Inhibition of the Acid Corrosion of Steel by n-Alkyltrimethyland n-Alkyltriethyl-ammonium Compounds

Abstract

Previous experiments with a dropping-mercury electrode indicated that n-alkyltriethylammonium ions are more strongly adsorbed than the corresponding n-alkyltrimethylammonium ions. In parallel with this, it has now been found that the former are better inhibitors of the acid corrosion of steel.

At concentrations giving up to 50% corrosion inhibition, the compounds of either series have no effect on the steel electrode potential, indicating that the anodic and cathodic reactions are equally inhibited. This is taken as evidence that the inhibitor ions are adsorbed generally over the metal surface rather than at specific anodic or cathodic sites.

With increasing concentration of inhibitor above the level for 50% inhibition, the potential begins to be displaced in a positive direction, suggesting that the anodic reaction is being inhibited more than the cathodic reaction. The results show that the proportion of cathodic inhibition is larger with the triethylammonium than with the trimethylammonium compounds.

The cathodic part of the inhibition appears to be due mainly to hindrance of the surface diffusion and recombination of adsorbed hydrogen atoms.