Corrosion inhibition by an aqueous extract of Ervatamia divaricata

• P. Shanthy¹, J.A. Thangakani², S. Karthika³, S.C. Joycee⁴, S. Rajendran⁴ and J. Jeyasundari⁵

¹ Department of Chemistry, Sri Meenakshi Government Arts College for Women(A), Maduari, India
² Department of Chemistry, The American College, Madurai, India
³ Department of chemistry, Kundavai Nacchiyaar Government Arts College for Women(A), Thanjavur, India
⁴ Corrosion Research Centre, Department of Chemistry, St Antony’s College of Arts and Science for Women, Dindigul 62405 India
⁵ PG Department of Chemistry, SVN College, Madurai, India

Abstract: The corrosion inhibition efficiency (IE) of Ervatamia divaricata extract (EDE) and Zn²⁺ system in controlling corrosion of carbon steel in ground water has been evaluated by weight loss method. Weight loss study reveals that the formulation consisting of 2.5 ml of EDE and 25 ppm Zn²⁺ has 98% inhibition efficiency in controlling corrosion of carbon steel immersed in ground water. Synergism parameters, calculated on the basis of blocking effect, suggest that a synergistic effect exists between EDE and Zn²⁺. FTIR study reveals that a protective film (blocking film) is formed on the metal surface consisting of Fe²⁺–Corynanthean complex and Zn(OH)₂. The anodic reaction is controlled by the Fe²⁺–Corynanthean complex formed on the anodic sites of the metal surface and the cathodic reaction is controlled by Zn(OH)₂ formed on the cathodic sites of the metal surface. The hardness of the metal surface containing the protective film is in between that of polished metal and that of the corroded metal in ground water. That is, the hardness of protective film is lower than that of polished metal but higher than that of corroded surface. This reveals that the protective film is very compact and close packed, due to blocking effect. Electrochemical studies such as polarisation study and AC impedance spectra have been employed to investigate the mechanistic aspects of the corrosion inhibition. In the presence of inhibitors, linear polarization resistance (LPR) increases, corrosion current decreases (I_corr), charge transfer resistance (R_t) increases, double layer capacitance (C_dl) decreases, impedance increases and phase angle increases. Adsorption isotherm study reveals that the adsorption of inhibitors on the metal surface obeys the Langmuir adsorption isotherm.

Keywords: corrosion inhibition, carbon steel, green inhibitor, environmentally friendly inhibitior, Ervatamia divaricata, electrochemical studies, hardness of metal surface

Int. J. Corros. Scale Inhib., 2021, 10, no. 1, 331-348 PDF (744 K)
doi: 10.17675/2305-6894-2021-10-1-19

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