Eco-friendly strategy for enhancing the surface properties of C38 steel using quinazoline-based inhibitors: Theoretical and experimental approach

While organic substances can significantly enhance engineering by protecting delicate metals from corrosive environments, the relationship between these substances and the processes involved in creating effective protective films is still not fully understood. Therefore, newly synthesized quinazoline compounds known as quinazolin-4(3H)-one (QZO) and 7-chloroquinazolin-4(3H)-one (CZO) were used as environmentally friendly inhibitors for C38 steel in a 15 % HCl solution. The goal was to manage the corrosion kinetics and investigate how the chloride atom influenced its interaction with the metal surface. Firstly Computational calculations based on density functional theory (DFT), density functional tight-binding (DFTB) and molecular dynamics (MD) simulations, were conducted to predict the interfacial mechanisms and adsorption behaviour of QZO and CZO on the metal surface. DFTB calculations indicate that CZO and QZO inhibitors adsorb parallel to the metal surface via heteroatoms and aromatic π-electrons, forming a robust protective layer that effectively mitigates corrosive attacks. Electrochemical corrosion assessments revealed enhanced stability against chloride ions, with the inhibitors facilitating the formation of a hybrid protective film. At a concentration of 10⁻³ M, the corrosion current densities for QZO and CZO were recorded at 60 × 10⁻⁶ A/cm² and 150 × 10⁻⁶ A/cm², respectively, while their corrosion resistance reached 573 Ω·cm² and 135 Ω·cm². Additionally, long-term immersion studies demonstrated exceptional stability, with a charge transfer resistance of 103 Ω·cm² after 48 h Furthermore, the electrochemical results revealed that QZO and CZO exhibited mixed-type characteristics, inhibiting cathodic and anodic reactions. Notably, QZO molecules demonstrated the highest inhibition performance compared to CZO, achieving a 96 % inhibition rate at a concentration of 10–⁻³ M. This inhibition behaviour can be attributed to the optimal arrangement of these molecules on the steel surface, effectively covering a large area. This enhanced performance is linked to the chloride atoms and the cyclic ring structure, which improves surface coverage. Additionally, the interaction mode between C38 steel and the inhibitors conformed to the Langmuir isotherm and involved physical-chemical interactions. SEM analysis further confirmed the presence of a protective layer, revealing numerous clusters on the surfaces of samples treated with QZO molecules. These results highlight the inhibitors’ potential for durable corrosion protection in harsh environments.