This work addresses the possibilities of using synthesized novel magnesium complex dyes in zinc pigmented organic coatings based on epoxyester resin to reduce the zinc content in these coatings while maintaining or increasing the anticorrosive efficiency of them. The magnesium complexes Mg-Dye-I (C₃₄H₂₆MgN₈O₆), Mg-Dye-II (C₂₆H₁₉MgN₃O₅), Mg-Dye-III (C₁₇H₁₀MgN₂O₃), and Mg-Dye-IV (C₂₅H₁₈MgN₄O₆) with a series of azo carboxylate ligands were prepared from the diazo-coupling reaction of anthranilic acid with 5-methyl-2-phenyl-3-pyrazolone (Dye I; C₁₇H₁₄N₄O₃), anthranilic acid with naphthol AS-PH (Dye II; C₂₆H₂₁N₃O₅), anthranilic acid with 2-naphthol (Dye III; C₁₇H₁₂N₂O₃), and 2-amino-5-nitrophenol with naphthol AS-PH (Dye IV; C₂₅H₂₀N₄O₆). The synthesized novel magnesium complex dyes were characterized by analytical methods. Model coatings containing these dyes at pigment volume concentrations (PVCs) = 1, 3, 5 and 10% and zinc at a ratio of pigment volume concentration/critical pigment volume concentration (PVC/CPVC) = 0.60 were formulated to study the inhibitory properties of the individual synthesized magnesium complex dyes. Model coatings containing inorganic pigments (MgO and Ca-Mg-HPO₄) at PVCs = 1%, 3%, 5% and 10% and zinc at PVC/CPVC = 0.60 were also formulated. The coating pigmented only by zinc at PVC/CPVC = 0.60 was prepared as a standard organic coating. Corrosion resistance was also evaluated by potentiodynamic polarization studies and electrochemical impedance spectroscopy. The properties of organic coatings were also tested using other standardized and derived corrosion tests. In addition, the mechanical properties of the studied organic coatings were determined using standard tests. The aim of the work was to verify the possible synergistic efficiency of novel magnesium complex dyes by improving the mechanical, anti-corrosion, and chemical properties of zinc pigmented organic coatings.

Four new compounds from perylene dianhydride were prepared and tested for their anti-corrosion properties. Dizinc salt of perylene-3,4,9,10-tetracarboxylic acid and dimagnesium salts of perylene-3,4,9,10-tetracarboxylic acid, 5,5′-(1,3,8,10-tetraoxo-1,3,8,10-tetrahydroanthra[2,1,9-def:6,5,10-d′e′f′] diisoquinoline-2,9-diyl) bis(2-hydroxybenzoic acid) and N,N′-bis[3,3′-(dimethylamino)propylamine]-3,4,9,10-perylenediimide were characterized by analytical methods (SEM, EDX, X-ray) and parameters used in the field of paints (density, oil number and critical volume concentrations of pigment). The pigments (in a pigment volume concentration series) were used to prepare paints also containing a perylene C₂₆H₁₄N₂O₄ (Compound I) derivative pigment plus inert titanium dioxide to maintain a constant concentration of solids in the paint film. A mixture containing zinc nitroisophthalate and both the perylene derivative and titanium dioxide served as the reference material. The paints were applied to steel panels in two layers with a ruler. The organic coatings were subjected to electrochemical measurements and accelerated cyclic corrosion tests. The highest corrosion resistance was found for the coating containing C₂₄H₈O₈Mg₂. Superior to the coating containing either C₂₆H₁₄N₂O₄ or the conventional corrosion inhibitor C₈H₅N0₆-Zn, this pigment type acted mainly by a mechanism based on the compound’s complexation capacity at the metallic surface/organic coating/corrosion medium interface. The organic coatings containing perylene acid salts also attained high mechanical resistance.

This paper deals with the properties and testing of newly prepared organic pigments based on melamine cyanurate containing magnesium or zinc cations depending on their composition and anticorrosive properties in model coatings. Organic pigments based on melamine cyanurate with Mg²⁺ in the form of a complex differing in the ratio of melamine and cyanurate units were prepared. Furthermore, a pigment based on melamine citrate with magnesium cation Mg²⁺, a pigment based on melamine citrate with magnesium cation, and a pigment based on melamine cyanurate with zinc cation were prepared. The properties of Mg-containing organic pigments were also compared with those of selected magnesium-containing inorganic oxide-type pigments. The above-synthesized pigments were characterized by inductively coupled plasma-optical emission spectroscopy, elemental analysis, scanning electron microscopy, and X-ray diffraction. In addition, the basic parameters that are indicative of the applicability of the pigments in the binders of anti-corrosion coatings were determined. The anti-corrosive properties of the tested pigments were verified after application to the epoxy-ester resin-based paint binder in three different concentrations: at pigment volume concentrations of 0.10%, 0.25%, and 0.50%. The anticorrosive effectiveness of pigmented organic coatings was verified by cyclic corrosion tests in a salt electrolyte fog (NaCl + (NH₄)₂SO₄) in an atmosphere containing SO₂ and by the electrochemical technique of linear polarization. Finally, the effect of the structure of the pigments on the mechanical resistance of the organic coatings was investigated. The results obtained showed that the new organic pigments exhibit anticorrosive properties, and at the same time, differences in performance were found depending on the structure of the pigments tested. Specifically, the results of cyclic corrosion tests and the electrochemical technique of linear polarization clearly demonstrated that synthesized pigments of the organic type based on melamine cyanurate containing magnesium or zinc cations ensure the anti-corrosion efficiency of the tested organic coatings. The highest anti-corrosion efficiency was achieved by the system pigmented with synthesized melamine cyanurate with magnesium cation (C₁₂H₁₆MgN₁₈O₆), whose anti-corrosion efficiency was comparable to the anti-corrosion efficiency of the tested inorganic pigment MgFe₂O₄, which was prepared by high-temperature solid-phase synthesis. In addition, these organic coatings achieved high mechanical resistance after being tested using the most used standardized mechanical tests.