Implications of the kosmotrope/chaotrope nature of the anions on the breakdown of passivity of iron by halides

The comparative aggressiveness of NaF and NaCl solutions on the breakdown of passivity of iron has been investigated once the passivating borate buffer solution has been removed. The results highlight the inhibitive action of borate anions towards the less aggressive kosmotrope fluorides. Without borates, the kinetics of attack by fluorides is slower as the prepassivation is longer, and it is considerably retarded when compared to the case with the chaotrope chlorides. The high positive viscosity B coefficient value of borate anion argues in favor of its use as an inhibitor or as an efficient electrolyte for anodization baths.