Protective behaviour of two phosphonate-based inhibitor systems containing lactobionic acid in corrosion control of carbon steel

Results of gravimetric measurements and polarization studies of corrosion control of carbon steel in aqueous medium containing chloride ions are presented. The selected inhibitors are ternary formulations containing phosphonic acids namely 1-Hydroxyethane-1,1-diphosphonic acid (HEDP) and Nitrilotris(methylenephosphonic acid) (NTMP), Zn(II) as a synergist and lactobionic acid (LBA) as the second synergist. In presence of lactobionic acid, the required quantities of both phosphonic acid and Zn(II) are reduced, making the ternary formulations extremely low toxic. Further, the dosages of the components for retention of protective behaviour are still lower. They are effective at pH from 5 to 8. The two new ternary systems are found to work efficiently for prolonged immersion times and also when the corrosive medium is non-static. The results of potentiodynamic polarization studies indicated that both the formulations function as mixed type inhibitors. The synergism of the inhibitor formulations is evident from the study.