Potentiodynamic anodic polarization curves were constructed for a Zn electrode in 0 multiplied by (times) 01, 0 multiplied by (times) 05 and 0 multiplied by (times) 1 M NaOH solutions containing different additions of Cl** minus ions. The critical pitting potential varies with the logarithm of Cl** minus ion concentration according to sigmoidal S-shaped curves. These curves were explained on the basis of formation of passivatable, limiting active and continuously propagated pits, depending on the range of Cl** minus ion concentration. Addition of aliphatic amines as well as urea shifts the critical pitting potential, into the noble direction. The increase of the efficiency of aliphatic amines as pitting corrosion inhibitors on increasing the alkyl chain length is in line with the prediction based on R. W. Taft, Jr. , constants for general corrosion. |
