Simulation of mass transfer in a kinetic experiment based on migration of flat layers of a solution in a melt in a temperature gradient field

Mass transfer upon migration of flat liquid layers of a solution in a melt under conditions of slow change in the average temperature at a constant rate has been analyzed for the dislocation and nucleation mechanisms of interface processes. It is shown that the experimental data on the dependence of the migration rate of flat layers on their thickness can be adequately described within the theory developed for strictly steady thermal conditions. A technique is proposed for determining the overall limitations on the mass transfer at interfaces and the migration rate in the diffusion mode from the experimental results obtained in a mixed migration mode.

     

Thermal stationarity criteria for a proper study on growth (dissolution) kinetics in systems with small volumes of solutions in melts

It is shown that an application of theories developed on the assumption of the stationary thermal conditions for discussing the results on kinetic experiments with small volumes of solutions in melts is incorrect if the strong measures on eliminating temperature oscillations in these experiments are not taken. The results on an analysis of the influence of various temperature changes on the velocity of migration of liquid interlayers through a crystalline wafer are presented and discussed. Criteria for thermally stationary conditions in kinetic experiments are deduced.     

Alternation of the flows of liquid components under asymmetric temperature oscillations

The mass transfer in a cylindrical inclusion of the melt with a rectangular cross-section in an anisotropic crystal in a nonstationary thermal field has been analyzed with due regard for the nonlinear solid-liquid interfacial kinetics. The possibility of the existence of a new effect is substantiated—alternation of the direction of the flows of liquid components depending on the rate of temperature variation. It is shown that the inclusion shape can be controlled by changing the shape of the temperature oscillations.     

Migration of liquid inclusions in a solid under asymmetric temperature oscillations

The existence of a new type of thermal migration has been found—the migration of the layer of a liquid phase between two substrates possessing different properties (e.g., two different cuts of a crystal) occurring under the action of asymmetric temperature oscillations. The effect can arise if three following conditions are simultaneously fulfilled: (1) the kinetic properties of the solid-liquid interfaces should be different, (2) the dependence of the growth (dissolution) kinetics on supersaturation should be nonlinear at least at one of the interfaces, and (3) the temperature oscillations should be asymmetric. It is shown that both sign and absolute value of the migration velocity depend on the shape of temperature oscillations. The velocities of migration for liquid layers of various thicknesses as functions of the amplitude of thermal oscillations, their shape, and frequency are calculated for the model Si-Al system.