Synergistic inhibition behavior of sodium tungstate and penicillin G as an eco-friendly inhibitor on pitting corrosion of 304 stainless steel in NaCl solution using Design of Experiment

In this study the synergistic behavior of sodium tungstate and penicillin G as an environmental-friendly co-inhibitor on pitting corrosion of 304 stainless steel in 3.5 wt% NaCl solution has been investigated. The simultaneous effect of temperature and inhibitor on inhibition efficiency has been evaluated by employing Design of Experiment technique according to Central Composite Design method. The temperature and concentration of inhibitors were selected as independent factors, while the extent of passive region and inhibition efficiency were considered as the responses of independent factors. Cyclic potentiodynamic polarization and electrochemical impedance spectroscopy were employed to determine the responses experimentally. The surface morphology and chemical composition of surface film were characterized by a Scanning Electron Microscope. The electrochemical measurements showed that increase in the concentration of penicillin G up to 50 ppm as co-inhibitor in the presence of 2.5 mM sodium tungstate resulted in the highest possible extent of passive region and inhibition efficiency. The increase in the extent of passive region and inhibition efficiency due to addition of penicillin G as co-inhibitor to sodium tungstate showed the synergistic behavior of the mixed inhibitors in controlling pitting corrosion of 304 stainless steel. It was revealed that the extent of passive region and inhibition efficiency decrease by increase in temperature of the solution due to increase in the kinetics of corrosion reactions and desorption of inhibitor from surface. The SEM observations indicated that the mixed inhibitors could provide a smooth and uniform surface due to formation of a protective film. (C) 2019 Elsevier B.V. All rights reserved.