Electrochemical and quantum chemical studies of new thiadiazole derivatives adsorption on mild steel in normal hydrochloric acid medium

In this work, a new class of thiadiazole derivatives, namely 3,5-bis(2-thienyl)-1,3,4-thiadiazole (2-TTH) and 3,5-bis(3-thienyl)-1,3,4-thiadiazole (3-TTH), have been studied as possible corrosion inhibitors for mild steel in molar hydrochloric acid (1 M HCl). Weight loss measurements, polarisation curves and AC impedance methods have been used. These studies have shown that the thiadiazole derivatives were very good inhibitors for mild steel in 1 M HCl. Comparison of results showed that 3-TTH was the best inhibitor. The potential of zero charge (PZC) of mild steel was studied by AC impedance method, and the mechanism of adsorption has been predicted. X-ray photoelectron spectroscopy surface analysis with thiadiazole derivatives shows that it chemisorbed at the mild steel/HCl interface. The adsorption of these inhibitors followed Langmuir's adsorption isotherm. The electronic properties of 2-TTH and 3-TTH, obtained using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies using the linear resistance model (LR). These inhibitors are considered as non-cytotoxic substances.