A study was made of the extent to which lattice and grain boundary diffusivities could be deduced from the concentration depth-profiles which resulted from the diffusion of tracers from a thin film source in the presence of equally spaced parallel boundary slabs. The problem was treated by placing a grid over the phenomenological system, and exploring the grid by using independent particles and Monte Carlo methods. It was shown that the transition from Harrison type-A kinetics (where the Hart equation provided the effective diffusivity) to Harrison type-B kinetics (where lattice and grain boundary sections of the depth profile were delineated) occurred at a much smaller diffusion length than had previously been thought. As well as the usual model, where the mobility of tracers at the surface source was matched to the immediate substrate, a model was also investigated in which this mobility was made equal to the grain-boundary mobility. Similar behaviours were found.

The Transition from Harrison Type-B to Type-A Kinetics in Grain-Boundary Tracer Diffusion. I.V.Belova, G.E.Murch: Philosophical Magazine A, 2001, 81[10], 2447-55