Measurements of the diffusion coefficients for chloride salts in non-protective magnetite were carried out. Non-protective magnetite was produced by corroding C-steel in a chloride solution, at 260C, under compression. The effective diffusion coefficients (figure 5) were measured at temperatures ranging from 54 to 260C. The effective diffusion coefficient was described in terms of the porosity of the magnetite, the NaCl bulk diffusion coefficient, and an empirically determined factor that accounted for the diffusion resistance which arose from the porous structure. It was found that this factor was a sensitive function of temperature, between 54 and 149C. The factor was not found to be a function of the applied pressure.

P.J.Millett, J.M.Fenton: Corrosion, 1990, 46[9], 710-6

Figure 5

Diffusivity of Cl and Na in Magnetite