Lattice discontinuities affecting the generation and annihilation of diffusible hydrogen and vice versa

Lattice discontinuities include lattice defects and surfaces both providing traps for hydrogen atoms. It will be discussed under which conditions discontinuities of a given distribution either release trapped hydrogen to become diffusible or capture diffusible H-atoms to become trapped. It will be shown that for any distribution, the self-diffusion coefficient of hydrogen is determined by the product of the H-diffusion in the perfect lattice times the fraction of hydrogen being diffusible. In this context, the quantities diffusible hydrogen, lattice hydrogen, thermodynamic activity of hydrogen and chemical potential of hydrogen are interchangeable in a general way. New discontinuities are generated during hydrogen embritllement (fracture surfaces, voids, dislocations) and dislocations move by kink pair formation. The production rate of these discontinuities depends on the chemical potential of hydrogen within the defactant concept or the generalized Gibbs adsorption isotherm. Thus, the chemical potential ...