Binary Liquid Metal Research Articles

Molecular-dynamics simulations of glass formation and crystallization in binary liquid metals: Cu-Ag and Cu-Ni

We used molecular dynamics ~MD! to obtain an atomistic description of the melting, glass formation, and crystallization processes in metal alloys. These studies use the quantum Sutton-Chen many-body potentials for Cu, Ni, and Ag to examine the Cu4Ag6 and CuNi alloys. Using cooling rates in the range of 2 310 12 to 4 310 14 K/s, we find that CuNi and pure Cu always form a face-centered-cubic ~fcc! crystal while Cu4Ag6 always forms a glass ~with Tg decreasing as the quench rate increases!. The crystal formers have radius ratios of 1.025 ~CuNi! and 1.00 ~Cu! while the glass former ~CuAg! has a ratio of 1.13, confirming the role of size mismatch in biasing toward glass formation. @S0163-1829~99!05205-4#

II. Surface and interfacial phenomena: Surface phases in binary liquid metal alloys: An X‐ray study

AbstractSurface‐sensitive x‐ray scattering techniques with atomic scale resolution are employed to investigate the microscopic structure of the surface of three classes of liquid binary alloys: (i) Surface segregation in partly miscible binary alloys as predicted by the Gibbs adsorption rule is investigated for Ga‐In. The first layer consists of a supercooled In monolayer and the bulk composition is reached after about two atomic diameters. (ii) The Ga‐Bi system displays a wetting transition at a characteristic temperature Tw ≈︁ 220°C. The transition from a Bi monolayer on Ga below Tw to a thick Bi‐rich wetting film above Tw is studied. (iii) The effect of attractive interactions between the two components of a binary alloy on the surface structure is investigated for two Hg‐Au alloys.

THERMAL RADIATIVE PROPERTIES OF LIQUID METAL ALLOYS FROM MEASUREMENT DATA OF HALL COEFFICIENTS AND DC RESISTIVITIES

Published values for the Hall coefficient and the electrical resistivity of liquid metal alloys can provide useful estimates of the reflectance and emittance of some groups of binary liquid metal and high-temperature solid alloys. The Drude free-electron parameters, and thence the optical constants and the radiant properties, are computed from the dependence of the Hall coefficient and direct current resistivity on alloy composition (the Hall coefficient gives the free-electron density and the resistivity gives the average time between collisions). We find the predictions of the radiant properties of molten cerium-copper alloy, which use the measured variations in the Hall coefficient and resistivity (both highly nonlinear) as a function of alloy fraction (rather than linear combinations of the values of the pure elements) yield a good comparison to published measurements of the variation of the normal spectral emittance.

A WCA study of binary liquid metal alloys with a non-additive hard-sphere reference system

We present a Weeks-Chandler-Andersen (WCA) perturbative approach to the structure of liquid binary systems using a non-additive hard-sphere (NAHS) reference system. Consequently former doubts about the uniqueness of how to determine parameters when using an additive reference system are ruled out. We present results for strongly non-additive systems as some specially chosen metal alloys and a metal-molten salt solution; comparison with experimental data shows good agreement.

Electron theory of long-wavelength concentration fluctuations in liquid metal alloys

It is shown that long-wavelength concentration fluctuations in a binary liquid metal alloy are determined by a pair interchange free energyw, which is exactly given by the sum of an elastic strain term and of the concentration-concentration direct correlation function. The latter is evaluated in an alloy of homovalent components by electron screening theory in the pseudopotential approach of Shaw and Harrison and shown to be entirely determined by nonlocal terms reflecting charge transfer to the more electronegative alloy component. Numerical calculations for the liquid Na−K alloy show strong cancellation between the two contributions tow at all concentrations, in qualitative agreement with experiment.

Electron theory of long-wavelength concentration fluctuations in liquid metal alloys

It is shown that long-wavelength concentration fluctuations in a binary liquid metal alloy are determined by a pair interchange free energyw, which is exactly given by the sum of an elastic strain term and of the concentration-concentration direct correlation function. The latter is evaluated in an alloy of homovalent components by electron screening theory in the pseudopotential approach of Shaw and Harrison and shown to be entirely determined by nonlocal terms reflecting charge transfer to the more electronegative alloy component. Numerical calculations for the liquid Na−K alloy show strong cancellation between the two contributions tow at all concentrations, in qualitative agreement with experiment.

