Determination of low temperature volume diffusion coefficients in an Al-Zn alloy

Low temperature volume diffusion coefficients relating to Zn diffusion in aluminium have been measured by monitoring the composition gradients across grain boundaries, developed during ageing [6]. The composition profiles were measured using STEM X-ray microanalysis and were consistent with the model of Aaron and Aaronson[7] as were the low temperature diffusion coefficients with extrapolated high temperature data.     

Benchmark values for the Soret,thermal diffusion and diffusion coefficients of three binary organic liquid mixtures

With the aim of providing reliable benchmark values, we have measured the Soret, diffusion and thermal diffusion coefficients of the three binary mixtures of dodecane, isobutylbenzene and 1,2,3,4 tetrahydronaphthalene for a concentration of 50 wt% at a temperature of 25C. The experimental techniques applied by the five participating laboratories are transient holographic gratings, annular and parallelepipedic thermogravitational columns, and vertical parallelepipedic columns with velocity amplitude determination by laser doppler velocimetry. The systems have also been studied in a annular thermogravitational column filled with a porous medium in the gap. There is a good agreement between the different experiments with deviations of the order of a few per cent in most cases (8.5% at most). The numerical values are tabulated in the paper.     

Temperature dependence of liquid volume

It is shown that the temperature dependence of the liquid volume is well described by the equation $ V = A + BT + CT^2 + V_e \exp ( - E/RT), $ V = A + BT + CT^2 + V_e \exp ( - E/RT), where A, B, C, V _e , and E are constants. This equation reflects two processes owing to which the liquid volume increases with temperature, namely, anharmonic oscillations of molecules and formation of “holes.”     

Scaling laws for diffusion coefficients in mixtures of alkanes

Natural fluids, such as crude oils, are often mixtures of a broad range of different molecules, and in situ measurement of their composition is highly desirable. Furthermore, the relationship between their composition and their physical properties has always been a challenge for such mixtures. We have analyzed diffusion in alkane mixtures to find a power law for the self-diffusion coefficient in terms of molecular sizes. We demonstrate that this power law can be used to obtain the molecular size distribution of crude oils using noninvasive measurements of diffusion distributions.     

Virial series around non-null density: density dependence of virial coefficients

It is shown that the equation of state of fluid systems can be expanded around non-null densities if the well known virial series is generalized by considering its coefficients as density dependent. This in turn leads to a hierarchy of differential equations that describe the coefficients b_j (ρ). Starting from the already known equation of state for hard bodies in d = 0,1,2,3 dimensions this hierarchy is analysed and the behaviour of both the reducible b_j (ρ) and irreducible β～ _j (ρ) cluster integrals is discussed. New virial coefficients b_j (ρ) have been introduced with a simpler density dependence. Their asymptotic (j → ∞) behaviour is discussed.     

The density and the binary diffusion coefficients of silver-tin melts

Temperature dependences of the density of liquid silver-tin melts containing 61.6 and 96.5 wt. % Sn (59.3 and 96.15 at. % Sn) have been determined using gamma-ray attenuation technique over the temperature range from liquidus line to 950 K. The density changes during solid-liquid transition have been directly measured for the first time for eutectic alloy (96.5 wt. % Sn). The temperature and concentration dependences of the thermal properties for Ag-Sn system have been constructed. Kinetics of homogenization of the melts with mean composition of 61.6 wt. % Sn has been investigated in the temperature range from 770 to 950 K. The coefficients of binary diffusion have been derived from these experiments.     

Temperature dependence of transport coefficients in liquid and amorphous metals

We apply the muffin-tin effective medium approximation to calculate the temperature dependence of the resistivity and thermopower of amorphous and liquid metals. The results show unambiguously that a large resistivity is accompanied by a negative temperature coefficient, in agreement with the experimental situation. This behavior is shown to result from a pseudo-gap which opens in the one-particle spectrum due to strong scattering at the quasi zone boundary and which tends to close under an increase in temperature. In turn the thermopower is found to have non-trivial density and temperature dependences.     

