Abstract: The inhibition effect of nitrotetrazolium blue chloride (NTBC) on the corrosion of cold rolled steel (CRS) in 1.0-5.0 mol·L^-1 HCl solution was investigated by weight loss method, potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that NTBC is a good inhibitor for CRS in 1.0 mol·L^-1 HCl solution and the adsorption of NTBC on the CRS surface obeys the Langmuir adsorption isotherm. Inhibition efficiency increases with inhibitor concentration while it decreases with hydrochloric acid concentration and temperature. The adsorption thermodynamic parameters (adsorption free energy ΔG⁰, adsorption enthalpy ΔH⁰, adsorption entropy ΔS⁰) and corrosion kinetic parameters (corrosion rate constant k, kinetic reaction constant B) were also calculated. Based on these parameters the inhibitive mechanism is discussed. Potentiodynamic polarization curves show that NTBC acts a mixed-type inhibitor. EIS spectra exhibit one capacitive loop at high frequency and this is followed by a small inductive loop at low frequency, and the charge transfer resistance increases with inhibitor concentrations. SEM clearly shows that the addition of NTBC can drastically retard the corrosion of steel in hydrochloric acid media.

Key words: Corrosion inhibitor, Nitrotetrazolium blue chloride, Steel, Hydrochloric acid, Adsorption