Ga-Pb Alloys Research Articles

The thermophysical properties of Ga-Pb liquid alloys

The higher amount of energy generated from renewable energy sources has caused the search for new storage energy materials. In this study, the density, surface tension, and viscosity of liquid Ga-Pb alloys with 2, 30, 60, and 94.6 (at. %) Pb additions were determined, in the temperature range from 573 to 1023 K. The isotherm of thermophysical properties were presented for a temperature of 873 K, along with literature data, and compared with values obtained from the Brillo and Egry models for density, the Butler model for surface tension, and the Sato, Gasior, Kaptay and Kozlov-Romanov-Pertov models for viscosity. The obtained result shows very good agreement with the literature data and models.

Investigation of the miscibility gap region in liquid Ga–Pb alloys

Abstract The miscibility gap of the Ga–Pb system has been investigated by different experimental methods and techniques. Viscosity, acoustic and electrical conductivity measurements were carried out through the entire immiscibility region. Possible reasons of revealed discrepancies in the absolute values of the phase separation temperatures are discussed in relation with peculiarities of the experimental methods employed. The shape of the miscibility gap has been analysed.

Liquid gallium-lead mixture phase diagram, surface tension near the critical mixing point, and prewetting transition

Quite recently, we reported a semianalytical equation of state (EOS) for the Ga-Pb alloy [Phys. Rev. B 78, 024205 (2008)], which was based on the first-order perturbation theory of fluid mixtures, within the simplified random phase approximation, in conjunction with the Grosdidier et al. model pair potentials for Ga-Ga and Pb-Pb with a suitable nonadditive pair potential between Ga-Pb unlike pairs. In the present work, we employ the present EOS to calculate the Ga-Pb phase diagram along the immiscibility gap region. The accuracy of the EOS is tested by consulting the empirical binodal curve. A statistical-mechanical-based theory for the surface tension is employed to obtain an analytical expression for the alloy surface tension. We calculated the surface tension along the bimodal curve and at extreme conditions of temperatures and pressures. The surface tension exhibits reasonably well the prewetting transition of Pb atoms at the surface of the Ga-rich liquid alloy and could qualitatively explain the prewetting phenomena occurring in the Ga-rich side of the phase diagram. The predicted prewetting line and wetting temperature qualitatively agree with the empirical measurements.

The study on microstructure and electrochemical properties of Al–Mg–Sn–Ga–Pb alloy anode material for Al/AgO battery

The microstructure of Al–Mg–Sn–Ga–Pb quinary aluminum alloy anode material and the influences of its electrochemical properties and self-corrosion rate in 4 mol/l NaOH +10 g/l Na2SnO3 medium were studied. The microstructure and morphology were characterized by metallographic microscope, transmission electron microscope, and scanning electron microscopy. The electrochemical properties were tested by electrochemical workstation, and the self-corrosion rate of Al alloy anode was studied by methods of recovery H2 gas by discharge water. The results show that homogenization has not much impact on the electrochemical properties and the corrosion rate of the cast aluminum alloy anode material; besides, return annealing treatment of the cold-rolled Al–Mg–Sn–Ga–Pb quinary aluminum alloy anode material can reduce the rate of self-corrosion and make Al anodic potential shift negative steadily and improve the properties of the material.

Phase transitions in wetting films at the surface of Ga–Pb alloys

Surface phase transitions at Ga-rich liquid surfaces have been investigated in Ga–Pb alloys with low lead content. In the region of the liquid–liquid miscibility gap, the Pb-rich liquid phase completely wets the surface of the Ga-rich phase at coexistence. Observations have been made of demixing and solidification of the Pb-rich liquid film. Ga-rich alloys, which are single-phase below the monotectic temperature, can be undercooled below the liquidus, as far as the metastable binodal line where the Pb-rich wetting liquid film forms and solidifies into thin {111} Pb crystals. These films completely redissolve upon reheating to the liquidus temperature. Freezing occurs at surfaces because of complete wetting of the liquid rich in the high melting point component and the hysteretic character of the solidification transformation. Such “surface” experiments allow assessment of the stable and metastable liquidus lines of the Ga–Pb phase diagram in the vicinity of the monotectic temperature.

