Time-dependent measurement of hydrogen penetration in ferric metal materials

Hydrogen diffusion in metal sheet has conventionally been investigated using a double electrochemical cell, so-called Devanathan-Stachurski (DS) cell. The authors reported that, when a flow-rate of electrolyte in an entry side cell is sinusoidally perturbed, an entry side current and an exit side current flow with sinusoidal waveforms and the latter shows a latency of phase shift θ depending on the alternation frequency, specimen thickness and hydrogen diffusion coefficient D_H in the sheet. In this study, the emphasis was put on a time-dependence of θ. Utilization of fast-Fourier-transform enabled the evaluation of θ in real-time. Hydrogen penetration measurement under potentiostatic polarization with sinusoidal flow-rate perturbation was applied to a ferric metal sheet. Under a standard ambient condition, the value of θ showed a circadian change, which was similar to the change in temperature of the experimental system. However, an Arrhenius-type analysis for the thermo-response of θ resulted in abnormally large values of activation energy and maximal diffusion coefficient, suggesting that the value of θ is dependent on not only temperature but also other parameters.