Inhibitive effect of an alcoholic extract of a seaweed Sargassum Muticum in controlling corrosion of mild steel in 0.5 N HCl

• V. Jeslina¹, S.J. Kirubavathy¹, A. Al-Hashem², S. Rajendran^3,4, C. Lacnjevac⁵ and R.M. Joany⁶

¹ PG and Research Department of Chemistry, PSGR Krishnammal College for Women, Coimbatore - 641 004, India
² Petroleum Research Centre, Kuwait Institute for Scientific Research, Kuwait
³ PG Department of Chemistry, Corrosion Research Centre St. Antony’s College of Arts and Sciences for Women Thamaraipadi, Dindigul – 624005, Tamil Nadu, India
⁴ Adjunct Professor, Pondicherry University, Puducherry, India
⁵ University of Belgrade, Faculty of Agriculture, Belgrade, Serbia
⁶ Department of ECE, Sathyabama University, Jeppiaar Nagar, Rajiv Gandhi Road, Chennai, Tamil Nadu – 600119, India

Abstract: The inhibitive effect of an alcoholic extract of a seaweed, namely, Sargassum Muticum, in controlling corrosion of mild steel in 0.5 N HCl has been evaluated by weight loss method (immersion period 1 day) and electrochemical techniques such as polarization study and AC impedance spectra. The protective film has been investigated by AFM and Vickers Hardness test. Weight loss method reveals that 500 ppm of inhibitor offers 99% inhibition efficiency to mild steel immersed in 0.5 N HCl. The adsorption of inhibitor molecules on the metal surface follows Langmuir adsorption isotherm. The R² value is very high, 0.998. Polarization study reveals that the corrosion potential is slightly shifted to anodic side. It is inferred that the inhibitor solution functions as mixed type corrosion inhibitor. In the presence of the inhibitor, the linear polarization resistance (LPR) increases and the corrosion current decreases. Because of the Blanket effect (formation of a protective film on the metal surface blocking the anodic sites and cathodic), electron transfer from the metal to the bulk of the solution is blocked. AC impedance spectra confirm the formation of a protective film on the metal surface. As the inhibitor concentration increases, the R_ct value increases and the double layer capacitance (C_dl) decreases, the impedance increases and the phase angle increases due to the blocking effect on the metal surface. It is found to be a monolayer of protective film. The Vickers hardness of the inhibited metal surface is lower than that of polished metal but higher than that of corroded surface. The average roughness, RMS roughness and maximum peak-to-valley height of inhibited metal surface are lower than those of corroded metal surface but higher than those of polished metal surface. The outcome of the study may be used in pickling industry where HCl is used to remove rust and at the same time metal surface is protected.

Keywords: corrosion inhibition, green inhibition, acid medium, Sargassum Muticum, Vickers hardness, AFM, adsorption isotherm, electrochemical studies

Int. J. Corros. Scale Inhib., 2021, 10, no. 4, 1454-1473
doi: 10.17675/2305-6894-2021-10-4-6

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