Size effects on melting and wetting in the Ga–Pb nano-alloy

Ga–Pb alloys with 15 at% Pb mean concentration have been prepared at the nanoscale by means of evaporation-condensation technique in ultra high vacuum conditions. Transmission electron microscope images indicate that at room temperature, the system is a two-components breath figure composed of liquid Ga nanodrops containing Pb nanocrystals. Some thermodynamic properties of this nano-alloy are investigated for different temperatures and particle sizes. The results obtained put in evidence a large modification of the Ga–Pb bulk phase diagram: a decrease of the melting temperatures of the two components as well as the ones of the miscibility gap. Changes in the microscopic structure of the system as a function of temperature have been investigated and a full wetting transition from a dry to a completely wet state has been put in evidence.

Liquid gallium-lead mixture spinodal, binodal, and excess thermodynamic properties

A statistical mechanical based theory is developed for incorporating the effect of the long-range forces in Ga-Pb alloy. In particular, the simplified random-phase approximation is employed in conjunction with the Grosdidier et al. [Phys. Rev. B 72, 024207 (2005)] model for GaGa and PbPb interactions while a suitable nonadditive pair potential is introduced between unlike atoms. We present analytical expressions for the equation of state and for the concentration fluctuations ${S}_{CC}(0)$, and then the role of the nonadditivity parameter is established by consulting the empirical critical parameters of the spinodal curve. It becomes possible to deduce the behavior of different thermodynamic functions such as Gibbs energy of mixing, excess Gibbs energy, isobaric heat capacity, and ${S}_{CC}(0)$ in the vicinity of the liquid-liquid critical point and under extremely high pressure. The impact of temperature and pressure on segregation, and compound-forming tendencies is also investigated. Moreover, the immiscibility gap of the alloy is calculated and compared with the empirical results. The results suggest that: (i) the nonadditivity of the potential tails plays a dominant role in the determination of the spinodal curve, (ii) ${S}_{CC}(0)$ is a very sensitive function in triggering the chemical short-range order, and (iii) the segregation or phase separation in Ga-Pb alloy is an outcome of the temperature dependence of the energy mismatch parameter. In conclusion, the present equation of state is sufficiently accurate that it provides a binodal curve, an excess Gibbs energy of mixing and isobaric heat capacity in quantitatively good agreement with the empirical results.

Investigation of structural changes near the critical point in liquid Ga-Pb alloys using an acoustic method

The anomalous temperature dependence of the sound velocity above the liquid-liquid coexistence curve in the Ga-Pb system is associated with the critical fluctuations. A fit of the Fixman theory of the sound velocity data at the critical composition allows determination of the correlation length ξ On the other hand, the temperature dependence of ξ of the alloy with critical composition can be calculated in frames of the two-scale-factor universality hypothesis using interfacial tension data. Recently we proposed a new method of extracting the values of the liquid-liquid interfacial tension and densities of contacting phases along the coexistence curve from the results of acoustic measurements. The correlation length values determined from the sound velocity and interfacial tension measurements are in a good agreement to each other and in a reasonable agreement with the results of small-angle scattering experiments. All the critical exponents are determined by two exponents only, β and μ, which can be obtained from the coexistence curve, density and interfacial tension data.

Thermal stability of surface freezing films in Ga-based alloys: An x-ray photoelectron spectroscopy and scanning tunneling microscopy study

We have investigated the thickness and surface structure of surface freezing films in Ga-Bi and Ga-Pb alloys over a wide temperature range between room temperature and the respective surface freezing transitions by x-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM). For the example of a Ga-Bi alloy dilute in Bi, XPS measurements show that the surface freezing film has a nearly constant value of approximately 25 A between the surface freezing temperature of 130 degrees C and room temperature if the sample is cooled slowly (5 Kh). On heating to 130 degrees C the film thickness exhibits a clear hysteresis on melting. On quenching the alloy sample (>100 Kh) the film thickness increases by almost a factor of 10. These observations indicate that the surface freezing films are metastable. The surface structure of the surface freezing films of various Ga-rich Ga-Bi and Ga-Pb alloys has been probed for the first time by STM at different temperatures below and above the bulk eutectic point. Atomically resolved STM images show the surface structures of pure Bi (0001) and Pb (111), respectively, at room temperature. On heating above the eutectic temperature the surface structure of the films does not change significantly as judged from the size and thickness of Pb or Bi terraces. These observations together with the film thickness variation with temperature indicate that the surface freezing films behave like a metastable independent surface phase. These results together with the wetting characteristics of these alloys suggest that surface freezing in these systems is a first order surface phase transition between wetting and metastable surface freezing films. The energy barrier for nucleation is strongly reduced due to a lowering of the interfacial energy if the nucleus is completely immersed in the respective wetting layer.

