Self-diffusion in liquid interfaces

For studying self-diffusion in liquid interfaces, 59Fe tracer diffusion was measured on ultrafine-grained Nd2Fe14B which undergoes an intergranular melting transition for low Nd excess. The diffusion coefficient in the intergranular liquid layers is found to be lower than in bulk melts indicating a hampered atomic mobility due to confinement. Well above the intergranular melting transition, the diffusivity in the liquid interfaces approaches a value characteristic for bulk melts.     

Self-diffusion in a liquid complex plasma

Self-diffusion has been experimentally studied in a two-dimensional underdamped liquid complex (dusty) plasma. It was found that the self-diffusion coefficient D increases linearly with the temperature T: D/omega(E)a2 = (0.019 +/- 0.007)(T/T(m) - 1), where T(m), omega(E), and a are the melting temperature, the Einstein frequency, and the mean particle separation, respectively. No superdiffusion was observed, whereas a subdiffusion occurred at temperatures close to melting.     

Self-diffusion in gaseous and liquid ethylene

Proton spin echoes at 24 MHz have been used in an accurate study of the self-diffusion coefficient in gaseous and liquid ethylene over a large range of density and temperature. The high temperature data are well described by the corrected Enskog theory. As the temperature is lowered, increasing deviations from the hard sphere behaviour are observed, which are in qualitative agreement with computer simulations on square-well and Lennard-Jones particles.     

Self-diffusion of BCC transition metals calculated with MAEAM

The energy during the process of self-diffusion in BCC transition metals Fe, W, Mo, Cr, Ta, Nb and V has been calculated by using modified analytic embedded-atom method (MAEAM). For each kind of three diffusion mechanisms nearest-neighbor (NN), next-nearest-neighbor (NNN) and third-nearest-neighbor (TNN), the energy curve is symmetric and the maximum value of the energy appears at the middle point of the diffusion path. Determined mono-vacancy formation energy , migration energy and activation energy Q_1v for self-diffusion agree well with available experimental data of NN diffusion and are better than those obtained by the analytic embedded-atom method (AEAM) and Finnis–Sinclair models. Compared the energies corresponding to three diffusion mechanisms, the NN diffusion needs the lowest activation energy (and thus the lowest migration energy). So that, the NN mono-vacancy diffusion is favorable in BCC transition metals.     

Self-diffusion in liquid lithium from coherent quasielastic neutron scattering

Using the method of quasielastic coherent neutron scattering by liquid lithium, the temperature dependence of self-diffusion coefficient is investigated and compared with analogous data extracted by the incoherent scattering method.     

Self-diffusion and inter-diffusion coefficients of liquid lithium isotopes

Experimental data on ⁶Li and ⁷Li diffusivities, as determined by Feinauer et al. [A. Feinauer, G. Majer and A. Seeger, J. Phys. Condensed Matter 6 L355 (1994)], are discussed in the framework of a theory previously developed by Omini [M. Omini, Phil. Mag. A 54 561 (1986)]. The scattering processes responsible for diffusion are described in terms of a Fourier-transformable pair potential through which the diffusing atom interacts with the atoms of the surrounding liquid. Two main improvements are introduced into the theory with respect to its original formulation: the first is represented by a more reliable form of trial function in the variational procedure used to solve the transport equation; the second consists of a reinterpretation of the long wavelength part of the potential, i.e. the part connected with collective modes of vibration. The theory provides an explanation of the dynamic isotope effects observed in self-diffusion and inter-diffusion coefficients.     

Self-diffusion coefficient of nematic liquid crystals from diffusion concentration gradient

A dynamic study of the mass transport by optical methods provides a new approach to evaluate the nematic self-diffusion coefficient. This value is obtained by extrapolation to C = 0 in an empirical relation D_C = D₀ exp (-βC), where D_C is the mass-corrected impurity diffusion coefficient and C is the local concentration of the diffusion profile.     

Self-diffusion in liquid lithium and lead from coherent quasi-elastic neutron scattering data

The temperature dependence of the self-diffusion coefficient of liquid lithium in the temperature range of 500–830 K has been investigated using coherent quasi-elastic neutron scattering. Good agreement with the results obtained from incoherent quasi-elastic neutron scattering experiments traditionally used for this purpose has been achieved, as well as with the corresponding literature data. In addition, one temperature point (623 K) has been obtained for the self-diffusion coefficient of liquid lead, which is a pure coherent scatterer.     

Ultrasound absorption in liquid metals

The excess longitudinal ultrasonic absorption over and above the classical value has been attributed to the solid-like mechanisms of the interaction of sound waves with the conduction electrons and the thermal phonons in liquid metals, both exhibiting a quadratic dependence on the sound frequency.     

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.     

Self-diffusion of nematic liquid crystals in the isotropic phase near the nematic-isotropic transition

Self-diffusion coefficients of two nematic-liquid crystals, PAA and MBBA, were measured by the spin-echo technique over a temperature-range ≈30°C above the nematic-isotropic transition. For both systems, activation energies derived from such measurements agree fairly well those determined earlier from viscosity data.     

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.     

Self-diffusion in polycrystalline silver

An experimental study of self-diffusion in polycrystalline silver has been carried out using the radioisotope Ag-110. The electrolytic sectioning technique was used for measuring. This method made it possible to determine the temperature range in which the self-diffusion of silver is not influenced by grain-boundary diffusion. The temperature was found where the grain-diffusion predominates over the volume diffusion so that the grain-boundary diffusion coefficient can be estimated by Fischer's treatment. Finally, it was found that the temperature range of 619°C< <718°C is the transition region where the electrolytic sectioning technique does not permit the volume or grain-boundary diffusion coefficients to be determined.     

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.