A Comparative Study of the Corrosion of Tin‐Free Steel and Iron in Sodium Bisulfite

We have examined the electrochemical behavior of tin‐free steel chromium type (TFS‐CT) and polycrystalline iron electrodes in sodium bisulfite containing perchlorate and nitrate solutions. Our experiments indicate that TFS‐CT corrodes on exposure to sodium bisulfite. The extent to which passivation is prevented depends on the supporting electrolyte. A very interesting feature that we have observed is that TFS‐CT exhibits a "memory" of exposure to sodium bisulfite, in that it does not repassivate when subsequently cycled in a bisulfite‐free supporting electrolyte. This "memory effect" and the extent of corrosion depend on the supporting electrolyte used. Polycrystalline iron electrodes on the other hand, corrode on exposure to sodium bisulfite, but repassivate when returned to a supporting electrolyte that is free of bisulfite. The results indicate that bisulfite attacks the protective chrome oxide coating partially or completely, inhibiting subsequent passivation even in bisulfite‐free electrolytes. The results also indicate that reactions of the bisulfite exposed surface with perchlorate or nitrate anions significantly affect corrosion behavior.