Metal-liquid Interface Research Articles

Structure and properties of the metal–liquid interface

Theoretical results are given for simple dipolar liquids in contact with a metallic slab. The metal is treated by employing a jellium model together with density functional (DF) theory. The liquid structure at the interface is given by the reference hypernetted-chain (RHNC) approximation. The liquid and metal interact electrostatically and the coupled DF/RHNC equations are solved iteratively to obtain electron density distributions and metal–liquid correlation functions which are completely self-consistent. The electron density, liquid structure, and potential drop across the interface are discussed in detail. It is found that dipoles in contact with the metal prefer to orient perpendicular to the surface with their positive ends out. This is in accord with earlier calculations for dipolar monolayers on metal surfaces. Further from the surface, the dipolar orientations oscillate and the liquid structure rapidly decays to the bulk fluid limit.

Diamond nucleation at the organic liquid-metal interface by laser-induced reactive quenching

Diamond particulates in the form of a film were deposited on tungsten surfaces by laser-induced reactive quenching of cyclohexane and decalin liquids whose stereostructure is closely related to that of diamond. Transmission electron microscopy, glancing angle X-ray diffraction, and laser Raman spectroscopic studies indicate that the deposited film consists mainly of a mixture of hexagonal polytypes of diamond. The analysis shows that these molecules serve as building blocks for the formation of diamonds.

特集／表面技術とその場測定 電極溶液界面および電解めっき過程のＳＴＭ観察

特集／表面技術とその場測定 電極溶液界面および電解めっき過程のＳＴＭ観察

Behavior of ceramic particles at the solid- liquid metal interface in metal matrix composites

Directional solidification experiments have been conducted to document SiC particle behavior at the solid-liquid interface in Al-2 pct Mg (cellular interface) and Al-6.1 pct Ni (eutectic interface) alloys. Particle size ranged from 20 to 150 μm diameter. Although predictions based on the thermodynamic approach suggest that no engulfment is possible, it was demonstrated that particles can be entrapped in the solid if adequate solidification rates and temperature gradients are used. The main factors responsible for this behavior are considered to be the difference between the thermal conductivities of particles and metal, the buildup of volume fraction of particles at the interface, and the morphological instability of the interface induced by the particles. A model including the contribution of drag and thermal conductivity has been proposed. Calculation with this model produced numbers for the critical velocity slightly higher than those evaluated experimentally. Various factors which can account for this discrepancy are discussed.

Hydrodynamic stability threshold of liquid metal current collectors

A mechanism derived from hydrodynamic theory to explain the ejection instability of liquid metal current collectors is presented. The ejection mechanism is shown to be caused by the onset of the Kelvin–Helmholtz instability resulting from the gradient of azimuthal (primary) flow at the interface between the liquid metal and cover gas. This new mechanism differs from the previous theory developed by Eriksson [in Electrical Engineering Series, no. 48, edited by M. Luukkala (The Finnish Academy of Technical Sciences, Helsinki, Finland, 1982), who analyzed the onset of the Kelvin–Helmhotz instability resulting from the gradient of meridional (secondary) flow at the interface. Considering the solution to the linearized Navier–Stokes equations at the liquid metal and gas interface, the azimuthally driven (primary flow) instability mechanism for the onset of ejection is much more prevalent than the meridional (secondary) flow driven mechansim. Furthermore, Eriksson’s theory requires an empirical multiplicative fractional factor that is not physically justified to predict experimentally measured ejection points, whereas the present theory is more self-consistent. Calculations of minimum ejection values from both theories were compared with corresponding experimental ejection data. The present theory appears to give significantly better engineering estimates, both quantitively and qualitatively, for minimum ejection threshold than Eriksson’s theory. The basic mathemtical model presented can serve as the basis for developing a more complex mathematical model for liquid metal ejection.

