An electrochemical and theoretical evaluation of new benzothiazine derivatives as a corrosion inhibitor for mild steel in HCl solutions

The inhibition effect of benzothiazine (3,4-dihydro-2h-1,4-benzothiazine-3-thione ): p1 in mild steel corrosion in 1m hcl acid was investigated by weight loss,potentiodynamic polarization and electrochemical impedance spectroscopy (eis) techniques. the result showed that corrosion rate was significantly decreased in presence of the inhibitor. the inhibiting action increases with the concentration of benzothiazine compound to attain 92 % at 10-3mol/l. the increase in temperature leads to a decrease in the inhibition efficiency of the compounds in the temperature range 313-343k. adsorption of benzothiazine p1 on the mild steel surface in 1m hcl solution obeyed the langmuir adsorption isotherm. attempt to correlate the molecular structure to quantum chemical indices was made using density functional theory (dft). eis measurements showed an increase in charge transfer resistance (rct) with concentration. potentiodynamic polarization study showed that the inhibitor act as mixed type,controlling both the anodic and cathodic reactions.