Investigation of the Effect of Hydrogen on the Passive Film on Iron by Surface Analysis Techniques

Abstract

The effects of dissolved hydrogen on the thickness, structure, and composition of the passive film on iron formed in a boric/borate solution at pH 8.4 were investigated by Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), and nuclear reaction analysis (NRA). AES analysis showed that hydrogen decreases the film thickness and the oxygen content in the film, reduces the valence state of iron, and increases both the iron content in the film and the degree of deviation of the oxide in the passive film from its nominal chemical stoichiometry. The decrease in the oxygen content in the passive film was confirmed by NRA measurements. SIMS results showed that hydrogen charging increases the hydroxyl content in the passive film. These results provide very useful information for elucidating the mechanism by which hydrogen decreases the corrosion resistance of passive films and promotes pitting of iron. © 2003 The Electrochemical Society. All rights reserved.