Relation between bulk and interface descriptions of alloy solidification

From a simple bulk model for the one-dimensional steady-state solidification of a dilute binary alloy we derive the corresponding interface description. Our derivation leads to exact expressions for the fluxes and forces at the interface and for the set of Onsager coefficients. The constitutive equations, connecting the crystallization and diffusion fluxes and forces, decouple in the low-velocity limit and there generate an occasionally negative, but nevertheless thermodynamically consistent friction coefficient. We, moreover, discover a continuous symmetry, which is independent of our model and allows to decouple the constitutive equations for the two components of the alloy for arbitrary growth velocities.