An enhancement on corrosion resistance of low carbon steel by a novel bio-inhibitor (leech extract) in the H2SO4 solution

Abstract In this research, to enhance the corrosion resistance of low carbon steel in the H2SO4 solution, the leech extract as a novel bio-inhibitor was utilized. Electrochemical tests were applied to investigate corrosion characteristics of steel in the corrosive acid solution. Moreover, the atomic force microscopy (AFM) and the field emission scanning electron microscopy (FE-SEM) techniques were performed for studying the morphology of corroded steel surfaces. Based on the polarization data, the inhibition efficiency raised from 75 to 91 % in the presence of the inhibitor with concentrations of 1 to 3 g/L. However, electrochemical impedance spectroscopy test results showed that such an increase was about 66 to 84%. When the test temperature increased to 40°C, the inhibition efficiency reduced from 91 to 44%. Polarization test results explained that the adsorption of leech extract molecules on metallic surfaces operated as a mixed inhibitor. In this situation, the measured activation energy increased from 65.28 to 152.93 kJ/mol.K. In addition, based on the obtained electrochemical data, leech extract molecules were adsorbed on steel surfaces through the Langmuir adsorption mechanism. Both FE-SEM and AFM micrographs from corroded metallic surfaces depicted that when the utilized bio-inhibitor was added to the H2SO4 solution a much smoother metal surface would be observed.