Chemiphoresis of montmorillonite particles

AbstractThe chemiphoresis of montmorillonite saturated with Na, K, Li or Ca was studied in a system where corrosive dissolution of Al, Fe, Zn or Cu metal plates took place in the presence of HF and H2O2. The deposition of the clay as well as metal dissolution were found to be a function of indicating that the electrochemical reaction is controlled principally by diffusion of the reacting species to the metal-liquid interface. The deposition increased with clay concentration and was lower for Ca-clay than for Na-, K- or Li-clay. It is shown that chemiphoresis alone does not provide sufficient data for the calculation of particle mobility and that other types of measurement are necessary. A relationship between particle deposition and electrical conductivity was developed, and examined experimentally with satisfactory results.

Picosecond photoemission and recombination dynamics at the metal-liquid interface

L'emission photoelectronique a partir de la surface de Zn immerge dans de l'hexane liquide engendre une population d'electrons quasi libres pres de la surface. Ces especes transitoires disparaissent par recombinaison de charge avec le metal

Instability of a planar liquid layer in a magnetic field with alternating longitudinal and uniform transverse components

In many cases of levitation, melting of metals and shaping of the liquid metal interface to form certain materials like glass, the interface is found to undulate in an alternating magnetic field. As undulations have undesirable effects, it is of considerable importance to study the stability of the liquid under similar circumstances. Earlier, investigations had been made to determine the stability criterion of a planar conducting liquid layer in an alternating longitudinal field and the critical value of the parameter M = B 0 2 μηω ( B 0, ω, μ and η are the amplitude of the alternating field, the angular frequency of the field, the magnetic permeability and the viscosity, respectively) was determined. It was shown that if M c was the critical value of M then the layer was stable or unstable according as M < or > M c . Since there is some possibility of additional magnetic fields such as the geomagnetic field or any other stray field to act along with the alternating field and affect the stability, we have investigated in this note the stability of a planar liquid layer in the presence of a uniform transverse field acting along with the alternating longitudinal field. The layer has been considered as thick with a perfectly conducting rigid boundary. After comparing with the earlier results we find that the critical value M c minimized with respect to the wave number decreases from the approximate value of 425 to an approximate value 80 even when B 1 is as small as 10 −4, where B 1 is the ratio of the strength of the uniform transverse field to the amplitude of the alternating field. It is also found that M c decreases further as B 1 increases and for B 1 = 10 there is no stability.

Cluster calculations of the H2O/Pt(111) system

AbstractThe electronic interaction between water and a Pt(111) surface as evaluated for different Ptx(H2O)y clusters is discussed. Hartree–Fock–Slater (HFS) one‐electron ground state energies, ionization potentials, partial densities of states, and Mulliken occupation numbers are related to bonding shifts, as well as initial and final state screening for different orientations of the molecule. The formation of PtH2O bonds are sensitive to the orientation since surface oriented H atoms bridge the spatial separation between O 2p and Pt 5d orbitals and thus increase the intermixing of metal and adsorbate orbitals. The dipole moment and the net charge of the H2O molecule is also discussed. Finally, approximations of the metal–H2O potential for use in statistical models of the liquid–metal interface are suggested.

Examination of the Reaction Kinetics at Solder/Metal Interfaces via High Temperature X-Ray Diffraction

There is a great deal of interest by the electronics Industry in understanding the reactions occurring at the interface between a solid metal and a liquid solder or braze. This is due to the complex nature of current microelectronics Packaging, where soldering or brazing operations often involve complex metallurgies and tightly controlled furnace profiles. However, to date only a few studies have been carried out on the reaction kinetics at a liquid metal-solid metal interface. This is due in part to the difficulty in carrying out such , experiments. In the past, two main techniques have been used to obtain solid-state kinetic data. The first, quantitative metallography, is slow and tedious to perform, and generally of limited accuracy. The second technique involves measuring the change of some property, such as electrical resistivity, that is a function of the concentration of one of the phases. The main disadvantages of these techniques are that absolute values of concentration are not obtained, and that the relationships between a property and constitution are rarely available. In addition, most physical properties are sensitive to factors other than constitution, and interference from these factors can often result in erroneous data.