Composition dependence of the ionic diffusion coefficients in yttria-stabilized zirconias

The diffusion coefficient of the O²⁻ ions in yttria-stabilized zirconia (1−x)ZrO₂·xYO_1.5 has been investigated as a function of the concentration of Y³⁺ ion over a range x = 0.131–0.261 by using quasielastic light scattering. The diffusion coefficients were deduced from the analysis of the temperature dependence of the scattering intensity at 3 GHz. It is concluded that the diffusion coefficient reaches its maximum value at x = 0.165. The composition dependence of the scattering intensity suggests that the concentration of the moving carrier decreases as the Y³⁺ content increases in spite of an increase of the oxygen vacancies.     

The 2D-J-DOSY experiment: resolving diffusion coefficients in mixtures

Many diffusion-ordered spectroscopy (DOSY) NMR techniques have recently been developed to aid in the deconvolution of complex mixtures. Spectroscopic separation based on chemical and physical properties facilitates the identification of mixture components while eliminating time-consuming separation steps and preserving the chemical environment. One way to improve resolution in such experiments is to spread the spectroscopic information into two dimensions. The 2D-J-DOSY experiment has been designed to resolve mixture components in terms of a chemical shift and proton coupling constant as well as distinguishing them on the basis of translational diffusion. Acquiring a series of spectra as a function of gradient amplitude permits the determination of diffusion coefficients for components that cannot be resolved in the one-dimensional (1D) (1)H NMR spectrum. Comparison of the resulting values with those obtained through the traditional 1D diffusion experiment for a mixture of sugars validates The 2D-J-DOSY technique.     

Temperature dependence of volume and surface symmetry energy coefficients of nuclei

The thermal evolution of the energies and free energies of a set of spherical and near-spherical nuclei spanning the whole periodic table are calculated in the subtracted finite-temperature Thomas–Fermi framework with the zero-range Skyrme-type KDE0 and the finite-range modified Seyler–Blanchard interaction. The calculated energies are subjected to a global fit in the spirit of the liquid-drop model. The extracted parameters in this model reflect the temperature dependence of the volume symmetry and surface symmetry coefficients of finite nuclei, in addition to that of the volume and surface energy coefficients. The temperature dependence of the surface symmetry energy is found to be very substantial whereas that of the volume symmetry energy turns out to be comparatively mild.     

The temperature dependence of magnetostrictive coefficients of Gd-Tb alloys

Measurements of the magnetostrictive coefficients λ^γ,2, λ^α,2₁ and λ^α,2₂ have been made for a range of alloy compositions and temperatures. The variation of λ^γ,2 with temperature and composition is consistent with the proposition that the strains are due to single-ion type interactions.Although the accuracy of measurement of the λ^α,2₁ and λ^α,2₂ coefficients is lower and the range of composition over which measurement could be made more restricted the results from these measurements also support a single-ion model.     

A simplified method to determine the coverage dependence of surface diffusion coefficients

A new method to determine the coverage dependence of surface diffusion coefficients from coverage-gradient experiments is presented. The initial coverage-gradient employed is an evacuated circular region surrounded by a constant coverage. In order to demonstrate this method, Fick's second law equation was numerically solved using coverage-dependent surface diffusion coefficients. An analysis of the results demonstrates that the coverage dependence of the surface diffusion coefficient can be determined using a simple extrapolation procedure. The coverage dependence can be obtained for a wide range of functional forms for the surface diffusion coefficient. The extrapolation procedure requires only that the number of adsorbates that have diffused back into the initially evacuated region be measured as a function of time. This method should be useful in the interpretation of coverage-gradient surface diffusion experiments, especially those performed using laser-induced thermal desorption techniques.     

Sample-shape dependence of the spinodals and the diffusion coefficients for hydrogen in niobium and tantalum

The spinodals for H in Nb and Ta are measured for wire- and foil-shaped specimens, using the Gorsky effect. A pronounced dependence on sample geometry is found and explained in the scope of the mode theory by Wagner and Horner. Also a shape dependence of the macroscopic diffusion coefficient as predicted by this theory has experimentally been verified.     

