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.     

Computed values of rotational collision number and diffusion coefficients for oxygen

Recent experimental data on thermal conductivity and viscosity are used to calculate values of rotational collision numbers and diffusion coefficients for oxygen in the temperature range 400–1600 K.     

Diffusion and thermal diffusion coefficients of a relativistic gas mixture

Values up to order c^-2 are given for the diffusion and thermal diffusion coefficients of binary relativistic gas mixtures of hard spheres and Israel particles.     

Comparison of spin and electron diffusion coefficients in a two-dimensional electron gas

The results from femtosecond four-wave-mixing experiments carried out in two-dimensional gas at the GaAs/AlGaAs heterojunction boundary under room temperature conditionsare presented. The obtained values of the spin and electron diffusion coefficients are 163.2 and 200 cm²/s respectively. The spin and electron relaxation times are found to be 50.7 ps and 3 ns respectively.     

Fluctuations in the diffusion of particles in a non-uniform medium

We study the thermal fluctuations of density and flow velocity of particles diffusing in a non-uniform medium with memory character. The fluctuation spectra are derived from the macroscopic equations with the aid of the generalized Nyquist theorem. A comparison is made with other methods.     

Studies of diffusion coefficients in disordered porous matrices confined in a slit-pore

We present a series of molecular dynamics simulations to study the structure of porous matrices confined in a slit-pore. The matrices were prepared by two different methods. In the first method we used direct simulations of a fluid at a fixed density and the matrix was taken from the last configuration of its particles. In the second method we simulated a binary mixture where one of the components served as a template material and the final porous matrix configuration was obtained by removing template particles from the mixture. In both methods the matrices were confined by two parallel walls (slit-pore) modeled by continuous solid surfaces. The results show that the matrix structure and porosity were affected by the method of preparation of the porous matrices. Moreover, we found smaller void cavities in these matrices than in matrices prepared without walls. Finally, diffusion of a fluid inside the matrices was investigated and it was found that the diffusion coefficient did not decrease with the fluid density, and presented a maximum at certain values of the fluid density.     

Cascade diffusion of water molecules in a porous granular medium

Water vapor inleakage to a porous granular adsorbent was studied by diode laser spectroscopy. Stepping in the temporal variation of the diffusivity, probably associated with porous matrix space fractality, was detected. The H₂O molecular sensing technique is proposed as a tool for experimental study of the structure of porous media and processes occurring in them.     

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.     

Mechanism of formation of delta FeOOH in a basic aqueous medium

The mechanism of oxidation of ferrous hydroxide precipitated by mixing FeSO₄ · 7H₂O and NaOH solutions depends on the ratioR=[FeSO₄]/[NaOH]. The study presented here concerns values ofR ranging from 0.38 to 0.43, i.e. Fe(OH)₂ is precipitated in the presence of an excess of caustic soda. The analysis made by Mössbauer spectroscopy of the final compounds of oxidation shows that the valueR=5/12 is particular. At this value, 8FeOOH is the main product of oxidation. Its formation is assumed to take place through an intermediate compound, which formula is deduced from the value R=5/12 to be: 3Fe(OH)₂ · 2Fe(OH)₃ ·nH₂O. This compound could be considered as a green rust one compound including excess OH^– ions in theAcB i BaC j CbA k stacking, whereA, B andC are the OH^– planes,a, b andc the iron planes, andi, j andk layers made of the excess OH^– ions and water molecules.     

