Concepts of steel protection by coatings with a reduced content of zinc pigments

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

“…Additional corrosion protection is provided by a passive barrier effect of the coating, therefore, these systems offer a double protection mechanism, which consists of cathodic protection and a barrier function. [ 12 ]…”

“…Zubielewicz et al summarise different influences on the performance of zinc‐rich primers. [ 12 ] To achieve a sacrificial behaviour, it is necessary to have a high amount of active zinc or zinc alloy pigments inside the coating, which is typically at 80 wt%, to guarantee electrical contact between the incorporated zinc pigments. These high pigmentation concentrations over the critical pigment volume concentration (CPVC) can lead, on the other hand, to insufficient mechanical properties of the coating, such as poor adhesion and blister resistance.…”

“…Further influences on the corrosion resistance of zinc‐rich primers are the size and shape (spherical or lamellar) of the pigments, the porosity of the binder, the composition of the used pigments (pure zinc or zinc alloys) and the presence and nature of a further topcoat. [ 12 ]…”

“…Additional corrosion protection is provided by a passive barrier effect of the coating, therefore, these systems offer a double protection mechanism, which consists of cathodic protection and a barrier function. [12] Besides the zinc flake systems which are used in this paper, it is also possible to incorporate zinc particles that have spherical or lamellar shapes in organic binder systems (e.g., epoxy systems). These so-called zinc rich primers, of which the above-mentioned zinc flake systems are a subgroup, similarly offer both cathodic protection and a barrier function.…”

“…Further influences on the corrosion resistance of zinc-rich primers are the size and shape (spherical or lamellar) of the pigments, the porosity of the binder, the composition of the used pigments (pure zinc or zinc alloys) and the presence and nature of a further topcoat. [12] Depending on the respective part geometry, one can choose between different application methods. Bulk goods, such as bolts or nuts, are coated using the dipspin method, in which a basket containing the parts to be coated is immersed in the coating tank and later centrifuged in a defined manner.…”