Ultrasound absorption due to electrons and phonons in alkali liquid metals

The excess longitudinal ultrasonic absorption over and above the classical value in four alkali liquid metals near their melting points has been accounted for by the mechanisms of interaction of sound waves with the conduction electrons and the thermal phonons (Akhieser mechanism), both exhibiting a quadratic dependence on sound frequency. An expression, similar to the Bridgman relation for liquids, for the phonon conductivity in the liquid metals has been developed. This approach briefly reported here yields good results.     

Self-diffusion in liquid metals

A survey is made of all published data on self-diffusion in liquid metals and an examination is carried out on the temperature-dependence of D for studies covering a wide range of temperatures. Log D versus 1/T and D versus T represent the best data equally well, while D versus T ^1/2 and D versus T ² do not. The proper functional form is taken to be D=CT experimentally, and a simple free diffusion theory is developed from the standpoint of vibrational atom motion. An equation having no adjustable parameters results (D=k ² ? _D T/hk), in which κ is the vibrational force constant. Values calculated for D at the melting point are in good agreement with experimental values for potassium, sodium, copper and silver, but are below the measured values for lead, indium, zinc and tin.     

Electronic states in liquid metals

An approximation scheme has been developed for calculating the density of states and autocorrelation of independent electrons in a dense array of weak stationary scatterers. This method, which avoids the customary perturbation expansions in powers of the scattering potential, requires a knowledge only of the autocorrelation of the potential. Results are presented of calculations for liquid Na at various temperatures. Comparison is made with the experimentally observed resistivity and angular correlation in positron annihilation experiments.     

Solute diffusion in liquid metals

The diffusion of several solutes in liquid silver and tin is discussed in terms of the fluctuation model, the modified critical fluctuation theory and the ‘hole’ theory of liquid diffusion, assuming the solute as a point charge equal to the difference in the charge of the solute and solvent atoms. The additional coulombic interaction of the solute was calculated in terms of the Thomas-Fermi approximation. In addition, the temperature dependence of solute diffusion in liquid tin is also evaluated from the self-consistent Hartree potential around an impurity charge. The theoretical and experimental values of relative diffusivity and its temperature dependence for various solutes, Ru, Co, Au, In, Sn and Sb, in liquid silver are in good quantitative agreement. Ru and Co in liquid silver appear to diffuse with effective valences of about -2 and zero, respectively.

The theoretical evaluation of solute diffusion in liquid tin provides only a qualitative agreement with the experimental data. The results obtained by use of the two potentials—the Thomas-Fermi and self-consistent Hartree potential around an impurity charge—are contrary to each other and provide only a qualitative agreement with the data on electromigration of various solutes in liquid tin.     

Ultrasound improves electrolytic recovery of metals

Ultrasound has been shown to improve the cathodic current efficiency of copper electrodeposited from a dilute acidic sulphate bath and also zinc from a dilute alkaline zincate bath. Depending upon the plating parameters the metal may be plated with an enhanced value as a foil, sheet or powder. This agitation may be utilised in the recovery of metal from waste solutions and also in the recycling of acids and alkalies.     

Structure of liquid metals

A brief review is given of the structure of liquid metals. The structure is examined from the viewpoints of how the pair potential in metals gives rise to various structural properties and how the structure of liquid metals effects other properties. Use is made of the Paskin and Rahman molecular dynamic calculations on liquid sodium to illustrate the insensitive nature of the structure to details in the pair potential. Diffraction data are used to demonstrate that a law of corresponding states exists, at the melting point, for simple liquids, metals and insulators. The molecular dynamic calculations of sodium are also used to demonstrate that some time dependent correlation functions may be more sensitive to the form of the pair potential than the structure factor is to the potential. Some analysis is also made of the role of structure in the electrical resistivity. It is noted that more accurate structure data are needed to answer some of the questions raised in recent attempts to use the structure to extract pair potentials and in detailed correlations of resistivity and structure data.     

