Corrosion inhibition of different metal pigments in aqueous alkaline media

Abstract In aqueous alkaline media aluminium and zinc pigments react with the evolution of hydrogen whereas the more noble copper and brass pigments react by the absorption of oxygen. All these different corrosion reactions can be inhibited with addition of the chelating agent 2-hydroxy benzoic acid (2-HBA). So, 2-HBA works in a reducing hydrogen atmosphere as well as in an oxidizing oxygen atmosphere. In contrast, the chelating 2-mercapto benzoic acid only inhibited the hydrogen evolution of zinc pigment, which can be explained with “Pearson’s principle of hard and soft acids and bases”. The non-chelating 4-hydroxy benzoic acid only inhibited the oxygen absorption of copper and brass pigments. So, for aluminium pigment chelation seems to be a basic requirement for corrosion inhibition whereas for copper and brass pigments chelation is not essential.