The ability of fluoride ions, in trace concentrations, to promote film instability and transpassive dissolution was shown for several corrosion resistant alloys. While the addition of fluoride ion was found to decrease the transpassive dissolution potential by approximately 0.1 V, the decrease was particularly pronounced in mildly acidic media (pH 5). Results suggest that the decreased potential range of stability for the heavily-relied-upon Cr(III)-rich oxide film is a concern in the presence of oxidizing impurities which may push the corrosion potentials toward the transpassive region. The decreased potential range of passive film stability was observed using both dynamic and static polarization experiments and supported by solution and surface analyses.

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