On static and dynamical young's condition at a trijunction

Using a consistent purely kinetic model we show that Young's condition at a trijunction results from a chemical and not a mechanical equilibrium, as is often believed in the literature. In an out-of equilibrium situation this condition is altered in a way such that the triple point acquires an effective mobility. The order of magnitude of the mobility is fixed by a velocity scale <(V)over tilde(att)> associated with chemical attachment at the interface, and not by the sound speed. While for ordinary eutectics (V) over tilde(att) is large (except in rapid solidification experiments) in comparison to the growth speed, implying a quasi-instantaneous mobility, finite mobility effects should show up for faceted eutectics as well as for eutectoid transformations.