This research aimed to develop a better understanding of the corrosion inhibition of the mild steel in acidic medium by new organic molecules. For this purpose, two new compounds namely, 2,3-dihydrobenzo[4,5]imidazo[2,1-b]thiazole (2-BIT) and 3,4-dihydro-2H-benzo[4,5]imidazo[2,1-b]thiazole (3-BIT) were synthesized and evaluated for mild steel (MS) corrosion in HCl. Analyses were carried out using weight loss measurements, electrochemical techniques, and scanning electron microscope (SEM). The adsorption of inhibitors onto the steel surface follows the Langmuir adsorption model. Generally, results showed that the corrosion inhibition efficiency of the investigated molecules was found to increase with increased concentration of inhibitors. Electrochemical tests, i.e., electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques, showed that the addition of our investigated inhibitors decreases the dissolution of the metal and generally act as mixed-type inhibitors. In addition, the influence of temperature (from 303 to 333 K) on the corrosion inhibition was studied, and the results demonstrated that with an increase in temperature, the inhibition efficiency decrease. SEM results confirmed that the inhibition process is due to a protective film that prevents corrosion. Similarly, the results showed that the inhibitory efficiencies reach 93% at 5 × 10⁻³ M in the case of inhibitor 3-BIT. These results revealed that this compound could effectively control and reduce the corrosion rate of mild steel in the corrosion test solution.

In the present study, the inhibition performance of two synthesized hydrazone derivatives (HDZs), namely, (E)-N′-(2,4-dimethoxybenzylidene)-2-(6-methoxynaphthalen-2-yl) propanehydrazide (HYD-1) and N′-cyclohexylidene-2-(6-methoxynaphthalen-2-yl) propanehydrazide (HYD-2) on mild steel (MS) in 1.0 M HCl was investigated using weight loss measurements, electrochemical techniques, and scanning electron microscope (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX). The experimental data suggested that the hydrazone derivatives exhibited a high inhibition performance, which increases with increasing their concentrations. HYD-1 and HYD-2 presented maximum inhibition efficiencies of 96% and 84%, respectively, at an optimal concentration of 5 × 10^–3 M. The principal observations that resulted from electrochemical studies are that HYDs affected both anodic and cathodic reactions (mixed inhibitors). Their adsorption, which is a combination of chemisorption and physisorption, obeyed the Langmuir isotherm model. Furthermore, the temperature effect was carried out at various temperatures ranging from 303 to 333 K to verify the corrosion inhibition performance of HYD-1 at higher temperatures. Moreover, SEM-EDX analysis confirmed that HYDs can ensure remarkable prevention against corrosion through the adsorption onto the metal surface.

The iminium surfactant p-benzylidene benzyldodecyl iminium chloride was synthesized, characterized and evaluated as a novel corrosion inhibitor for plain carbon steel in 1 M HCl solution at 30, 40, 50 and 60 °C using gravimetric analysis, spectrophotometric analysis of iron ions, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and density functional theory (DFT). The evaluated compound acted as an efficient corrosion inhibitor for plain carbon steel in 1 M HCl solution. The inhibition efficiency of the compound increased with an increase in concentration and solution temperature. The iminium surfactant gets adsorbed onto the plain carbon steel surface via mixed types of adsorption with predominantly chemisorption. The adsorption of the inhibitor was found to follow the Langmuir adsorption isotherm. The surface morphology of corroded plain carbon steel in uninhibited and inhibited acid, as investigated by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX), clearly showed different results. The different quantum chemical parameters were used to correlate the inhibition efficiency of the inhibitor and its molecular structure.

There has been substantial research undertaken on the role of green synthesized corrosion inhibitors as a substantial approach to inhibit the corrosion of metals and their alloys in acidic environments. Herein, electrochemical studies, surface characterization, and theoretical modeling were adopted to investigate the corrosion inhibition proprieties of novel synthesized quinoxaline derivatives bearing 8-Hydroxyquinoline, namely 1-((8-hydroxyquinolin-5-yl) methyl)-3,6-dimethylquinoxalin-2(1H)-one (Q1) and 1-((8-hydroxyquinolin-5-yl)methyl) quinoxalin-2(1H)-one (Q2) on mild steel corrosion in 1 mol/L HCl solution. The principal finding of this research was that both inhibitors acted as good corrosion inhibitors with Q1 having the highest performance (96% at 5 × 10⁻³ mol/L). Electrochemical results obtained via potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques demonstrated that quinoxaline compounds belonged to mixed-type inhibitors; their presence significantly increased the polarization resistance, preventing simultaneously anodic and cathodic reactions. Further, experimental results provided preliminary insights about the interactions mode between studied molecules and the mild steel surface, which followed the Langmuir adsorption model, and physical and chemical interactions assisted their inhibition mechanism. Besides, SEM analyses confirmed the existence of protective film on the metal surface after the addition of 5 × 10⁻³ mol/L of quinoxalines. In addition, the temperature and immersion time effects on inhibition performances of quinoxalines were investigated to evaluate their performances in different operating conditions. Besides, Density Functional Theory (DFT) and molecular dynamics (MD) simulations were carried out to explore the most reactive sites of quinoxaline inhibitors and their interaction mechanism. Theoretical results revealed that the inhibitor molecule with additional electron-donating functional group strongly interacted with the steel surface.