Amphiphilic esters of gallic acid as corrosion inhibitors for aluminium and zinc pigments

Aluminium and zinc pigments corrode in aqueous alkaline media with evolution of hydrogen which can be measured gasvolumetrically. These corrosion reactions can be inhibited by different esters of gallic acid. Conductivity measurements showed that long-chained esters of gallic acid can be considered as surfactants with chelating hydrophilic groups. Hydrogen volumes decrease with both aluminium and zinc pigment (i.e., corrosion inhibition increases) with increasing chain-length of the ester alcohol of the gallates. Furthermore, with aluminium pigment there is an exponential correlation between the hydrogen volumes evolved and the number of carbon atoms of the ester alcohols of the gallates; thus, there is a mathematical relationship between the chemical structure of the examined corrosion inhibitors and their efficiency.