Heterocyclic corrosion inhibitors for aluminium and zinc pigments Available to Purchase

Aluminium and zinc pigments react in aqueous alkaline media (e.g. water‐borne paints) by the evolution of hydrogen which can be measured gasvolumetrically. Certain organic heterocycles are well‐known corrosion inhibitors for different metals. The six different heterocyclic compound which were examined inhibited the corrosion reaction of zinc pigment in aqueous alkaline media. The most efficient inhibitors were 1H‐benzotriazole at pH 8 and 10 and 2‐(5‐aminopentyl)benzimidazole only at pH 10. In contrast, with addition of all heterocycles there was no corrosion inhibition on aluminium pigment. This complete difference in the corrosion inhibiting effect of the heterocycles with respect to the two different metal pigments can be explained with Pearson’s “Principle of Hard and Soft Acids and Bases”.