Mono- and dicationic benzothiazolic quaternary ammonium bromides as mild steel corrosion inhibitors. Part II: Electrochemical impedance and polarisation resistance results

Seven quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 M HCl using electrochemical impedance and polarisation resistance techniques. Adequate structure models of the interface as well as some data on the kinetics of the partial processes are presented. Experimental data revealed frequency distribution of the capacitance, simulated as constant phase element. The values of the structure models and the time constants have been found by fitting the experimental curves. The values of the resistances were compared with those obtained from dc polarisation resistance measurements. The inhibitor efficiency of the studied compounds was determined.

Research highlights
► The investigated quaternary ammonium salts are good corrosion inhibitors for steel in 1 M HCl.
► In EIS one or two time constants appear depending on concentration.
► Two structural models for the interface were used to determine the process parameters.
► Polarisation resistance measured with dc technique and is in good agreement with EIS data.