Sounds the best way

Industrial inspection often calls for ultrasonic techniques, but this could mean putting sensitive equipment either in a hostile environment or in a stainless steel box. Neither approach is satisfactory, in the latter case because a metal–liquid interface represents a mismatched boundary and typically only 12% of the energy is transmitted.

Overview of the current status of solid—liquid interface science

An overview of the current status of S-L interface science is presented, together with some comments about its relevance to solar energy conversion technologies. A discussion of the diffuse layer includes past and current perspectives of the structure of H 2O in the double layer and its role on potential changes at the metal-liquid interface. The difficulties of considering the potential changes of semiconductor- or insulator-liquid interfaces are related to surface states and dangling bonds. The methods available for investigating the S-L interface are reviewed, i.e. sweep, ellipsometric, radiotracer, AES, XPS and Mössbauer methods. Frumkin's contributions and the potential of zero charge (PZC) are also discussed. The difficulties and prospects of measuring and/or calculating absolute potentials of S-L interfaces from understanding the PZC are then considered. Organic and ionic adsorption isotherms and the factors limiting their contribution to increasing the understanding of the S-L interfaces are reviewed. Future prospects and needs for research on the S-L interface are outlined in the concluding section. Developments in this field are in an early stage, compared with the S-G interface, but the subject material has a more practical bearing on real systems. New theoretical approaches, including modeling of the double layer and diffuse layer using quantum mechanical and Monte Carlo approaches, are clearly needed. A need for elucidating the structure at semiconductor-liquid interfaces and its bearing on photoelectrochemical solar energy conversion is indicated. The need for applying in situ spectroscopic and direct measurements to study the S-L interface is clearly required for extending our present understanding in this field.

Charge transfer at metal-dielectric liquid interfaces evidence from the solid state

The transfer of charge between metal electrodes and dielectric liquids is invariably invoked in explanations of conduction and breakdown in dielectric liquids. The details of such processes, however, have hardly been studied at all, mainly because of the great difficulty of investigating the metal-liquid interface without disturbance. It is, however, possible to study charge transfer at metal-solid hydrocarbon polymer interfaces and the realization that this will be very similar to the metal-liquid hydrocarbon interface can give new insights into liquid conduction and breakdown. A range of measurements on charge transfer at metal-polymer interfaces are reported using non-contacting charge induction techniques. The main features of these measurements allow new proposals to be made about the initiatory phases of breakdown in liquids under impulse and steady voltage conditions.

Mechanism of charge formation in double layer appearing at an hydrocarbon liquid-metal interface (comparison of theoretical models with experiments)

To understand some phenomena appearing in conduction in dielectric liquids, it is important to know the mechanism of charge formation at the interface between the metal and the liquid ((1), (2), (3)). In this paper, we study this mechanism without an applied electric field, but the liquid flowing past the metallic surface. At the contact between a metallic surface and an hydrocarbon liquid an electrical double layer appears. The thickness of the compact and the diffuse layers are such that only the diffuse layer can be affected by the flow. For a liquid flowing through a circular tube of finite length the charge convected at the exit of the tube depends on the process of charge formation in the diffuse layer appearing at the inner wall of the tube. A theory is presented for the process of charge convection in a laminar tube flow. The liquid is assumed to be electrically neutral at the entrance of the tube. The development of the diffuse layer is computed in terms of parameters such as the distance from the entrance, the radius of the tube, the Reynolds number of the flow, the conductivity of the liquid and the charge at the wall. In order to understand the mechanism of charge formation inside the pipe we have then computed the value of the space charge convected with different models and compared the results with experimental data. Experimental data are presented for liquid heptane flowing through stainless-steel tubes of radius of 0.24 mn and length between 0.08 m and 4 m. The comparison between experiment and theories permits us to infer the development of the charge on the wall for this experiment, and then to comment on the mechanism of charge formation.

