N.P. Ouglev, N.S. Boosov, S.N. Uglev.
ABSTRACT
The main goal of this work is to clarify the mechanism of diffusion in melts and its relationship with the mechanism of separation of metals in capillaries. When a binary melt is stratified in a capillary at a given temperature, a stable equilibrium distribution of the concentration of components along its height is established in 1–2 hours, which does not change further. A number of works have shown that this distribution is associated with the barometric distribution of clusters of components of a certain size in the planet’s gravitational field, which strongly depends on temperature. As the temperature rises, the delamination depth decreases. Obviously, in the presence of concentration gradients inside the capillary, there are also diffusion fluxes of both components directed against the separation process; therefore, the achieved equilibrium state is probably stationary. This assumption was verified in an experiment involving the creation of special conditions in a capillary with a melt, under which the separation process is excluded, but the conditions for diffusion remain unchanged. For this, capillaries with a Sn + 40 wt. % Pb after reaching equilibrium was heated to a higher temperature. In the experiment, the dynamics of the transition of the concentration curve along the height of the capillary to a new state of equilibrium was investigated. The experimental results confirmed that in the state of stationary equilibrium, both processes occur simultaneously: diffusion concentration equalization and stratification directed in opposite directions. The results of processing experimental data based on a mathematical model of the separation process based on the concept of the motion of components in the form of a monoatomic film suggest that the diffusion process also proceeds according to the mechanism of flow of components in the form of a film between melt clusters. This indicates a common carrier of these processes. The method of conducting the experiment and processing the experimental data additionally made it possible to determine the diffusion coefficient of lead in tin, corresponding to the literature data, and therefore this method can be recommended for practical use.
KEY WORDS:
stratification of metals, stratification in capillaries, barometric distribution of clusters, Landau equation, reverse stratification of metals, diffusion coefficient, surface stratification mechanism, single carrier.
DOI: 10.31857/S0235010621020080