Surface Segregation and Related Properties in Binary Liquid Transition Metal Alloys Containing Mn and Cr

Abstract In solid transition metals, the bulk modulus varies systematically with the filling of the d-band. Assuming this behaviour remains true just above the melting temperature, 21 binary liquid transition metal alloys with Mn as solute in dilute concentration are predicted to exhibit Mn surface segregation while the remaining 5 alloys may or may not. With Cr replacing Mn, the corresponding numbers are 9 and 17. Certain Cr rich alloys are also deemed worthy of further investigation.

The relation between the heats of mixing of the liquid and solid in metallic systems

The average heat of mixing for binary liquid metal alloys is 1.05 k J/mol more negative than that of the solid solution. This result applies for systems that have very negative heats of mixing to those with very positive values. Real systems show a standard deviation of 1.25 k J/mol from this model. It is clear that those factors which are responsible for the heats of mixing having a certain value in a given solid solution operate similarly in the liquid. In particular, size differences do not appear to be an important factor in determining the heats of mixing.

The Effect of a Magnetic Field on Convective Instability in a Horizontal Layer of Binary Liquid Metal

The role of the Soret effect on convective instability in a horizontal layer of binary liquid metal in the presence of a magnetic field is examined using linear stability theory. It is shown that even if a magnetic field is present the presence of the solute plays a prominent role through the Soret effect and that even if the solute is present the magnetic field inhibits the onset of instability.

Magnetic properties of liquid metal alloys

Abstract The extensive field of the magnetic properties of (mainly) binary liquid metal alloys is reviewed. Special attention is paid to the behaviour of liquid transition metal AB alloys, both with A and B as transition elements and with B as a non-transition element. It is found that some of the main features can be understood without taking careful account of the liquid structure. However, the large charge transfer that then needs to be invoked is confronted with photoabsorption and with soft X-ray emission data. The simple explanation of the magnetism must almost certainly be transcended to account also for the optical behaviour.

Correlations in binary liquid and glassy metals

It is shown, starting from a nearly-free electron approximation, how correlations can occur in the atomic positions of binary liquid and glassy alloys. In particular, it follows from energy considerations that for an alloy of a transition metal with a metalloid there is a concentration region where there should be no metalloid-metalloid nearest neighbors. This concentration region is just the same as that where glass formation is often observed in these systems.

The activity coefficient of nitrogen in binary liquid metal alloys

The activity coefficient of nitrogen in binary liquid metal alloys

The activity coefficient of oxygen in binary liquid metal alloys

The Wagner model with one energy parameter,h, for describing the effect of alloying elements on the activity coefficients of nonmetallic solutes in liquid metals is extended to have two energy parameters,h 1andh 2. The validity of both the Wagner one-parameter equation and the newly derived two-parameter equation is tested using data available in the literature for twelve ternary metal-oxygen systems. In order to have consistent thermodynamic data, all the relevant binary, as well as the twelve ternary metal-oxygen systems are evaluated using the same thermodynamic values for the reference materials which were used in carrying out the experimental measurements. It is found that the twoparameter equation is capable of quantitatively accounting for the compositional dependences of the activity coefficients of oxygen in all twelve ternary systems while the Wagner one-parameter equation is not. A correlation between the Wagner parameter,h, and the thermodynamic properties of the respective binary metal-oxygen and binary metals systems is found, from which the value of this parameter may be predicted without referring to any ternary data. Accordingly, the two-parameter equation is more useful in evaluating ternary experimental data while the Wagner one-parameter equation in connection with the correlation betweenh and binary data is capable of predicting ternary data without any experimental investigation in the ternary region. Based on the one-parameter and the two-parameter equations, theoretical equations for the first-order and second-order free energy interaction parameters,(∈ 0 j )sand(ρ 0 j )s, are derived in terms of the model parameters. The values of(∈ 0 j )s and(ρ 0 j )s for all the systems are derived and are found to vary linearly with the reciprocal of temperature. Furthermore, linear relationships between these two interaction parameters and their slopes with 1/T are found, from which the temperature dependence of the interaction parameters may be estimated in the absence of experimental data.

