| In recent years, the problem of metal surface rusting before painting has plagued many people. It’s necessary to remove surface rust because the complexity and diversity of the rust composition will not only affect the adhesion of coating, but also the corrosion resistance of coating. The traditional cleaning methods can cause some problems such as environmental pollution and cost increased, so the method that directly painting on the rust has become a hot area of research. Phosphoric acid and tannic acid have been mainly used to dispose the rust, but they can’t seep into the porous rust inside, and the quantity of acid is difficult to control.To solve these problems, this paper chose PFOA which with the high surface activity to study, focusing on the function between rust and PFOA, the contents and results of research are as follows:(1) Rusty surfaces were treated by immersion in PFOA solution. The chemical structure, elementary composition, surface morphology, wettability and corrosion resistance of treated surfaces were characterized and analyzed by a series of detection methods which included FT-IR(Fourier transform infrared spectroscopy), EDS(energy dispersive spectroscopy), SEM(scanning electron microscopy), LSCM(laser scanning confocal microscope), contact angle and electrochemical polarization curves. The results show that PFOA solution has great diffusivity and wettability and can penetrate the porous rust layers into the substrate surface to form adsorption film. The adsorption film can destroy the combination between rust and substrate, thereby making rust off. In addition, it was found that the performance of treated surfaces was satisfied when the concentration of PFOA solution was 150g/L.(2) Although the wettability and permeability of PFOA is great, it’s unable to improve corrosion-resistant and adhesive of rusty surface significantly. And silane coupling agents have many great advantages such as environmentally friendly, wide application, good film-forming property and excellent adhesive strength to organic coatings, therefore, in this paper silane coupling agents(KH550, KH560) were mixed with PFOA to pretreat rusty surface. After immersion treatment, the surfaces were heated to solidify into membranes. The best paramenters of hydrolysis process and curing process were determined after the performance tests of membranes. The results show that the cross-linking reaction have taken place no matter on PFOA/KH550 film or PFOA/KH560 film, and adherence between the PFOA/KH550 film and substrate was much stronger. The properties of the film such as thickness, coating rate, closure, wettability and corrosion resistance were the best as compared with the film obtained in other processes when the mass ratio of KH550 to PFOA was 1:1, the concentration of KH550 was 10%, the curing time was 1.5h, the curing temperature was 150℃. The properties of PFOA/KH550 film are always better than PFOA/KH560 film whether the films are prepared in different hydrolysis processes or different curing processes.(3) To combine with the coating is the ultimate aim of rusty surface pretreatment. The effect of adherence between three different surfaces and epoxy organic coatings were studied. Three different surfaces included untreated rusty surface, surface treated by PFOA/KH550 and surface treated by PFOA/KH560. The results show that the mechanical properties of samples which surface was treated by PFOA/KH550 were superior to the others. After immersion in brine through 62 days, only the sample which surface was treated by PFOA/KH550 showed the smallest destruction and micro discoloration. After the drawing test, the sample which surface was treated by PFOA/KH550 showed better adhesion of epoxy coating than the other two surfaces. And the corrosion current density of this surface coating decreased significantly compared to the other two coatings, therefore it showed the best anticorrosive effect. |
PDF Full Text Request