The inhibition of CO2 corrosion of L360 mild steel in 3.5% NaCl solution by imidazoline derivatives

• A.I. Obike^1,2,3, P.C. Okafor², K.J. Uwakwe², X. Jiang³ and D. Qu³

¹ Department of Pure & Industrial Chemistry, Abia State University, Uturu, Abia State, Nigeria
² Corrosion and Electrochemistry Research Group, Department of Pure & Applied Chemistry, University of Calabar, Calabar, Nigeria
³ SINOPEC Research Institute of Safety Engineering, 218, Yan'an 3rd RD, Qingdao, P.R. China, 266071

Abstract: [2-(2-Henicos-10-enyl-4,5-dihydro-imidazol-1-yl)-ethyl]-methylamine (HDM), 2-(2-henicos-10-enyl-4,5-dihydro-imidazol-1-yl)-ethanol (HDE) and 2-henicos-10-enyl-4,5-dihydro-1H-imidazole (HDI) were synthesized using the solvent free microwave assisted organic synthesis method and characterized by FT-IR. The corrosion inhibition properties of these compounds on mild steel L360 in 3.5% NaCl solution were investigated by weight loss, potentiodynamic polarization, electrochemical impedance and scanning electron microscopic techniques. The synthesized inhibitors were tested at 60°C and 80°C with concentrations of 10, 50, 100, 200 and 300 ppm, respectively. The results from the study showed that the inhibition efficiency increased with increase in the concentration of the inhibitor to a maximum and decreased with rise in temperature. An adherent layer of inhibitor molecules on the surface is proposed to account for their inhibitive action in which the organic molecules adsorb on the active anodic and cathodic sites following Langmuir isotherm. The effectiveness of these inhibitors has been correlated to their chemical structures and were in the order of HDM > HDE > HDI. The values of activation energy, free energy of adsorption and heat of adsorption were also calculated to elaborate the mechanism of corrosion inhibition. The values obtained from the heat of adsorption (Q_ads) for the three inhibitors studied (HDM, HDE and HDI) are –58.53 kJ mol^–1, –103.27 kJ mol^–1 and –133.67 kJ mol^–1, respectively. These negative values indicate that the adsorption of the inhibitors on the mild steel is exothermic signifying physical adsorption. The potentiodynamic polarization data show that the compounds studied are mixed type inhibitors. The surface characteristics of inhibited and uninhibited metal samples were investigated by scanning electron microscopy (SEM).

Keywords: corrosion, corrosion inhibition, imidazoline derivative, mild steel, adsorption

Int. J. Corros. Scale Inhib., 2018, 7, no. 3, 318-330 PDF (615 K)
doi: 10.17675/2305-6894-2018-7-3-3

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