Application of EIS and SEM to evaluate the influence of pigment shape and content in ZRP formulations on the corrosion prevention of naval steel

The effects of pigment volume concentration and morphology of zinc particles employed in the formulation of zinc rich paints (ZRP) suitable for the corrosion protection of naval steel in sea water, have been investigated using electrochemical impedance spectroscopy combined with open circuit potential measurements and SEM micrograph analysis. Different ZRP samples were tested during exposure to artificial sea water for up to 70 days. The characteristics and properties of the naval steel/ZRP coating/sea water systems were determined from an impedance transfer function model which involves the reactions occurring at the metal/ZRP and ZRP/solution interfaces as well as diffusion processes through the active ZRP coating. Information concerning the influence of concentration and shape of the zinc pigment on the corrosion protective behaviour of ZRP coatings and on the exposure time dependence of the system parameters allowed to interprete the form in which the galvanic action and the barrier effect diminish progressively. The degree of rusting of the steel substrates as well as the blistering resistance of the formulated ZRP have been also evaluated according to conventional ASTM standards.