| Coating as one of the most economical and effective means of corrosion protection of steel,it is necessary to pretreat the surface before painting(degreasing,descaling and removing impurities),some large,complex and special parts of steel structure,it is difficult to achieve the basic requirements of the coating process,under this condition,the technique of coating with rust has become a hot research topic.Currently,the research on the rust paint mainly added organic acids,inorganic acids or their salts to the film-forming system,in order to make the use of its special functional groups transform the rust layer or stable rust,However,these additives are acidic substances,Seriously affecting the stability of the film-forming system,supporting the poor and toxic shortcomings in the course of the use.In this paper,the transformation liquid with good conversion effect on the surface of rusted carbon steel was prepared.The effects of different conversion acids,solvents and additives on the transformation efficiency were studied.The conversion liquid was directly applied on the surface of the rusted substrate,and the effect of the conversion film on the performance of the subsequent epoxy coating was discussed.The effect and mechanism of phytic acid conversion coating as pretreatment film on the performance of the rusted coating was studied by electrochemical impedance spectroscopy,polarization curve,scanning electron microscopy,salt water resistance test,adhesion test and so on.1.Through experiment to explore adhesion as the initial screening conditions,the surface of the rust substrate were coated respectively with phytic acid tannic acid,sulfosalicylic acid and phosphoric acid four kinds of conversion solution.The results show that the phytic acid conversion membrane is the best choice for as the pretreatment film,made the adhesion of epoxy coating with rust has been greatly improved.SEM and FTIR microanalysis were used to analyze the reasons.2.The sand blasted steel and the rusted steel substrate were studied.The corrosion behaviors of the samples were studied by electrochemical impedance spectroscopy(EIS)and scanning electron microscopy(SEM),under the samples were immersed in 3.5%NaCl solution containing sulfonic salicylic acid,tannic acid,phosphoric acid and phytic acid respectively.The results showed that the corrosion behavior of the samples with 0.5%phytic acid had a certain degree of corrosion inhibition.3.The preparation technology of phytic acid conversion film on the surface of rusted substrate and the morphology,composition and functional group composition of the phytic acid conversion film under the optimum conditions were systematically studied,and analyze the factors influencing the corrosion resistance of phytic acid conversion film.Integrated adhesion,EIS,LEIS and micro-SEM photos and other performance test results,showing that the conversion film and the composite coating have the best corrosion resistance when the phytic acid concentration is 2%,and good repair ability,and reveal its repair mechanism,these studies on the practical application of the conversion film has important guiding significance.4.(JFC)and(KH-550)were added to the epoxy varnish coating and the mixed solution respectively,the results of adhesion and EIS data show that,the dry and wet adhesion of the composite coatings with 5%KH-550(mass fraction)added to the epoxy varnish coating and 2%phytic acid conversion coatings have greatly improved,contrast with the rust-resistant epoxy varnish coating,dry adhesion increased by about 6MPa,the increase rate of 178%.The corrosion resistance of the substrate with the rust is the best. |
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