Corrosion inhibition performance of carbon steel in 1 N hydrochloric acid by an aqueous extract of Syzygium cumini Linn (SCL) plant leaves

Inhibition of corrosion of carbon steel in 1 N hydrochloric acid by an aqueous extract of Syzygium cumini Linn (SCL) plant leaves has been investigated by mass loss method. It is observed that as the concentration of the inhibitor increases the inhibition efficiency increases. The mechanistic aspects of corrosion resistance have been studied by potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). A maximum inhibition efficiency of 91.83% is achieved by this inhibitor system. Potentiodynamic polarization technique reveals that the inhibitor system functions as a mixed type of inhibitor, controlling anodic and cathodic reactions. It is noted that in presence of inhibitor, linear polarization resistance value increases, and corrosion current decreases. Electrochemical impedance studies reveal that a protective film (blanket effect) is formed on the metal surface, since in the presence of inhibitor system the charge transfer resistance value increases and double layer capacitance value decreases. This is due to adsorption of the molecules of the active ingredients of the extract on the metal surface. The inhibition efficiency increases owing to the adsorption of inhibitor molecules present in SCL plant leaves extract on the carbon steel surface. The maximum inhibition efficiency and the lower corrosion rate is obtained at high concentration 10% v/v for SCL plant leaves extract. Further increase in inhibitor concentration above 10%, the inhibition efficiency and corrosion rate almost remained constant. So, the 10% concentration is fixed as the maximum inhibition for the SCL plant leaves as corrosion inhibitor. This concentration corresponds to the attainment of a saturation value in surface coverage of carbon steel. The protective film formed over the carbon steel surface has been characterized by Fourier Transform infra-red spectroscopy. The surface morphology of the protective film of carbon steel immersed in hydrochloric acid in the absence and presence of inhibitor has been studied by Scanning electron microscopy. The elemental analysis of polished carbon steel, carbon steel immersed in hydrochloric acid and carbon steel immersed in hydrochloric acid with inhibitor has been analyzed by Energy dispersive analysis of X-rays. The outcome of the study can be used in pickling industry, wherein, hydrochloric acid is used to remove rust from carbon steel surface.