Electrochemical behaviour of N,S-containing corrosion inhibitor for C38 Steel in molar HCl

The influence of 2-phenylthieno (3,2-b) quinoxaline (P4) on the corrosion of steel in 1M HCl solution has been investigated by potentiodynamic polarisation and impedance spectroscopy (EIS) methods. The inhibiting action increases with the concentration of P4. The highest efficiency 95 % is obtained at the 5x10-4 M P4. We note good agreement between potentiodynamic polarisation and EIS methods. Polarisation measurements show also that P4 acts as a mixed inhibitor. The cathodic curves indicate that the reduction of proton at the steel surface happens with an activating mechanism.