Effect of some thiophene derivatives on the electrochemical behavior of AISI 316 austenitic stainless steel in acidic solutions containing chloride ions: I. Molecular structure and inhibition efficiency relationship

The electrochemical behavior of austenitic stainless steel (AISI 316) was studied in an acid medium that contains chloride ions in absence and presence of some thiophene derivatives. The corrosion rate as well as pit growth of the steel was inhibited variably with each of the sulfur-containing compound present in the corroding medium. The thiophene derivatives studied were 2-acetyl thiophene (AcT), 2-thiophene carboxylic acid (TCA), 3-thiophene carboxyaldehyde (TCAL) and 2-thiophene carboxylic hydrazide (TCH). Electrochemical techniques such as potentiodynamic polarization, Tafel experiments, polarization resistance and electrochemical impedance spectroscopy were used to investigate the electrochemical behavior of the steel. The results showed distinct effects for the different thiophene derivatives used that depended on the molecular structure and the electron density of the sulfur atom of the thiophene ring. The order of inhibition efficiency was TCH > TCA > TCAL > AcT. It was also concluded that the inhibitors studied were of the mixed type. This conclusion was realized by comparing the change in the values of the anodic and cathodic Tafel slopes. Inhibition efficiencies of ca. 97% were achieved using these inhibitors in 0.5 M H2SO4.