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F.D. Fischer, E. Kozeschnik, G. Mori, J. Svoboda:
"The influence of traps on the diffusion of interstitial";
Talk: Colloquium Material Modelling IMWF, Stuttgart; 2014-05-22.

Interstitial atoms as H, C, O, N can be trapped during their diffusion along interstitial positions by substitutional impurities ("foreign" atoms), dislocation cores, incoherent nano-particles as nano-carbides, etc. Vacancies may act as traps, too, and can be considered as "foreign" atoms. The distribution of atoms as well as traps is explained within the context of thermodynamics of trapping. The diffusive flux of the interstitial atom is formulated. Two final types of diffusion equations are demonstrated, expressed either by the concentration of the interstitial atoms in the lattice or by their total concentration. Consequently, a diffusion equation is derived with a chemical diffusion coefficient, which is rationally obtained from the current concept and strongly depends on the total concentration. This fact is often ignored, e.g. by the experimental investigation of the diffusion coefficient of hydrogen in steel. The according experimental setting is explained. Then we show that the established ASTM and EN-ISO procedure cannot reproduce the actual diffusion behaviour of hydrogen.