Corrosion inhibition efficiency and surface activity of benzothiazol-3-ium cationic Schiff base derivatives in hydrochloric acid

Two series of cationic Schiff base surfactants namely: 2-(benzylideneamino)-3-(2-oxo-2-alkoxyethyl)-1,3-benzothiazol-3-ium bromide and 2-[(4-methoxybenzylidene)amino]-3-(2-oxo-2-alkoxyethyl)-1,3-benzothiazol-3-ium bromide were prepared and confirmed using elemental analysis, FTIR, and 1H NMR spectra. The surface activity of the synthesized Schiff bases showed their tendency towards adsorption at the interfaces. The prepared compounds were evaluated as corrosion inhibitors for carbon steel in 0.5 M HCl solution using gravimetric and polarization measurements. By fitting the gravimetric data, some thermodynamic and kinetic parameters were estimated. The adsorption of the inhibitors on the carbon steel surface obeyed Langmuir adsorption isotherm and had a physical mechanism. Polarization measurements showed that the synthesized inhibitors act as mixed inhibitors for carbon steel in the acidic media. The results of the corrosion inhibition using two different methods showed narrow differences in the obtained values between the two methods within 5%.

Research highlights
► Benzothiazolium inhibitors show high corrosion inhibition for carbon steel.
► Weight loss and corrosion rates decrease by increasing inhibitor dose.
► Inhibition mechanism suggested as physisorption mechanism supported by adsorption free energy values.
► The adsorption of the inhibitors obeys Langmuir isotherm.
► Side chains have ascending order on the corrosion inhibition of the different inhibitors.