Polyhydrazide Incorporated with Thiadiazole Moiety as Novel and Effective Corrosion Inhibitor for C-Steel in Pickling Solutions of HCl and H2SO4

Abstract

In this paper polyhydrazide incorporated with thiadiazole moiety (S5) was prepared and its chemical configuration was confirmed by spectroscopic methods (FTIR, 1H NMR, and 13C NMR). The inhibitive action of S5 polymer and its monomer 2,5-dihydrazinyl-1,3,4-thiadiazole (M1) on the C-steel corrosion in pickling acids solution was investigated by weight loss, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements. PDP method exhibited that the investigated polymer is mixed-type corrosion inhibitor in both acids (HCl and H2SO4). The data revealed that S5 compound is a good inhibitor for Csteel in studied acids, and protection efficiency (P%) follows this sequence: H2SO4<HCl. Also, it was found that, the P% of the S5 polymer is higher than that obtained for its monomer (M1). Adsorption of the titled polymer obeyed the isotherm of Langmuir and involves both chemical and physical adsorptions. Scanning electron microscopy (SEM) investigations established the protective layer formation from the studied polymer on the metal substrate and shield it from direct Cl- and/ or $$\rm{SO}_4^2-$$ attack.