Statistical theory of diffusion in concentrated bcc and fcc alloys and concentration dependencies of diffusion coefficients in bcc alloys FeCu,FeMn, FeNi,and FeCr

The statistical theory of diffusion in concentrated bcc and fcc alloys with arbitrary pairwise interatomic interactions based on the master equation approach is developed. Vacancy–atom correlations are described using both the second-shell-jump and the nearest-neighbor-jump approximations which are shown to be usually sufficiently accurate. General expressions for Onsager coefficients in terms of microscopic interatomic interactions and some statistical averages are given. Both the analytical kinetic mean-field and the Monte Carlo methods for finding these averages are described. The theory developed is used to describe sharp concentration dependencies of diffusion coefficients in several iron-based alloy systems. For the bcc alloys FeCu, FeMn, and FeNi, we predict the notable increase of the iron self-diffusion coefficient with solute concentration c, up to several times, even though values of c possible for these alloys do not exceed some percent. For the bcc alloys FeCr at high temperatures T ? 1400 K, we show that the very strong and peculiar concentration dependencies of both tracer and chemical diffusion coefficients observed in these alloys can be naturally explained by the theory, without invoking exotic models discussed earlier.     

Joint diffusion of rays in a homogeneous medium with random inhomogeneities

Fluctuations of the direction and amplitude of two rays propagating in a homogeneous, on aver-age, medium with random inhomogeneities of dielectric permittivity are considered. The solution to the problem is based on the method of ray diffusion, which enabled us to obtain the probability densities of the distribution of the relative amplitude and the relative direction of the rays.     

Precise determination of the Soret,thermal diffusion and mass diffusion coefficients of binary mixtures of dodecane,isobutylbenzene and 1,2,3,4-tetrahydronaphthalene by a holographic grating technique

Within the framework of an international benchmark test, the Soret coefficient S T , thermal diffusion coefficient D T and mutual mass diffusion coefficient D of the three binary mixtures of dodecane, isobutylbenzene and 1,2,3,4-tetrahydronaphthalene with a concentration of 50 wt% of each component at a temperature of 25C have been measured with a holographic grating technique. For the analysis of the experimental data a new numerical correction algorithm based on linear response theory has been employed. The corrections applied are on the order of 1% for S T and 5% for D . The coefficients S T , D and D T are determined with relative errors of a few per cent.     

Dynamics of conformations,hydrogen bonds and translational diffusion of poly(methacrylic acid) in aqueous solution and the concentration transition in MD simulations

The dynamic behaviour of chain conformations, hydrogen bonds and translational diffusion of aqueous poly(methacrylic acid) (PMA) solution as a function of polymer volume fraction Φ_p across dilute to concentrated regimes inclusive of the pure polymer amorphous state was studied by molecular dynamics simulations. The behaviour of the relaxation time (τ) of the backbone dihedral angle auto-correlation function (ACF) reveals slower relaxation at higher level of polymer concentration and the existence of a concentration-driven relaxation transition for the aqueous polymer solution which occurs in the polymer volume fraction range, specifically 54% < Φ_p < 82% for this system. The relaxation constant τ for backbone dihedral angle exhibits a linear variation with Φ_p, indicating a first-order kinetic transition. The intermittent ACF for decay of the H-bond correlation shows that H-bonds among water molecules relax faster than those of the PMA–PMA and PMA–water type. The relaxation rate of PMA–water H-bonds shows a decrease up to Φ_p = 72% and becomes faster at Φ_p = 82% due to the confining influence of neighbouring PMA chains. PMA–water and water–water H-bond dynamics show transitions around Φ_p = 72% PMA. With increase in Φ_p PMA diffusion coefficient decreases exponentially and water diffusion coefficient decreases linearly, in agreement with experimental observations using fluorescence and nuclear magnetic resonance (NMR) spectroscopic studies.     

Algorithms for statistical modeling of radiation diffusion in a medium with a reflecting surface

An algorithm has been developed for calculating the transient propagation of a narrow collimated light beam in a scattering medium near a reflecting surface. The solution is applicable to a medium with an arbitrary scattering indicatrix and particle-size distribution. The angular reflection function and the albedo of the reflector are also arbitrary. Tabulated transmission functions are supplied, which allows the algorithm to be extended to the infrared region.We are indebted to G. V. Rozenberg and V. E. Zvev for proposing the topic.