ON THE MECHANISM OF HYDROGEN PERMEATION IN IRON IN ALKALINE-MEDIUM

Hydrogen permeation tests were performed in pure iron in sodium hydrox ide at 298 K, based on the electrochemical technique. Hydrogen chargin g was conducted under potentiostatic control, simultaneously registeri ng both the permeation (i(p)) and the cathodic (i(c)) currents until s tabilization. After a first polarization transient at -1105 or -1355 m V/NHE, potential increments or decrements were performed, allowing in both cases the currents to stabilize. Based on the analysis of the exp erimental data, a model was developed, which takes into account the ex istence of a 0.5 to 1 nm thick unreduced air-grown oxide film on the i nput side of the samples in spite of long cathodic polarization times. A good correlation between the potential distribution at the oxide/so lution interface and the calculated oxide thickness was obtained. (C) 1998 Acta Metallurgica Inc.