Mode conversion of Rayleigh and Lamb waves to compression waves at a metal-liquid interface

A theoretical treatment is given of a potentially useful ultrasonic mode-conversion process, from Rayleigh or Lamb waves (SAW's) to angled compression waves in an adjacent liquid. Since the compression waves can form a well-defined beam, with typical angular width of only 1° or 2°, it is possible to use this technique in under-liquid viewing applications. Another use, in liquid level measurement, has advantages over conventional ultrasonic methods. Attractive features are the high power efficiency of the mode-conversion, in both directions, and its inherent separation of electromechanical transducer from the liquid, which may be vital in certain hazardous environments. With such applications in mind, the emphasis here is on ultrasonic processes in the liquid. After a descriptive account of pressure wave generation in the liquid, the main part of the paper is a general treatment of far-field beam profiles and includes transverse beam-width and discussion of pulsed operation. Finally we examine inverse mode conversion (compression wave to SAW), to identify the main physical processes occurring and arrive at a figure for power efficiency. This turns out to be 80% (max) against nearly 100% for transmission. Two papers by the same authors describing practical applications of the mode conversion are scheduled for inclusion in the next issue.

Transmission Infrared Spectroscopy of Liquid-Solid Interfaces

Although there are several spectroscopic techniques for studying solid-air interfaces (which mainly yield information on the solid surface), there are few methods available for studies of solid-liquid interfaces. When the solid is a metal film, the number of useful techniques becomes even smaller. Infrared spectroscopy combined with attenuated total reflection (ATR) techniques has been used for such studies of liquid-metal interfaces, but availability of the metals has been limited to the metals used in ATR crystals. We have demonstrated that ATR can be extended to other metals by showing that spectra could be obtained on metal-coated ATR crystals. By coating a thin film of iron onto a germanium ATR crystal, we were able to observe reactions at a liquid-metal interface. However, these ATR experiments are tedious and difficult to use for studies of the effects of variables (such as temperature and pressure) on the interface reactions. In addition, polarized ATR spectra of the adsorbed film only yield certain information about the molecular order and geometry of these films, i.e., the angle the molecule makes with the metal film. Polarized transmission infrared spectroscopy would provide much needed supplemental information on molecular orientation.

Determination of the thermal boundary resistance in the transport approach

We present a new theoretical determination of the thermal boundary resistance at a metal-liquid helium interface. The phonon temperature drops and heat flux densities at the interface are deduced from the numerical solution of the phonon Boltzmann equation inside the metal, with only electron-phonon scattering considered. A calculation of the thermal boundary resistance is performed and a comparison with the Khalatnikov theory is made ; the results differ considerably, the transport approach giving a far smaller resistance, though the phonon boundary conditions in our work are also determined by the classical acoustic theory.

An analysis of thermal resistance at a solid-stationary liquid metal interface due to the presence of gas cavities

A mathematical analysis of the thermal interface resistance is carried out on an idealized elemental heat flux tube for the case of a gas cavity interposed between a solid and a stationary liquid metal. The thermal resistance is expressed in terms of the thermal conductivities of the solid and liquid metal, the number of gas cavities per unit apparent area and a wettability number. The last part of the paper is devoted to a qualitative comparison between the theory and the test data of Bleuven et al. Good agreement was observed within the assumptions made.

Collection of charge from a moving stream of liquid dielectric

Scavenging of charge from a flowing stream of insulating liquid containing unipolar carriers can be effected only with some difficulty. Experiments involving a number of different collector arrangements immersed in the paraffin hexane have shown that efficient charge extraction requires the collector to have a large area of liquid-metal interface and to be free of gross surface contamination. Complete scavenging occurs if the charge density in the liquid exceeds a certain threshold value.

Electric Breakdown in n-Hexane

ALTHOUGH the phenomena of breakdown and conduction in liquid insulants have received considerable attention, the degree of understanding that has been achieved is limited, a fact illustrated by the co-existence of several widely differing models for the breakdown process. The main reasons for this failure are the absence of a satisfactory theory of the bulk liquid or the metal–liquid interface and also the difficulty of the experimental techniques involved. Some of the hitherto uncontrolled experimental variables have only recently been revealed, an important one being the oxygen content of the liquid1.