Inhibition action of triazolyl blue tetrazolium bromide on cold rolled steel corrosion in three chlorinated acetic acids

© 2018 Elsevier B.V. The inhibition effect of triazolyl blue tetrazolium bromide (TBTB) on cold rolled steel (CRS) in three chlorinated acetic acids of monochloroacetic acid (ClCH2COOH), dichloroacetic acid (Cl2CHCOOH) and trichloroacetic acid (Cl3CCOOH) was studied by weight loss, potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) methods. Meanwhile, the adsorption mechanism of TBT+ (organic part of TBTB) was theoretically investigated by quantum chemical calculation and molecular dynamics (MD) simulations. The results show that TBTB acts as a good inhibitor, and inhibition efficiency in three chlorinated acetic acids follows the order: ClCH2COOH < Cl2CHCOOH < Cl3CCOOH. The maximum inhibition efficiency of 1.0 mM TBTB from weight loss method is 85.8% in ClCH2COOH; 91.7% in Cl2CHCOOH; and 95.5% in Cl3CCOOH. The adsorption of TBTB on CRS surface obeys Langmuir isotherm, and the adsorption free energy (ΔG0) is about −34 kJ mol−1. In each chlorinated acetic acid solution, TBTB behaves as a mixed inhibitor, and the presence of TBTB shifts the both anodic and cathodic curves to lower current densities. With the addition of TBTB, the corrosion potential almost does not alter in ClCH2COOH, while becomes more positive in Cl2CHCOOH, and moves negative position in Cl3CCOOH. EIS exhibits one large depressed capacitive loop at high frequencies followed by a small inductive section at low frequencies. In the presence of TBTB, the charge transfer resistance increases, while both constant phase element and double layer capacitance decreases. SEM micrographs reveal that the corrosion of CRS can be efficiently retarded by TBTB. TBT+ can be further protonated by H+ in acid solution to form TBTH2+. Both TBTH2+ and TBT+ could easily physical adsorb on steel surface owing to high dipole moment values, and TBTH2+ exhibits stronger physisorption than TBT+. The electron densities of both HOMO and LUMO are localized principally on tetrazole and thiazole rings, which are chemical adsorption sites. TBTH2+ strengthens accepting electrons while weakens donating electrons as compared with TBT+. Both TBT+ and TBTH2+ adsorb onto Fe (001) surface with nearly flat orientation mode, and the adsorption energy of TBT+ is a little higher than that of TBTH2+.