FREQUENCY RESPONSE METHOD FOR DETERMINATION OF THE DIFFUSION COEFFICIENT OF HYDROGEN IN METAL By

A new electrochemical method, termed as "the frequency response method", for the determination of the diffusion coefficient D in metal is proposed. In the bielectrode system, there appears a phase lag in th.e hydrogen permeation current, when the hydrogen charging constant current is overlapped with a sinusoidal current. The relation between the phase lag and the D value is given by solving the diffusion equation. Measurements were carried out for hydrogen and deuterium in the a-phase systems of Pd/H and Pd/D in the temperature range of 0 ° to 40°C, and the following values were obtained: DH = 3.44 X 10-3 exp (-5.39 X 103 cal/RT) cm2/sec, and DD = 2.46 X 10-3 exp (-5.08 X 103 call RT) cm2/sec. The time lag method based on hydrogen charging by a constant current was also carried out; it was found that by this method the same D value is obtained as that by the frequency response method