Passive Films on Iron: The Mechanism of Breakdown in Chloride-Containing Solutions

摘要

Electrochemical and spectroscopic techniques were applied to the problems of distribution of hydrogen or water within passive films and the distribution of chloride ions in the bulk of passive films after exposure to chloride-containing films. Criteria derived from electrochemically derived kinetic data was sharply inconsistent with several models for passive film breakdown: adsorption-displacement, pore or flaw, and chemico-mechanical. It is not inconsistent with the following: ion exchange processes, point defect models, and hydrated polymeric oxide models. Spectroscopic data pointed to a dehydrated structure. It was also concluded that the thickness of passive films remains unchanged for various times of exposure to chloride ions before and after breakdown.