Inhibition of iron corrosion in different acid media by N-Decyl-Pyridinium derivatives

Some derivatives of N-Decyl-Pyridinium (DP) ion have been tested as iron corrosion inhibitors in H2SO4 and HCl solutions at 25 and 70 °C. These inhibitors were tested both as bromides (in HCl and H2SO4 solutions) and as hydroxides or sulphates (in H2SO4 solution). The efficiency of DP ion can be improved by the introduction of suitable substituents in the position 3 of the aromatic ring. In all the acid solutions tested, the most efficient ion at 25 °C proved to be N-Decyl-3-hydroxy-Pyridinium ion, while at 70 °C, N-Decyl-3-carboxy-Pyridinium ion. These derivatives acted mainly by physical adsorption between the organic cation and the anions (chlorides or bromides) pre-adsorbed at the electrode metal surface. However, in order to explain all the experimental data, other types of interactions have to be considered, such as : Van der Waals attractive forces between the alyphatic chains, interaction of electrons with the metal surface, and adsorption on to the metal surface via -COOH or -OH groups. These organic cations inhibit mainly the cathodic reaction, but, when present in higher concentrations, they also inhibit the anodic reaction