Mono- and dicationic benzothiazolic quaternary ammonium bromides as mild steel corrosion inhibitors. Part I: Gravimetric and voltammetric results

Seven quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 M HCl using gravimetric and polarisation techniques. For comparison gravimetric experiments were carried out in 1 M H2SO4 as well. The inhibitor efficiency was found to depend on both concentration and molecular structure of the inhibitor. The polarisation curves revealed that the inhibitors were of mixed type. The adsorption of almost all inhibitors was well described by the Frumkin isotherm. The adsorption isotherm parameters were determined. Conformational changes in the molecular structure favour the adsorption and thus increase the inhibitive effect.

Research highlights
► Quaternary ammonium heterocyclic compounds are good corrosion inhibitors in acid media.
► Adsorption is well described by Frumkin isotherm.
► Conformation changes enable formation of more condensed adsorbed layers.