In this investigation, an oxadiazole namely 5-(4-(1H-pyrrol-1-yl)phenyl)-2-mercapto-1,3,4-oxadiazole (PMO), was synthesized and explored as an inhibitor against the corrosion of mild steel in 1.0 M hydrochloric acid environment at various solution temperature 303-333 K. gravimetric, and microscopic techniques, namely, weight loss (WL), and scanning electron microscopy (SEM), have been used to evaluate the inhibitive performance of the tested PMO. The results of the WL method displayed that the inhibition efficiency (%IE) was found to increase with the inhibitor concentration, while it reduced with increasing temperature. Furthermore, the WL results reveal that PMO inhibits corrosion display an IE of 95% at the highest concentration of 0.005 M. The SEM images of the mild steel surface coupon after adding PMO revealed a wide coverage of PMO molecules on the mild steel surface. Hence, the high inhibiting efficiency acquired by the tested inhibitor was explained by the strong adsorption of PMO molecules on the surface of mild steel. A protective layer has been constructed and it separating the mild steel surface from the hydrochloric acid solution, and such adsorption was found to obey Langmuir adsorption isotherm. Moreover, the thermodynamic parameters suggested that the adsorption nature of PMO molecules on the coupon surface was chemo-physisorption. Quantum chemical calculations were conducted by density functional theory (DFT) which help correlate the methodological findings with the theoretical investigations. The mechanisms of PMO molecules as corrosion inhibitor for mild steel surface in the corrosive environment was also discussed.
A corrosion inhibitor namely N′-(4-hydroxy-3-methoxybenzylidene) nicotinohydrazide was synthesized and the inhibition efficiency of the investigated inhibitor toward the mild steel corrosion in 1 M HCl was studied. The anticorrosion effect has been investigated by weight loss (WL) techniques and electrochemical analysis includes potentiodynamic polarization (PDP) studies and electrochemical impedance spectroscopy (EIS). The current investigation has demonstrated that the tested inhibitor is suitable in corrosive environment and the inhibitive efficacy up to 97% in 1 M HCl. PDP measurements showed that the nicotinohydrazide is a mixed type inhibitor. EIS measurements showed that an increase in the inhibitory concentration leads to an increase in the charge transfer resistance (Rct) and a decrease in the double-layer capacitance (Cdl). Experimental results for the inhibitory performance of WL methods and electrochemical techniques (PDP and EIS) are in good agreement. The tested inhibitor molecules adsorbed on the surface of mild steel in a hydrochloric acid solution followed Langmuir’s isothermal adsorption. Quantum chemical parameters based on density function theory (DFT) techniques were conducted on oxygen/nitrogen-bearing heterocyclic molecule employed as a corrosion inhibitor for mild steel in HCl to evaluate the correlation between the inhibitor structure and inhibitory performance. The parameters including the energy gap (ΔE), dipole moment (μ), electronegativity (χ), electron affinity (A), global hardness (η), softness (σ), ionization potential (I), the fraction of electrons transferred (ΔN), the highest occupied molecular orbital energy (EHOMO), and the lowest unoccupied molecular orbital energy (ELUMO) were also calculated and were in good agreement with the experimental results.
There is growing interest in using corrosion inhibitors and protective treatments to limit the degradation of mild steel, leading to the development of numerous Schiff bases as cutting-edge inhibitors. In this study, the effectiveness of a Schiff base, 3-((5-mercapto-1,3,4-thiadiazol-2-yl)imino)indolin-2-one (MTIO), to prevent mild steel corrosion in HCl was investigated using weight loss measurements, potentiodynamic polarization measurements, electrochemical impedance spectroscopy techniques, and surface characterization. The experimental results showed that 0.5 mM MTIO exhibited a satisfactory inhibitor efficiency of 96.9% at 303 K. The MTIO molecules physically and chemically adsorbed onto the mild steel surface following the Langmuir model, forming a compact protective film attributed to the presence of a thiazole ring in the MTIO structure. Theoretical calculations were combined with experimental techniques to investigate the anticorrosion performance and mechanism of inhibition.
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