Study On Protective Mechanism Of Zinc Rich Coating Based On Corrosion Conversion

The coating is widely used for the protection of metal.However,due to the inherent porosity and defects of the traditional coating,the self-healing coating has been developed by the researchers.As a traditional self-healing coating,zinc rich coating is widely used in industrial anticorrosion.Although the protective effect of zinc coating is mainly derived from the sacrificial anode of zinc powder and the shielding effect of zinc corrosion products,the protection mechanism of the zinc rich coating has still not been completely illustrated.According to the current researches,the chemical shielding of zinc powder in the zinc rich coating by self-corrosion conversion is systematically studied in this paper.Such effect was verified through three experimental systems.Firstly,the effect of self-corrosion of zinc powder on the corrosive behavior of the medium was studied.Results show that the self-corrosion of zinc powder reduces the corrosion of the medium by decreasing the oxygen concentration and rising pH of the medium.Then,the effect of self-corrosion conversion of zinc powder on the protection performance of zinc coating on A3 steel was evaluated using zinc rich coating as an interlayer.Results show that the protective effect increases with the increase of zinc content in the zinc rich intermediate layer.After the coating was scratched,the oxygen reduction current of FC/ZRI/FC in the scratch area was obviously smaller than the blank sample at the initial stage of immersion.The impedance during the early immersion was one order of magnitude higher than the blank sample,when the thickness of the middle layer of zinc powder was 2 mm.The above results show that the chemical shielding of zinc self-corrosion conversion plays an important role in the performance of zinc coating.During the infiltration of corrosive medium through the in the middle layer toward substrate,zinc powder preferably consumes the dissolved oxygen and enhances the local pH.Such low oxygen basic microchemical environment in the coating slows the diffusion rate of oxygen to the matrix and effectively protect the carbon steel substrate.Furthermore,the influences of the self-corrosion conversion of zinc rich coating on the life of zinc rich primer was evaluated,where fluorocarbon paint was selected as the middle layer.The results of immersion test show that 80 wt.% zinc rich finish prolong the life over 30 days compared with the blank test(4 days).Besides,scratch test reveals that the 96 h of the sample with the thickness of is still not invalid,and no corrosion products were detected in the scratched area.These effects are due to that the microchemical environment slows the consumption rate of zinc powder of the zinc rich primer for cathodic protection,which prolong the its protective life.This paper studies the protective mechanism of zinc rich coating from the viewpoint of corrosion conversion and enrich the anti-corrosion mechanism of zinc rich coating.