Crystallization Of Binary Melt Research Articles

Crystallization of binary melt with a periodically varying rate

The time dependence of the crystallization rate at crystal pulling to the cold zone with a velocity that has a sinusoidal component has been investigated within a one-dimensional time-dependent model of solidification of a diluted binary melt by the net method. It is shown that the regularities that were obtained previously by the analytical method for pulling rates with small oscillations are repeated in many respects when considering oscillations of larger amplitudes. At significant oscillation amplitudes, the time-averaged values of impurity concentration at the interface for the stationary and vibrational crystallization modes may differ by several dozen percent.

Influence of high-frequency vibration on the morphological instability in the directional crystallization of binary melts

The influence of various types of vibration on the morphological instability of the directional crystallization front in binary melts is investigated numerically under microgravity and terrestrial conditions. The vibration frequency is assumed to be high and the amplitude to be small and an averaged approach is used. It is shown that high-frequency rotational vibration generates an intense mean flow localized in the neighborhood of the crystallization front and the direction of this flow is opposite to the direction of gravity-convection flow. Under terrestrial conditions the interaction between vibration flow and gravity convection leads to the gravitational vortex being pushed away from the crystallization front. Under both terrestrial and microgravity conditions rotational vibration has a strong stabilizing action on the morphological instability and prevents the formation of an axial hollow.

Kinetics of Crystallization of Binary Melts of Eutectic-Forming Substances

The crystal nucleation and growth rates in eutectic-forming melts are experimentally determined using a universal technique for finding the kinetic parameters of processes involving phase transformations. It is shown that, with an increase in the concentration of the impurity component, the crystal nucleation and growth rates gradually decrease and reach a minimum at a eutectic point. It is confirmed that inter- and extrapolation equations known in the theory of crystallization of one-component melts can be used to obtain reliable values of the kinetic parameters in the crystallization of binary melts at large supercoolings.

Solidification with a quasiequilibrium two-phase zone

A set of nonlinear equations describing solidification with a two-phase zone (mushy region) is analytically solved in a general form in the case of quasi-steady-state crystallization of binary melts. Concentration, temperature distributions and the bulk fraction of the solid phase as functions of a spatial coordinate and physical and operating parameters of solidification are found within the mushy zone. The mushy region thickness and algebraic equation for the bulk fraction of the solid at the boundary solid phase–mushy zone are determined for the first time in a general form. A theory under consideration strengthens a hypothesis about a self-similar structure of the two-phase zone.

Crystallization of binary melts and decay of supersaturated solid solutions at the ostwald ripening stage under non-isothermal conditions

In this paper a theory on the initial stages of binary melt crystallization and decay of supersaturated solid solutions at the Oswald ripening stage is developed. Examination of the crystallization is performed for systems forming a continuous series of solid solutions and systems which are insoluble in each other when in the solid state. The work consists of two parts. In the first part all the processes are considered for conservative systems. In so doing it is shown that heat fields formed due to evolution of latent heat of crystallization are imposed during the Ostwald ripening of nuclei of the new phase. In the second part, the effects of arrival or removal of matter and heat on processes originating in crystallization of binary melts and decay of supersaturated solid solutions are investigated. An entire set of equations describing the above processes is derived. As a result of an asymptotic solution, the size distribution functions for nuclei of the new phase are obtained. The relationship between changes in the mean radius and density of nuclei as a function of time is found. It is shown that sources (or sinks) of matter and heat are coupled with each other. It is also discussed how heating (or cooling) of a system and also sources (or sinks) of matter influence changes in the size distribution of nuclei of the new phase and their composition. The possibility of controlling the structure of decomposed solid solutions and crystallized binary melts is shown to exist. Our treatment can be used to examine other disperse systems which are at the Ostwald ripening stage.