It was shown that that the diffusivity was different when measured during or after cathodic charging. The diffusivities at 25C were equal to 3 x 10-6cm2/s during charging and 3.4 x 10-7cm2/s after charging. The overall results could be described by:

during charging:     D (cm2/s) = 1.48 x 10-4 exp[-0.1(eV)/kT]

after charging:     D (cm2/s) = 3.11 x 10-4 exp[-0.175(eV)/kT]

They were explained in terms of 2 different types of H trapping; one type being reversible (during charging) and the other being irreversible (de-gassing after charging).

H.Veysseyre: Met. Corros. Ind., 1966, 495, 405-24

 

Table 56

Diffusivity of H in Fe at 20C as a Function of Rolling Deformation

 

Deformation (%)

D (cm2/s)

Trap Density (/cm3)

Dislocation Density (/cm2)

8.8

5.1 x 10-5

5.7 x 1018

5.6 x 109

20

5.5 x 10-5

4.5 x 1018

8.6 x 109

22

5.1 x 10-5

5.7 x 1018

9.1 x 109

28

4.3 x 10-5

8.5 x 1018

1.07 x 1010

30

4.4 x 10-5

8.1 x 1018

1.13 x 1010

41

4.4 x 10-5

8.1 x 1018

1.42 x 1010

51

4.1 x 10-5

9.4 x 1018

1.68 x 1010

60

4 x 10-5

9.9 x 1018

1.92 x 1010