Localized electron microscopy analysis of steel corrosion processes in the presence of zinc phosphate flake-type particles

Zinc phosphate particles are used in coatings that protect steel from corrosion. The corrosion of coated steel was examined at the microscopic scale in proximity of zinc phosphate flakes. The coatings were prepared by dispersing the zinc phosphate flakes in epoxy-phenolic resin matrix, spray coating on the steel substrate, and curing. Such prepared coatings were then scratched, and corroded in the artificial weathering conditions by means of a condensate climate test. The ongoing corrosion process was examined using environmental scanning electron microscopy (ESEM). By applying this approach, we observed the influence of the anisotropic particles of zinc phosphate on the formation of corrosion products. Local areas at the edge of the scratch that were in direct contact with the zinc phosphate aggregates, revealed the formation of a different crystal type compared to the plain areas of the scratch. The obtained data indicates that a partial dissolution of the zinc phosphate particles took place, and suggests that the influence of zinc phosphate on the formation of corrosion products was mediated by the presence of water.