Silanization And Molecular Dynamics Simulation On Carbon Steel Surface

The organic coating system is currently the most widely used for corrosion protection of metals,in which pretreatment layer plays a vital role between the metal matrix and the organic coating.Generally,there are two important roles:First,short-term physical barrier against aggressive species for the coating/metal interface.Second,the adhesion between coatings and metals.Recently,silanization has become a hot spot in pre-treatment research.It may become an alternative to carcinogenic chromate and phosphate conversion coatings,which will achieve large-scale industrial applications.However,there are still two major problems in achieving industrial application for carbon steel.First,the carbon steel is difficult to be silanized,silane film formed on its surface is relatively thin,uneven,and non-uniform,thus leading to poor protection performance and binding with top paints,which hardly meet the actual demands.Due to the uneven distribution of carbon steel surface,it may be difficult in silanization on carbon steel surface.Thus it is urgent for us to find suitable silanes for carbon steel.Second,sustainable use of silane solutions still remains a problem,the property of easy hydrolysis and polymerization of silane solution(the silane solution "failure")make it difficult to be industrialized,which cause economic loss.In response to the above two questions,specific research contents of this paper include:(1)For the difficulty in silanization of carbon steel surface,corrosion performance test including EIS,immersion test,damp heat test,copper sulfate drop test,and binding force test experiments such as tensile test,cross-cut test were used in this paper.Three silanes of 1,2-di-[triethoxysilyl]ethane(BTSE),tetraethyl silicate(TEOS)and 3-(methacryloyloxy)propyltrimethoxysilane(MAP)were studied.Results showed that the BTM ternary composite silane film had the best corrosion resistance and interfacial bonding properties than the single silane or two silane composite silane films.XPS showed that BTM film was more thicker than BM film.(2)For the sustainable use of silane solution,the effects of hydrolysis time of silane solution on the protective properties of silane membrane and solution stability were studied.The EIS,SEM,immersion test,damp heat test and copper sulfate drop experiment showed that the corrosion resistance of the composite silane film increased first and then decreases with the prolongation of hydrolysis time.The same as the area/number of sheets that can be effectively formed(the corrosion resistance of the silane film obtained by the copper sulfate drop test was determined,and the corrosion resistance time of the silane film is set to a certain value t,below which the silane film is ineffective to form a film),conductivity test confirms the above viewpoint.(3)Molecular dynamics simulations were carried out to simulate different kinds of silane molecules(BTSE,MAP and their combined silane BM and TEOS-containing BTM ternary composite silane)on the surface of Fe,FeOOH and Fe3C.The silane molecules were adsorbed by comparing the interaction energy of different substrates.The difference in the interaction energy and the concentration distribution of silane molecules indicated the adsorption selectivity difference of silane on carbon steel.The results showed that FeOOH matrix can form a strong combination with silane,while the other two matrics-Fe and Fe3C demonstrated a poor interaction between silane and matrix.Silanes were particularly difficult to adhere to the surface of pure Fe.For the same substrate,BTSE benefits from the properties of its disilane,with more hydroxyl groups interacting with the matrix,which exhibited highest binding energy than other silane systems(MAP,BM,BTM).Although the BTM silane system is slightly inferior in binding energy,BTM can be more evenly distributed on the surface of the substrate compared to other silane systems,thus providing good coverage for the substrate.