Investigations on structural and electronic effects in acid inhibitors by AC impedance

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Abstract
Ac impedance investigations were performed at high‐purity iron and mild steel in de‐aerated 10% hydrochloric acid under free corrosion at room temperature in the presence of quaternary ammonium compounds. Systematic studies of specially selected and synthesized pyridinium and quinolinium derivatives revealed that the inhibition efficiency increases with increasing number of aromatic systems in the molecule and is determined not only by geometric and electronic molecule factors influencing the adsorption but also by dielectric effects exerted by the inhibitor molecule after adsorption. Most of the substances tested were significantly less effective on steel than on high‐purity iron. The best results at all materials were found with 1‐naph‐thylmethylquinolinium chloride.