Effect of vertical temperature variation on the oscillatory wetting instability in a fluid Ga–Pb alloy

Oscillatory wetting instabilities driven by capillary-gravitation forces have been explored very recently in the binary fluid Ga-Pb alloy [A. Turchanin, R. Tsekov and W. Freyland, J. Chem. Phys., 2004, 120, 11 171]. This system is characterized by a complete wetting transition at liquid-liquid coexistence. Due to its metallic nature the bulk and interfacial instabilities are strongly coupled via variation of the respective emissivities. In our previous work we have investigated these phenomena at different cooling cycles and at constant temperature inside the miscibility gap. In this study we present for the first time the observations of the oscillatory wetting instabilities also in heating cycles. The interfacial properties of a Ga0.95Pb0.05 alloy at conditions inside the miscibility gap have been investigated by following the second harmonic generation (SHG) intensity changes. Corresponding model calculations of the Pb-rich wetting film instabilities have been performed taking into account the effect of a temperature variation vertical to the bulk sample. The influence of this temperature variation on the occurrence of the oscillations is discussed.

Viscosity of liquid Ga-Pb alloys in the miscibility gap region

Viscosity of liquid Ga-Pb alloys in the miscibility gap region

Quasi-two-dimensional freezing and melting at the liquid/vapour interface of a Ga–Pb alloy

We have studied the quasi-two-dimensional freezing and respective melting at the liquid/vapour interface of a dilute lead-in-gallium alloy (0.52 at.% Pb) for the first time by XPS and AES spectroscopy at different temperatures below and above the transition temperature of 183.5 °C. Pb-rich wetting films of roughly 1 monolayer have been determined. At the onset of surface freezing (SF) the film thickness rises to a value of ∼2 monolayers and reaches a maximum of ∼4 monolayers of nearly pure Pb at ∼1 K below the SF temperature. These film characteristics are reproducible in different heating and cooling cycles.

Interfacial and bulk oscillatory instabilities in a binary fluid metal: the example of a Ga–Pb alloy

First observations of an unusual oscillatory instability in a binary metallic fluid exhibiting liquid–liquid phase separation are reported. For this aim, the liquid/vapour interface of the Ga 0.95Pb 0.05 alloy has been studied by a surface sensitive optical second harmonic generation (SHG) probe over a wide temperature range (465–313 °C) at conditions above and inside the miscibility gap. Regular oscillations of the SHG intensities with a period of ∼40 min are found, which correlate strongly with temperature oscillations of the bulk fluid with amplitudes of ∼5–8 K. It is shown that these oscillations are driven by wetting and dewetting characteristics at the interface during phase separation via a periodic variation of the interfacial emissivities. A qualitative explanation of the surface induced bulk instabilities is presented.

Investigation of the miscibility gap region in liquid Ga–Pb alloys

Abstract The miscibility gap of the Ga–Pb system has been investigated by different experimental methods and techniques. Viscosity, acoustic and electrical conductivity measurements were carried out through the entire immiscibility region. Possible reasons of revealed discrepancies in the absolute values of the phase separation temperatures are discussed in relation with peculiarities of the experimental methods employed. The shape of the miscibility gap has been analysed.

