Preparation And Anti-corrosion Study Of Silane/Graphene Film On AA-2024 Alluminum Alloy

Aluminum alloy has been widely used in aerospace,automotive,electronics,food containers and other various departments of the national economy due to the high strength to weight ratio,high thermal conductivity,stiffness,strength,ductility,easy to be processed.The surface treatment and corrosion protection of aluminum alloy are very important.In recent years,many studies have been done about using silane coupling agent treatment as replacements for chromate treatments.However,the thickness of silane film is generally not more than micron scale,and the brittleness is large,so it is not suitable to be used as an independent film.On the other hand,graphene is considered to be a potential ideal anticorrosive material and there are few studies on the construction of silane graphene composite films using graphene oxide.In this dissertation,silanes and graphene oxide(GO)were used to construct a silane graphene film upto several or tens micron meters with good thermostablity and anti-corrosion properties.In addition,the perforamce of silane composite film was further improved by adjusting the distributuion pattern of GO in silane film.First,thick silane films were prepared by increasing silane concentration and rolonging hydrolysis time.GPTMS monomers,dimer or trimer are the main hydrolysates containing a large amount of active silanols within short hydrolysis time.After long time hydrolysis,the amout of ativce silanols decreased,the molecular weight increased and the solution became viscosity.The thick silane film prepared by cross-linking of active silanol has better corrosion resistance.GO sheets was used to solve the brittleness and thickness problem of silane films.GO can be complexed with aluminum ions to form a gel film on the surface of aluminum alloy.The crosslinking of Al3+ ions with GO can improve the strength of GO gel.After graphene oxide was added in the silane solution,active silanol is preferentially adsorbed on the surface of aluminum alloy,and the grafted GPTMS graphene oxide layer attached to the substrate via condensation between silanols.A GPTMS/rGO film with upto tens of micron meters thick was fabricated.The film has good adhesion.GO sheets could distribute pressure and restrain the formation and development of the microcracks which improved the microhardness.The stacking structure of GPTMS and GO sheets makes GPTMS/rGO film have good thermal stability and thermal shock resistance,and also has good barrier performance and UV aging resistance.The distance between two parallel sheets in the cross-section of GPTMS/rGO film observed by TEM is about 7-10 nm,about 2～4 GPTMS monomers big,which inhibited the crosslinking of silanols in the vertical direction of GO layers.GO sheets in GPTMS/rGO blocked the formation of linear and cyclic siloxane,which reduced the degree of crosslinking of silane.Therefore,we try to regulate the distribution mode of the GO sheets with fluorosilane,so as to obtain a better corrosion resistance composite film(FG/rGO).Fluorosilane almost dispersed uniformly in the film.The group-CFx was a low surface functional group.and fluorosilane changed the local wettability of the hydrolysate which caused the change of the adsorption mode of the hydrophilic GO sheets.The irregular distribution of GO and increased of space between GO sheets increased the crosslinking degree.The surface of the film was flat with less defects and the crosslinking degree increased.The electrochemical results show that FG/rGO has better corrosion resistance than GPTMS/rGO.The corrosion inhibitor 8-HQ was introduced into silane hydrolysate so as to change the distribution of GO sheets by steric hindrance and repulsion between benzene rings of 8-HQ and a self-healing composite film was prepared.8-HQ and GPTMS are combined with GO to form a composite film(HG/rGO).GO sheets distribucted like network in the film.The film surface is flat without wrinkles and the defects decreased.The 8-HQ could react with Al3+ forming insoluable AIQ3 which would block the micropores and cracks and impede the development of cracks in depth after the film was broken.Thus the coating has better corrosion resistance.