The effect of Zn pigment modifications on the structure and mechanical properties of anticorrosive coatings

摘要

Typically,anticorrosive coating system consists of a primer,one or several intermediate coats,and a topcoat.The function of the primer is to ensure good adhesion to the substrate and to protect it from corrosion,mainly by the surface active compounds which are present there.For this purpose,zinc pigments are often formulated into such primers,where they act as sacrificial anodes.During lifetime of such systems Zn is transformed in its corrosion products,which tend to seal the pores between the Zn particles to a point at which the system becomes electrically nonconductive(barrier stage).Since the performance of sacrificial coatings is based on transfer of galvanic current,which implies metallic contact between the individual active pigments,such coatings are typically very highly pigmented,which sometimes causes losses in cohesive strength and in resistance to impacts.Therefore-and because Zn is known to be harmful to the environment and becoming a rare chemical element-research aims at Zn primers with reduced Zn content and even better long time performance.It may be pursued by use the mixture of Zn pigments with different shape(dust,flakes)and different size,Zn alloy pigments(Zn/Sn,Zn/M)as well as by chemical or metallic surface treatment of such pigments and an addition of graphene or carbon nanotubes.