The inhibition efficiency (IE) of phyllanthus amarus extract (PAE)-Zn 2+ system, in controlling corrosion of carbon steel in an aqueous solution containing 60 ppm of Cl-, has been evaluated by weight loss method. Weight loss study reveals that the formulation consisting of 2 mL of PAE and 25 ppm of Zn 2+ has 98% inhibition efficiency in controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl-. Synergistic parameters suggest that a synergistic effect exists between PAE and Zn 2+. Polarization study reveals that this system functions as mixed type of inhibitor controlling the cathodic reaction and anodic reaction to an equal extend. AC impedance spectra reveal that a protective film is formed on the metal surface. The FTIR spectra reveal that the protective film consists of Fe 2+-phyllanthus complex.

The inhibition efficiency of sodium gluconate (SG)-Zn 2+ system in controlling corrosion of carbon steel in sea water has been evaluated by weight-loss method. The formulation consisting of 250 ppm of SG and 75 ppm of Zn 2+ has 98% IE. Influence of duration of immersion on the IE of SG-Zn 2+ has been evaluated. The mechanistic aspects of corrosion inhibition have been investigated by polarization study and AC impedance spectra. The protective film has been analysed by FTIR and luminescence spectra. The surface morphology and the roughness of the metal surface have been analysed by atomic force microscopy. The protective film consists of Fe 2+ -SG complex and Zn(OH) 2 . It is found to be UV -fluorescent.

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