On the solidification front of a dilute binary alloy: Thermal diffusivity effects and breathing solutions

The asymptotic equation derived in [6],

, to describe the interfacial structure of the solidification front of a dilute binary alloy in the limit in which the solute rejection coefficient is close to unity, is demonstrated to be also valid to lowest order when the thermal diffusivities in the liquid and in the solid are unequal. At higher order nonequal thermal diffusivity effects contribute an integral term. A uniformly valid approximation for the interfacial structure is obtained. The integral term is shown to be capable of producing slowly travelling waves or breathing solutions along the interfacial front when the thermal diffusivity of the liquid is sufficiently larger than the thermal diffusivity of the solid. This slowly oscillatory behavior may signal the proximity of a chaotic region located within the region of linear instability. Latent heat of fusion effects are also discussed.     

Effect of electric field on reentrance transition in a binary mixture of liquid crystals

Employing a phenomenological mean field theory, we analyze the effect of an electric field on the N ? SmA phase transition for pure liquid crystal and on the reentrant nematic phase in a binary mixture of liquid crystals exhibiting the phase sequence I ? N ? SmA ? N_R on cooling. The basic idea of the work is to explain the phase transition behavior of the system by assuming that certain Landau coefficients associated with the order parameters coupling terms of the free-energy density expansion are field dependent. These parameters play a crucial role and show a rapid variation at the SmA ? N_R transition as compared to the SmA ? N transition.     

Transport properties of a binary mixture of CO2-N2 from the pair potential energy functions based on a semi-empirical inversion method

The potential energy snrface of a CO2-N2 mixture is determined by using an inversion method, together with a new collision integral correlation [J. Phys. Chem. R@ Data 19 1179 （1990）]. With the new invert potential, the transport properties of CO2-N2 mixture are presented in a temperature range front 273.15 K to 3273.15 K at low density by employing the Chapman-Enskog scheme and the Wang Chang-Uhlenbeck de Boer theory, consisting of a viscosity coefficient, a thermal conductivity coefficient, a binary diffusion coefficient, and a thermal diffusion factor. The accuracy of the predicted results is estimated to be 2% for viscosity, 5% for thermal conductivity, and 10% for binary diffusion coefficient.     

Convective instability mechanism for a binary mixture heated from above

It is shown that the intensification of a stabilizing buoyancy flux directed from the surface to the bulk of a binary mixture (e.g., salt water) may give rise to convective instability.     

Diffusion-stress coupling in liquid phase during rapid solidification of binary mixtures

An analytical model has been developed to describe the diffusion-viscous stress coupling in the liquid phase during rapid solidification of binary mixtures. The model starts with a set of evolution equations for diffusion flux and viscous pressure tensor, based on extended irreversible thermodynamics. It has been demonstrated that the diffusion-stress coupling leads to non-Fickian diffusion effects in the liquid phase. With only diffusive dynamics, the model results in the nonlocal diffusion equations of parabolic type, which imply the transition to complete solute trapping only asymptotically at an infinite interface velocity. With the wavelike dynamics, the model leads to the nonlocal diffusion equations of hyperbolic type and describes the transition to complete solute trapping and diffusionless solidification at a finite interface velocity in accordance with experimental data and molecular dynamic simulation.     

On relativistic kinetic gas theory: XIV. Transport coefficients of a binary mixture. General expressions

A relativistic method to calculate transport coefficients is developed for a binary mixture with arbitrary particle interaction. The heat conductivity, the diffusion coefficient, the thermal-diffusion coefficient, the shear viscosity and the volume viscosity are expressed in terms of relativistic omega integrals.     

Mass analysis of fast ions from a glow discharge in a binary mixture

The ratios of the various ions do not correspond to those of the neutral species or to the ratios of the ionic components in the negative column [1]. The results indicate that charge transfer in the cathode dark space causes altered energy distribution and a mass spectrum for the fast ions passing to the cathode from the negative column.I am indebted to Dr. A. V. Bondarenko for direction in this work.     

The nature of oscillations of the crystallization front in a diluted binary melt during the initial transient process

The cause of oscillations of the crystallization rate of a binary melt that arise in the initial transient process and have been revealed earlier in numerical experiments is investigated theoretically. Within a simple time-dependent model of directed crystallization, the problem of impurity diffusion in the melt from which a crystal is drawn at constant rate is solved in a linear approximation. It is shown that, under certain conditions, the solution represents a superposition of two concentration waves, a traveling and a standing wave. The concept of a characteristic distance of directed crystallization of a binary melt is introduced. It is established that the nonmonotonic behavior of the crystallization rate during the initial transient process, in particular, its damped oscillations, is attributed to the accumulation of impurities in the melt that is excessive with respect to its distribution in the stationary regime. Impurities in the melt are accumulated excessively when the characteristic distance of directed crystallization starts to exceed the characteristic diffusion length of the impurity in the melt.     

