The Effect of Chloride on Passive Oxide Film Breakdown on Stainless Steels and Aluminum

The evidence for adsorption or incorporation of chloride ions (Cl-) in the passive oxide film on stainless steels and Fe-Cr alloys appears to be contradictory, with some investigators reporting Cl- in the oxide and others reporting its absence. We consider this issue by determining Cl- adsorption and/or incorporation as a function of potential (below the pitting potential) on 316L stainless steel using Xray photoelectron spectroscopy and compare our results to the literature on uptake of Cl- by stainless steels and to studies on uptake of Cl- on aluminum. The important finding is that no Cl- is observed in the oxide film on 316L stainless steel whereas in the case of aluminum, Cl- is incorporated into the oxide film. We present the case for those instances where Cl- is observed in the oxide films on stainless steels and Fe-Cr alloys, these observations are a result of the experimental procedures employed.