Rezumat
CZU 621.35
A comparative study of Fe and Cr complexes with a Schiff-base ligand (1-[(2-hydroxyethyl)amino]-2-(salicylideneamino)ethane) as inhibitors for carbon steel corrosion in 0.5M HCl solution at 25°C was carried out. Corrosion measurements based on the weight loss method, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS) indicate that Fe complex, in most cases, accelerates carbon steel corrosion in HCl while Cr complex act as moderately inhibitor. The UV-visible and the attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) studies of the electrode surface confirmed existence of an adsorbed film of the complexes on the electrode surface. Adsorption of Cr complex obeys the Langmuir adsorption isotherm with a very low value of free energy of adsorption ΔG° (physisorption). Cr complex acts as mixed type inhibitor, with the dominanting effect on the anodic dissolution of iron. The mechanism of adsorption is discussed and it is concluded that the adsorbed chloride ions on the metal surface could be stabilized in their anionic form by hydrogen bonding of oxygen and nitrogen atoms in the tail of the complexes, like a crab-claw. The accelerating properties of Fe complex could be due to the formation of non adherent and/or soluble complex that is readily removed from the metal surface.
Keywords: acid corrosion inhibitors, adsorption isotherms, Schiff-base complex, carbon steel.