Pitting corrosion and its inhibition for Cu-Fe and Cu-Al-Fe alloys in sodium chloride solutions

ABSTRACT

The pitting corrosion of Cu-5% Fe alloy [1] and Cu-10%Al-4,9%Fe alloy [II] in sodium chloride solutions was studied, using the potentiodynamic anodic polarization and galvanic current-time measurements. From the potentiodynamic anodic polarization curves the pitting corrosion potential was evaluated. The pitting potential of the two alloys varies with the logarithm of Cl[-] ion concentrations according to sigmoidal curves, which was explained on the basis of formation of passivitable, limiting active and continuously propagated pits depending on the concentration of chloride ions. Alloy [I] had higher resistance to pitting corrosion than alloy [II]. The integrated charge amount, q[a], in presence of Cl[-] ions was taken as a measure of the extent of pitting corrosion, while the difference in values between pitting potential and repassivation potential [E[pit]-E[p]] was taken as a measure of pit repassivation ability. The galvanic current-time measurements indicated that the induction periods become shorter with the increase of Cl[-] ion concentrations. Addition of inorganic anions individually or in mixtures to sodium chloride solutions caused inhibition of pitting corrosion of both alloys. This was indicated from the shift of E[pit] to noble direction in presence of these additives. The inhibition efficiency of the additives was calculated from the change of the integrated anodic charge [q[a]] and induction period in the absence and presence of inhibitors. It was found that the inhibition efficiency depends on the concentration and type of the additive. The synergistic effect manifested itself in presence of mixed additives