Organic-inorganic Composite Layer Protects The Corrosion Resistance Of Metal Materials In High-salt Environments

Metal materials generally refer to materials with metallic properties,including pure metals,alloys,intermetallic compounds and special metal materials.The development of human civilization and social progress are closely related to metal materials.Due to the copper and its alloys have excellent electrical conductivity,thermal conductivity,mechanical plasticity,they are widely used in industrial production such as wires,sheets,tubes,as well as marine industry.In general,copper has good corrosion resistance,but it is easy to form coordination ions in oxygenated water,solutions containing CN^-,Cl^-,and NO₃^-.Seawater,with plenty chloride ions,are thus severe corrosive media for copper.Magnesium and its alloys have good specific strength and specific stiffness,excellent damping and shock absorption properties,and good casting properties.They have been recognized as one of the lightest green metal structural materials in the industry.However,magnesium and its alloys have poor corrosion resistance,which seriously hinders their industrial application.Corrosion of metals,due to oxidation or chemical action of the material with the surrounding medium,is very common.During corrosion,a chemical or electrochemical heterogeneous reactions would occur on the metal surface,which would cause the metal to undergo an oxidized?ion?state,resulting the reduction of the mechanical properties,strength,ductility and toughness;destruction of the geometry of metal components;increasing wearing between parts;deteriorating the physical properties such as electrical and optical properties;shortening the service life of equipment and even causing the catastrophic incidents such as fire and explosion.Corrosion of metals is very common.Anti-corrosion,aiming to prolonging its service life,refers to the protection of metal surfaces from corroding in corrosive environments could be achieved by various means,such as plating,surface protection layer,anodic or cathodic protection.In this paper,the nanocomposites of polydopamine along with the multi-walled carbon nanotubes were used to study the corrosion inhibition performance of copper metal in high salt environment.Moreover,composite coating with inhibitor loaded mesoporous MCM-41 and polydopamine materials on magnesium alloy AZ91b in high salt environment were also investigated.The specific research contents are as follows:Part 1.In this part,nanocomposites of polydopamine wrapped functionalized multi-walled carbon nanotubes were designed for the protection of the copper metal from corrosion in high salt solution.The corrosion inhibition efficiency of the composites could reach 98.9%.Part 2.Nano-container,MCM-41,adsorbed inhibitor,stearic acid?SA?,was synthesized for hydrophobic self-healing corrosion inhibitor of magnesium alloy AZ91b.Polydopamine,with its adhesive ability,along with the SA loaded MCM-41nano-containers,was attached on the?3-mercaptopropyl?trimethoxysilane,one of the silane coupling agents,pretreated AZ91b surface.The corrosion inhibition performance of the composite was up to 87.3%measured by electrochemical impedance spectroscopy.The self-healing properties of the composite were investigated by SEM and contact angle measurement.After immersion in 3.5 wt.%NaCl solution for 24 h,the embedded corrosion inhibitor,stearic acid,can be released on the damaged magnesium alloy surface and form a protective coating layer.The coating restored its hydrophobic property after the self-healing process.Part 3.Mesoporous polydopamine as the nano-container and stearic acid as the loaded corrosion inhibitor was synthesized on the basis of part 2.After the protection coating was damaged,with the melanin-based properties of polydopamine,photothermic property,laser was induced on the damaged area.The loaded SA?with relatively low melting point?was then melt and could flow to the defects of the coating and achieve self-healing property.This process was verified by SEM and contact angle measurements.The corrosion inhibition performance of the composites was 90.9%.