Research Of Rare Earth Passivation Craft On Galvanized Steel

The application of chromate passivation of zinc has been prohibited already and gradually at domestic and international,because of its toxicity,carcinogenic, disadvantage in human beings and environmental protection.Now,according to present condition,there is no non-chromium passivation craft which can substitute chromium passivation.So the need of looking for a kind of replaceable craft is very urgent affair.With the research of the rare earth salt at the surface treatment of zinc,the rare earth salt associate with BTA is applied to surface treatment of zinc.Rare earth passivation films are obtained on surface of galvanized steels by using chemical immersion process.According to studying the composition of passivation solution, temperature and time and by orthogonal design,the optimization craft is proposed. The influence of composition of passivation solution,passivation temperature and immersion time has been studied each.During the research of the rare earth passivation films,the corrosion resistance of passivation films is studied by Pb(Ac)₂·9H₂O drop test and weight lose method, compared with the optimal passivation craft without the additive of BTA.The corrosion resistance of passivation films is analyzed ulteriorly by tafel polarization curves and electrochemical impedance spectroscopy measurements(EIS).The composition structure and morphologies of coating are identified by SEM(electron microscope),X-ray diffraction analysis(XRD),Raman spectra and X-ray photon spectroscopy(XPS).In a word,the appearance of galvanized steel treated by the optimization passivation craft is golden,color and luster is uniform.The scanning microscopic examination indicated that the passivation films forms on the galvanized steels are homogeneous.The passivation films can endure Pb(Ac)₂·9H₂O drop for 300s.The corrosion rates of rare earth passivation films in 3.5%NaCl reduced greatly.The technological process is so simple that the unfamiliar operators can manipulate it. Furthermore,the consumption of expenses is small during passivation process. Accordingly,it is a kind of perfect chromate-free passivation technique and can solve the problem that chromate passivation is prohibited gradually but no equal subsititute technique.It has promising prospect in industrial applications.