Abstract
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.
Highlights
Corrosion damage results in high costs for inspection, repair, and replacement, but it poses a public safety risk, necessitating the production of new substances that function as corrosion inhibitors, especially in corrosive environments [1]
The experimental findings confirmed that PMO acts as an excellent inhibitor for mild steel corrosion in a 1 M hydrochloric acid environment
The inhibition efficiency was increased with the PMO concentrations, while it reduced with increasing temperature
Summary
Corrosion damage results in high costs for inspection, repair, and replacement, but it poses a public safety risk, necessitating the production of new substances that function as corrosion inhibitors, especially in corrosive environments [1]. Organic compounds with high electron density heteroatoms, such as phosphorus, sulfur, oxygen, and nitrogen, as well as those with multiple bonds that serve as adsorption centers, are effective corrosion inhibitors [4,5,6,7]. Oxadiazole derivatives have a unique affinity for preventing metal corrosion in acid solutions [8,9]. Because of their high chemical activity and low toxicity, these heteroatom-rich compounds can be considered environmentally friendly inhibitors [10]. The current investigation intended to synthesize an oxadiazole derivative and investigate it performance as a corrosion inhibitor for mild steel in 1 M HCl solution utilizing weight loss and scanning electron microscopy techniques. To realize the relation between the structure of PMO molecule and its inhibition performance, theoretical parameters namely energy gap (ΔE), highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), global hardness (η), softness (σ), absolute electronegativity (χ) and the fraction of electrons transferred (ΔN) and the dipole moments (μ) were calculated and investigated
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