Preparation And Corrosion Resistance Of Extrinsic Self-Healing Epoxy Coatings For Seawater Systems In Nuclear Power Plant

The combination of coating and cathodic protection is usually adopted to protect the steel equipment in nuclear power plants.However,it is necessary to consider the selection and replacement frequency of anode materials,daily maintenance cost and continuous power supply cost when using cathodic protection for corrosion protection.In order to further reduce the cost of human and material resources,it is urgent to find a simple and cost-effective corrosion protection method.In this paper,four kinds of smart anticorrosive coatings with excellent barrier properties and self-healing properties were prepared based on the synthesis strategy of external self-healing coatings.The corrosion resistance and self-healing mechanism of the composite coating were discussed.The prepared external self-healing coating is expected to replace the commonly used anti-corrosion method of seawater system in nuclear power plants,thereby achieving long-term corrosion protection of nuclear power equipment.A graphene oxide-based nanomaterial（GAS）was prepared by covalently grafting hollow mesoporous silica（HMS）onto the surface of GO.HMS grafted on GO surface can realize uniform dispersion of GAS in epoxy resin coating by forming steric hindrance and covalent bond with epoxy group in epoxy resin,thus endowing the epoxy coating with enhanced barrier performance.In addition,the prepared GAS nanomaterials can also achieve the loading and p H responsive release of the corrosion inhibitor 2-mercaptobenzothiazole（MBT）.MBT loaded GAS（GASM）was added to the epoxy coating to make an anti-corrosion coating（GASM-Coat）.Electrochemical impedance spectroscopy（EIS）results show that the low-frequency impedance value of GASM-Coat with artificial hole defect has a trend of first decreasing and then increasing,with a self-healing efficiency(r_self-healing)of 60-72 hours up to 892 KΩ·cm²·h^-1,which confirms the excellent self-healing performance of GASM-Coat（active corrosion protection）.GASM-Coat will provide a reference for the development of smart anti-corrosion coatings.A highly dispersed carbon nanotube-based composite（HAC）was prepared by surface modification of carboxylated carbon nanotubes（CCNT）.The excellent dispersion of HAC nanomaterials in epoxy coatings is not only due to the stability of HAC themselves,but also related to the improved compatibility of fillers caused by the ring opening reaction between HAC and epoxy resin.Epoxy coating containing corrosion inhibitor BTA loaded HAC（HACB）（HACB/EP）exhibits excellent corrosion resistance,its low frequency impedance value remains at 9.61 GΩ·cm² after 30 days of immersion.The self-healing performance of HACB/EP is confirmed by immersion experiments of scratch coatings.r_self-healing of HACB/EP with artificial defects（De-HACB/EP）changes from a negative value to a positive value from the second stage（24-48 h）.In addition,no significant corrosion products are observed inside the scratch of De-HAC/EP and the content of O element at the scratch is only 4.23wt%.A dodecahedral layered double hydroxide（LDH）nanocage（ZL）was prepared using ZIF-67 as a precursor.Polyethylene glycol（PEG）was used to encapsulate the imidazoline（IM）loaded ZL to synthesize 2D/3D structure-function integrated nanomaterials（ZLIP）.Then,ZLIP was added to epoxy resin to construct a self-healing epoxy composite coating（ZLIP/EP）.The LDH lamellar structure（2D）on the ZLIP surface can delay the penetration time of the electrolyte in the coating,thereby enhancing the barrier performance of the coating.When the coating is damaged,IM stored in the hollow structure（3D）of ZLIP can be released and adsorbed to form a protective film.It is worth noting that a portion of IM is intercalated between the LDH layers,so ZLIP can capture chloride ion and release IM through ion exchange.Based on the above mechanism,ZLIP/EP exhibits excellent corrosion resistance and self-healing performance.The low-frequency impedance value of ZLIP/EP is 68.8 MΩ·cm² and the adhesion loss is only 33%after immersion for 40 days.The low frequency impedance value of ZLIP/EP with artificial scratches（ZLIP/EP@S）begins to rise after 48 hours of immersion and last until 96 hours,eventually reaching 79.2 KΩ·cm².ZLIP/EP can provide long-term corrosion protection for steel substrates.A double layer self-healing coating（C-DMS-EP/P-DMS-EP）was prepared by using dendritic mesoporous silica（DMS）as a nanocontainer based on the synergistic effect of cysteine（Cys H）and iron polyacrylate（PAAFe）.The corrosion inhibitor salt solution immersion experiment shows that PAAFe can promote the oxidation of Cys H and capture harmful H⁺.The excellent corrosion resistance of C-DMS-EP/P-DMS-EP is confirmed by EIS test.The low-frequency impedance value of C-DMS-EP/P-DMS-EP remains at 8.33 GΩ·cm² after 40 days of immersion,which is much higher than that of pure epoxy coating（86.03 MΩ·cm²）.In addition,the low frequency impedance value of C-DMS-EP/P-DMS-EP with artificial scratches increases rapidly after immersion for 36 hours and finally reaches 768 KΩ·cm²,indicating its efficient self-healing performance.