Macrocyclic Corrosion Inhibitors for Steel in Acid Chloride Environments^☆

The effectiveness of phthalocyanines as acid corrosion inhibitors for steel were studied. Water soluble tetrasulfophthalocyanines are very poor corrosion inhibitors. Water insoluble tetraaminophthalocyanines serve as better corrosion inhibitors than the water soluble ones when the metal surface is coated with an adsorbed layer of the phthalocyanine. The inhibitor efficiency was still far too low to be of any significance. Water insoluble polymeric phthalocyanine coatings based on Fe(III) centers gave inhibitor efficiencies as high as 82%, as confirmed by both slow potentiodynamic technique and the AC impedance analysis. Polymerization was achieved by simple dip coating followed by heat treatment of the coated surface at 450 C in an inert atmosphere. The resulting coating is adherent and electrically conducting, thereby providing a unique set of conducting polymer inhibitors that can be used in acid environments.