Self-diffusion in high-purity iron was measured using serial sectioning and radioactive tracer 59Fe at 523 to 703K using type-C kinetics. The grain boundary self-diffusivity δDgb was measured between 873 and 1173K using type-B kinetics. The results were described by:

δDgb(m3/s) = 6.35 x 10-15exp[-55.7(kJ/mol)(1 + 1.28s2)/RT]

where s was the ratio of spontaneous magnetization of bulk iron at TK to that at 0K. The grain boundary self-diffusivity obtained here was much higher than previous values. The activation energy for grain boundary self-diffusion in paramagnetic α-iron (55.7kJ/mol) was only 22% of the activation energy for volume diffusion. The above factor of 1.28 was some 8 times that for volume diffusion.

A.Inoue, H.Nitta, Y.Iijima: Acta Materialia, 2007, 55[17], 5910-6