Steel corrosion lowering in front of the saline solution by a nitrogen-rich source of green inhibitors: Detailed surface, electrochemical and computational studies

This study aims at finding a plant possessing effective organic compounds to protect the low carbon steel (LCS) surface against corrosion in neutral chloride solutions. Former studies by biologists indicate the presence of effective nitrogen-based and alkaloid compounds in the structure of Peganum harmala (Called Esfand) seeds. Therefore, the inhibitive role of Esfand seed extract (ESE) on the corrosion mitigation of LCS substance in saline media was investigated by several analyses. Surface characterizations were performed by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), Ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), Grazing Incidence X-ray diffraction (GIXRD), atomic force microscope (AFM) and contact angle (CA) measurements. The inhibitive function of ESE in neutral chloride solutions at different contents was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization spectroscopy (PPS) techniques. Moreover, electronic/atomic level computations based on molecular dynamics (MD) associated with density functional theory (DFT) were utilized for exploring the surface adsorption capacity of extract constituents. The results of surface analyses indicate the formation of a hydrophilic high-volume film on the samples exposed to the electrolytes containing ESE. The presence of lots of effective functional groups from different classes as well as the construction of organic/ inorganic complexes was proved by UV-Vis, FT-IR, and GIXRD analyses. Electrochemical studies revealed the ESE effectiveness in the corrosion prevention of the metallic samples by an inhibition power of 93.2% at 1000 ppm ESE after 216 h. This is a highly acceptable and desirable level of inhibition for green inhibitors in saline solution as most of them are not effective compounds in this media. The investigation of the polarization curves manifested the mixed-type inhibition response of the ESE. MD simulations illustrated the adsorption of green molecules on the iron adsorbent supporting the experiments. (C) 2020 Elsevier Ltd. All rights reserved.