Synthesis of Di- and Tricationic Surfactants and Comparison of Their Activity on Oxidation of Metal in HCl Media

In this study, two surfactants with the same long chain were synthesized. One shows dicationic and the other tricationic properties. Various spectroscopic methods such as FT-IR, ¹H NMR and ¹³C NMR were used to confirm the structures of the synthesized surfactants. The inhibition activities of two synthesized surfactants against mild steel corrosion in 1.0 M HCl solution were determined using the weight loss method. The 24-h corrosion tests on metal coupons immersed in acidic solutions were carried out using different inhibitor concentrations and similar and successful inhibition was obtained for both surfactants. Current density was determined by potentiodynamic polarization at a single inhibitor concentration to compare with the inhibition efficiency results obtained by decrease in weight method. Based on the current density, the inhibition efficiencies of the surfactants were calculated by Tafel extrapolation method. The inhibition efficiency results obtained by both weight loss and Tafel method were close and consistent. According to both methods, the corrosion inhibition of dicationic surfactant was slightly better than that of tricationic surfactant. By determining the critical micelle concentration for the two surfactants, some physicochemical parameters such as surface tensions and free energy of micelle formation at this concentration were calculated and correlated with their corrosion inhibitory activity. Scanning electron microscopy was used to ascertain the surface roughness conditions of metals submerged in an acidic solution, thus visually proving that surfactants protect the metal surface from corrosion.