  Boundary conditions for the solid-liquid interface of the solidifying pure
melt have been derived. In the derivation the model of Gibbs interface is used.
The boundary conditions include both the state quantities of bulk phases are
taken at the interface and the quantities characterizing interfacial surface
such as the surface temperature and the surface heat flux. Introduction of the
surface temperature as an independent variable allows us to describe the
scattering energy at the interface. For the steady-state motion of the planar
interface the expression for the temperature discontinuity across the phase
boundary has been obtained. Effect of Kapitza resistance on the interface
velocity is considered. It is shown that heat resistance leads to non-linearity
in solidification kinetics, namely, in "velocity-undercooling" relationship.
The conditions of the steady--state motion of the planar interface has been
found.