Transport of volume in a binary liquid

In this paper, the transport of volume in a binary liquid mixture is theoretically investigated in three steps, with strong implications for the measurement of mutual diffusivities in non-dilute mixtures. In a first step, the velocity of volume transport is determined from the transport velocities of the two components and the thermodynamic relation of state of the liquid mixture in equilibrium. The role played by Galilean invariance and the choice of a rigid frame of reference for reckoning current densities is highlighted. The divergence of the volume-transport velocity field is found to involve the isothermal compressibility and the thermal expansivity of the liquid together with the spatiotemporal variations of pressure and temperature. In a second step, a linear-response relation is introduced between the interdiffusion current density and the gradient of composition; this relation phenomenologically defines the mutual diffusivity of the binary liquid in a manifestly Galilean-invariant way. In a third step, it is examined whether the practical measurement of that diffusivity in a constant-volume container entails a vanishing mass-transport or volume-transport velocity. From a singular-perturbation analysis of the hydrodynamic equations, it is shown that the mass-transport velocity vanishes in the limit of a diffusion of composition that is much slower than the diffusion of momentum. As a consequence, the volume-transport velocity does not vanish during interdiffusion even though the law of additive volumes of the components holds. The physical meaning of the non-vanishing volume velocity is interpreted by means of the thermodynamic results obtained in the second step. Some of the conclusions carry over to multicomponent liquid mixtures.     

Mechanism of convective instability of a binary mixture

Even a very slow background vertical motion can strongly affect convection in a stratified fluid. A previously unknown mechanism of convective instability is demonstrated for a binary mixture in the flow field of such motion.     

Optical study of a convective instability in a binary liquid mixture heated from above

We report the results of optical measurements performed on a thin horizontal layer of a binary liquid mixture characterized by a negative thermal diffusion ratio. We present evidence of the onset of a new type of convective instability occuring when heating is done from above.     

Long-time tails of the green-kubo integrands for a binary mixture

The long-time tails for the mutual diffusion coefficient, the thermal diffusivity, the thermal conductivity, and the shear and longitudinal viscosities (from which the tail of the bulk viscosity can be calculated) of a nonreactive binary mixture are calculated from mode-coupling theory, and compared with a prior calculation by Pomeau. Three different choices of the thermal forces and currents are considered, with the results found to take their simplest form in the case of the de Groot double-primed set. The decompositions into the kinetic, potential, and cross terms are given.     

磁场对二元合金凝固过程中糊状层稳定性的影响

利用线性稳定性方法研究了外加磁场对二元合金凝固过程中糊状层稳定性的影响,且模型同时考虑了温度场、浓度场和流动的耦合作用.利用计算得出的色散关系式分析了磁场对糊状层稳定性的影响,其中包括直接模式和振荡模式.给出了不同情况下外加磁场对糊状层稳定性的影响,发现磁洛伦兹力可以减小由浮力引起的失稳效应.振荡模式下外加磁场对糊状层产生稳定作用,但直接模式下外加磁场对糊状层的稳定作用具有不确定性.本文所给出结果为工业中利用外加磁场改善产品的质量提供了重要的理论参考.     

Numerical simulation of dendrite growth and microsegregation formation of binary alloys during solidification process

The dendrite growth and solute microsegregation of Fe-C binary alloy are simulated during solidification process by using cellular automaton method. In the model the solid fraction is deduced from the relationship among the temperature, solute concentration and curvature of the solid/liquid interface unit, which can be expressed as a quadric equation, instead of assuming the interface position and calculating the solid fraction from the interface velocity. Then by using this model a dendrite with 0 and 45 degree of preferential growth direction are simulated respectively. Furthermore, a solidification microstructure and solute microsegregation are simulated by this method. Finally, different Gibbs-Thomson coefficient and liquid solute diffusing coefficient are adopted to investigate their influences on the morphology of dendrite.     

Shear viscosity of a binary mixture of simple liquids

Russian Physics Journal -     

Transport properties of a random binary side-coupled chain

We investigate the transport properties of a random binary side-coupled chain by using the transfer-matrix technique. It is found that there are resonant states in the systems with short-range correlations between the host chain atoms and the side-coupled atoms. The analytic expressions for the extended states are also presented in the systems with the side couplings between like atoms and between unlike atoms.