Gravimetric, electrochemical and surface studies on the anticorrosive properties of 1-(2-pyridyl)-2-thiourea and 2-(imidazol-2-yl)-pyridine for mild steel in hydrochloric acid

Abstract

1-(2-Pyridyl)-2-thiourea (TP) and 2-(imidazol-2-yl)-pyridine (IP) are described here for the first time as inhibitors of mild steel corrosion in acidic medium based on investigations such as weight loss tests, potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The experimental results revealed that 1-(2-pyridyl)-2-thiourea and 2-(imidazol-2-yl)-pyridine are effective corrosion inhibitors for mild steel in acidic medium, and their maximum corrosion inhibition efficiencies at 4 × 10⁻⁴ M are 93.57% and 96.66%, respectively. TP and IP are determined as mixed-type inhibitors based on polarization studies, and their adsorption on the mild steel surface follows the Langmuir adsorption isotherm and physical adsorption is dominant. The formation and characteristics of the protective layer on the steel surface were verified by scanning electrochemical microscopy (SECM), UV-visible spectroscopy, FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS) methods. Besides, the correlation between the inhibition efficiency and the molecular structure of inhibitors was theoretically studied via quantum chemical calculations.