  A new approach that is a combination of classical thermodynamics and
macroscopic kinetics is offered for studying the nucleation kinetics in
condensed binary solutions. The theory covers the separation of liquid and
solid solutions proceeding along the nucleation mechanism, as well as
liquid-solid transformations, e.g., the crystallization of molten alloys. The
cases of nucleation of both unary and binary precipitates are considered.
Equations of equilibrium for a critical nucleus are derived and then employed
in the macroscopic equations of nucleus growth; the steady state nucleation
rate is calculated with the use of these equations. The present approach can be
applied to the general case of non-ideal solution; the calculations are
performed on the model of regular solution within the classical nucleation
theory (CNT) approximation implying the bulk properties of a nucleus and
constant surface tension. The way of extending the theory beyond the CNT
approximation is shown in the framework of the finite-thickness layer method.
From equations of equilibrium of a surface layer with coexisting bulk phases,
equations for adsorption and the dependences of surface tension on temperature,
radius, and composition are derived. Surface effects on the thermodynamics and
kinetics of nucleation are discussed.
