Pitting Corrosion of Pure Iron Electrode in OH-/Cl- Solutions and its Inhibition by Sulfated Water Soluble Natural Polymer

K. S. Khairo and I. Zaafarany*

Chemistry Department, Faculty of Applied Science, Umm Al-Qura University, Makkah Al-Mukaramaha, P.O.Box - 118 (Saudi Arabia)  

Pitting corrosion of an iron electrode in 0.1M NaOH solution containing increased addition of NaCl solutions was studied. As the concentrations of NaCl increases the pitting potential was shifted to more negative direction indicating the acceleration of pitting corrosion. The pitting corrosion potential changes with the concentrations of Cl- ion according to sigmoid S-shaped curves. This behavior was explained on the basis of the formation of passivatible active and continuously propagated pits. Addition of sulfated water soluble natural polymer (carrageenan compounds) caused a shift of the pitting potential in the noble direction accounting for increased to a pitting attack.

Iron; pitting corrosion; inhibition; carrageenan compounds