Inhibition behavior of imidazoline phosphate compound inhibitor on Q235 steel in hydrochloric acid medium

The inhibitive effect on Q235 steel and the adsorption behavior of a compound inhibitor, including imidazoline phosphate (IPI) and potassium iodide (KI), were studied in 1 mol/L hydrochloric acid (HCl) solution using the weight-loss method, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Results showed that the inhibition efficiency increased with an increase in inhibitor concentration, and temperature had no significant effect on inhibition efficiency. The compound inhibitor was a mixed-type inhibitor that mainly inhibits cathodic processes. The best inhibition efficiency was obtained at an immersion time of 120 h. The adsorption of the compound inhibitor on Q235 steel could befitted to a Langmuir isotherm and the values of the adsorption free energy ΔG _ads are close to -40 kJ/mol over the studied temperature range. The adsorption process is a spontaneous chemical adsorption.