Corrosion inhibition of mild steel in NH4Cl + NaOH environment containing Azadirachta indica leaf extract

• P. Baitule and R. Manivannan

Department of Chemical Engineering, National Institute of Technology Raipur, Chhattisgarh 492010, India

Abstract: In this work, corrosion suppression of mild steel (MS) in the presence of 1 wt.% NH₄Cl + 1 wt.% NaOH solution using Azadirachta indica (neem) leaf extract was investigated. Weight loss studies of MS coupons immersed in different alkali concentrations, various immersion periods, and at various temperatures were carried out with and without inhibitor. The results showed that the effectiveness of the suppression increases with an increase in inhibitor concentration and was found to be a maximum of ~82% at 1000 ppm. Thermodynamic parameters were computed, including activation energy, enthalpy, and entropy (ΔS_a). A decrease in the activation energy (E_a) confirms that the corrosion inhibition (CI) process is physisorption and an enthalpy (ΔH_a) value of 66 kJ·mol^–1 suggests that the inhibition process is endothermic. Among all the isotherms studied in this work, Langmuir adsorption isotherm was best fitted. Tafel plots showed that the corrosion current density (icorr) value goes down with an increase in neem leaf extract (NLE) which corroborates a decline in corrosion rate (CR) and an increase in inhibition efficiency (IETafel). SEM pictures show that the protective coating on the metal has formed. Fe₂O₃, a stable oxide coating was established on the MS surface, lowering the CR. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis were conducted to understand the CI behaviour of NLE on MS. The phytochemical compounds in the NLE were detected, and the results of the metal coupon immersed in the extract were shifted, confirming an interaction between MS and extract that caused corrosion to be suppressed. According to XPS results, inhibitor molecules protect MS from oxidation, preventing over-oxidation of MS. NLE’s anti-corrosion action is successfully supported by the finding that an inhibitor component creates a complex and thus hinders the corrosion of MS.

Keywords: adsorption isotherm, Tafel plot, EIS, inhibition mechanism, FTIR, SEM

Int. J. Corros. Scale Inhib., 2024, 13, no. 1, 121-143
doi: 10.17675/2305-6894-2024-13-1-7

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