| The heavy amount of zinc particles in zinc-rich coating can provide an active cathodic protection for the steel substrate,but the presence of such the heavy amount of zinc particles in the paint will increase its viscosity and decrease its spraying ability,which results in many problems to the coating after spraying,such as high porosity,weak adhesion strength to the steel substrate and poor surface leveling.Additionally,the use of cost for zinc-rich coating is too high.shows a huge potential in the field of anti-corrosion materials attributed to its exceptional properties,for example,excellent conductivity,ultrahigh specific surface regions,and super impermeability.In this dissertation,graphene and modified reduced graphene oxide were added in waterborne epoxy zinc-rich coating,and its properties were characterized.In addition,effects of graphene on the corrosion evolution of zinc particles in the coatings were discussed.The main findings are as follows:?1?The graphene/waterborne zinc-rich epoxy coatings were prepared,and effects of graphene content and zinc particles content on the surface micro-morphology,adhesion properties and anticorrosion properties of the coatings were investigated.The results of scanning electron microscopy?SEM?and adhesion test showed that the addition of graphene made no difference to the micro-morphology of the zinc-containing 40%in dry film?40Zn coating?,but wrinkled the surface micro-morphology of the zinc-containing 60%in dry film?60Zn coating?,increased the zinc-containing 85%in dry film?85Zn coating?pores,and weaken the adhesion of the 85Zn coating.Result of salt spray test showed that the addition of graphene in 40Zn and 60Zn coating,which do not show cathodic protection performance,can effectively improve its cathodic protection performance.Electrochemical impedance spectroscopy?EIS?test results showed that the lowest frequency?|Z|0.01 Hz?impedance modulus of 60Zn coating significantly decreased from 3.291×107?·cm2 to 5641?·cm2 after66 days immersion.Meanwhile,lowest frequency impedance modulus of 60Zn containing0.6%graphene?60Zn0.6G?coating was 1.287×108?·cm2 at the initial immersion,then decreased gradually to approximately 2.883×106?·cm2 after the 66 days immersion,and which indicating that 60Zn0.6G coating showed a good protective performance.The influence of graphene on the corrosion evolution of zinc particles in the coating is mainly as follows:a galvanic cell at the interface between the zinc particles and the steel base forms after the corrosive media reached the interface between the coating and steel substrate,and consequently the zinc particles near the interface played a easily accessible sacrificial anode to protect the steel substrate from corrosion.Besides,the zinc particles,which were far away from the substrate and isolated,also provided the cathodic protection to the substrate due to the connection of graphene.and then zinc particles continued to be corroded from the interface to upper part of the coating since they could provide the cathodic protection to the substrate thanks to the electrical connection of graphene.Meanwhile,Xray diffraction?XRD?patterns confirmed the corrosion products of the zinc particles were mainly consisted of Zn5?OH?8Cl2·H2O.?2?Polyethyleneimine?PEI?was used to graft onto the Graphene oxide?GO?,and hydrazine hydrate was used to reduce GO,and the obtained polyethyleneimine-reduce graphene oxide?PEI-r GO?was prepared.FTIR and XPS results showed that the PEI was successfully grafted on graphene oxide in the form of chemical bond?-CO-NH-?,and the C/O?6.42?of PEI-r GO was much higher than GO?2.12?,showing a good degree of reduction for PEI-r GO.In addition,PEI-r GO has good dispersibility in water.Adhesion test and salt spray test results showed that 60Zn containing 0.6%PEI-r GO?60Zn0.6PEI-r GO?coating demonstrated the better adhesion and cathodic protection performance compared to the 60Zn coating.EIS results showed that the lowest frequency impedance modulus of 60Zn0.6PEI-r GO coating was not only much higher than 60Zn coating,but also higher than 60Zn0.6G coating during 66 days immersion,which indicating that 60Zn0.6PEI-r GO coating showed a good protective performance.The observed results may be attributed to the layered structure of PEI-r GO which can increase the length of diffusion path of corrosive media,and the crosslinking reaction of-NH2 on the PEI-r GO and the oxygen-containing functional groups of epoxy resin which can effectively improve the corrosion resistance of the coating.On the other hand,after reduction,PEI-r GO was beneficial to the cathodic protection of zinc particles. |
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