The transition between Harrison type-B and type-A kinetics in grain boundary diffusion and the corresponding relevance of the Hart equation were studied. Using a Monte Carlo simulation of particle random walks on a grid mapped onto the continuum problem it was shown that the onset of Harrison type-A kinetics occurred at the much higher value of Λ (≤ 0.4) (where Λ = 2L/√D1t, 2L was the boundary spacing, D1 was the lattice diffusivity and t was the time) rather than 0.0067 as previously thought. The limit was not affected by the β/LeClaire parameter.

Analysis of the Hart Equation in Fine-Grained Material. I.V.Belova, G.E.Murch: Defect and Diffusion Forum, 2001, 194-199[2], 1223-6