The Construction Of Polydopamine/8-hydroxyquinoline And Other Composite Coatings And Their Self-repairing Metal Anti-corrosion Performance

Metals,such as copper and low carbon steel,with excellent eminent electrical and thermal conductivity,perfect mechanical workability,weldability,high strength at low temperature,are being widely applied in the marine industries as condenser pipes of ships,civilian pipes and coastal power plant heat exchangers.Copper and mild steel have certain corrosion resistance,but are easily being corroded in oxygen-containing water,oxidizing acid,and environment containing CN^-and Cl^-.Metal corrosion will bring huge threat to the mechanical properties of materials,change their original geometry and physical properties such as electrical conductivity and optical property,which causing huge economic losses to industrial facilities.Among many protective methods,organic coatings have the widest application due to their advantages of good stability,low cost and easy formation.However,the environment adversely affects the coating,causing the internal defects which resulting the destruction of the coating,and therefore,accelerate corrosion.Hence,it is a hot issue to improve the active corrosion resistance and self-healing ability of coatings.Dopamine（DA）molecules can spontaneously polymerize and adsorbe on many materials surface,including metals,oxides,polymers,semiconductors and ceramics to form polydopamine（PDA）coatings.Coatings can,to some extent,hinder the ion migration and electron transfer from the corrosive media to the metal surface,thus provide corrosion inhibition ability.However,the cracks of the PDA coating,forming during DA polymorization,would cause the coating being further destroyed and peeled off from the metal surface,especially when heat or force were applied.For better anti-corrosion and self-healing performance,this paper focused on8-hydroxyquinoline and 8-hydroxyquinoline-loaded intelligent pH-responsive halloysite nanotubes（HNT）or 8-hydroxyquinoline-loaded intelligent pH-responsive polydopamine nanotubes（PNT）embedded PDA coatings as the high-efficiency corrosion inhibitors.In this paper,X-ray photoelectron spectroscopy（XPS）and infrared spectroscopy（FTIR）were used to characterize the successful preparation of composite coatings.Electrochemical impedance spectroscopy（EIS）and electrochemical polarization curves were used to study the corrosion inhibition performance of different coatings.The corrosion inhibition efficiency was also obtained.In addition,the self-healing properties of different coating were verified by electrochemical methods and scanning electron microscopy（SEM）.The specific research contents are as follows:In the first work,a corrosion inhibitor 8-HQ was added during the DA polymerization,and a PDA coating containing 8-HQ was directly prepared on the copper surface.The corrosion inhibition performances of the composite coating with8-HQ at different concentrations were investigated.It could be concluded that when the 8-HQ concentration is 0.02 mol·L^-1,the corrosion inhibition effect of the coating is the best,and the corrosion inhibition efficiency could reach as high as 97.7%.In addition,the study found that the composite coating with the highest corrosion inhibition efficiency also provide the best self-healing ability.In the second work,the corrosion inhibitor 8-HQ was loaded in the sulfated acidized halloysite nanotube（HNT）under negative pressure.Then polyelectrolyte sodium polyacrylate（PSS）and poly（allylamine hydrochloride）（PAH）were deposited in turn outside of the HNT to prepared a pH-responsive HNT/8-HQ/PSS/PAH micro-nano container.Those micro-nano containers were added spontaneously during DA polymerization process to prepare a composite coating directly on the surface of low carbon steel Q235.By investigating the corrosion inhibition performance of the composite coating,it could be known that the coating′s corrosion inhibition efficiency was as high as 98.4%,with excellent self-healing property.In the third work,the high corrosion inhibitor loading PDA nanotube（PNT）was prepared by template method.After loading the corrosion inhibitor 8-HQ under negative pressure,polyelectrolyte sodium polyacrylate（PSS）and poly（acrylamide hydrochloride）（PAH）were deposited in turn outside of the PNT to prepare a pH-responsive PNA/8-HQ/PSS/PAH micro-nano container.Similarly,DA with those micro-nano containers were directly polymerized on the Q235 surface.The corrosion inhibition efficiency of the composite coating could reach up to 96.4%with outstanding self-healing property.