Corrosion inhibition mechanism of vitamins on steel bars in chloride environments: Experimental analysis and quantum chemical calculation

The inhibition potency of thiamine (VB1), nicotinic acid (VB3), pyridoxine (VB6) and ascorbic acid (VC) against the reinforcement corrosion and their adsorption behavior on the surface of steel bars in chloride environments are studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. Based on the density functional theory (DFT), quantum chemical calculation is also performed to further reveal the corrosion inhibition mechanism of vitamins at the electronic level. The results indicate that these four kinds of vitamins are proven to be potentially applied as corrosion inhibitors to effectively reduce the risk of chloride-induced reinforcement corrosion in a simulated concrete pore solution with 0.05 M NaCl, and VB6 shows the best corrosion inhibition effect since the bonding stability between its highest occupied molecular orbital (HOMO) and the 3d-orbital of iron is the strongest among these vitamins. Under the experimental conditions of this study, there is a specific concentration value for each vitamin to achieve the optimum corrosion inhibition efficiency (IE%). At this time, VB1 and VB3 act as anodic corrosion inhibitors, while VB6 and VC act as mixed-type corrosion inhibitors. With the increase of vitamin concentration, IE% shows a fluctuating value, which is ascribed to the further aggravated imbalance between the cathode and the anode when the cathodic reaction is inhibited due to the adsorption of polar groups on the steel surface.