Abstract
The inhibition efficiency (IE) of sodium molybdate (SM) in controlling corrosion of carbon steel in an aqueous solution containing 120 ppm of Cl-, in the absence and presence of Zn2+has been evaluated by weight-loss method. A synergistic effect exists between SM and Zn2+when the concentration of Zn2+is 25 ppm and above. Inhibition efficiencies obtained are greater than 85%. Antagonistic effect exists between SM and Zn2+when the concentration of Zn2+is 10 ppm and below. The SM-Zn2+system shows excellent IE up to third day. Above third day IE decreases. Acceleration of corrosion takes place. Excellent IE is shown at pH 5,7 and 12. At pH 9, IE decreases since Zn2+is precipitated as Zn(OH)2in the bulk of the solution. Polarization study reveals that SM-Zn2+system functions as a mixed inhibitor. FTIR spectra reveal that the protective film consists of Fe2+-SM complex and Zn(OH)2.
Highlights
Sodium molybdate is an effective corrosion inhibitor even at very low concentration
FTIR spectra reveal that the protective film consists of Fe2+-sodium molybdate (SM) complex and Zn(OH)[2]
The present work is undertaken (i) to evaluate the inhibition efficiency of sodium molybdate (SM) in controlling corrosion of carbon steel in aqueous solution containing 120 ppm of Cl- in the absence and presence of Zn2+ (ii) to study the synergistic and antagonistic effect of the SM-Zn2+ system (iii) to analyze the protective film by FTIR (iv) to study the mechanistic aspects of corrosion inhibition by polarization study and (v) to propose a suitable mechanism of corrosion inhibition based on the results from the above studies
Summary
Sodium molybdate is an effective corrosion inhibitor even at very low concentration. The present work is undertaken (i) to evaluate the inhibition efficiency of sodium molybdate (SM) in controlling corrosion of carbon steel in aqueous solution containing 120 ppm of Cl- in the absence and presence of Zn2+ (ii) to study the synergistic and antagonistic effect of the SM-Zn2+ system (iii) to analyze the protective film by FTIR (iv) to study the mechanistic aspects of corrosion inhibition by polarization study and (v) to propose a suitable mechanism of corrosion inhibition based on the results from the above studies. Carbon steel specimens in triplicate were immersed in 100 mL of the solutions containing various concentrations of the inhibitor in the presence and absence of Zn2+ for one day.
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