Investigation on the inhibition synergism of new generations of phosphate-based anticorrosion pigments

• Assessing behavior of ZCP and ZAM as modified phosphate-based anticorrosion pigments.
• EN analysis of effectiveness of the modified phosphate-based anticorrosion pigments.
• Finding correlation between EIS and Electrochemical noise data.
• Electrochemical examining the corrosion inhibition synergism offered by ZCP and ZAM.
• Film formation in the presence of ZCP and ZAM was studied by SEM/EDX and XPS.

The role of zinc aluminum molybdenum orthophosphate hydrate and zinc calcium strontium aluminum orthophosphate silicate hydrate as new generations of phosphate-based anticorrosion pigments in corrosion protection of mild steel exposed to 3.5% sodium chloride solution was studied using electrochemical techniques as well as surface analysis. Compared to conventional zinc phosphate, superiority of the modified pigments was shown through taking advantage of electrochemical impedance spectroscopy, polarization curves and electrochemical noise measurements. Moreover, a good trend was also observed between electrochemical noise data and the results obtained from electrochemical impedance spectroscopy and potentiodynamic polarization. Protective films deposited on the surface were detected using SEM/EDX in the presence of zinc aluminum molybdenum orthophosphate hydrate and zinc calcium strontium aluminum orthophosphate silicate hydrate releasing more inhibiting species. The effect of immersion time on the film formation was studied through the electrochemical methods. XPS technique was also employed to analyze the sample surface exposed to 3.5% NaCl solution containing combination of the modified pigments. In addition to the surface analysis data, various parameters extracted from the electrochemical measurements revealed corrosion inhibition synergism of the two pigments.