Inhibitive properties of quaternary ammonium bromides of N-containing heterocycles on acid mild steel corrosion. Part I: Gravimetric and voltammetric results

Four quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 M HCl and 1 M H2SO4. Polarisation curves, polarisation resistance and gravimetric methods were used. The inhibitor efficiency was found to depend on both concentration and temperature. The inhibitors were of mixed type, influencing predominantly the anodic process. From the temperature dependences the apparent activation energy in 1 M HCl was determined in the presence of all studied compounds, found to be inferior to the activation energy in absence of inhibitor. The adsorption of the inhibitors was well described by the Frumkin or the Langmuir adsorption isotherms in both acidic media and the adsorption isotherm parameters were determined at room temperature. The influence of the molecular structure was discussed taking into account the different number of positive charges and the different heterocycles. The best inhibitive properties had 1-(carbamoylethyl)-4-methylpyridinium bromide.