Theoretical analysis of entrapment kinetics in hydrogen permeation experiments

A simulation program has been developed to analyze hydrogen entrapment during hydrogen permeation experiments where the input side hydrogen concentration is constant and the exit side hydrogen concentration is zero. The simulations performed focused on the effect of traps on the exit side hydrogen flux and that on the capture and release of hydrogen by traps as a function of the distance from the entry surface. The number of dimensionless parameters to be defined in the presence of traps was much higher than in the absence of traps. It was found that in several cases the first breakthrough time of hydrogen is a linear function of the trap concentration. However, when the capture of hydrogen by traps is slow, the permeation curve may have a very unusual shape, and the trap saturation profile changes substantially during the permeation experiment. The impact of the hydrogen entrapment kinetics on the result of permeation experiments in connection with the industrial test of enamel-grade steel plates is also discussed.