Boundary condition for grain boundary segregation

Impurity segregation at grain boundaries in polycrystalline solid is expressed with a diffusion equation combined with the boundary condition which describes impurity flux into the grain boundaries. At present, for the model of boundary condition for grain boundary segregation, the two following models have been proposed; one is that the interface of a grain and a grain boundary is at equilibrium leading to the constant impurity concentration ratio across the interface, and another is that the impurity flux across the interface is determined with a transport coefficient. However, these models are applicable only to the limited cases. By considering the behaviour of impurity atoms around the interface, a new boundary condition is proposed. The new boundary condition and the conventional one are discussed comparing with experiments.