Chemical potentials, concentration fluctuations, etc., in binary metal alloys

Abstract Relationships among transport parameters and the mean square composition fluctuations as determined by measurements of the chemical potentials are described for a variety of binary liquid metal alloys. The measurement of the chemical potential is described and the thermodynamic basis for the analysis given in terms of the concentration correlation functions as well as more traditional thermodynamic parameters. Alloys involving group IIIA metals with Te are used as an example

Short-Range Order and the Electronic Structure of Binary Alloys and Liquid Metals: A Comparison of Different Approaches

A number of exact results concerning the effects of short-range order on the energy spectrum of disordered systems are derived. In a single-band model of the substitutional alloy, it is shown that the height and width of the minority subband must scale as ${[\frac{x}{(1+\ensuremath{\epsilon})}]}^{\frac{1}{2}}$ and ${[x(1+\ensuremath{\epsilon})]}^{\frac{1}{2}}$, respectively. Here $x$ is the impurity concentration and $\ensuremath{\epsilon}$ is a parameter that specifies the degree of short-range order, i.e., the enhanced probability that impurity atoms will be nearest neighbors. These results depend only on the form of the (nearest-neighbor) two-site distribution function and it is, therefore, rather surprising that they are not reproduced exactly by any of the existing theories of short-range order. In each case, the difficulty can be traced to an improper factorization of the three-site distribution function. As a simple model of the liquid metal, we consider a close-packed array of nonoverlapping spherical-well potentials of depth $\ensuremath{\delta}$, radius ${R}_{m}$, and mean density $n$. This model is used to compare alternate formalisms: the quasicrystalline approximation of Lax, and the more recent approaches of Gyorffy, and of Schwartz and Ehrenreich. The fact that the short-range order guarantees that the potentials are nonoverlapping allows us to extract from each order in perturbation theory the leading contribution to the moments of the electron self-energy. The result is simply expressed in terms of the renormalized cumulants ${Q}^{(p)}(x)$, where $x$ is the dimensionless density parameter $x=\frac{n4\ensuremath{\pi}{{R}_{m}}^{3}}{3}$. These contributions isolate just those terms of higher order in $x$ that are most important for the moments of the electronic spectrum and are reproduced to all orders by only the equations of Schwartz and Ehrenreich.

Condensation Heat Transfer of a Binary Liquid Metal Vapor

An experiment was performed in order to provide the necessary data to design condensers for the magnetohydrodynamic generators using binary liquid metal as well as to clarify the characteristics of the binary liquid metal in condensation heat transfer by determining condensation heat transfer rate in forced convection in a pipe with regard to the binary liquid metal with a small quantity of impurities on the basis of radial temperature distribution in vapor. With this end in view, the experiment of the forced convective condensation heat transfer of ternary alloy vapor composed of mercury, bismuth, and lead in a loop was performed, and the measured radial temperature distribution in vapor brought about the following results: the condensation heat transfer rate of the binary liquid metal with small quantity of impurities was found to be nearly equal to that of one component liquid metal; the condensation heat transfer rate of the binary liquid metal with some uncondensed vapor was found to be lower than that without vapor; and to nearly agree with the calculated rate for one component liquid metal vapor. (JA)

Condensation Heat Transfer of a Binary Liquid Metal Vapor

Condensation Heat Transfer of a Binary Liquid Metal Vapor

The Measurement of Diffusion Coefficients in Binary Liquid Metals with a Concentration Cell

An experimental technique has been developed for measurement of diffusion coefficients in liquid metals. A liquid metal concentration cell was designed to measure cell potential and discharge current while insuring that diffusion in the cathode was the over‐all rate limiting process. The technique was used to obtain diffusion coefficients in three binary liquid metal systems; potassium‐mercury, sodium‐lead, and sodium‐tin.