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 chromi um type (TFS-CT) and polycrystalline iron electrodes in sodium bisulfi te containing perchlorate and nitrate solutions. Our experiments indic ate that TFS-CT corrodes on exposure to sodium bisulfite. The extent t o which passivation is prevented depends on the supporting electrolyte . A very interesting feature that we have observed is that TFS-CT exhi bits a ''memory'' of exposure to sodium bisulfite, in that it does not repassivate when subsequently cycled in a bisulfite-free supporting e lectrolyte. 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 repassiv ate when returned to a supporting electrolyte that is free of bisulfit e. The results indicate that bisulfite attacks the protective chrome o xide coating partially or completely, inhibiting subsequent passivatio n 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.