Electromagnetic absorption of acoustic-wave packets in metals

Damping of quasimonochromatic sound-wave packets in metals caused by the electromagnetic interaction of lattice vibrations with resonant current carriers is studied. It is assumed that the acoustic wavelength λ is much shorter than the electron mean free path length l but much longer than the characteristic damping depth σ of an electromagnetic wave in metals under anomalous-skin-effect conditions. It is also assumed that the transit time of a resonant particle through the region of field nonuniformity (∼λ) is shorter than the electronic relaxation time , where is the characteristic velocity of the resonant electrons). The distribution of the potential of the eddy electromagnetic field accompanying an acoustic radiopulse with a prescribed shape is found by solving the kinetic equation and Maxwell’s equations. The force exerted on the lattice by the resonant electrons is investigated, and the equation from the theory of elasticity that describes the evolution of a sound wave is solved. It is shown that a weak damping (of the order of the small parameter a) at the extrema of the deformation on the pulse edges as well as the appearance of high-frequency precursors near the pulse boundaries are characterisic for the evolution of a powerful transverse radiopulse. Such precursors were observed earlier by Fil’ et al., as components of a noise burst arising on the leading edge of a powerful transverse radiopulse propagating in ultrapure gallium. Fiz. Tverd. Tela (St. Petersburg) 40, 966–973 (June 1998)     

High frequency waves in liquid metals

The inelastic scattering of long wavelength neutrons from coherently scattering metals has been used to examine the collective motions of atoms in the liquid state and to make comparisons with the polycrystalline solids. Well-defined peaks in the velocity spectra of the scattered neutrons have been found in both states for lead, rubidium, tin, bismuth and aluminium. These have been used to present parts of the dispersion curves for vibrational modes of motion in the frequency range 1 to 20 × 10¹² rad/sec and wave number range 1 to 3 Å^?1, and to estimate lifetimes of the modes of the order 0.4 × 10^?12 sec in the solid near the melting point and roughly half these values in the liquid.

In polycrystalline aluminium the major contribution to the observed intensity in the solid is due to transverse modes and the observed similarity of the liquid and solid spectra suggests that transverse motions are observed in the liquid also.     

液态金属结构研究新进展

文章介绍了用内耗方法研究金属液态结构的新进展，发现了随温度变化金属液态结构发生不连续的变化，并经差热分析、X射线衍射等实验证实了这种变化．这对认知金属液态结构提供了新的实验依据。     

The physics of liquid metals

Liquid metals have many fluid properties in common with non-metallic liquids, and many metallic properties in common with solid metals. In recent years experimental techniques familiar in solid-state physics have been helping to increase our empirical knowledge of fluid metals. At the same time attempts have been made to form conceptual links between liquid-state physics and metal physics. The article describes some of the current activity in this field, reviews some of the progress that has been made, and points out some of the major difficulties.     

Electronic structure of liquid metals

A review is given of the electronic structure of liquid metals. The theoretical formalism is developed in terms of the density matrices of the system, and the conditions under which these can be obtained are described, and the limitations found at present. The experimental material is then reviewed and it is shown how experimental results are interpreted in terms of values and averages over the density matrices.     

液态金属结构研究新进展

文章介绍了用内耗方法研究金属液态结构的新进展,发现了随温度变化金属液态结构发生不连续的变化,并经差热分析、X射线衍射等实验证实了这种变化.这对认知金属液态结构提供了新的实验依据.     

The Poley absorption in liquid crystals

The far infrared torsional oscillatory absorption of a nematic liquid crystal has been isolated for the first time free of higher frequency proper modes. This has been achieved using a molecule specially synthesised for this purpose with a dipole moment engineered perpendicular to the long axis so that torsional oscillation about this axis modulates this component only. The far infra-red power absorption of the liquid crystal in the isotropic, nematic, solid and supercooled conditions is therefore a Poley absorption, i.e. the torsional oscillation about the rigid long axis of the liquid crystal molecule itself. The effect of phase changes on a macroscopic level is to sharpen and intensify this absorption. This is clear evidence to the effect that phase changes in liquid crystals are cooperative phenomena, the molecular librational dynamics about the long axis are little different from those in a regular molecular liquid.     

Relations between structure factors in liquid metals

Relations between the electron-electron, electron-ion and ion-ion structure factors in metals for the arbitrary wave vector are obtained in the adiabatic approximation, assuming weak coupling between the electron and ion components.