| As a new anti-corrosive technology in the field of metal anti-corrosion,Dacromet coating has been widely used in many fields due to its excellent corrosion resistance.However,the chromate in Dacromet coating can cause environmental pollution and is toxic to human health.Therefore,it is very important to study a new Dacromet coating without chromium.Chromiumfree Dacromet coating is more environmentally friendly than traditional Dacromet coating,but its corrosion resistance,hardness and other properties have been reduced,so how to improve the performance of chromium-free Dacromet coating is extremely urgent.Graphene is considered as an excellent reinforcement in the field of metal anticorrosive coatings due to its excellent barrier,chemical and thermal stability.However,its development is limited by its high surface energy and easy agglomeration.Therefore,in view of the above problems,this paper first modified graphene oxide with rare earth cerium to improve its dispersibility.Secondly,the modified graphene was added to the optimized chromium-free Dacromet coating as reinforcement phase,and the influence of modified graphene on the performance of chromium-free Dacromet coating was studied in depth from the conventional properties and corrosion resistance of the coating,and the anti-corrosion mechanism of the chromium-free Dacromet coating containing modified graphene was explored.The results are as follows:1.Graphene oxide(GO)was modified by using rare earth cerium,and CeO2 nanoparticles with average particle size of 12.24 nm were successfully loaded onto reduced graphene oxide nanosheets by hydrothermal method to obtain CeO2@rGO composite powder.2.The optimized formulation of chromium-free Dacromet coating was obtained by orthogonal test method,Zinc aluminum alloy powder 24 wt.%,corrosion inhibitor 1.8 wt.%,binder 8 wt.%,ethylene glycol 8.4 wt.%,Tween-20 7.2 wt.%,sodium tungstate 0.12 wt.%,methanol 1.07 wt.%,thickener and defoaming agent(≤1 wt.%),residual deionized water.3.The chromium-free Dacromet coating was sprayed on Q235 steel substrate and sintered at 280℃ for 25 min.The coating was compact and uniform,with a thickness of 8-12 μm and a hardness of 98.9 HVo.025.The binding force between coating and substrate reaches grade 0.The coating is mainly composed of zinc-rich phase and aluminium-rich phase,and its surface is silver gray.After soaking in 5%NaCl solution for 145 h,no obvious corrosion products were found on the coating surface,but there were small acicular zinc aluminun chloride hydrate and a small amount of Fe(OH)3 corrosion products locally.4.The chromium-free Dacromet coating with 0%～0.27%modified graphene was sprayed on Q235 steel matrix.After curing by the same process above,the surface color and composition phase of the coating do not change,but the hardness,wettability and bonding force increased with the increase of modified graphene content.When the modified graphene content is 0.18%,the surface of the coating has the best compactness,minimum roughness and hydrophobic properties.It shows the best corrosion resistance in ammonium nitrate rapid corrosion test,full immersion corrosion test,interimmersion corrosion test and 720h neutral salt spray test.In the electrochemical test,the corrosion current density and corrosion potential were 9.643 μA·cm-2 and-0.5605 V,respectively.Compared with the unprotected Q235 steel,the corrosion current density decreased by 70.1%,and the corrosion potential decreased by 24.2%.5.Chromium-free Dacromet coating in addition to containing modified graphene sheet zinc alloy powder physical shielding layer structure,zinc aluminum alloy powder as a sacrifice anode cathodic protection,molybdate passivation with metal ions and the corrosion products of poorly soluble in water to fill the coating frayed self-healing,nano-sized layered modified graphene can fill the pore of coating,improve the coating compactness.The conductive channel formed by uniformly dispersed modified graphene is beneficial to the full anodic reaction of Zn-Al powder. |
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