Investigation On The Corrosion Protection Performance Of Fluorinated Graphene/Polymer Functional Coatings

The main problems of the anticorrosion coating of industrial heat transfer equipment are that the coating with good anticorrosion property has poor heat transfer property,and the coating with desirable heat transfer property has poor anticorrosion property.Corrosion of heat exchange equipment is a main reason for its failure,and the working efficiency of the equipment is affected by its heat transfer property.The preparation of coatings with excellent anticorrosion property and good heat transfer property is one of the hot topics in the corrosion field.Graphene with excellent thermal conductivity and impermeability provides a new opportunity for the development of anticorrosive coating for heat exchange equipment.However,graphene/polymer composite coatings have the potential to induce galvanic corrosion of the metal,causing the problem of electrochemical corrosion promoting activity.As a derivative of graphene,fluorinated graphene inherits the two-dimensional structure of graphene.Meanwhile,it has excellent impermeability,insulation,hydrophobic properties and high thermal conductivity.Based on the above characteristics,this paper proposed two strategies to inhibit the electrochemical corrosion promotion activity of graphene and improve the corrosion protection performance of coating:one is to control conductivity of graphene by fully fluorination modification,and the other is to control oxygen reduction reaction(ORR)activity by partial fluorination modification.The inhibition mechanism of corrosion promotion activity of fluorinated graphene was revealed.Based on the surface hydrophobicity of fluorinated graphene composite coating,the synergistic effect on improving corrosion resistance and enhancing condensation heat transfer were further studied.The main findings are as following:(1)Synthesis of fully fluorinated graphene and its corrosion protection performance.Fully fluorinated graphene(FG)with the fluorine content of 59.2 wt.%was prepared by liquid-phase ultrasonic exfoliation technique.The introduction of fluorine changed the carbon atoms from sp2 into sp3 hybrid,which increased the band gap of graphene.The electrical conductivity of FG decreased from 48 S/cm to 8.3 × 10-8 S/cm.The micro pores and defects of polyvinyl butyral(PVB)coating matrix were reduced by adding 0.50 wt.%FG into PVB coating.The gas barrier and corrosion resistance of the coating were improved,and the lifetime of the coating was prolonged by more than 9 times.Mechanism studies showed that the galvanic corrosion between FG and copper was blocked by the incorporated insulating FG,and the corrosion rate of copper substrate would not be accelerated after the coating was damaged.The corrosion promotion effect can be effectively inhibited by controlling the conductivity.(2)Tuning ORR activity of graphene through fluorination modification to inhibit its corrosion promotion activity.Partially fluorinated modified graphene(PFG)was prepared by replacing oxygen-containing functional groups with carbon fluorine bonds.By controlling the fluorination degree of PFG,and the electrocatalytic activity of cathode ORR of PFG was decreased.The electrochemical corrosion promoting activity was further inhibited.The results showed that the PFG nanosheets were multilayer structure,and the electrochemical corrosion promoting activity of PFG was completely inhibited when the content of F was increased to 15.2 wt.%.Adding only 0.3 wt.%PFG filler to PVB coating can improve the gas tightness and shielding anticorrosion performance of the coating,and prolong the coating lifetime to more than 90 days.(3)Construction of fluorinated graphene/epoxy superhydrophobic coating and its enhanced corrosion protection performance.Based on the low surface energy properties of fluorinated graphene,superhydrophobic surface was constructed.The superhydrophobic surface was used to form an air film to prevent the penetration of corrosive medium,so as to improve the anticorrosion performance of the coating.FG/epoxy composite coating(FG/ERC)with contact angle of 154° and rolling angle of 4° was prepared by surface modification technology.Compared with hydrophilic coating,the corrosion resistance of FG/ERC was improved by 99.6%and the coating resistance was increased by 2 orders of magnitude.Moreover,FG/ERC superhydrophobic coating also exhibits excellent self-cleaning properties.mechanical wear resistance and chemical stability,which is of great significance for the preparation of anticorrosion and antiscaling coating on the surface of heat exchanger.(4)Study on synergistic enhancement of corrosion protection and condensation heat transfer performance of fluorinated graphene composite coating.Aiming at the poor compatibility of anticorrosion and heat transfer performance of heat exchanger coating(DH22c),based on the characteristics of insulation,shielding,hydrophobic,thermal conductivity and low surface energy of FG,the FG/DH22c composite functional coating with thermal conductivity,anticorrosion,hydrophobic and enhanced condensation heat transfer was constructed.The thermal conductivity of FG/DH22c was increased from 0.174 to 0.237 W/(m K).The lifetime of FG/DH22c was extended from 15 d to more than 90 d when immersed in natural gas condensate at 90?,and the average corrosion rate of the metal substrate decreases by 3 orders of magnitude.The contact angle of FG/DH22C was improved from 83.5°to 129.9°,and the surface energy was decreased from 41.6 to 29.76 mJ/m2.The condensation heat transfer coefficient of FG/DH22c was increased to be 1.30 times higher than that of DH22c.It not only enhances the anticorrosion performance of the coating,but also enhances the condensation heat transfer process by synergistic effect.