Preparation And Performance Of Environmentally Friendly Organosilicon-metal Ion Self-assembled Film

Metal plays an important role in people's production and life,but the appearance of corrosion greatly limits the use of metal products.The function of chemical conversion film is like to double-sided adhesive tape,which can connect the metal substrate and the outer coating closely,and protect the metal from corrosion in the production process.On the one hand,it can prevent the bottom metal from being eroded by the corrosive medium;on the other hand,it can be firmly combined with the outer paint film to increase the adhesion between the paint film and the metal.It can prevent the corrosive medium from eroding the base when the paint film is damaged or spreading through the gap and prolong the service life of the workpiece.Traditional surface treatment methods include chromate passivation and phosphate conversion.However,studies have found that hexavalent chromium ion has carcinogenic effect and seriously endangers human health.The discharge of phosphorus containing wastewater during the phosphating treatment process is easy to cause eutrophication of water body.The empty orbitals of metal ions are complexed with the lone pair electrons in O,N,P atoms to form complexes.By using the complexation reaction,a dense chemical conversion film is formed on the surface of metal substrate by self-assembly method to improve the corrosion resistance of metal.The silane coupling agent and epoxy modified silicone resin in silicone can hydrolyze to form a large amount of Si-OH,which provides active sites for the reaction.At the same time,the special functional groups at the organic end can be firmly combined with the outer paint film to improve the adhesion of metal paint film.In this paper,the PVZ composite film was prepared by the synthesis of PVZ composite and complexation with zinc ions.The protection efficiency of PVZ conversion film and PA,VTEO,PA-Zn,VTEO-Zn conversion film on cold rolled steel substrate were comprehensively investigated.The influence of different treatment time on the micro morphology of PVZ film and the adhesion of PVZ film was also explored.The film forming mechanism was further analyzed.Then,the chemical conversion film with excellent corrosion resistance and strong adhesion was prepared on the surface of aluminum alloy by solution self-assembly method.The effect of the amount of additives on the performance of the conversion film was discussed,and the film-forming mechanism was preliminarily speculated.The experimental contents and results are as follows:(1)Preparation and properties of PVZ conversion coating with corrosion resistance and high adhesion on cold rolled steel surfacePV composite was prepared by the condensation reaction between Si-OH hydrolyzed by vinyl triethoxysilane(VTEO)and P-OH in phytic acid(PA).Then zinc ions were added to the PV composite to form a dense chemical conversion film on the surface of cold rolled steel by solution self-assembly.Further study shows that the Si-O-P bond is formed between VTEO and PA,and the maximum protection efficiency of PVZ-45 composite film reaches 99%.XPS results show that zinc ions participate in the film formation through the formation of zinc phosphate and ZnO,and the PV composite can form Fe-O-P and adsorb on the substrate surface.PVZ-15 has excellent performance in neutral salt spray test,block test and impact test,and the film adhesion is the best.This may be related to the thickness and surface condition of the conversion film.Too thick will lead to the instability of the system and too thin will lead to the low coverage of the film and the low content of effective substances,which will affect the adhesion performance of the conversion film.At the same time,the rough surface can increase the bonding sites between the film and the conversion film,which greatly increases the adhesion of the film.(2)Preparation and properties of organic inorganic self-assembled chemical conversion coatings with corrosion resistance and high adhesion on aluminum alloyThe epoxy modified silicone resin was hydrolyzed and complexed with magnesium ion.The dense and uniform chemical conversion film was obtained on the surface of aa5052 alloy by soaking in solution.The electrochemical test showed that the order of corrosion resistance(the concentration of silicone resin in the treatment solution)was:9 mL/L>12 mL/L>6 mL/L>3 mL/L>AA5052 after treatment with metal silicone resin treatment solution.When the concentration was 9 mL/L,the corrosion inhibition performance of the conversion film was the best,which was further confirmed by copper sulfate drop test.When the concentration of additives was 9 mL/L and 12 mL/L,the conversion film showed excellent adhesion properties in the salt water boiling experiment.The conversion coating with organic coating can improve the hygrothermal resistance of aluminum alloy to a certain extent.SEM results show that the surface morphology of the conversion film is rough when the additive concentration is 9 mL/L,and the increased specific surface area may increase the binding sites between the conversion film and the paint film,thus increasing the film adhesion.The treatment solution is clear and transparent,without phosphorus and chromium,and the film forming process is simple and fast,which is suitable for large-scale production and application.