A study of the two-bulb method for measuring diffusion coefficients of binary gas mixtures

The concentration dependences of the binary diffusion coefficients of the systems He-Ar and He-O₂ are reported at 300 K and 1 atm pressure. Two independent sets of data, obtained with a two-bulb cell and a shearing-cell of Loschmidt design, agree within the error of measurement. The data for the two-bulb cell were obtained at pressures where Knudsen effects are important. It was found necessary to improve the extrapolation procedure of van Heijningen et al. by using the results of the dusty-gas model as described by Mason et al.     

Simultaneous tracer diffusion and interdiffusion in a sandwich-type configuration to provide the composition dependence of the tracer diffusion coefficients

In this paper, a new formalism of a combined tracer and interdiffusion experiment for a binary interdiffusion couple is developed. The analysis requires an interdiffusion couple that initially contains a thin layer of tracers of one or both of the constituent elements at the original interface of the couple (sandwich interdiffusion experiment). This type of interdiffusion experiment was first performed in 1958 by J.R. Manning. The theoretical analysis presented in this paper is based on a newly developed phenomenological theory of isotopic interdiffusion combined with the Boltzmann–Matano formalism. This new analysis now provides the means to obtain the composition dependent interdiffusion coefficient and tracer diffusion coefficients simultaneously from analysis of the interdiffusion and tracer profiles in a single sandwich interdiffusion experiment. The new analysis is successfully applied to the results of Manning’s original ‘sandwich interdiffusion’ experiment in the Ag–Cd system (six couples in total) and is validated with an independent determination of the Ag and Cd tracer diffusion coefficients by Schoen using the conventional thin film technique. Suggestions for further development of the sandwich interdiffusion experiment and analysis to the case of multicomponent alloys are provided.     

HCl vibrational fundamental band: Line intensities and temperature dependence of self-broadening coefficients

Self-broadening in the vibrational fundamental of HCl is inversely proportional to the temperature for transitions which lie near the Boltzmann rotational maximum and becomes monotonically less temperature-dependent as the rotational quantum number increases. We have determined the rotationless transition moment to have the value of 5.57 ± 0.13 × 10^?3 (Debye)² and the first Herman-Wallis factor, C = ?2.543 ± 0.019 × 10^?2.     

Second law of thermodynamics in volume diffusion hydrodynamics in multicomponent gas mixtures

We presented the thermodynamic structure of a new continuum flow model for multicomponent gas mixtures. The continuum model is based on a volume diffusion concept involving specific species. It is independent of the observer?s reference frame and enables a straightforward tracking of a selected species within a mixture composed of a large number of constituents. A method to derive the second law and constitutive equations accompanying the model is presented. Using the configuration of a rotating fluid we illustrated an example of non-classical flow physics predicted by new contributions in the entropy and constitutive equations.     

The viscosity and diffusion coefficients of the binary mixtures of xenon with the other noble gases

This paper presents new experimental data for the viscosity of binary mixtures of xenon with the remaining monatomic gases, helium, neon, argon, and krypton. The measurements have been performed in a high precision oscillating-disk viscometer at atmospheric pressure and within the temperature range 25–500°C. The data have an estimated uncertainty of ±0.1% at 25°C increasing to ±0.3% at 500°C. The collision integrals for the interactions of xenon with the other monatomic species conform to the extended law of corresponding states formulated by Kestin, Ro and Wakeham. For each binary interaction the scaling parameters σ_ij and ∈_ij have been obtained. The ensemble of experimental results can be correlated by means of the appropriate kinetic theory expressions reinforced by the extended law of corresponding states. The deviations do not exceed 0.5%. The binary diffusion coefficients were calculated from the measured mixture viscosity and compared with the available experimental results. The standard deviation was estimated as ±2% which is within the mutual uncertainty of the two sets.