E. Perre, S. Albayrak, C. Becker-Willinger
INM - Leibniz Institute for New Materials,
Keywords: zinc phosphate, manganese phosphate, flake-type particles, active corrosion protection
Summary:Metal phosphates and in particular, zinc phosphates are known to show interesting protection effect on steel against corrosion. The detailed mechanism of their anticorrosive effect is still not fully understood yet. In this direction not only barrier properties but also passivation function, shielding abilitiy or anti-cathodic disbonding effect were reported and discussed in literature. In the present study, we report the formation of in-house synthesised crystalline, anisotropic flake-type shaped zinc phosphates and mixed zinc-manganese phosphates as new corrosion protection pigments and their dispersion in epoxy coating matrix in order to form composite type Nanomer® coatings for the application on mild steel. Their advantage compared to commercially available particles having more or less spherical shape is directly connected to their flake-type shape providing diffusion barrier effect and at the same time easier release of phosphate on demand to re-passivate the steel surface in areas where the coating has been damaged. The corrosion protection ability of the different Nanomer® coatings on steel was investigated by means of neutral salt spray test as well as artificial weathering in dependence on the particles morphology and the molar ratio of zinc to manganese. Standard electrochemical measurements such as polarization and electrochemical impedance spectroscopy were used to assess the overall corrosion inhibition effects induced by the flake-type particles. The corrosion behaviour of the coated steel in the area of the artificial scribe could not only be correlated to the internal composition of the different metal phosphate particles but also to their aspect ratio and distribution over the matrix.