Effective inhibition of mild steel corrosion in 1 M hydrochloric acid using substituted triazines: an experimental and theoretical study

Inhibition of mild steel corrosion in 1 M hydrochloric acid with three different 1,2,4-triazine precursors were investigated by polarization (Tafel), electrochemical impedance (EIS), adsorption and computational calculations at room temperature. Polarization studies showed that these molecules act as mixed-type inhibitors. As the electron density around the inhibitor molecule increases the inhibition efficiency also increases. Obvious correlation were found between corrosion inhibition efficiency and some quantum chemical parameters such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), HOMO–LUMO gap energy and electron density. Calculated results indicated that the difference in inhibition efficiencies between the compounds can be clearly explained in terms of frontier molecular orbital theory. The inhibition efficiency depends mainly on the type of functional group (CH2Ph, But or Me) substituted on the triazine ring. The order of efficiency is ABTDT (CH2Ph) > ATTDT (But) > AMTDT (Me).