vaporization, and the aspect ratio. The correlation proposed for tube geometries is developed from a data base of 170 data points compiled from 11 sources, and the correlation for flow through rod bundles is derived from the results of 13 tests.