New Heterocyclic Compound as Carbon Steel Corrosion Inhibitor in 1 M H₂SO₄, High Efficiency at Low Concentration: Experimental and Theoretical Studies

Abstract

A new aromatic Schiff base with azo linkage has been synthesized and characterized by FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopy. The new compound 2-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)-4-(p-tolyldiazenyl)phenol (5, denoted as AT) was tested as a carbon steel corrosion inhibitor in 1 M H₂SO_4. The presence of AT in 0.04 mM concentration at 303 K achieved excellent inhibition efficiency values, 96.6 and 97.4% by potentiodynamic polarization and weight loss measurements, respectively. The adsorption process of AT on carbon steel surface was found to obey Langmuir adsorption isotherm with the highest K_ads value 476,190 M⁻¹ at 313 K, and ΔG values −25.53, −26.49, −25.97, and −25.78) kJ mol⁻¹ over the studied range of temperatures 303–333 K, indicating the spontaneous formation of stable protection film through a strong adsorption process. Density function theory (DFT) studies were employed for further investigations about the nature of the interaction between the molecules of AT (both of its tautomers) and metal surface. SEM and AFM analysis were used to confirm the inhibition by comparing the morphology of the corroded surface with the inhibited one.

Keywords:

• Thiadiazole
• azo
• Schiff base
• carbon steel
• organic corrosion inhibitors
• acidic corrosion

Acknowledgments

The authors would like to thank the University of Babylon and the University of Karbala for their financial support. Dr. Yusuf Sert is grateful to Prof. Fatih Ucun from Süleyman Demirel University for offering access to workstations and software used in the theoretical studies.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Author contributions

Mahmood A. Albo Hay Allah: methodology, investigation, and validation. Asim A. Balakit: conceptualization, investigation, validation, writing—original draft, writing—review and editing, and supervision. Hamida Edan Salman: conceptualization, investigation, validation, and supervision. Ali Ahmed Abdulridha: methodology, investigation, validation, writing—original draft, and writing—review and editing. Yusuf Sert: methodology, software, writing—original draft, and writing—review and editing.