Abstract:

The inhibition effect of synthesized diethyl 3,4-bis(4-methoxybenzylideneamino) thieno[2,3-b] thiophene-2,5-dicarboxylate (Inh I) and diethyl 3,4-bis(benzylideneamino) thieno[2,3-b] thiophene-2,5-dicarboxylate (Inh II), on corrosion of mild steel in 15% HCl solution was investigated using weight loss measurements, electrochemical polarization, and electrochemical impedance spectroscopy techniques. The experimental results show that the inhibition efficiency of studied inhibitors increased with the increase of inhibitors concentration but decreased with the increase of temperature. Corrosion inhibition efficiencies of 94.5% and 92.1% were obtained with 250 ppm of Inh I and Inh II at 303 K, respectively. The potentiodynamic polarization measurements indicate that the studied inhibitors act as mixed inhibitor. The thermodynamic parameters of the corrosion and adsorption processes were calculated and evaluated. The adsorption of these inhibitors was found to obey Langmuir adsorption isotherm. Scanning electron microscopy was used to characterize the surface morphology of the mild steel specimens in presence and absence of inhibitors. The mechanism of the inhibition process was discussed in the light of the chemical structure and quantum-chemical calculations of the investigated inhibitors.

Key words: Mild steel, Corrosion, Polarization, EIS, Acid inhibition