On the mechanism of hydrogen permeation in iron in alkaline medium

Hydrogen permeation tests were performed in pure iron in sodium hydroxide at 298 K, based on the electrochemical technique. Hydrogen charging was conducted under potentiostatic control, simultaneously registering both the permeation (i(p)) and the cathodic (i(c)) currents until stabilization. After a first polarization transient at -1105 or -1355 mV/NHE, potential increments or decrements were performed, allowing in both cases the currents to stabilize. Based on the analysis of the experimental data, a model was developed, which takes into account the existence of a 0.5 to 1 nm thick unreduced air-grown oxide film on the input side of the samples in spite of long cathodic polarization times. A good correlation between the potential distribution at the oxide/solution interface and the calculated oxide thickness was obtained. (C) 1998 Acta Metallurgica Inc.