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The presence of organic molecules containing active groups in the aqueous extract of Kiwi fruit shell converted it as a low cost and rich source of green inhibitors in corrosion control of carbon steel. In the present study, the synergistic inhibition effect of Kiwi fruit shell extract and zinc nitrate on the corrosion behavior of carbon steel in 3.5 wt.% NaCl solution was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. By means of scanning electron microscopy (SEM) the morphology and chemistry of surface were investigated. In addition, the Fourier transform infrared (FT-IR) spectroscopy was applied to recognize the functional groups of Kiwi fruit shell extract and its mixture with zinc nitrate. The EIS results indicated that after 24 h immersion of steel sample in NaCl solution containing 200 ppm Kiwi fruit shell extract and 600 ppm zinc nitrate the maximum inhibition efficiency of 85% was achieved. The potentiodynamic polarization analysis demonstrated that the corrosion inhibition dominantly occurred through anodic half-reactions. The interactions and complex formation of organic molecules of Kiwi fruit shell extract with iron cations and also the zinc cations adsorption on the cathodic sites resulted in the deposition of effective corrosion resistant film on the mild steel surface. Moreover, the images obtained from SEM analysis proved that the increase in the concentration of zinc nitrate resulted in the steel surface corrosion resistance increment so that with addition of 600 ppm zinc nitrate to the solution a uniform layer with less porosity was formed over the surface. These observations confirm the successful adsorption of inhibitor molecules on mild steel surface.

Keywords: Synergistic Effect, Carbon Steel, Corrosion, Green Inhibitor, Polarization, EIS, FT-IR, SEM

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