Inhibition of Iron Corrosion in Different Acid Media by N-Decyl- Pyridinium Derivatives

Abstract

Some derivatives of the N-Decyl-Pyridinium ion (DP) have been tested as iron corrosion inhibitors in sulphuric and hydrochloric acid solutions at 25°c and 70°c. Theseinhibitors were tested both as bromides (in hydrochloric and in sulphuric acid solutions) and as hydroxides or sulphates (in sulphuric acid solutions). The efficiency of theDP ion can be improved by the introduction of suitable subsituents in the 3-position of the aromatic ring. In all the acid solutions tested, the most efficient ion at 25°c proved to be the N-Decyl-3-hydroxy-Pyridinium (D30P) ion, while at 70°C,. the N-Decyl-3-carboxy-Pyridinium (D3CP) ion was the most efficient.

These derivativesact mainly by physical adsorption between the organic cations and the anions (Cr⁻ or Br⁻) pre-adsorbed at the metal surfaceof the electrode. But 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 aliphatic chains, interaction of Πelectrons with the metal surface, and adsorption on to the metal surface via –COOH and –OH groups. The organic cations studied inhibit mainly the H⁺ ion discharge, but when present in higher concentrations they also inhibit the iron dissolution reaction.