Enhanced corrosion inhibition effect of tannic acid in the presence of gallic acid at mild steel/HCl acid solution interface

By I.B. Obot and A. Madhankumar
Published in Journal of Industrial and Engineering Chemistry NULL 2015

Abstract

The corrosion inhibition behaviour of tannic acid (TA), gallic acid (GA) and their blends on mild steel in 1 M \HCl\ solution was studied via electrochemical methods, namely, polarization (Tafel plots) and electrochemical impedance spectroscopy (EIS). The surface morphology of mild steel in 1 M HCl, \TA\ alone, and in combination with \GA\ was elucidated using scanning electron microscopy (SEM). The results show that \TA\ can protect mild steel from acid corrosion better than GA. However, inhibition effect of \TA\ can be enhanced by its combination with GA. The adsorption behaviour of \TA\ against steel corrosion obeyed Langmuir adsorption isotherm. Furthermore, polarization results suggest that \TA\ and \GA\ blends behaves as mixed-type inhibitor of predominant anodic effect. \EIS\ results reveal that the charge transfer resistance value of the steel inhibited by \TA\ in combination with \GA\ is significantly higher than that of steel inhibited by \TA\ alone. The \SEM\ images confirmed the enhanced film formation on the steel surface in the presence of \TA\ and \GA\ blended in the ratio 9:1 when compared with \TA\ alone. Quantum chemical calculations have been used to provide insights into the mechanism of interaction of \TA\ and \GA\ on mild steel.

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