Abstract: A mathematical model is proposed for the electrochemical hydrogen-permeation under the nonequilibrium entry condition, and the corresponding expressions for the permeation-current transients are derived. The new model is characterized by the boundary condition at the cathodic side of metal specimen, the so-called "constant hydrogen concentration" and "constant hydrogen flux" boundary conditions in the literature are considered as its special cases. It is pointed out that the kinetics of entry process can be determined by the relation between the steady-state permeation currents and the specimen thickness. The dependance of apparent values of hydrogen diffusion coefficient on the cathodic polarization is also discussed.

Key words: Hydrogen permeation, Permeation-current transient, Hydrogen diffusion coefficient