Characterisation of the galvanic protection of zinc flake coating by spectroelectrochemistry and industrial testing

Abstract

The properties of hot-dip galvanised and electroplated zinc coatings on steel have been widely studied, but the corrosion mechanisms of zinc flake coatings have not yet been investigated in similar detail. Here, we investigate the protective effect of inorganic lamellar zinc coatings, comparing the metallic dissolution rates of different zinc, aluminium and alloyed flakes using an inductively coupled plasma mass spectrometry (ICP-MS) flow cell. These experiments were carried out on both intact and predamaged coatings with different electrolytes. Data were also compared to accelerated laboratory corrosion tests and outdoor weathering results. The chloride concentration, and its effect on the passive oxide film, appears to be a key aspect moderating the dissolution rate and hence sacrificial zinc dissolution under various conditions. The complementary use of accelerated tests and ICP-MS flow cell analysis provides new insights into both the influence of the corrosive environment and the impact of the zinc flake (alloy) used. Based on this approach, tailored coating solutions using zinc flake coatings can be developed.