Preparation And Properties Of Composite Anti-Corrosive Materials With Low-Surface Treatment

With the implementation of China’s marine strategy,marine equipment is used more and more widely.In the marine environment,the equipment is facing a huge risk of corrosion failure,which brings serious hidden dangers to the production safety,so the anti-corrosion treatment of steel components is very important.When components are treated with anti-corrosion treatment in marine environment,the surface of the workpiece often contains moisture,rust,oil and salt,which is commonly referred to as the"four zone"surface,and also referred to as the"low surface"in the industry.These moisture,rust,oil and salt are difficult to remove,so how to prepare long-term anti-corrosion coating in such an environment is a big problem.The special-shaped structure inside the cabin has complex shape,uneven surface,many cracks and edges,and it is difficult to form a complete and firm coating with traditional coating and painting methods.The research and development of composite anti-corrosion tape suitable for the low surface treatment of this complex workpiece,which can convert the rust,salt,water and oil on the workpiece surface into the composition of the coating,is an important way to realize the corrosion protection of components in the marine environment.This project focuses on the absorption and transformation of sodium chloride on the surface of the workpiece,and has carried out in-depth research from the aspects of material preparation,adsorption mechanism,adsorption process,etc.the low surface treatment composite anti-corrosion adhesive plaster and tape are prepared,and its anti-corrosion performance and mechanism are studied through salt spray test and electrochemical impedance test.（1）Preparation,chlorine absorption property and action mechanism of calcium aluminum salt（Ca O/Na Al O₂）The product structure of calcium-aluminum salt after absorbing chloride ion was characterized by SEM and XRD analysis,and the change of chloride ion content in the solution was detected by chemical analysis method.the preparation method of calcium-aluminum salt by ultra-high lime method and the adsorption law and mechanism of chloride ion were studied.The result showed that when m（Na Al O₂）:m（Ca O）=1:2.5 and premix were added synchronously,compared with that precipitate prepared in advance,the adsorption capacity and removal efficiency of chloride ion were maximum;the adsorption mas per unit reached 63.50mg/g when the reaction temperature was 25℃,the stirring time was 60min and the concentration of sodium chloride was 2000 mg/L.The results of SEM and X-ray diffraction analysis showed that Ca₄Al₂（OH）₁₄with layered structure was formed by the reaction of calcium oxide and sodium aluminate in the solution.OH^-between the layers exchanged with external chloride ions,and friedel salt(Ca₄Al₂Cl₂（OH）₁₂)with the same layered structure was formed.Excessive Na Al O₂or Ca O could make OH^-binding more firm and was not conducive to chloride ion adsorption.The adsorption complied with the Freundlich model and the two-stage kinetic function,and it was dominated by multi-layer chemical adsorption,with the theoretical adsorption amount of 69.68mg/g.It belonged to an exothermic reaction.If the temperature was too high,it was not conducive to adsorption.If the temperature was too low,the molecular motion and diffusion dynamics were decreased,and the chloride ion adsorption amount was decreased.（2）Preparation of magnesium aluminum hydrotalcite（LDHs）and study on that adsorption property and mechanism of chloride ion.Mg/Al double hydroxyl composite metal hydroxide with interlayer anion of CO₃^2-was prepared by co-deposition method using Al（NO₃）₃·9H₂O and Mg（NO₃）₂·6H₂O,and then modified Mg-Al hydrotalcite（Mg/Al-CLDH）was obtained after high temperature calcination modification.The adsorption law and action mechanism of chloride ion were studied.Mg/Al-LDHs with N（Mg）:N（Al）ratio of 4:1 were prepared by co-deposition.After modification by high temperature calcination at 550℃,the adsorption effect of Mg/Al-CLDH was the best.Under the conditions of 65℃,initial p H value of 8,and stirring for 180min,the adsorption capacity of Mg/Al-CLDH hydrotalcite for chloride ion was 172mg/g in 2000mg/L sodium chloride solution,and the adsorption balance was basically reached.SEM images showed that the external layered structure of Mg/Al-CLDH partially collapsed,and the internal layered structure was relatively intact and distributed in sheets.Water and CO₃^2-BET ween the sheets separated in the form of gas,forming a mesoporous structure with uniform distribution,about 20nm pore size,and bet surface area of 200.411m²/g.Chloride adsorption followed the Langmuir model and two-stage kinetic mechanism,and was dominated by single-layer and chemical adsorption.Part of the chloride ions entered the interlayer to supplement the vacancy caused by CO₃^2-and at the same time,the chloride ions could exchange with the remaining CO₃^2-between the layers to fix the chloride ions.The theoretical saturated adsorption capacity calculated was 182.88 mg/g.（3）Preparation and anti-corrosive performance of composite anti-corrosive daub.The lithium-based grease and epoxy resin were used as matrix materials,and the salt conversion material prepared in this study was combined with the rust conversion,water conversion,and oil conversion materials developed by us.through salt spray test,aging resistance test,high temperature test,and electrochemical impedance test,the anticorrosion performance of the anticorrosion mastic was studied,and the effects of the type of salt conversion material,coating thickness,the content of salt conversion agent,and the proportion of lithium-based grease and epoxy resin on the performance of the anticorrosion mastic were investigated.The results showed that when the polished smooth Q235 substrate was treated with a paste thickness of 3mm,the addition of salt conversion material Mg/Al-CLDH of 5%and the ratio of lithium-based grease to epoxy resin of 3:1,only a small amount of mildew was generated on the surface during the neutral salt spray experiment of 1200h,and no rust was generated inside the substrate after the coating was peeled off.The surface of rust substrate was coated with anti-corrosion mastic with Mg/Al-CLDH content of 5%.after salt spray test for 1200h,the coating was stripped and it was found that part of the rust on the surface disappeared and a part of the bright substrate was exposed,indicating that the addition of salt conversion material would not hinder the rust conversion of mastic.The salt spray resistance of anticorrosive daub with various salt conversion materials is:Mg/Al-CLDH>mixed Mg/Al-CLDH and Mix-A>Mix-A>no salt conversion materials.（4）Preparation and anticorrosive performance of anticorrosive adhesive tapeAccording to the optimum composition of composite anticorrosive daub,anticorrosive daub with a thickness of 3mm was uniformly coated on smooth Q235 substrate to prepare anticorrosive adhesive tape.The composite anti-corrosion mastic adhesive tape still has high viscosity on the low-surface substrate,and the adhesive tape and the adhesive tape adhesive do not have any appearance change after the adhesive tape is pasted on the substrate and subjected to the salt spray test for 1200h h.The adhesive tape was peeled off the surface of the substrate and it was found that the adhesive tape had a good protection effect on the substrate and could effectively inhibit or slow down the corrosion process of the substrate when it was applied to the substrate with rust.