Cathodic disbondment of epoxy coating with zinc aluminum polyphosphate as a modified zinc phosphate anticorrosion pigment

As an approach to improve the resistance of protective coatings to the disbondment, modification of the formulation through incorporation of zinc aluminum polyphosphate anticorrosion pigment representing third generation phosphates was examined in this paper. The data obtained from cathodic disbonding test, electrochemical impedance spectroscopy and pull-off indicated that introduction of zinc aluminum polyphosphate within epoxy coating could provide improved resistance to cathodic disbonding as well as superior adhesion strength. The superiority in the presence of the modified pigment was connected to deposition of a layer at the disbonding front and locally controlled pH as well. The precipitation restricting active zone available for electrochemical reaction was confirmed by SEM.