Surface freezing and wetting in Ga–Pb alloy: Second harmonic and plasma generation study

The surface freezing and wetting behaviour at the liquid/vapour interface of Ga-rich alloys of Ga and Pb has been studied as a function of temperature at selected compositions both in the homogeneous liquid and the fluid two phase demixing regime. The interfacial phase transitions have been probed by second harmonic generation (SHG) in combination with plasma generation (PG) measurements at different cooling and heating cycles. In the composition range between the eutectic and monotectic points the occurrence of surface freezing is clearly indicated by distinct changes of the SHG and PG intensities, respectively. It is not observed below the eutectic composition for solution very dilute in Pb. Qualitatively, these results agree with the recent observations made in Ga–Bi alloys. A new wetting characteristic is found crossing the miscibility gap at constant composition with varying temperature. A Pb-rich macroscopic wetting film forms which must be concluded from the SHG intensities. This interfacial phase transition causes a clearly detectable drop of the sample temperature which is explained by the corresponding discontinuous change of the optical emissivity at the interface. These interfacial phenomena related with the miscibility gap have not been reported before.

Thermodynamic analysis of the Ga-Pb binary system

Thermodynamic properties of binary Ga-Pb alloys were investigated experimentally and analytically. Quantitative differential thermal analysis was used for determination of integral mixing enthalpies for the gallium-reach alloys, at the constant temperature inside the liquid two-phase region. Calculation of gallium activities in the temperature range of 800-1000 K was done using Chou?s calculation model developed for binary systems with miscibility gap existence.

Wetting, prewetting and surface freezing transitions in fluid Ga-based alloys: asurface light scattering study

The surface energy and entropy of liquid Ga–Bi and Ga–Pb alloys have beenstudied by means of surface light scattering measurements at various compositionsand temperatures between the respective eutectic and monotectic points. Analysisof these results using the Gibbs adsorption equation gives evidence for wettingand prewetting transitions in these alloys completely consistent with a tetra-pointwetting scenario (Dietrich S and Schick M 1997 Surf. Sci. 382 178). Surfacefreezing transitions are observed for conditions near the liquidus curves. In viewof their viscoelastic properties and their relation with the wetting filmcharacteristics, we suggest a simple explanation for the observed surface freezingphenomena in terms of nucleation of strongly undercooled wetting films.

Activity measurement of Ga in liquid Ga-Pb alloys by EMF method with zirconia solid electrolyte

EMF measurement of the electrochemical cell with zirconia as solid electrolyte was performed to determine the gallium activity from 950 to 1150K in the entire composition range of liquid Ga-Pb alloys. In the whole concentration range, activity of Ga shows moderately positive deviations from ideality, and activity of Pb which is derived by Gibbs- Duhem equation shows also positive deviation from ideality. These are compared with published data obtained by different experimental methods.

Surface energy, adsorption, and wetting transitions in ternary liquid alloys

Surface energy measurements have been performed on liquid Ga-Sn binary and on Ga-Pb-Sn as well as Ga-Pb-Tl ternary alloys, by the sessile drop technique under ultrahigh vacuum conditions. The purpose of these measurements was to investigate the change in adsorption behavior of Pb in Garich alloys as a consequence of ternary additions. In order to aid in the interpretation of the results, a multilayer model of surface segregation was formulated in the regular solution approximation. The results show evidence of site competition effects between the two solutes, which reduce the surface concentration of Pb in relation to binary Ga-Pb alloys. The effects of Sn on previously studied wetting-related adsorption transitions in Ga-Pb were also investigated. It was concluded that Sn additions are likely to raise the wetting temperature of the Ga-Pb alloy.

The effects of Tl additions on a wetting-related adsorption transition in liquid Ga–Pb alloys

This paper reports the effects of Tl additions on Pb adsorption to the surface of liquid Ga–Pb alloys. Adsorption of Pb and Tl was measured by Auger electron spectroscopy, as a function of temperature, for six ternary alloys ranging in composition from Ga–3.33×10 −1 at.% Pb–1.65×10 −1 at.% Tl to Ga–1×10 −4 at.% Pb–5×10 −5 at.% Tl, all having a 2:1 ratio of Pb:Tl. The temperature of the prewetting critical point in binary Ga–Pb alloys had previously been estimated to lie at about 240 K. The motivation for this work was to raise the temperature of the prewetting critical point by the addition of Tl. However, the results show that whereas Pb adsorption is enhanced by Tl additions, as expected from simple models, the estimated temperature of the prewetting critical point is lowered even further to about 215 K.