Concurrence of bulk and surface processes in kinetics of hydrogen and nitrogen release from metals into vacuum

Concurrence of bulk (diffusion, transition to an adsorbed state) and surface (recombination, desorption) processes in the kinetics of hydrogen and nitrogen release from metals into vacuum has been systematically described. General analytical dependences of the time behaviuor of mean, near-surface and surface concentrations have been derived for samples of different geometry. It has been found that character of the release is determined unequivocally by the product value of the mean concentration in the solution and the sample size, that is by the number of monolayers dissolved in its bulk. It is shown that there exists a characteristic for each metal critical number of dissolved monolayers above which the kinetics is controlled preferentially by the diffusion rate and below which by the recombination rate. The temperature dependences of this value product by the sticking coefficient have been plotted that enable obtaining a general picture of the position of the boundaries of diffusional and kinetics regimes for several transition metals. Specific feetures of the kinetics of hydrogen and nitrogen release in the systems with exo- and endothermal type of dissolution are discussed